TDI Pumpe Duse PD Cam Bearing Oiling and Related Wear (eddif)

eddif

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TDI Pumpe Duse PD Cam Bearing Oiling and Related Wear (eddif)

This thread will give information necessary to understand the cause of cam wear, cam-bearing wear and cam-bearing wear indications on the TDI Pumpe Duse. It is somewhat involved, difficult to see, and time consuming, but worth the effort.

The VW Pumpe Duse TDI PD engine is a great engine, but suffers from insufficient lower cam bearing backup. IMHO. The lower cam bearings do not have support under their whole area. The problem occurs when the original design had the cam pushed up by valve spring pressure. In the pushed up position the cam had full cam bearing area, but the followers had cutouts that reduced the lower cam bearing area. The PD design had an added injection roller rocker that overcomes the valve spring pressure and forces the cam down onto not fully supported cam bearings.

The reduced cam-bearing backup area causes the cantilevered cam bearing area to deflect downward. This downward deflection causes the end two bearings to cock in their bores and cause early copper release on the belt end bearing. The three center bearings deflect equally during use and cause limited support during operation. This pressure causes minute head cam bore wear and the second and third bearings sets have reduced life. The cam is forced, over time, to the front of the car (over the cam-bearing oil slot) obstructing oil flow to the cam bearing and followers.

There are multiple approaches to the problem and this article is intended to show the solutions I think will work, and to invite other solutions. Of course any modifications to a car that came equipped with a warning sticker about oil type and usage causing severe danger, are at your own risk. VW marketed a design they never totally made trouble free, and you are listening to my opinions. In my own private vehicle cam bearing replacement helped restore oiling to the followers and allowed copper streaked lobes, on a failing cam, to make a recovery and survive more miles. The copper came from worn cam bearings. Most of the cam-bearings looked fair, but cam bearing cocking caused early release of the copper layer, of the belt end cam bearing. After cocking is resolved and more oil is supplied, copper release should be delayed and life should be longer.

This first labeled view is from the timing belt end of the engine. The link view is from the flywheel end of the engine. Backwards from our situation, so I reversed the drawing and show a drawing that agrees with the link.

The link describes a crankshaft, but a camshaft is still a moving shaft in bearings. The main difference is the injection roller pressure that directs the camshaft position. The higher oil hole will allow the oil wedge to develop over more miles, and may allow longer cam bearing wear.

I have a plan for cam bearing modification to allow longer life. The first step is to simply connect the two stock oil delivery slots together with a slot. The slot will probably be .75 mm deep in the Babbitt side of the cam bearing and 5 mm wide. These dimensions are open to change and Hurst89 and others are welcome to calculate the dimensions to overcome rotational oil turbulence , meet flow parameters, to keep too much oil flow from going to the upper bearing oil slots. We may make the lower shell cut different (deeper) from the top shell cut, to allow a top bearing change after 90,000 miles. Hopefully as the top new oil flow pushes the oil into the wedge it will self regulate by interaction with the old oil slot still in position. When the old hole is uncovered, a little, it will flow more oil again. Here is the point that the old hole may have to be blocked and the new hole uncovered, but time will tell. No, this is not all tested and firm, but is open to others trying for the best design. If I waited around till it was completed, the cars would all be junk.

The quality of the following drawings, are sure not to impress anyone but will possibly help others understand.

Since it is posted some copy write legal aspects exist. You are welcome to use this information for personal repair on your car. Any other use will require permission before use.

http://www.zddplus.com/TechBrief11%20-%20Internal%20Combustion%20Engine%20Lubrication.pdf

http://machinedesign.com/article/gro...more-lube-0522










The above simple left hand drawing shows the original position of the camshaft when the engine is new. The right hand drawing shows the position as the bearing wears and the oil supply begins to decrease. If the cam continues to move almost all oil is cut off to the bearing and most of the oil flowing down to the followers almost stops. Always look for the cam position rather than the amount of wear. Wear indicates position of operation in the PD. When the cam-bearing oil hole is blocked oil supply decreases. Always remember copper release in the PD defines cam-bearing wear / failure.

The next view is flipped to allow link to agree with drawing.





