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

[eddif]

If I am following your thinking and if the root cause is in the wear in the cam bearings, is this something that might be monitored via accurate oil pressure monitoring. Ie. A quality mechanical gage? Or, do you suspect that the condition will not show becuase of the pressure relief?

Bob

I finally think, see paragraph three, cam-bearing oil gallery pressure will be expressed as a percentage of the block pressure supplied to the mains. Bob you can just read three to see the answer to your question.

This all has so many factors that it is hard to pin this down to one or two simple statements. It has been pointed out to me before that the actual wear on the cam bearings is small. The only thing is, there seems to be a relationship between the wear and the final resting /running place of the cam over the oil slots / holes. So in one sense it is position of the camshaft that kills the oil flow that would pour over on the followers / lifters / tappets / lobes. Our health has things that affect it: diet, exercise, rest, stress, relationships. Which one is the root?

The guage thing is going to require at least two guages, one on the supply that the crankshaft sees, and one on the cam-bearing oil gallery. It will finally be probably expressed as a percentage of the higher number. I suspect that the pressure in the cam-bearing oil gallery gets higher when the cam covers the holes. Oil used, style of driving, climate, OCI everything plays a part, but you must have full oil supply to the followers to operate with the least wear.

In the good old days (sometimes now) worn cam-bearings would dump most of the oil pressure in an engine, but now, at times, there is restriction (either gallery size or a planned restriction) going to the cam bearings to maintain crank rod pressure after it (cam bearing wear) reaches a certain flow. Engineering has progressed in a lot of cases. Just stop here. The VW PD does not flow more oil with cam bearing wear, it flows less. Just backwards of all we normally think. You cover the oil holes and the pressure rises in the cam-bearing oil gallery. This pressure rise causes the followers to press harder on the cam, and flow less spillage to lubricate the folowers. Higher oil slot placement will help. The oil slot was just placed in a loaded area (loaded after slight wear).

I have to watch it or I just repeat it all again (I know I just did- sorry). I do not know if the oil pressure guages will tell the whole story. I just observed that new cam bearings changed the condition of my cam wear. I see signs of oil slot covering that is worse the more the cam bearing wear. Thanks to all those that posted and continue to post cam bearing wear pictures.

We need a head cut into 20 pieces so we can know the whole story. Where does the second guage need to tap in? Do we need to make a new tap hole? Or, we can just fix the bearings to operate like new bearings, for a longer time. The cams do not fail the first 25,000 miles US. They seem to slow the oiling, and at a mileage (that differs from person to person) rapid wear begins to accelerate. IMHO. We are watching cams now to see what the story is.

eddif

 

[eddif]

Got some more

If I am following your thinking and if the root cause is in the wear in the cam bearings, is this something that might be monitored via accurate oil pressure monitoring. Ie. A quality mechanical gage? Or, do you suspect that the condition will not show becuase of the pressure relief?

I appreciate your helping me see a faulty train of thought I went down in the past. While your post is not the direct answer it triggered the correction. I once thought of reducing the cam-bearing lifter oil gallery pressure with an extra by-pass / relief valve. to stop the high follower lifter contact on the base circle of the camshaft. That pressure reduction action, by virtue of the possibility of lowered cam bearing oiling and oil spillover for the followers, is just wrong. The engineers must have the restriction engineering very close, or either the unworn position of the cam to the oil slots is very accurate. The wear that allows the cam to cover the oil slots just destroys their plan. Why discuss this again? Read the next paragraph (link and snip).

http://www.cranecams.com/?show=faq&id=5
"What is the importance of valve spring seat pressure?
Adequate seat pressure is necessary to:

1) Insure tight contact between the valve face and the valve seat to seal the combustion chamber and provide proper heat transfer from the valve to the cylinder head.

2) Keep the valve from bouncing on its return to the seat. If the valve bounces, cylinder pressure (power) is lost. Repeated bouncing of the valve is like a hammering action that can result in the head of the valve deforming ("tuliping") or actually breaking from the valve stem resulting in catastrophic engine failure.

3) With a hydraulic cam the valve spring must exert enough pressure against the valve lifter (or lash adjuster) plunger to keep it centered in its travel to prevent "lifter pump-up". When pump-up occurs the valve is held slightly off its seat resulting in a significant loss of power and possibly a misfire. It is this loss of power and misfire that is often misdiagnosed as a fuel system or ignition system problem.

