John B

Brass in the pan and rear main bearing looks like the crank tried to move forward. The motor had about 50 total hours on it. It was rebuilt buy a Mercruiser dealer and had sat for 3 years. 10 hours after re-installation the main bearings are shot in the rear of the engine.
The pan was removed because of rear main seal leak. What could cause this? We would not want to fix the engine without knowing what the cause was, and have it happen again.

Could roping (too much oil) cause this?
Wrong flex plate?
Rubber engine mounts?
Shaft alignment?
???

Thanks for any thoughts, John B

Crazyhorse

Possibly the drive was creating forward pressure on the crankshaft/thrust bearing because of misalignment? Just a guess.
I know JimV had that on a boat a few years ago.

Raylar

I am not sure from your description whether the crank and block were previously matched parts, but it definitly sound like an improper clearance issue. The rear main has to be clearance to the crank thrust faces for proper clearance and usually about .005 to .006 is a good setting. If it was instsalled to tight or way to loose the thrust faces would breakdown under loads. The other thing puzzeling here is there is no brass in main engine bearings just generally tin, copper or aluminum. Are you sure its brass, which will generally remain shiney and look gold in color. If it is brass, check for a brass drive gear on your distributor. If it is installed on the wrong material cam gear it will wipe out quickly and could put a lot of brass in the oil which could get at the bearing. Oil pressure problems or oil temperature extreme can also lead to premature bearing failure. What kind of oil pressure where you seeing warm at idle and lets say at 3000 or so rpms. Also check your drive shaft input and coupler for correct alignment and make sure the input shat if not binding on its forward thrust, which could overload the crankshaft thrust faces. A properly misaligned input shaft , engine to drive ,can cause a lot of vibration and can actually damage crankshaft bearings. I have actually had customers who have snapped off crankshaft snouts because of drive alignment problems. Sorry for the number of possibilities, but that's why you are going to have to become Sherlock Holmes on this one!

Good Luck, I hope you findtrhe Gremlin soon!
Ray @ Raylar

SeaRay Jim

Just curious, did you pick it up in the last 3-4 months from a guy clearing out a handfull of 502's from a shop that closed, including selling them on on eBay?

John B

Jim, Actually I sold this motor that I have had for 3 years, it has not been on Ebay. I got a call from the new owner's mechanic, who told me of this failure. They want me to help make good on it (like pay for the repairs?). So I'm trying to determine the cause first, before determining what avenue I should take. I certainly don't want it to break again either way.

Raylar, The material in the pan is probably copper and tin etc, I haven't seen it yet. The clearances should have been good since the re-builder is renowned for it's work for a national organization (so I woun't name them).
Could an over zealous break-in do this?
The motor sat, could this be pat of the problem?
The installer has always been fanatical about the alignment of drives.

Thanks for the information, this could hurt!

John B

formula31

Take a real good look at the coupler, check for out of balance and out of true. I just found a damaged rear main and the only thing I could find was the coupler was not neutral but was very heavy on one side. The runout was within .003 however which is pretty darn good. Ive seen some out .025.

John B

Formula, I'll check that. I just read some past posts where oil lines were plumbed backwards. I'll also check into this.

Thanks, John B