The following cam-bearings show the general shape, The area from green line to red crescents is the unworn portion often seen on a used bearing.. The red wedge area is a .50mm deep removal of babbitt and steel removed to stop cocking / flexing of the bearing in the bore. When the babbitt is removed the oil film will not carry load in that area, but the bottom is retained to direct oil to the cam follower face. The white area between the green line and the red area should carry load after removing the red area surface. The red square area is a .75 mm deep and about 5 mm wide, where babbitt and steel are removed to allow oil to flow to the top bearing. The right bearing has the Square area removed, but not the red crescent / crescents and is the top bearing. The left bearing is the drive belt end lower cam bearing. If you move the cut to the left side you have a flywheel end lower cam bearing. The center cam-bearing fits in the lower center three positions. The right cam bearing is the upper cam bearing for all positions. Eventually I hope we post actual bearings cut for service, Anytime anyone can help by posting better drawings feel free to post away.




lower belt end ……... lower middle three … ….Top all positions


This thread asks for your questions. The PD has multiple failed camshafts and we seek to find a solution that allows more miles than the stock engine. Oil slots in the follower bores (from the lifter oil supply hole) will supply more oil at the follower / lifter / tappet ---- cam-lobe interface area. A groove in each bottom cam bearing may help, and in fact the square is a type of groove. This thread is about maintaining or possibly increasing cam and cam-bearing oiling. Any method of increased oil supply will help. This thread will also try to find if, when the cam bearing oil holes are covered, the follower oil gallery pressure rises. If the follower oil pressure rises, the follower pressure on the cam lobe follower interface point may increase, also causing increased wear. Eventually I hope to use 150 HP injectors to reduce loading. This article / thread is open to solving the problem and not about making a point.

eddif
 

eddif

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TDI Cam bearing update page


Counter clockwise
Anti clockwise Flywheel end
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Clockwise Cam Rotation
Belt end
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Update option #! (August 1 2009)
Top row stock replacement bearings.
Second row GEN I cut replacement bearings with backside cut.

The picture below suggests that the cam moved due to the cantilever effect reduction. We can use the 1st generation cut bearings (bottom row) without worry IMHO. After testing the 2nd generation cut bearings (not shown) we might go back and make more changes, but if you need bearings now I would not feel bad using GEN I cut bearings.. If you are brave the cut bearings should move the cam into better alignment and give better oiling.

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This buckweat diesel photo shows the reason for all this work. If the cam bearings had been supported the cam wear and cam / follower oiling would have been better. Just too narrow a support area for a wide bearing.

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The most misleading ploy in the last 50 years. (thanks dieseldorf for posting the sticker)

How many people chased the oil trail when it was really 5 engineering faults? Pretty good ploy by VW to send us down the wrong trail.
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eddif

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TDI PD Cam, Bearing , Follower Picture Post

This page is left to post Pictures, that others will post. I will use Edit to move some pictures here.
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eddif 1st generation cut bearings. Note cuts on backside of upper bearings. The lower bearings have cuts to match that take oil to the top unuesed oil slot. This reestablishes oil flow when the original slots are covered. Arc cuts are to stop cantilever forces that especially cock the end bearings. About page 11

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eddif bearings from personal car The upper row bearings are the upper bearings, that do not wear except for cocking wear on the two end bearings. The middle row is a set at 105,000 miles US bearings that had a copper release wear streak on the belt end bearing (right side in picture). The lower row of bearings are a stock set of bearings with no cuts that show the oiling slots uncovered and have 5,000 miles US on them.

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Better eddif bearing view of the pointed out view of the copper release point. About page 21

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SBAtdijetta's 39,000 mile US belt end bearing that shows the copper release spot that seems to be the first spot to wear. IMHO this wear spot causes copper flakes under the valve cover that cause copper wear streaks, that are the cause of the final lobe and follower damage. IMHO this is the point of most loading of all the bearings and that little wear spot shredded the copper that put SBA out and down for the count. About page 18

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SBA's full set of cam bearings at that 39,000 mile US set that show the difference in a BRM set. The little copper wear streak is barely visable in the picture but was blown up on the previous picture (left bearing marked #1 and is belt end bearing). About page 18

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The copper deposited on a cam lobe. IMHO the start of the wear streakes. It can occur with just the one little streak shown on the belt end bearing, I had a number of copper streaks and they went away with cam bearing replacement. I had minor copper streaks, there are no comments on more wear and replaced bearings yet (heard rumor someone was trying).

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Relationship of bearing to follower. Shows the follower lubrication path when bearings are well oiled.

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Picture of cut bearings after 5,500 miles US

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SBA's lower bearing backside (more wear than normal) are the best example of the extent of the force that can exist with WOT and high RPM that makes the 26,000 lbs ? of injection force. This is not a gentle nudge but raw force in high performance conditions IMHO.