High oil pressures and high viscosity oils aggravate "lifter pump-up" in hydraulic lifters. When either oil pressure or oil viscosity is going to be increased beyond the manufacturer's recommendation, a corresponding increase in spring seat pressure is necessary to prevent "pump-up" (even with an "anti-pump-up" lifter). Since oil viscosity in no way relates to the oil's film strength, and the scuffing protection provided by the film strength, Crane Cams recommends following the OE manufacturer's recommendation with respect to engine oil." ----end of link

.................................Thus...................................
I know I posted this link before, but never could make the statement I am about to make a little clearer. The amount of pump-up experienced in the PD is just below the valves being all the way open, but when the pressure goes up in the cam-bearing oil gallery the exhaust valves experience reduced seat pressure and the valves do not release their heat to the valve seat enough to cool them ( cool them as designed). This extra heat that the valve stems experience is what is causing the exhaust followers to wear more than the intake followers. IMHO That is not to say there are not other factors, but this heat, from partial pump-up and reduction of seat pressure, is a major player in our whole wear problem.

So I have been in fear of getting the spillover too much, when all we have to do is be sure we have enough follower oil gallery pressure (after the cam bearing cutting and oil delivery point change) and we can possibly trust that VW has all the gallery restrictions correct. So now i just need to find the pressure tap point for the follower oil gallery (hopefully near cylinder #1), and build the testing high box valve cover to see the amount of flow. Those two things (flow and follower gallery oil pressure) should get us close.

If it were not for your comments I would never get where we are going.

eddif

 

[Bob S.]

A different thought. And back to the various other threads about PD's, cam wear, oil, etc... Does anyone have definitive information about how VW's test mules fared (either in vehicle or static dyno run)? Presumably, those engine did not exhibit this problem or it would have been corrected? The next question is how are the PD Euro version faring? Are those engines having similar problems? If so, what are they doing about it? If they are not having similar problems, what are the peculiar differences between NA versions in the head? Oiling? or Oil?

 

[eddif]

Cam Bearing Wear

A different thought. And back to the various other threads about PD's, cam wear, oil, etc... Does anyone have definitive information about how VW's test mules fared (either in vehicle or static dyno run)? Presumably, those engine did not exhibit this problem or it would have been corrected? The next question is how are the PD Euro version faring? Are those engines having similar problems? If so, what are they doing about it? If they are not having similar problems, what are the peculiar differences between NA versions in the head? Oiling? or Oil?

I only tried two fixes.

Three times the normal ZDDP levels will not heal a lightly wearing cam.

New cam-bearings will heal a lightly wearing cam (very light wear). Copper streaks went away.

Has anyone else tried cam bearing replacement?

eddif

 

[SBAtdijetta]

I only tried two fixes.

Three times the normal ZDDP levels will not heal a lightly wearing cam.

New cam-bearings will heal a lightly wearing cam (very light wear). Copper streaks went away.

Has anyone else tried cam bearing replacement?

eddif

Eddif,

Friday we will replace my cam, lifters, bearings etc. We will take a good look at them before coming to any conclusions about their state of wear. I'll be sure to let you know how mine look, although I bet they will be fine as my cam is not very far into eating itself (thank goodness).

 

[eddif]

Eddif,

Friday we will replace my cam, lifters, bearings etc. We will take a good look at them before coming to any conclusions about their state of wear. I'll be sure to let you know how mine look, although I bet they will be fine as my cam is not very far into eating itself (thank goodness).

Welcome back. Vacation?

Remember, it is not how much they wore, but how the wear shows how close the cam came to the oil slots. See if there is any copper showing anywhere (even a place 1mm X 4mm can release copper (especially on the belt end bearing). We have got to stop the cocking / deflection.

eddif

Edit: my spot of copper was about 3mm by 11mm kind of oval in shape and where the cam bearing was cocked up on the belt end. This was a radial streak and not the end of cam to end of cam wear the bearings usually show. To look at it you would wonder how something that small could cause problems, but there were several lobes with copper from that litttle spot. When the bearings were replaced the copper went away.

The pointer, in the picture, shows the minor wear needed to release copper. The wear (all less than .0005" US) is small, but the location of the cam by the oil slots is cutting off lubrication flow to the followers. The wear at the copper is about .0011" US.

 

[SBAtdijetta]

Welcome back. Vacation?

