Re: Worst tractor engine repair mistake

Posted by Mark - IN. on February 06, 2013 at 17:14:40 from (50.151.181.250):

In Reply to: Worst tractor engine repair mistake posted by RBnSC on February 06, 2013 at 04:00:07:

Not a tractor engine, but rather a 402 (factory .030 over 396) in my buddy's '70 Chevelle. He just rebuilt it, spending $$$ for machining, balancing and stuff. He had it almost ready to drop in the car, but no cam. He came over and asked to borrow one, so I went out and looked at several on a shelf and handed him a hydraulic Crane Fireball with good streetable lift and duration. Next day he tells me got it all together, dropped it in the car, fired it up, lost all oil pressure, turned that engine into high $$$ scrap. He thought the oil pump failed. I went over, helped him pull it, took it apart, and there was nothing wrong with that oil pump. I kept going through the parts over and over and finally the problem jumped out at me. The engine was a '70, and without thinking, I handed him a cam that was pre-'69 that I bought specifically for a '68 427 street Impala I built, but decided on a different cam. Chevy changed the rear bearing oiling hole and cam journal in '69. From '65 to '68, the rear cam journal had a groove cut in it, down the center, about 1/8" wide from memory, and the bearing oil hole was about 3/16" to restrict the oil flow and maintain higher oil pressure throughout the engine. In '69, Chevy did away with the groove in the rear cam journal, but to make up for lack of oil to the face of the journal, increased the size of the oiling hole in the bearing to about 1/8". They simply reversed the two, but I have no idea why. The cams were basically interchangeable in the big blocks PROVIDED that you used the correct bearings with the correct sized oiling hole to restrict oil flow through the rear oil passage in the block to maintain proper oil pressure.

My buddy showed up and asked to borrow a cam for his '70 ('69 or newer) engine with larger oiling hole in the rear bearing that should have used a rear cam journal with no groove cut in it. Without thinking, I handed him a '68 or older design cam with a huge groove cut in the rear journal for increased oiling due to the smaller oiling hole in the rear bearing for the '68 or older engines. Maybe because they moved from the cartridge oil filter to the spin on in '68, but I knew better and just didn't think about it. So when my buddy mated that '68 or older cam with that big oiling groove with the '69 or later bearing with the bigger oiling hole, there was nothing to restrict the oil flow in the rear journal right above the pump (source) of oil flow to force the oil through and to the other passages throughout the engine block and components. No oil to the crank or rods, no oil to the cam and lifters, and that engine seized and became scrap, at whole lot of $$$ worth of scrap. The fix to use the older cam with the newer bearing, would have been to solder the oiling hole shut in the rear cam journal, then redrill it smaller at 3/16", install it and all would have been fine.

It was so long ago and I honestly don't remember if I told him or not. He didn’t punch me, which he should have, so I’m pretty sure I might not have told him. I might have though. I honestly don’t remember.

Mark

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