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eddif

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Invitation to Experiment

Now that the thoughts are posted the actual experiment begins. The first essential need is for the bearings. It is pretty serious to start cutting on perfectly good bearings without complete knowledge of where I / We are headed. Will the layered bearing respond to surface removal of material without setting up something that is going to peel in service? I suppose since there is no evidence of much peeling in failed bearings I will be safe to go for it. I wonder how many failures in cutting the bearings will be needed to get a set to try? I am thinking of using carbide burrs to do the cuttung. This all talks easy, but I am well aware of the human clutz factor in all this. I can describe nice clean cuts, but by the time you slip a few times there is no telling what it will look like. Nice to know that the price is just $14.00 US per individual bearing shell. Anyone out there is welcome to machine away and report in as to what works. So far the bits I have found are way too rough to so a slick finish. Then, do I coat the bare steel surface when the babbitt is removed? Too thick a coating and this product will smear as bad or worse than the copper. Wrong product and it may cause a reaction. Phosphate treatment? POR-15 ? I would love a nice set from a manufacturer, but then if price was no issue, this thread would not be here. I am open to suggestions and reasons. I need all the failed bearings anyone will sell me. I need some thrown outside to watch rust, some to cut on, and somehow some to post pictures of.

Measure it with a mike, mark it with chalk, cut it with an axe, paint it so it will not rust and wonder why it looks so bad. This should be interesting. Anyone have a cnc machine that will take some of the human element out of this?

eddif
 

eddif

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Cam Bearing Pictures

dr.zed said:
This head has bearings for the cams?
One of the best views of the location of the cam bearings is:
http://forums.tdiclub.com/showthread.php?t=172713
You can note the area of unsupported bearing at this thread also.

The first page shows the close relationship with the followers and how the oil could leave the bearing and be right next to the followers. IMHO this is the source of the major oiling for the followers, and without the oil spillover the follower fails.

eddif
 

hdeptech

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ok so now are the followers that are the worse the ones next to the worse bearing??? your picture puts it into words I can see....your on to something, so what if the injector adjustment is causing to much down ward force of the cam????? note not all injectors are adjusted exact....
 

eddif

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Follower Oil Gallery Pressure Increase

rentstdi said:
After looking at the pictures of the cam bearings it that thread, I understand exactly where you are going with this.

How about the bearings here
http://forums.tdiclub.com/showthread.php?t=216617&highlight=pd+cam+pic


Also, wouldn't there be an increase in oil pressure if the cam prevents flow?
Thanks for the two sets of cam bearing pictures. Their wear shows the cam location closing in on the oil slots (by looking at their wear patterns). I have mentioned the increase in follower oil gallery pressure before. Your observation is completly logical. This gallery pressure increase, increases the pressure the followers exert on the base circle of the cam (as well as all around the lobe). For a time I thought the followers had a defect, but I finally realized that the followers were just responding to increased pressure. It is a vicious circle more pressure equals more wear; more wear is less oil and more pressure; and round and round it goes. Since the injection pressure is far greater than the Valve spring pressure there is no relief from the cycle of disaster. We need a way to measure follower oil gallery pressure. The gallery pressure compared with bottom end pressure may be an indication of how worn the cam bearings are. You could relieve the gallery oil pressure with slots, but will not help the cam bearings without moving the oil delivery location for the cam bearings. The higher location should work.

Congratulations you have just proved how stupid I am. It took me 90 days to get what you got in 20 minutes. There are days I spent 5 hours a day for days on end reading and looking. Finally it was sitting at the compurer looking at my worn replaced cam bearings that I saw what was happening. I knew there was too much base circle pressure long before I knew why. I felt I was on the right track, months before I saw all this.

Thanks

eddif

Edit added the word pressure in one sentence ; changed my second sentence statement;
 
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eddif

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More Than One Factor

hdeptech said:
ok so now are the followers that are the worse the ones next to the worse bearing??? your picture puts it into words I can see....your on to something, so what if the injector adjustment is causing to much down ward force of the cam????? note not all injectors are adjusted exact....
You are right to put the question marks in there. Many have said that the exhaust followers wear more than the intake followers. The heat is the main reason most have quoted as the most logical cause. If you have heat (in this case bad) and less oil (in this case bad); you have a higher probability for failure. There can be more factors we are not seeing yet, or more factors that posters have mentioned that have not been agreed with. If we get on the same page we will probably be able to read this story.