Remember, it is not how much they wore, but how the wear shows how close the cam came to the oil slots. See if there is any copper showing anywhere (even a place 1mm X 4mm can release copper (especially on the belt end bearing). We have got to stop the cocking / deflection.

eddif

Haha lol sort of... but not really, I have just been to the ER and OR a few times lately, but I'm good as new now.

I will have a good look at them for you; after I have a look at them I can even mail them to you or somebody else who has tools to measure them accurately if anybody wants them.

 

[Bob S.]

http://forums.tdiclub.com/showthread.php?t=242795 Link FWIW

 

[SBAtdijetta]

http://forums.tdiclub.com/showthread.php?t=242795 Link FWIW

Thanks Bob, I found this particularly interesting to this subject:

I would be leary of the diesel rated oils because these are manufactured by major oil blenders who have a bad habit of changing formulations willy nilly without prior notice. Diesel engine oil specifications are in a state of turmoil just like gasoline engine oils and zinc additives could easily disappear from these oils too. In fact railroad diesel engine oils have always been zinc free due to conflicts with bearing materials.

 

[Bob S.]

In fact railroad diesel engine oils have always been zinc free due to conflicts with bearing materials.
That sure is an interesting statement. So many similar threads are ongoing on this topic that it is beginning to be difficult to stay on top of it.

 

[eddif]

ZDDP can be an issue for a cam and followers / lifters / tappets / lobes when the almost correct amount of oil is applied to lubricate a frictional interface junction of two elements. This thread is trying to show that without the lubrication amount being correct, no amount of additives will heal a terrible situation. I agree that ZDDP is an issue, but not the only issue.

1.. Narrow lobes
2.. Steel rather than cast iron cam
3.. Low ZDDP levels (other additives as well)
4.. Poor support for cam-bearings
5.. Cocking cam bearings
6..Early copper release from cam-bearings
7.Oil holes covered and placed in a loaded area
8..Other things

This thread will acknowledge all the oil issues, but I am trying to show that without sufficient oil the additives will not save the day. New cam bearings restored my cam to temporary health, but cantilevered bearings, closed off oil supply, increased follower oil gallery pressure need to be addressed.

I once worked on radar equipment that had physical holes (around cable connectors) that allowed waves to enter a controll box. They developed a compound that was supposed to cure the problem. The only problem was the holes were so large the compound would not close the gaps. I wound up close to being in trouble for acting like a witch doctor annointing the problem with the compound. They needed a re-design not an attempt at a fix. The additive fix (VW special oil) tried to apply magic to an engineering problem. The problem is just a little larger than the ZDDP can fix. I truly tried way high levels of ZDDP and it will not heal a cam. Flooding the interface point with oil and ZDDP will work. IMHO I know I sound brash, but this oil supply thing has worked for me and it will work for those who will try it before wear gets started. Tried too late you can tell me I do not know what I am talking about. Tried in time it may bring a super smile to your face.

My supply of cheap cam bearings may have turned out to one VW dealership selling a few sets of cam bearings at a pair price rather than the real each price. They caught their mistake so back to the search for cheaper bearings. If anyone has a reduced price supplier let us know. We are talking a lot of cam bearings (even if we just do the lower set. And the upper shells are worn on the edges from all the flexing / cocking against the lower replaced bearings. Both upper and lower really need to be replaced together; sorry. I just replaced the lower ones, but I am going back with a full set of machined bearings. If any dealership is selling the box of two bearings for $14.00 US let us know. I want 10 boxes or more.

eddif

 

[Bob S.]

eddif; Is it possible for you to post large photos of each matching bearing and identify where they were from? It would be helpful to me to see who each differs.

You are correct that once the wear starts and the wear surfaces are gone, or worn, no magical additive will restore it.

 

[SBAtdijetta]

eddif; Is it possible for you to post large photos of each matching bearing and identify where they were from? It would be helpful to me to see who each differs.

That may be interesting.

You are correct that once the wear starts and the wear surfaces are gone, or worn, no magical additive will restore it.

I agree fully, that is why I think you need to start fresh with everything you can (ZDDP) included, bearing issues addressed if substantial. So even though my cam is not toast yet, I want to start over with all new parts and then see how she goes.

Sorry Eddif OT comments aside.

 

[eddif]

eddif; Is it possible for you to post large photos of each matching bearing and identify where they were from? It would be helpful to me to see who each differs.

