Cam bearing Reengineering for PD motors

myke_w · Jul 28, 2009

I too like the idea of using non tty studs / bolts. I wonder if arp has somthing in a similar size?

Frank - I'm just curious, could'nt you achieve a similar result with a single center groove to get the oil all the way around the bearing shell? Might be easier to manufacture too?

ex - main bearing halves on right.

As you know that's what they use in the bottom end to achieve lubrication in 360 degrees on the crank rotation.

Franko6 · Jul 28, 2009

I wouldn't groove through the load-bearing bottom shell, but will not deny that grooving through the top shell would not be damaging. My idea of cross-slotting was a matter of metering oil through the bearing shell so it would be slung at the tops of the cam followers.

I believe there are two issues in the bottom shell; oiling and support. Both functions are poorly done. I'm not going to put up another tired shot of cam bearings that you can find OVER and OVER... they all look the same. Where the lower bearing shell is unsupported, the lower bearing surface has no wear. The width of the wear point is in the center 40% of the bearing.

Either the bearing shell must be thicker or have a stiffer shell material.

The reason I feel drilling the caps is an appropriate process is, 1) it is relatively quick and easy, and 2) Once it is done, future cam bearing shells won't need any additional work, assuming I retro or custom build the properly designed top bearing shell.

As for TTY bolts, I do not see any purpose in using TTY bolts on the cam caps. There is not an upward force to warrant them. However, the upward force on the PD rocker bolts, an ARP style stud and bolt would be a reasonable alternative, if available. If the ARP's are not available, the OEM rocker arm shaft bolts should be used.

The single biggest justification for stud and bolt ARP style replacements and reusable cam bolts is the the elimination of about $110 of expense when doing cam/ lifter/ cam bearing inspections. That cost would keep owners from inspecting cam bearing wear.

hdeptech · Jul 28, 2009

Please Keep Us Posted....

coalminer16 · Jul 29, 2009

Just a question but do the bearings fail that much on the PD engine? I have only read about the cam lobe failing and not the bearing.

myke_w · Jul 29, 2009

Coalminer16, do some searching on that, but the short answer is yes. Every picture of a worn out cam / lifters I've seen (or have personally removed) has always been accompanied by a pretty worn out set of bearings.

I just changed my cam / lifters out and there was very minimal wear on the cam / lifters themselves, (just beginning). The bottom bearings were showing some wear from the downward loading Frank has been talking about.

Lightflyer1 · Jul 29, 2009

Franko6,

Do you have any evidence that adding these oil passages has worked? I am not critical of your idea, just want to know how you were able to tell if it worked or not. Thanks for the info!

David

andreigbs · Jul 29, 2009

Subscribed, EXCELLENT work (as usual) Frank. Will be watching with interest.

And for the $64K question: how much would you charge a PD owner to do this along with a cam & lifter set?

Rod Bearing · Jul 30, 2009

In another thread here, oldpoopie suggested making a return oil fed camshaft drip lube system under the valve cover, consisting of some tubing mounted inside the valve cover. He suggested routing the return oil from a by-pass filter to this drip rail, which would cast a substantial quantity of cleaned return flow onto the camshaft. I REALLY like the idea. It's a fairly simple task to design something along these lines. Getting additional oil onto the camshaft, especially freshly filtered return oil from the by pass filter surely might be a way to prolong the life of this obviously piss poor camshaft/cyl head design

Franko6 said:
I wouldn't groove through the load-bearing bottom shell, but will not deny that grooving through the top shell would not be damaging. My idea of cross-slotting was a matter of metering oil through the bearing shell so it would be slung at the tops of the cam followers.

I believe there are two issues in the bottom shell; oiling and support. Both functions are poorly done. I'm not going to put up another tired shot of cam bearings that you can find OVER and OVER... they all look the same. Where the lower bearing shell is unsupported, the lower bearing surface has no wear. The width of the wear point is in the center 40% of the bearing.

Either the bearing shell must be thicker or have a stiffer shell material.

The reason I feel drilling the caps is an appropriate process is, 1) it is relatively quick and easy, and 2) Once it is done, future cam bearing shells won't need any additional work, assuming I retro or custom build the properly designed top bearing shell.

As for TTY bolts, I do not see any purpose in using TTY bolts on the cam caps. There is not an upward force to warrant them. However, the upward force on the PD rocker bolts, an ARP style stud and bolt would be a reasonable alternative, if available. If the ARP's are not available, the OEM rocker arm shaft bolts should be used.

The single biggest justification for stud and bolt ARP style replacements and reusable cam bolts is the the elimination of about $110 of expense when doing cam/ lifter/ cam bearing inspections. That cost would keep owners from inspecting cam bearing wear.

oldpoopie · Jul 30, 2009

I still think this would help the cam lobes some, but it certainly wont help the bearings, and it looks like that is where this mess is starting.

TonyJetta · Jul 31, 2009

Frank,
Has this been tried? What is the oil pressure, before and after?

Tony

Franko6 · Aug 1, 2009

Lightflyer1 said:
Franko6,

Do you have any evidence that adding these oil passages has worked? I am not critical of your idea, just want to know how you were able to tell if it worked or not. Thanks for the info!