Force vectors on the PD cam are a story unto themselves. The cam belt itself may pull the cam slightly to the front of the car, or the increased loading at the belt end may cause more friction ,climb toward the front. Thank goodness the belt drive does not terribly increase wear on that end. Cam bearing cocking sure kills the two end bearings. You can read the force at the pump end (flywheel end) where the cam goes just a tiny bit more to the rear (the cocking is pretty bad). No telling what the pump pressure is doing to all this loading. End to end the wear is fairly even. Follower gallery pressure may be more at the #3 exhaust area (some have mentioned that is where the oil comes to the top of the head, and may taper off toward each end.

There should be a flood of thought on the matter. Question marks are a good tool.

The injection rocker pressure can be lowered by fitting 150 HP injectors and lowering the cam driven primary pump upper pressure limit. From what most say the idle pressures are not too high, but as the speed rises the primary cam driven pump pressure rises to 105 psi US. Since the 150 HP injectors will black smoke at full throttle, we could limit the cam driven pump pressure on the top end pressure ( I have suggested less than half. The rocker and innjection pressures should fall, and thus decrease the cam loading. This is all expensive though. Modified cam bearings may help enough for most drivers. This is theory, but based on a well known diesel brand that had a similar problem.

Thanks
eddif

Edit: spelling and writing errors
 
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mctdi

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eddif said:
This gallery pressure increase, increases the pressure the followers exert on the base circle of the cam (as well as all around the lobe). For a time I thought the followers had a defect, but I finally realized that the followers were just responding to increased pressure. It is a vicious circle more pressure equals more wear; more wear is less oil and more pressure; and round and round it goes. Since the injection pressure is far greater than the Valve spring pressure there is no relief from the cycle of disaster. We need a way to measure follower oil gallery pressure. The gallery pressure compared with bottom end pressure may be an indication of how worn the cam bearings are.
eddif

I think I am missing something here.

The followers [ lifters ] are a hydraulic cylinder with a check valve to hold oil in. The cylinder is designed so that even with full engine oil pressure they do not push open the valves, just fill the gap between the valve stem and cam lobe. The check valve then hydraulically locks the follower so the cam lobe can push the valve open. And hydraulic pressure within the follower goes up to match the valve spring force as the valve is open.

So is it being said that the valve cam lobe loading is going above the valve spring force to open the valve?????
 

GoFaster

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The loading on the cam lobe can never exceed the load it takes to open the valve. If it did ... the valve would simply open. Causing compression loss. Causing "engine not running".

I think eddif's thought is that it is not the valve opening pressure that is related to the cam journal failures, but rather the pressure from the P-D injectors.

Although, my thinking is that the cam journal failure is an effect, not a cause. So far, I've only seen extreme cam journal wear on engines that have had a lifter that completely failed. This would suggest the following course of events: Lifter breaks completely, gives oil a low-resistance leakage path, which starves the cam bearings of oil, which leads to excess cam bearing wear.

Seen it happen (under different circumstances) in bottom-ends many times. Usually a big-end rod bearing lets go first (tap-tap-tap-tap), which causes a massive leakage path (knock-knock-knock-knock), which starves everything else in the engine of oil (rattle-rattle-rattle-rattle), which trashes every big-end and main bearing including those not involved in the original failure (ka-BOOM).
 

eddif

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Follower Behavior

mctdi said:
eddif

I think I am missing something here.

The followers [ lifters ] are a hydraulic cylinder with a check valve to hold oil in. The cylinder is designed so that even with full engine oil pressure they do not push open the valves, just fill the gap between the valve stem and cam lobe. The check valve then hydraulically locks the follower so the cam lobe can push the valve open. And hydraulic pressure within the follower goes up to match the valve spring force as the valve is open.

So is it being said that the valve cam lobe loading is going above the valve spring force to open the valve?????
Hydraulic followers, that work so well today, are the result of long development. I will give you a link to an aircraft problem that took years to resolve. The particular page may not be the one you need, but the site is the correct one (hope). Look around the site. These engines had a pump up problem at one time. Just be open to a problem being able to exist, and I will approach it when I have a little more time. If you find the right page I will not be necessary at all.

http://precisionengine.home.mindspring.com/engine5.htm

eddif

Edit: http://egaa.home.mindspring.com/valves.html All Articles

http://www.sacskyranch.com/eng140.htm Pump up similar to what we may be facing.
 