You are correct that once the wear starts and the wear surfaces are gone, or worn, no magical additive will restore it.

Of course I mentioned I used just the bottom bearings in my engine. So there is no top set to see. There was no wear on the top bearing shells at all. We do have an excellent set of bearings posted on the first page that are in order and matched. The great thing also is that they have enough wear to tell the story better than my bearings ever would.

Left side is the Timing Belt side............Right side is the pump /flywheel side #4 cyl

The tang sides go together just as sitting. Fold the slot side of the bearings forward so the slots are over each other and you have the running position (as viewed from the front of the car).

The right side bearing (flywheel / pump end) shows the cantilevered position has cocked the bearing to such an extent the lower bearing wear is not even, and the top bearing mate shows the cocked bearing assembly has caused wear on just one side of the upper bearing. Look at the inside unworn place of the lower bearing (it looks like the shape extended would point to the belt end). Now imagine force placed on the inside bottom bearing by some oil tilting the whole assembly till the top inside edge of the top bearing touches the top of th cam (the bottm inside edge goes down and away from the cam and the top inside edge goes down and the top touches on the top of the cam toward the belt end (repeated for effect) . Cut a toilet paper tube into some imaginary bearings (draw wear and oil slots) and hold them in position and you will see the relationship. I have my lower bearings to use, but you can make some models to see the relationship. And I know it will take some people 2 seconds to see the cocking and others two hours. Hey I am so stupid it took me nine or so hours.

The belt end wear can be seen also, but it is a little more difficult to see since the belt gives a little twist to the equation.

If you need any other help I will try again. Insert commas as needed.

eddif

Edit: A way to see my bearings larger is to copy the picture go to paint open the top identify area, paste picture; go to view and then zoom and you can make each one large enough to see. Someone else describe another way for them to view a larger image.

 

[2footbraker]

Makes you wonder if, when VW did their bearing load calculations, they used the bearing surface area or the bearing support surface area. Seems they used the bearing surface area. They should have made a removable lower bearing support so you could get the follower installed and then bolt a support on and place the lower bearing shell on that.

It looks like there is enough clearance above the follower to line bore the lower cam bearing journal and put a reinforcement under the lower cam bearing. The thing is, the only time I would ever consider doing this is if I had the cylinder head out and was doing a complete engine overhaul.

 

[Bob S.]

2foot; Thanks, that photo helped me to understand the wear pattern.

Simply, while VW probably provided adequate bearing wear surface; they point loaded the bearing support (it appears as though approx. 50% +/- is supported) resulting in the unsupported bearing shell deflecting under load. Thus the uneven wear.

Add to that the shaft deflection at the belt end to explain that bearing's wear.

The bearing set with the uneven top and bottom wear at the photo right side (vehicle left side, aka: flywheel end) is the one that was cocked. Correct. Not all bearing were cocked. Correct?

So, in effect, what it appears as though we have are at least two contributing factors (there maybe more, we should known as more data is compiled about engine origin, etc):
- Insufficient support for the cam bearings.
- Oil bending issues resulting from Federal mandated emissions regulations.

Please correct my understanding that:
- The Euro PDs are not having this problem?
- The Euro PDs are using different oils?
- The euro heads are similar in design to the NA's?

Thus the Root Cause is: Insufficient support for the cam bearings and a Contributing Cause, and probably the initiating cause, is: Oil bending issues resulting from Federal mandated emissions regulations.

So, if one simply changes to a different oil, the wear many decrease. But, what remains are worn bearings that may have lubrication problems because of the worn bearing surfaces and resultant decreased oil pressure therein.

Is this understanding correct?

 

[eddif]

Refining the Cuts

2foot; Thanks, that photo helped me to understand the wear pattern.

Simply, while VW probably provided adequate bearing wear surface; they point loaded the bearing support (it appears as though approx. 50% +/- is supported) resulting in the unsupported bearing shell deflecting under load. Thus the uneven wear.

Add to that the shaft deflection at the belt end to explain that bearings wear.

The bearing set with the uneven top and bottom wear at the photo right side (vehicle left side, aka: flywheel end) is the one that was cocked. Correct. Not all. Correct?

Both end bearings are cocked.