David

David,

Time constraints delay me...

There is a conventional wisdom: do is what has worked for years... put the oil in at the right spot. As it is, the oiling is entering 'after the fact' and just past the highest point of pressure. LIke closing the gate after the cows got out, that don't work...

The second issue as I see it, is support. Unless something is done with the support of the bottom cam bearing shell, virtually 1/2 of the intended support is failing. Initially, I thought a thicker shell, but there may be stronger bearing shell materials that would work. I would rather not cut larger cam bearing journals.

The third issue (not necessarily in that order) is lifter oiling and cooling. Another method is to create a secondary oiling galley that has oil squirts aimed directly at the lifters and tapped into the oil galley. I'd think that a ball check valve at idle would reduce the oil pump volume loss that would be likely to happen. I"ve seen several race cars with that type of setup.

As for the pressure loss due to cutting a proper oil channeling in the top bearing shell, there will be no ill consequence. What I am arranging by oil passage is the correct way it should oil.

Last point... I will be cutting stock shells for a center line oil path similar to what Mike_W shows in the Glyco crankshaft main bearing set. Sticking with a conventional methodology of bearing oiling is fine by me.

Franko6 · Aug 1, 2009

TonyJetta said:
Frank,
Has this been tried? What is the oil pressure, before and after?

Tony

No, I've not done oil pressure testing on the PD motor. What I can tell you is whatever difference in oil pressure there is, that is what extra oil is going to pass NEW bearings and be thrown onto the cam followers. I am not removing any of the load-bearing cam and if there is any reduction of oil pressure it will be nominal and only at low engine speed

Where has it been tried? Go back one generation of motor from the PD's. Every other diesel engine made by VW is oiled on the non-load bearing side of the cam. In those engines, with aluminum cam journals, I've seen my share of 300,000+ miles on the odometer with no journal problems. Of course, the cam load for the predecessor engines are lower than on the PD's, so I can't make a direct comparison.

When I have the opportunity, I'll do a 'before and after' oil pressure test. Anybody who does take the steps to modify their cam journals, feel free to post results.

TonyJetta · Aug 1, 2009

Thanks Frank!

As always, Top Notch Work!

Franko6 · Aug 25, 2009

I did cam install on a BRM. The slotted bearings I machined are similar to what the slot in the crank bearings have in the top shell.

The most interesting part of the job was taking apart the lifter plungers to find that the ruined ones were missing a spring. Also, the BRM engines only put nitrided lifters on the exhaust valves.

I will be trying to determine if the lifter manufacturing error is the contributing factor for the cam failure, or the whole cause.

Also, I've gotten sets of rocker bolts and cam bearing cap bolts that are high quality rolled threads and REUSABLE. I have to figure the final cost, but they would be in the neighborhood of $40 for the cam bearing set, delivered. $100 of stretch bolts need to be replaced every time a cam is inspected. That keeps people from doing what needs to be done.

myke_w · Aug 25, 2009

Frank - If it helps any I had a cam sent off and analysed by a metallurgical lab with particular attention paid to the depth and uniformity of the surface hardening in regard to valve lobe wear. Nothing was out of the ordinary according to the rerport.

Bob S. · Aug 25, 2009

myke_w said:
Frank - If it helps any I had a cam sent off and analysed by a metallurgical lab with particular attention paid to the depth and uniformity of the surface hardening in regard to valve lobe wear. Nothing was out of the ordinary according to the rerport.

That is interesting. Thanks for the leg work. The question that pops to mind: Is it represengtative of all the PD cams. I think, unless other info comes forth, we should assume it is. It sure would be nice to finally be able to begin crossing causal factors.

Mach1 · Aug 26, 2009

Frank, I am interested in a set of the rolled thread fasteners(after you get the final pricing)..

I have listened and ready to do some independent testing if you would like.

I would be willing to add some of your modded bearing shells and bolts as also other mods. I have considered drilling the oil galleries as you have described as well.

I do OA at every OCI. I am in Texas where it has been very hot this year..averageing 105+ for the last 2 months straight..if heat effects operation, I cant think of a better place to test it then here in Texas..

Tell me what you think..I have 2 BRMs as well...

DanG144 · Aug 26, 2009

I am interested in doing the new oil passages, new bearings and new bolts as well, on my BEW.

spooner miller · Aug 26, 2009

Hey Frank I have 2 of these cars with bad cams, the one actually threw the rod at 110,000 miles because it got so bad. My question is why are you drilling holes and and snaking the oil across the top bearing when the oil passage needs to be runs across the pressure point, that 7 oclock position. Just like the main bearings on these cars i'm going to just cut a small groove across the bottom bearing and bring oil to that pressure point. I was told by a John Deere mechanic for over 20 years that this way would work 100% better. Just thought i'd run that by ya and see what you think. Thanks! Eric

DanG144 · Aug 26, 2009

That will not work on these bearings, in my opinion.

You have to supply the oil to the point with the widest gap (unloaded area), not to the point that has the most load. The oil supply is only 50 psi or so.

The pressure of the oil wedge at the loaded area is thousands of psi.