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GoFaster

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I read that article. Keep in mind that that article pertained to a push-rod engine, in which the lifter is very remote from the rocker-box (connected through a very long push-rod running inside a tube). On a VW OHC engine, any oil fed through the cam bearings spills all over the place as it goes out the sides of the bearing, and part of that splashes everywhere onto the top of the lifter.

BUT ... I'm not discounting the possibility of slight oil starvation.

eddif, if you want to do an interesting exercise ... research the path by which oil gets from the main oil gallery in the bottom-end, up the block, through the annular clearance between one of the head bolts and the hole in the cylinder head through which it passes, and into the oil gallery inside the head.
 

eddif

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GoFaster said:
The loading on the cam lobe can never exceed the load it takes to open the valve. If it did ... the valve would simply open. Causing compression loss. Causing "engine not running".

I think eddif's thought is that it is not the valve opening pressure that is related to the cam journal failures, but rather the pressure from the P-D injectors.

Although, my thinking is that the cam journal failure is an effect, not a cause. So far, I've only seen extreme cam journal wear on engines that have had a lifter that completely failed. This would suggest the following course of events: Lifter breaks completely, gives oil a low-resistance leakage path, which starves the cam bearings of oil, which leads to excess cam bearing wear.

Seen it happen (under different circumstances) in bottom-ends many times. Usually a big-end rod bearing lets go first (tap-tap-tap-tap), which causes a massive leakage path (knock-knock-knock-knock), which starves everything else in the engine of oil (rattle-rattle-rattle-rattle), which trashes every big-end and main bearing including those not involved in the original failure (ka-BOOM).
The Injection rocker roller pressure overcomes valve spring / valve opening pressure and finally forces the cam to reside next to the cam bearing oil slot (after a small amount of wear). So yes the Injection load causes the cam bearing wear (to a point). The cam also walks by friction of operation toward the front also (see links at first).

At the hole covering point (wear is not severe at this point), all that happens next is the result of the oil holes being covered. The cam bearing wear accelerates (the oil hole area does not have enough room to develop the wedge of oil to properly lubricate the bearings). The follower lubrication is almost stopped from the cam bearing overflow slowing. Cam friction increases causing more friction to walk the cam forward toward the oil holes. Copper (usually) is released due to cam bearing cocking ( without cocking it would be miles before copper would be released). Heat is generated by several friction issues. A wear loop develops.

So a cause brings about an effect and that effect is the cause of another effect------. All these things kill the followers and lobes. The injection pressure helps close the cam bearing holes that cut down the cam journal oiling and decrease the follower lubrication that allows the copper to stick more that runs heat up and all of a sudden it all runs in circles, after the oil holes are covered. The injection pressure never increases in all this but after a point all other things going on influence the other causes and effects.

I hope I said what I intended. There are so many factors you wind up sounding like you are lost or rambling. At times one persons order of operations might even be a little different. I left out ZDDP oil type and a host of other things that are also involved in this.

Cam failure is the end result of many things. The vicious wheel turns.

eddif
 

GoFaster

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Sorry but I need to shoot another hole in your theory. I understand what you are saying about the camshaft being off-centered in the hole (all journal bearings do this) and this is potentially towards the side where the oil is fed in. But, the camshaft is FAR from a case of steady loading. The loading is in the up direction when the valves are mid-opening-cycle and in the down direction when the injector is pushing down and can be in opposite directions on adjacent cylinders, so in reality the off-centering of the cam journal would be all over the place as the engine rotates. And this is NORMAL. More oil gets pumped in when the oil-feed side of the journal is unloaded and less when it's loaded, but the oil that was previously pumped in half a revolution ago is still enough to lubricate the bearing.

I re-iterate something I said in another thread. Every motorcycle engine has its MAIN bearing journals fed from the bottom - exactly the opposite side that you would think based on the (erroneous) steady-state "downward" loading assumption, but they don't mysteriously blow up the bottom ends for no apparent reason.

A systemic case of poor lubrication by design would result in those journal bearings failing prematurely and catastrophically in EVERY instance, and that is simply not the case. I have yet to see a case of cam journal bearings worn through to the copper in which that condition was NOT in conjunction with a catastrophically failed lifter (which causes a massive oil pressure loss in the top end).
 

eddif

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GoFaster said:
I read that article. Keep in mind that that article pertained to a push-rod engine, in which the lifter is very remote from the rocker-box (connected through a very long push-rod running inside a tube). On a VW OHC engine, any oil fed through the cam bearings spills all over the place as it goes out the sides of the bearing, and part of that splashes everywhere onto the top of the lifter.