There is machine work done on the cam flywheel / pump end that does not put pressure on the flywheel end bearing to hold it straight. Note the unworn area on the flywheel lower bearing. That unworn area next to the flywheel / fuel pump, is there because the camshaft tang drive for the fuel pump removes the effective shaft bearing area / shaft length (the shaft is long enough just machined for the pump drive). The flywheel end bearing cocks more due to the lack of full cam shaft (load bearing length) machined area for support.

If someone has a picture of the shaft sitting in place, it would save me stumbling all over my words trying to paint a word picture. It is similar to two kids on a se-saw. If one kid (of equal weight) sits too close to the pivot he goes up. There were several cam photos somewhere (photos showing the pump drive end).

The belt drive end is cocking also, and there is wear on the matching top bearing that shows it also. The top bearing wear is more to one side than than the flywheel end bearing. The cocking is what caused the copper wear on the picture of my cam bearings. Put the photo in paint or word and blow it up / zoom in, to see it better. Shaft deflection (of the magnitude to cause the marks) IMHO would result in shaft breakage. The cam actually sits slightly at an angle in the engine (ever so slightly).

We will probably cut the bearings differently (different amounts) for several of the bearings. The center bearing will probably receive no cuts.
1.. The flywheel end will be cut most.
2.. The belt end will be cut the least.
3.. #2 & #4 will be moderate balanced cuts (may be same distance as the belt end bearing).

Since the cuts will leave open steel we will leave a little overhang of babbitt to over balance (similar to what is happening now) the end bearing overhangs. Everytime iI see the pictures the design changes a little. If VW had taken a little more time they might would have done all this. Of course by the time I get through, it will be like putting together a puzzle, and there are very few engines that have a map to place bearings (although there are a few that you have to watch bearing placement). It can be made more dummy proof by cutting the center three the same (but the center bearing support must be wider from what the pictures show).

This post is too wordy. I hope we get some pictures soon to straighten all this out. I need some cheap bearings to practice on.

eddif

 

[eddif]

2foot; Thanks, that photo helped me to understand the wear pattern.

Simply, while VW probably provided adequate bearing wear surface; they point loaded the bearing support (it appears as though approx. 50% +/- is supported) resulting in the unsupported bearing shell deflecting under load. Thus the uneven wear.

Add to that the shaft deflection at the belt end to explain that bearing's wear.

The bearing set with the uneven top and bottom wear at the photo right side (vehicle left side, aka: flywheel end) is the one that was cocked. Correct. Not all bearing were cocked. Correct?

So, in effect, what it appears as though we have are at least two contributing factors (there maybe more, we should known as more data is compiled about engine origin, etc):
- Insufficient support for the cam bearings.
- Oil bending issues resulting from Federal mandated emissions regulations.

Please correct my understanding that:
- The Euro PDs are not having this problem?
- The Euro PDs are using different oils?
- The euro heads are similar in design to the NA's?

Thus the Root Cause is: Insufficient support for the cam bearings and a Contributing Cause, and probably the initiating cause, is: Oil bending issues resulting from Federal mandated emissions regulations.

So, if one simply changes to a different oil, the wear many decrease. But, what remains are worn bearings that may have lubrication problems because of the worn bearing surfaces and resultant decreased oil pressure therein.

Is this understanding correct?

you are keeping me busy

Correct, the bearings themselves are probably ok if supported.

Shaft deflection probably does not exist on any perceivable level. Cam bearing cocking exists on the belt end too. The force vectors are just different for the drive end and give a little different result.

Drive belt end bearing is cocked also. Center bearings are balanced, but deformed.

Many factors. Oil blending and oil bending

Euro cars are experiencing the problem, but maybe not on our magnitude.

We will possibly never know the whole oil story. Europe has many versions of 505.01 oil. The poor US person went to the store and bought what he could (and lied like a dog about what he used on that one trip where he could not get the correct oil). Ok lied is a little strong. He had temporary loss of memory as to what he bought. If we get more oil to the cam / lobe interface, the oil will not be so much an issue. IMHO

All PDs are similar in design. Injector size, injector rocker arm ratio, tune, boost pressures, driving habits,and a multidude of other things exist, that we are blind to, might cause differences from country to country as to wear and failure rate. The US driver usually puts far more miles on a car in a shorter time frame.

The root causes are many factored. Let me give everyone an A+ for their thoughts, and if I make a "D" , I will rejoice.

