Don Terrill’s Speed-Talk

I'm hoping someone here can help me out with a problem I have been having.

I've had recent cam bearing failures. Two different block, two different cams. This is a 4.6L Jeep stroker engine. 4.0L block, 258 crank, 4.0L rods, KB pistons, Harland sharp roller rockers. Nothing special.

The first block was fine with a Comp Cam. Had a few thousand miles on it then changed it for an Isky cam and new lifters (with less lift than the Comp). Cam spun when it was installed with little pressure. Main and rod bearing clearances were .0018"-.0020. Cam breakin went fine using Joe Gibbs 50wt break in oil 30 minutes between 2000-2500 rpm, flat tappet hydraulic. Oil pressure started out good then I started noticing the pressure was dropping at idle. Standard volume oil pump, Clevite bearings. Bearing material was pushed out at the bottom and babbit looked like it had been spread about. All the oil holes on the cam bearings lined up with the galleys. No binding in the valve train. Plenty of room on the springs before bind as well as with the retainers to stem seals in rocker pivot. Cam tunnel checked out straight and true.

Taken from the bottom of the block.



New block ,new parts, crank turned. New Clay Smith cam, new lifters, bearing, oil pump, etc. Used Durabond cam bearings this time around. Same thing. Oil pressure started out good then dropping to less than 20 PSI at a hot idle. Used 30wt Brad Penn break in oil. Main and rod bearings were .0018"-.0020" again. Cam spun fine, and bearings lined up with the galley holes. Looks like #2 is worse, then #3, then #1 and #4 being the best.

My machinist thinks oil volume is being bled off through the push rods (.080" hole in push rod, nearly a straight shot to open air). However, Other people have used this combo with out this issue. As well as initial oil pressure was good. Possible, but I don't know. I left out a lot of details trying to keep this short. Any ideas would be greatly appreciated. Or let me know if you want more details.

IMHO, the cam tunnel is not straight, may need align boring and oversize bearings,

What is the clearance on the cam bearings ?

Clearance is .0018"- .0021"

Cam tunnel was checked for straightness twice. If the cam tunnel wasn't straight, wouldn't the bearing wear be located in different spots instead of all in the same spot?

A forum member on another board which I frequent had a similar problem, he wiped out two sets of bearings VERY quickly and they looked just like these. He had been running an aftermarket cam (successfully) and decided to try a cam from a different supplier with disastrous results; changed cam bearings and tried again, same results. Put in the old cam (with new bearings, of course) and no problems whatsoever. All of the clearances were in spec with both cams and they spun freely when installed; there was some speculation that perhaps the cam journals had been polished in the wrong direction. I dunno, but it certainly appeared to be the fault of the cam.

Do you know if his two cams were from the same company? His situation does sound like mine.

Any way you can set the cam up in Vee blocks to chech the cam for run-out on the bearing journals and base circle on each lobe?

tom

We checked for run out when the second cam was installed.

Have you tested the oil flow to the cam bearings?

Seem there's no adequate oil volume at the bearings...

Is the bearing demage at the opposite side of the oil hole??

You should check the oil passages for dirty or clogged.

My two cents

BrazilianZ28Camaro wrote:Have you tested the oil flow to the cam bearings?

No, how is that done?

Seem there's no adequate oil volume at the bearings...

Thats along the lines of what my machinist said with the lifters/pushrod/rocker combo bleeding off volume. The crank and rods don't look that bad though given the situation. Not eaten up like that. Oil pressure starts out good.. even at a hot idle. Never gets to 0. Lowest it got was 15 on one of the cams before I pulled the engine. Verified with a mechanical gauge. However, the sensor is positioned right after the oil filter, prior to the main galley, which the lifters sit in.

Is the bearing demage at the opposite side of the oil hole??

A bit hard to describe from the image above, but the oil hole is apposite the shadow in that image. Yes, there is some damage there. I'll see if I can post some better pics later.

You should check the oil passages for dirty or clogged.

Have. No obstructions or dirt. Definitely going to check and clean it again. Probably see if I can see anything else with the boroscope we may have missed the previous two times.

SilverXJ wrote: No, how is that done?

I'm not familiar with your specific engine and oil passages, but if you can turn the oil pump with a drill and watch the oil flow through the bearings with the engine all assembled but the oil pan...would be a little messy but...there is a better idea:

You should measure all clearances involved in the oil pressure ... lifter to body clearance, lifter oil metering, crank and rod bearings...a loose clearance can bleed enough oil pressure and volume to cause a problem like yours...

Assuming that the first place the oil pump pressurize is the oil filter, 15 psi at idle measured at that point seem pretty low IMO.

Some engines loose much more pressure than that through the oil system.

Hope this helps.

SilverXJ wrote:Do you know if his two cams were from the same company? His situation does sound like mine.

The good cam came from Crane, the other one was from a well-known company that caters to inline sixes.... Naturally, they denied everything. They even tried to say that the ZDDP additive caused this.

He described the symptoms exactly as you have; started up fine, good oil pressure at first, then a steady loss of oil pressure; teardown revealed ALL of the bearings wiped out just as yours with the bearing material smeared and pushed out. This was in a Ford 300 six.
Joe

SilverXJ wrote:I'm hoping someone here can help me out with a problem I have been having.

I've had recent cam bearing failures. Two different block, two different cams. This is a 4.6L Jeep stroker engine. 4.0L block, 258 crank, 4.0L rods, KB pistons, Harland sharp roller rockers. Nothing special.

The first block was fine with a Comp Cam. Had a few thousand miles on it then changed it for an Isky cam and new lifters (with less lift than the Comp). Cam spun when it was installed with little pressure. Main and rod bearing clearances were .0018"-.0020. Cam breakin went fine using Joe Gibbs 50wt break in oil 30 minutes between 2000-2500 rpm, flat tappet hydraulic. Oil pressure started out good then I started noticing the pressure was dropping at idle. Standard volume oil pump, Clevite bearings. Bearing material was pushed out at the bottom and babbit looked like it had been spread about. All the oil holes on the cam bearings lined up with the galleys. No binding in the valve train. Plenty of room on the springs before bind as well as with the retainers to stem seals in rocker pivot. Cam tunnel checked out straight and true.

Taken from the bottom of the block.



New block ,new parts, crank turned. New Clay Smith cam, new lifters, bearing, oil pump, etc. Used Durabond cam bearings this time around. Same thing. Oil pressure started out good then dropping to less than 20 PSI at a hot idle. Used 30wt Brad Penn break in oil. Main and rod bearings were .0018"-.0020" again. Cam spun fine, and bearings lined up with the galley holes. Looks like #2 is worse, then #3, then #1 and #4 being the best.

My machinist thinks oil volume is being bled off through the push rods (.080" hole in push rod, nearly a straight shot to open air). However, Other people have used this combo with out this issue. As well as initial oil pressure was good. Possible, but I don't know. I left out a lot of details trying to keep this short. Any ideas would be greatly appreciated. Or let me know if you want more details.

You welded on the rig with a ground that went through the bearing. I did that myself so don't feel bad.

No welding. Haven't welded on it in over a year.

Quote
Assuming that the first place the oil pump pressurize is the oil filter, 15 psi at idle measured at that point seem pretty low IMO.


I think the old IHC Scouts was 0-10psi at idle...

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