BUT ... I'm not discounting the possibility of slight oil starvation.

eddif, if you want to do an interesting exercise ... research the path by which oil gets from the main oil gallery in the bottom-end, up the block, through the annular clearance between one of the head bolts and the hole in the cylinder head through which it passes, and into the oil gallery inside the head.
The article you read is used only to speak to the issue of lifter operation (brought up by mctdi). The pump up bleed off and general operation is covered in the aircraft link and is to be used only to discuss follower operation. The first two links in the main post proper speak to the oiling issue we face.

I try to discuss as many questions as spring up, but not every thing discussed will apply to just one area. Sorry if I jumped a rabbit on a deer hunt, and you thought we were on a rabbit hunt. That kind of thing happens.

eddif
 

eddif

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GoFaster said:
Sorry but I need to shoot another hole in your theory. I understand what you are saying about the camshaft being off-centered in the hole (all journal bearings do this) and this is potentially towards the side where the oil is fed in. But, the camshaft is FAR from a case of steady loading. The loading is in the up direction when the valves are mid-opening-cycle and in the down direction when the injector is pushing down and can be in opposite directions on adjacent cylinders, so in reality the off-centering of the cam journal would be all over the place as the engine rotates. And this is NORMAL. More oil gets pumped in when the oil-feed side of the journal is unloaded and less when it's loaded, but the oil that was previously pumped in half a revolution ago is still enough to lubricate the bearing.

I re-iterate something I said in another thread. Every motorcycle engine has its MAIN bearing journals fed from the bottom - exactly the opposite side that you would think based on the (erroneous) steady-state "downward" loading assumption, but they don't mysteriously blow up the bottom ends for no apparent reason.

A systemic case of poor lubrication by design would result in those journal bearings failing prematurely and catastrophically in EVERY instance, and that is simply not the case. I have yet to see a case of cam journal bearings worn through to the copper in which that condition was NOT in conjunction with a catastrophically failed lifter (which causes a massive oil pressure loss in the top end).
The wear marks seem to show stable operation ( defined from the roller location and wear area toward oil holes. No bouncing at startup seems to mark the top bearings or back car side of the lower cam bearing. I see no indications of wear to support the movement you suggest. Not to say it could not bounce, just I see no markings to show it.

The links at the start of the post suggest unloaded areas for oil introduction. Since they seem to have a good description, I am going with them.

If I can't use aircraft, how can you use motorcycles. By the way you were once going to post that information.

If the oil pressure piston sticks in a oil pump, the pressure piston shows no great failure symptoms ( in fact it may be temporarily stuck with trash and you have trouble telling what happened), but it causes great damage.

eddif
 

eddif

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Sticking To 4 Points ?

I can already tell that I keep way too many things in my head at one time, and all these things are confusing to others. While follower operation does influence the wear of the PD cam, I think it would be wise to either move the follower operation to a new thread or just ignore it for now. Me jumping from cam bearings to followers is just going to be a bit much. Using the follower gallery oil pressure to test cam bearing wear may be just as confusing to some (it takes comparison pressures and speeds into consideration and is confusing at the simplest level).

That will still leave:
1.. cam bearing bore cocking due to cantilevered end bearings
2.. cantilevered areas on center 3 bearings
3.. early copper release
4.. heat of friction
5..Cam bearing wear due to cam proximity to oil hole -- oil supply decreased
7..Follower wear due to cam proxcimity to oil hole----oil supply decreased
8.. Cam walking due to friction (see first links + follower friction walk)

That is probably enough for here. It will just actually be the machine work descriptions, to modify the cam bearings. If we drop all the other stuff, there will be nothing to drive the cam bearing modifications. We do need to know why we are doing all this.

My cam was going bad; changed cam bearings slicked it up. The new unmodified cam bearings will only last 1/2 as long (guess). I need a more permanent fix. The semi permanent fix is the modified stock cam bearings.

Help this thread stay peaceful and to the points needed. We need a fix not a long winded discussion of everything automotive. This means me too.

eddif
 
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mctdi

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2010 Jetta
eddif said:
The Injection rocker roller pressure overcomes valve spring / valve opening pressure and finally forces the cam to reside next to the cam bearing oil slot (after a small amount of wear). So yes the Injection load causes the cam bearing wear (to a point). The cam also walks by friction of operation toward the front also (see links at first).