Changing to a different oil may may / not help. The covering of the oil holes, by the cam, will not change much, and thus the followers will continue to get less oil than they need. A thinner oil may spray through the shrinking gap sooner, but eventually the oil holes / slots get covered too much, and rapid wear begins regardless of the oil. I wish there was an oil pill to solve this problem. I tried to join the oil is the major problem group, but these other factors keep screaming for re-design.

Oh for the simple life.

eddif

Edit: removed word

 

[Bob S.]

eddif; You use the term bearings are cocked". What I am trying to get an understanding of is why do you say the bearings are cocked? Are they really cocked? Did you plasatigage or otherwise measure them prior to disassembly & after reassembly? Or are is it because of the wear pattern?

I have a hard time understanding how the bearing can shift in their seat, ot how the factory machined surfaces could be that far out. Could that wear pattern simply be because of the shaft loading and the bearing support?

 

[eddif]

eddif; You use the term bearings are cocked". What I am trying to get an understanding of is why do you say the bearings are cocked? Are they really cocked? Did you plasatigage or otherwise measure them prior to disassembly & after reassembly? Or are is it because of the wear pattern?

I have a hard time understanding how the bearing can shift in their seat, ot how the factory machined surfaces could be that far out. Could that wear pattern simply be because of the shaft loading and the bearing support?

I am using the wear pattern. Measurements would verify location. The actual displacement in the bore can be minute and still amount to movement enough to cause strange wear. When we are talking of cam-bearing coating only being a total of.0015" US thick including copper (guess - you can measure it), it is difficult to measure.
Measurement is difficult becauses of the resting assembled forces and all the rockers in the way. By the time you remove all the parts to allow measurement all the forces have changed. Note the gouge (deeper depression in the flywheel end lower cam-bearing ---right at end of wear pattern. Then notice the top bearing half,on the flywheel end, contacts on the oppisite side of the bearing assembly (these wear patterns show shifting /cocking). Measurements are handy but not always easily possible. Tire wear is a good example for me. You can usually read the amount of camber change necessary to stop tire wear (with enough experience). Sitting at rest might not give the readings you need. Hanging out under the car at 70 mph to get the measurement on curves could be difficult (car manufacturers have equipment and computer programs to show such measurements). A camber change and better wear is good enough (safer too) . VW probably knows the amount of deflection. The top layers of babbit / tin / ? are about .0005" US total thickness so reading that gets a little rough when assembling and restressing the rockers / cam towers. Pressures could give enought stress to mash (good southern word) the plastiguage and give a false measurement. Using plastiguage works well in some cases, but when things are taking up slack and moving during diss-assembly and re-assembly it is just about impossible for you and the plastiguage to get the measurement ( and any other sort of measureing devices we might own). So .0002" US wear in the right place could result in copper release.
I have not mentioned (lately) the belt end cam bearing is turning on the locator tangs showing the stress involved.

The factory probably did a good job on the machine work. It is just the pry-bar / lever effect of hanging a oil loaded bearing out over thin air at 4000 rpm while a rocker roller is helping generate 20,000 psi that might have a little effect on that unsupported bearing.

eddif

 

[Bob S.]

I am using the wear pattern. eddif

Understood. My sense is that it is simply the loads and inadequate bearing support (point loads) surfaces that are resulting in the uneven wear and not the bearings moving in their seats.

eddif & others. Thanks for the info & posts herein. I think I now understand what is occurring here. I was struggling to understand how this was simply an oil spec. problem. I think I now have a plan of action in my mind to include switching oil types, re-pullling the VC to inspect the cam with the additional info in this post, taking OA's every change and finally planning an early T-belt change (maybe about 90k) to include removing the cam to check the bottom bearings.

It would probably be wise if we all used the same oil lab in an effort to try to reduce the variables. This effort sure helped with the Ford 6.0 L oil issues. Back to the UOA thread.

 

[SBAtdijetta]

The factory probably did a good job on the machine work. It is just the pry-bar / lever effect of hanging a oil loaded bearing out over thin air at 4000 rpm while a rocker roller is helping generate 20,000 psi that might have a little effect on that unsupported bearing.

Understood. My sense is that it is simply the loads and inadequate bearing support (point loads) surfaces that are resulting in the uneven wear and not the bearings moving in their seats.

Can it (the cam bearing issues/thoughts) all be boiled down to this then?

 

[Bob S.]

As above, my current thinking is:
The Root Cause is: Insufficient support for the cam bearings.
A Contributing Cause, and probably the initiating cause, is: Oil bending issues resulting from Federal mandated emissions regulations.