TonyJetta · Aug 26, 2009

DanG144 said:
The pressure of the oil wedge at the loaded area is thousands of psi.

And...you need a quality film of oil already on the cam and bearing surface to prevent metal-to-metal contact. Trying to squeeze 20-50psi oil into a loaded bearing will not work.

Tony

Franko6 · Aug 27, 2009

The reason for slotting the top bearing shell is very simple. It's the time-tested approach for oiling on a wide variety of cam bearing shells.

The reason for the full radius slot... Instead of finding the exact location for oil injection, the full width slot removes any guess-work.

Bob S. · Aug 27, 2009

TonyJetta said:
And...you need a quality film of oil already on the cam and bearing surface to prevent metal-to-metal contact. Trying to squeeze 20-50psi oil into a loaded bearing will not work. Tony

That is my understanding. Now, will the lower bearing oiling slot in the "as manufactured location" disrupt the oil wedge formed by oil introduction from the new top bearing entry point? The lower slot remains located at just prior to the maximum load area. It remains somewhere in the 50 psi+/- range as the passages are not blocked off.

My sense is that the original lower slot will cause oil wedge disruption unless something is done so that it will not disrupt it. My conclusion is that the lower shell should be rotated 180 deg. so that the slot is after the max load point.

Franko6 · Aug 27, 2009

Ok, I see what the thinking is... Here is my thinking.

The problem with the lower slot, in certain situations, is being virtually cut off by wear and cam pressure. The camshaft has no time or place to gather oil onto itself before it is forced into the peak pressure area.

By laterally slotting the upper cam bearing, the cam picks up oil in the dwell side of the cam bearing and carries the oil into the pressure side of the cam bearing. The camshaft needs the spacing of the dwell side of the cam to 'paint' the non-loaded bearing surface of the cam. Once the oil has wet the camshaft, it will carry past the other oiling hole.

I don't know if there is any advantage to reversing the lower bearing. The lower oil slot isn't going to act like a scraper. If there is that worry, maybe you would want to put an oil wedge on lower slot, but I doubt it. Also, a poorly made bearing tang relief cut could do more damage then good.

TonyJetta · Aug 27, 2009

Franko6 said:
By laterally slotting the upper cam bearing, the cam picks up oil in the dwell side of the cam bearing and carries the oil into the pressure side of the cam bearing. The camshaft needs the spacing of the dwell side of the cam to 'paint' the non-loaded bearing surface of the cam. Once the oil has wet the camshaft, it will carry past the other oiling hole.

I have to agree with Frank's reasoning.

Once the cam bearing is 'painted', even though it is under extreme pressure, the oil film will not exit the bearing.

Think about it...if this WAS the case, plain bearings like these that have been used for >100 years would fail after only a few revolutions.

Tony

2footbraker · Aug 27, 2009

Any tribology textbook will tell you the optimum location for an oil supply hole in a journal bearing is opposite the highest load.

Bob S. · Aug 27, 2009

Franko6 said:
Ok, I see what the thinking is... Here is my thinking.

The problem with the lower slot, in certain situations, is being virtually cut off by wear and cam pressure. The camshaft has no time or place to gather oil onto itself before it is forced into the peak pressure area. ...

I don't know if there is any advantage to reversing the lower bearing. The lower oil slot isn't going to act like a scraper. If there is that worry, maybe you would want to put an oil wedge on lower slot, but I doubt it. Also, a poorly made bearing tang relief cut could do more damage then good.

Understood that the lower slot will not act as a scraper. But, is it not possible that it will act as a low pressure point in a highly loaded area and disturb the oil wedge just prior to the max load area. Further complicating the matter is that the lower oil port is almost as wide as the bearing support as between the cylinders.

Agreed, a poorly made tang will do more harm than good. What's that old rule: "First, do no harm"???

spooner miller · Aug 27, 2009

My mechanic and I still don't see the point in the "painting" effect. Just like in all "properly engineered" engines they supply the oil by using slots in the bearings. If you believe damage will be caused by cutting a slot how is that different then cutting a slot across the top. Pressure is what lubes bearings, and because the cam isn't the last place to get oil there is not enough oil pressure to the cam bearings, that's the major flaw. If oil can't go to the cam then it's going to get pushed up to the rockers. Even if the bottom bearing doesn't have a perfectly cut slot it's made of soft brass and aluminum so it will break in right away and not hurt the cam at all anyway. I'm surprised nobody, including VW, hasn't come out with a replacement bearing cut with these oiling slots machined into them.. I'm not trying to be a dick but just trying to state a point. Why make things complicated when it's actually a simple fix.

Lightflyer1 · Aug 27, 2009

Please document/photograph everything you do and post it up in a new thread with your results. It should be interesting reading.

Rod Bearing · Aug 27, 2009

oldpoopie had the best idea and I just thought of something else to do along the same lines.

What do you all think about drilling and tapping each camshaft bearing cap and making an oil rail that's fed from the bypass filter return?

It would enable fresh clean oil coming from the bypass filter to be piped right to the top half of the cam bearings. The added flow in that area would surely spill off enough to help the lifters too.

Cam bearing Reengineering for PD motors

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