At the hole covering point (wear is not severe at this point), all that happens next is the result of the oil holes being covered. The cam bearing wear accelerates (the oil hole area does not have enough room to develop the wedge of oil to properly lubricate the bearings). The follower lubrication is almost stopped from the cam bearing overflow slowing. Cam friction increases causing more friction to walk the cam forward toward the oil holes. Copper (usually) is released due to cam bearing cocking ( without cocking it would be miles before copper would be released). Heat is generated by several friction issues. A wear loop develops.

So a cause brings about an effect and that effect is the cause of another effect------. All these things kill the followers and lobes. The injection pressure helps close the cam bearing holes that cut down the cam journal oiling and decrease the follower lubrication that allows the copper to stick more that runs heat up and all of a sudden it all runs in circles, after the oil holes are covered. The injection pressure never increases in all this but after a point all other things going on influence the other causes and effects.

I hope I said what I intended. There are so many factors you wind up sounding like you are lost or rambling. At times one persons order of operations might even be a little different. I left out ZDDP oil type and a host of other things that are also involved in this.

Cam failure is the end result of many things. The vicious wheel turns.

eddif

eddif

Thanks for the added input. As now I think I follow your thought on the issue.

Now we need a window in the valve cover to see what is going-on in there.
 

eddif

Veteran Member
Joined
Dec 17, 2006
Location
MS
TDI
2004 Jetta PD Automatic
mctdi said:
eddif

Thanks for the added input. As now I think I follow your thought on the issue.

Now we need a window in the valve cover to see what is going-on in there.
The window is really no problem . The valve cover top is almost flat and a lexan top can be made that seals off with 50 screws and nuts. A little sealer and leave off the breather system till testing is done (will require brearhing hole). Might have to do a couple of oil changes to keep the oil from being so dark. Anyone have a used valve cover?

Just tell me when something needs to be made more clear. I re-write all the time. I even try and turn it to be seen from another viewpoint.

eddif
 

TdiRacing

Vendor
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Aug 19, 2003
Location
Baltimore, MD
TDI
2006 Jetta TDI Cup
You will not see anything putting a window in the cover. It will immediately get slopped with oil and nothing will be visible. I tried a similar thing when the New Toyota Celica engine came out and had lots of failures. I was trying to see the oil level and it was impossible. Ended up using an external tube to see the level. Engines sucked all the oil into the head and the return holes were too small to get it back into the block fast enough at high RPM no oil=BOOM!

Anyway, a window will not work.
 

eddif

Veteran Member
Joined
Dec 17, 2006
Location
MS
TDI
2004 Jetta PD Automatic
TdiRacing said:
You will not see anything putting a window in the cover. It will immediately get slopped with oil and nothing will be visible. I tried a similar thing when the New Toyota Celica engine came out and had lots of failures. I was trying to see the oil level and it was impossible. Ended up using an external tube to see the level. Engines sucked all the oil into the head and the return holes were too small to get it back into the block fast enough at high RPM no oil=BOOM!

Anyway, a window will not work.
Since experience is a type of vision, could you help with the size of the new passage from the lower oil slot to the upper oil slot? That is really what I think we need to know. I was hoping to do one bearing and see how much different it was from a stock flow. A gusher would mean I had the pathway too large, and no difference in flow would mean it was too small.

eddif

Edit: would a triple deep open top box be better to look down into? Idle speed should be about all that is needed, except for one blip or two. Also thanks for the warning about too much oil. That is why I invited Hurst89 to calculate the bearing connection channel, I knew that would be critical; but I did not think of the drain-back issue. I do know you can over oil and overwhelm the breather system.
 
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Rod Bearing

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Sep 18, 2007
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Fort Worth
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Several
If you're trying to add oil to the bearing's loaded surface during operation, chamfer the oil supply hole a third of the diameter of the hole in the direction of journal travel, and taper it such that the hole then winds up looking like a cam lobe and make the chamfer ramp up to the journal surface where the chamfer ends. It's an age old technique that creates a pump action as the cam rotates in the bearing shell. I've seen great results doing this to rod and main bearings in racing applications.

If the underlying cam bearing support structure in the head is unsound enough in it's design to support the load, as it appears it could be in this situation, then the only fix for that is to either line bore the head and enlarge the bearing bores which would require steel backup sleeve supports, or, get someone to make you some better bearings with a thicker base shell to make up the difference. The wear patterns on the bearings seen in a majority of the pictures on this site tell me the design is borderline at best.
 

eddif

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Joined
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Location
MS
TDI
2004 Jetta PD Automatic
Rod Bearing said:
If you're trying to add oil to the bearing's loaded surface during operation, chamfer the oil supply hole a third of the diameter of the hole in the direction of journal travel, and taper it such that the hole then winds up looking like a cam lobe and make the chamfer ramp up to the journal surface where the chamfer ends. It's an age old technique that creates a pump action as the cam rotates in the bearing shell. I've seen great results doing this to rod and main bearings in racing applications.