So, if one simply changes to a different oil, the wear many decrease. But, what remains are worn bearings that may have lubrication problems because of the worn bearing surfaces and resultant decreased oil pressure therein.

I may have the root & contributing/initiating causes reversed. More data on the Euro engines would help with this understanding. Does this make sense? Or am I missing something?

 

[eddif]

Can it (the cam bearing issues/thoughts) all be boiled down to this then?

Bob and I draw different conclusions. When the cut bearings have been installed for 10,000 miles (another guess), a cam bearing reading should show which way is correct. Unless it is tried we will just go back and forth on what we believe. I am convinced by the bearing marking evidence, that the lack of support and pressures applied cause bearing cocking and the wear we can see. Bearing oiling goes down , cam follower oiling goes down and cam oiling gallery pressure goes up.

Peace

eddif

 

[Bob S.]

eddif; I agree with you that the only way we will know is via more data. And the only way to we are going to get it is by collecting it & reducing & changing the variables. I may change my opinion once I open up my bearing caps & see what is there. The part that is still bothering me is the apparent difference in failure between the Euro & NA versions of very similar heads & valve trains and the NA versions are detuned at that. It makes no sense.

 

[GoFaster]

Makes you wonder if, when VW did their bearing load calculations, they used the bearing surface area or the bearing support surface area. Seems they used the bearing surface area. They should have made a removable lower bearing support so you could get the follower installed and then bolt a support on and place the lower bearing shell on that.

Tolerance stack-up would be an issue. A simpler solution at the OEM manufacturing stage, if this is an issue, is simply to make the bearing shells thicker so that they don't deflect as much. But, 99% of the journal bearing shells that I've seen, regardless of engine, are all about the same thickness "that's the way they're made" - doesn't make it right, but it is what it is.

Normally these bearing shells are crush-fitted. When initially put in, they project slightly out of the bore, then they are crushed into a press-fit situation when the mating parts are assembled. The locating tangs are only to position them at the right place for assembly (and not all engines have them). Once in, they don't move.

I've mostly stayed out of this, but there are still some things that bug me about this theory.

The width of the wear area still has me unconvinced - some engines have con-rod bearings narrower than the wear area and that is a far heavier loading situation. (For example, VW/Audi/Bugatti W12 engines have big-end rod bearings only 12mm wide ... necessary when you have so many cylinders in such a short engine.)

The bearings in the photo look like they were starved of oil - I don't question that, the question is WHY. Eddif has his theory that the camshaft is somehow being deflected to block the oil fill hole. I'm not buying it, because the camshaft is not under steady loading - it will go all over the place when the engine is running. It IS possible that the entire top end is starving for oil for some reason. But, why would this be an issue on some engines and not others? It is equally possible that a general top-end oil starvation issue would affect camshaft/lifter wear.

Oil for the top end of these engines goes up through the annular opening around one of the cylinder head bolts (I think it's the second-in from the flywheel end on the side facing the front of the car). I have not had one of these engines apart enough to follow the path, but it seems to be a rather torturous one. Could it be ...
- partially blocked with assembly debris? (it's fed from after the oil filter, but engines aren't necessarily totally clean inside at the factory, and if the oil filter ever goes into bypass, the engine is being fed partially unfiltered oil)
- marginally too restrictive, to the point where inevitable tolerance variations during machining and assembly mean that some engines are okay and others aren't?
- slightly *loose* fit between lifters and bores leading to excess oil leaking out via the lifters-to-lifter-bores path and oil starvation to the journals?
- fit between camshaft journals and bearings too tight (starvation right away - not enough oil can get into the gap) or too loose (starvation because there is insufficient supply through the feed hole to entirely replenish the bearing)?

Next step - measure the oil pressure in the head somehow and compare it to the oil pressure in the main gallery in the bottom-end!

 

[Bob S.]

GoFaster; Good analysis, But, still the question as to why not on the Euro engines? Presumably, they would have the same design, manufacturing, assembly variables. Measuring & monitoring the oil pressures sure makes sense to me.

 

[abctdi]

After going thru all the posts, I get the impression this is talking about the NA 1.9 PD only and not the NA 2.0 PD?

 

[DPM]

Does ETKA show any check-valves/ balls/ orifices etc fitted in the head or the gallery to it?

 

[donDavide]

Interesting stuff