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We have a Chevy grain truck with a 366 engine. Last fall we were using it and it went to missing, so we pulled the valve cover off. It had eaten a push rod. We discovered it was not pumping oil out the push rods. We were thinking it probably spun a cam bearing. What does anyone else think?
 
Of all the cam bearings that COULD cause the, the rear one would be the most likely.

Does it oil on the other side... (could be a front lifter oil gallery plug missing).

Or, just a bunch of gummy lifters.
 
not sure if spinning a cam bearing is common or not, but I know sludge build-up is. seems like sludge in the dist. shaft area can do this on big block gm.
 
Go to a school bus forum. Those mechanics know the 366 in and out. It was the only gasser GM put in their large buses. I had only Ford buses - can't help with those.
 
Could be low oil pressure.If I remember correctly,some gm engines had a relief valve spring near the oil filter that would weaken or sludge up over a period of time.I had a 85 Chevy C-65 8 yard dump with a 366 . Good engine. Liked fuel!
 
need more info, did you fix it or is it sitting apart? have you pulled the lifters out and looked at the bottoms? have you checked the camshaft for wear? what tells you it was not pumping oil? you cant come to a conclusion by just guessing without an inspection of the valve train.
 
Hmmm. My FIL's grain truck with a 366 also started missing during harvest this year. We figured it is just a plug wire but we'll have to check this out as well.
 
I do know that they are fussy on oil weight used in them . We tried to use 15/40 oil in 2 of them and within 150 miles they had lifters rattling . We then put the 10/30 in them that they called for and they got quiet. Some of them may even call for 5/30 depending how new.
 
Well, if you are not sending oil out the push rods, you have a serious problem. The oiling operates this way on Chevys. Crankshaft operates the cam shaft, the camshaft operates the distributor, the distributor has a shaft in the base of it that drives the oil pump. Its possible, but unlikely that the shaft between the distributor and the oil pump broke or wore out, BUT its possible that the pin inside the base of the distributor shaft below its drive gear broke. Thats possible.

You didn't happen to lose, replace a worn or broken cam gear, did you? Nylon toothed cam gears were the biggest culprits of clogging the oil pump sump pickup screen when they break off, although metal ones can and do as well. The teeth on a cam gear break off, go down into the oil pan, get sucked up by the oil pump, clog the screen in the pickup, stop oil flow...and bad things happen...spun bearings, worn cam lobes, mushroomed lifters on their base, everything that moves internally inside of the engine gets damaged because oil isn't flowing through the engine passages to the moving parts.

Why don't you have oil pressure? Bad oil pump? Clogged pickup screen? Cam from a 1968 or older BB was inserted in a 1969 or newer BB using the newer cam bearings without solering their holes shut and redrilling at 3/16"?

If you got no oil to your lifters, its a short distance from your pump sump pickup to those lifters...pump, oil passages cast into the block, to the lifters. In the front of the block behind the timing cover are 3 plugs that are removed with allen head wrenches that run straight back to the back of the block. If my memory serves me correctly, at the back of the block they are plugged by freeze plugs. You pull the freeze plugs out, unscrew the allen head plugs at the front, and clean those passages out using a gun cleaning kit during a rebuild. At the back of the block, those 3 passages are tied to the passage fed directly from the oil pump, all cast into the block and machined for flow.

Its pretty simple. Oil pump sends oil up into its passage at the rear of the block. That passsage sends oil into the 3 passages that flow parallel to the cam, towards the front of the block. Those passages feed the cam bearings, crankshaft bearings, and the oil makes it to either the mechanical lifters, or into the hydraulic lifters to pump them up, either of which goes up the hollow push rods to lubricate the rocker arms, valve guides, anything that moves internally within the engine.

You have a blockage, or something physically broken that is stopping the pump from doing its job.

Good luck.

Mark
 
So, none of the rockers were oiling or just the one?

Best I recall, oil goes to the lifter galleys first and feeds everything from there. So, if no oil was getting to the lifters, no oil was getting to anything... That would be indicated by low or no oil pressure. If only that one rocker was not oiling, could have just been because there was slack from the bad pushrod, all the oil going down instead of up the pushrod.

Those engines were known for eating valves. The end of the rocker would dimple out, putting side load on the valve stem until the valve broke. Not that the valve train was weak, the rest of the engine was so strong it just outlasted the top end!
 
More information on the motor - this is a machine shop rebuilt motor, probably has at least 20,000 miles on it, it replaced a 427 motor, so it is a little undersized for the truck - a 10 wheeler twin screw with a 13 speed. It gets driven like a dragster. Sometime last fall we put a new air pump on it for the air brakes. The old air pump was having trouble pumping up full pressure due to blow by and it was pumping oil thru the air system so we replaced it with a new one. That is the only thing we have done to the motor since putting it in. This motor didn't use any oil - I used 15/40 oil in it like everything else, and always have. The motor is still in the truck - it just got hauled to our shop today. One of the boys was driving it and said it went to missing. They traced it to which side and hole was missing and ended up pulling the valve cover off and the push rod was gone. They put another push rod in it, and had it running, but they didn't think it was pumping oil like it should since it wasn't pumping oil out on the manifold and fender. They said it still had oil pressure. I don't know if it was higher or lower - it always had good pressure. We parked it for the rest of the fall and are just now getting to work on it.
 
Most of the time a miss is caused by burnt plug wire, The manifolds get hooooot. and cook the wires
 
One thing I have been trying to remember is where the oil gage plumbed in at. Most small blocks plumb in at the top, back of block. If this is the same way I would think it would show no oil pressure if there is a blockage. But this motor I think picks up lower on the block which could show pressure to the bottom end, I would think.
 
Were the rockers properly adjusted? If they were left too lose, they won't oil right. Should be backed off to clicking, tight to quiet, then 1 1/2 more turns.

If it has oil pressure, the rockers will be oiling.

Rockers are a common problem on those engines. Not a good place to shortcut!
 
Hopefully that is all it is. With all the other challenges during harvest this year (literally a foot of rain during the month of June!) we don't need any more disasters!
 
Picture of the grain truck.
a161870.jpg
 

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