If the underlying cam bearing support structure in the head is unsound enough in it's design to support the load, as it appears it could be in this situation, then the only fix for that is to either line bore the head and enlarge the bearing bores which would require steel backup sleeve supports, or, get someone to make you some better bearings with a thicker base shell to make up the difference. The wear patterns on the bearings seen in a majority of the pictures on this site tell me the design is borderline at best.
You are correct in most of what you say in the first paragraph if the backup is there for the bearings or at least the backup is balanced for the bearings. It is true if all you want to do is take care of the cam-bearings to be oiled by themselves, but if you are trying to secure oiling for the followers/lifters you need more to be done. The additional thing you need to consider is the camshapt needs the oil introduction to be higher, so that the the oil introduction will build the wedge sooner and help push the camshaft to the rear of the car. Plus the higher introduction will spill more oil on the lobe follower interface point.

The second paragraph is true to a point. I thought of the backup sleeves for all the lower cam-bearings for a time. The increased bore diameter would help surface area contact. The problem is the cocking would still exist on the two end bearings (belt end and flywheel end). This cocking can be stoped by releiving some of the babbitt and steel to where the leverage would not be present to cock the bearing. The cocking area is being deflected (cocked) to the extent it is slowly wearing the cam support area, and causing early copper release.

The main reason for stopping the machine work thoughts:
1..Most people would choose not to have the trouble and cost of the whole machine work process. A set of bearings that wil survive for 175,000 miles US (wild guess) would let a new set of cam bearings be put in each timing belt change without any worry or great expense.

2.. After you did the machine work you would have trouble if the person doing the modification quit selling the service or the back-up sleeves, and you would still need the special cut cam bearings to stop cocking. You can modify the cam-bearings with a correct size half round file in your own baackyard (favorite shade tree). That is really the whole idea here, to supply instructions to allow anyone to fix the car, or how to tell your favorite repair person what to do. I realize full well the resistance that everyone will face. So everyone ask questions so you can face those who resist the ideas.

So all I posted (here) is a compromise that is intended to allow us to use up the engines without much expense or trouble and move on with life. This compromise should let all those who want to just survive the trouble and move on, to do just do that, move on.

If however, you are in racing, then the sleeve method would get the best use of the engine. It is just what do you want.

It is the cam bearing cocking, with the early release of copper, that puts a kink in the whole thing. That and the pump end of the cam that will not allow a wider bearing to balance the load there. Just a bunch of things that cause trouble. I just do not remember if a wider bearing can be fitted on the belt end. The wider bearing thing was an afterthought.

I have a tool ordered to shape the bearings. I hope it works. It is a carbide cylinder burr one inch in diamerrer that I plan to use at 12.5 degrees to cut out the crescents with. No high tech here. I am working on moving the cut slightly to the rear. Of course there will be a delivery lag time to make things interesting.

Thanks for the comments
eddif

eddif
 

eddif

Veteran Member
Joined
Dec 17, 2006
Location
MS
TDI
2004 Jetta PD Automatic
Cam bearing cutting tool

The following tool was made to give some repeat ability on cutting cam bearings. I have not used it yet and I may have to change the angle. A much simpler holder could be made for a vertical mill. The main purpose was to give a hint as to what one might do. Of course a hand held die grinder with spunk can give the same result. In fact a round or half round file will cut the bearings, As soon as I get some more bearings, I will give it a shot.


Air tool 15 3/5" long, 25 mm carbide burr, plastic body, cam bearing in cutout under burr.

eddif
 

rentstdi

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Feb 18, 2005
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River of fall
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jetta, 05, platnum
I remember doing something like this to a Nordberg diesel generator, but we followed the machining with a crocous cloth (fine emory cloth)
 

Bob S.

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Central MD.
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A B4V, some ALHs & BRMs
A warning to any new reader of this thread. On post #847:
So now I sit at 231745 km with 40 cam bearings through my engine. Have stared at cam bearings for a long time. If I had not replaced the cam bearings once I would have had a cam failure. eddif
Cut bearings and frequent bearing changes may not be answer.
 
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