So yeah, looks like the engine needs to come back out again for a re-bearing.

I ran into this before using this factory high pressure oil pump from GM, but over the space of 100k miles. It wore the front main and cam bearings out.

Since it took over a 100k to do it, I decided to use the pump again since I didnt plan on running the car that long, and the other bearings looked OK. But, after only 10k it did it again! The front cam bearing is down to the copper backing. The surface is smooth and uniform, but severely worn, like it was overloaded. Could the high pressure oil pump + high pressure springs be to blame?

I cant see it being an oil issue with only one bearing bad and the others looking ok along with the top end having lots of oil. The bearing is also aligned correctly, so it should have been recieving oil.

I just cant win with this damn thing.

 

the only time a Hi pressure Pump Gives you a Prob. is when everything is tight to start with..

it could be nothing..but i would check the front of the cams runout. to see if its true.. then also check the block to see if the cam holes are also true... the Oil pump starts it's Job at the Back of the Block and moves forward.. look in the Lines it runs and feeds the front of the Cam..

 

Check the cam journals for roundness. Was oil contaminated at all to cause the wear out?
What timing chain you running? Cam walking on you?

 

I was running the factory single roller thats used with the goodwrench engines. I do recall it being somewhat tight, but nothing extreme. The chain still had a little slack in it.

I cant say for sure if the cam was walking or not. The next one will be a roller, so walk will not be an issue as there will be a thrust button.

I think the block is true as the cam just sort of sank down into the bearing as opposed to having one spot wear, but I will be keeping an eye out for it when I get teh bearing out. Im pretty sure they where all in line and the cam was ok, because the cam turned freely when I first put the motor together, and I had no issues installing it. The cam journal went down into the bearing at least .060", so I think I would have noticed that much mis-alignment on install.

As far as the oil pumps go, these are the ones that GM supplies with their crate engines. I was running 5W-40 syn., so the oil was not too thick.

Ill take a look at the oil gallies, but I cant see that being an issue as theyre drilled straight down the length of the block, unless that bearing's oil passage is partially restricted.

I do recall that it took a lot of torque to turn the engine over when the valvetrain was fully assembled. Baring the engine over, I could feel each lifter go over the top of the cam lobe. That, and all the tops of the lobes where pitted. I wasn't running a ton of spring, but i was running close to 270 over the nose because thats what it took to get the engine to 6k w/o valve float with this cam. When there are no rockers, the motor spins easliy. I suppose that its just an issue of all the torque needed to turn the cam + pump along with the force from the springs was just too much to support.

 

I do recall there being more extremely fine metal particulate than normal when I changed the oil, but thats more likey a symptom than the cause. There wasn't anything visible in the filter. The above-normal particulate made me suspect there was something up, so I did check the filter each time.

 

I was taking a look at the types of bearings available, and the bi-metal alum-silicon alloy ones look like a better bet for a performance application with bigger springs and what-not. Theyre harder than the soft tri-metal ones.

 

I was reading a thread on cam bearing failures on another forum and it seems that if you have higher volume higher pressure pumps with little oil restriction at the top of the engine, you can starve the cam bearings of oil. Its a redirect of oil flow. Oil will flow thru the lifters/pushrods/rockers to reach the top of the heads. If you dont restrict that flow, you can have large amounts of oil flow going to the heads and not thru the block to the cam bearings.

Seems to make sense. Sounds as if you do have some sort of starvation at the front cam bearing which is furthest away from the pump.

If you were to spin the oil pump shaft with the valve covers off, how much oil comes up thru the pushrods? If it comes out fast with lots of volume, that could be causing a problem.

Then again maybe your having oil starvation from lack of pump volume? May need more than just high pressure but also higher volume?

 

Thats an interesting thought. With the oil pump driven by a drill, the rockers had more or less a small flow of oil similar to what you would see with a stock engine. I would think that it would take a lot of oil loss thru the top end to actually cause a 60-80 PSI pressure drop along the length of the oil galley and starve the front bearing, to the point that it would drag the overall oil pressure down, especially at idle. This engine made 80-100 PSI at all times. Obviously that doesnt exclude a restriction ahead of the cam/lifter oil supply, but it does seem to indicate that the pump was moving as much or more oil than could flow through the whole system.

As far as oil volume from the pumps standpoint, I would assume that its a function of pressure alone in a SBC oiling system. Basically whatever oil doesnt circulate thru the system is bypassed back into the pan, so a HV pump operating at the same pressure would just bypass more oil, no?

To me, this looks more like an overload failure. The bearing didnt smear or get scored, it just wore out real fast, like the oil film collapsed. The surface of the bearing is more or less smooth. I'll take a pic of it later on.

 

As far as the front cam bearing goes, the last few motors I've opened up have had this same problem. I did a cam swap on my motor about 1.5 years ago and the bottom of the front bearing was gone. My motor only had about 250 miles on it then. Then about 1 year ago we did a cam swap on my brothers truck which had about 5000 miles on his new GM crate engine and the front cam bearing was gone. A friends truck with unknown miles also had the front cam bearing gone.

I have a newer block that has a 1/8" npt hole right above the timing chain cover. I'm really considering running a line from the back of the intake to this hole to give a little more volume of oil up front.

 

Its possible that it could be getting enough oil to build up a film the journal, but not enough to actually get the journal properly lubricated in the bearing.

The question is: is it due to high loading, or lack of oil?

 

Actually, one way to test that is to look at the front main and front-most rod bearings.

IIRC, those are fed off of the center galley, and the same circuit as teh front cam bearing.

Ill have to see what I find...

 

After a few searches, this appears to be a real common problem in all the GM pushrod motors, right up to the LS1s. The common agreement for failure is the distance from the oil pump along with the timing chain.

I guess the only way to fix it is to switch fron the soft babbit to the harder silicon-aluminum alloy bearings, and make sure the timing chain is not too tight.

 

Could a different cam bearing oil hole position help?
http://www.dura-bondbearing.com/Port...20Bulletin.pdf
http://www.dura-bondbearing.com/TechSupport.aspx

 

IIRC, the oiling hole of the front bearing is near the 60 deg. position, above the CL of the journal.

 

dimented24x7 I'd like to resurrect your tread, did u end up using the -silicon-aluminum alloy bearings- with better results?

thanks

Thomas