3.4 P/R knock - cam?

[fyrebird68]

My first post on a great forum. Pleae pardon the long explanation, but I have done a lot of work on this and want to make sure I put all important information out there. I am out of ideas and hoping for new direction.

I have a 3.4 P/R from a 95 Camaro that was a fresh rebuilt short block (rebuilt by someone else). Ran OK for 400 mi., then developed a knock. It wasn't constant - an irregular tapping, which occurred only at idle and when the motor was warm. Also had low oil pressure when the motor was warmed up.

I pulled the motor to check the bearing clearances and oil passages. The motor and oil inside was FILTHY. It was supposed to have been tanked and cleaned but I am guessing nobody ran a brush through the galleys. Bearing clearances were wide (.08') but within the tolerances I found listed for the motor. Only light scoring. I was thinking I had a clogged oil passage somewhere that caused the knock so I cleand it up and put it back in. Still had the knock.

Listened and poked around some more and decided that the sound was too deep for a lifter/valve and too light for a piston or bearing. I pulled the motor again. The timing chain was loose (supposedly new) and I could move the cam in/out enough that it would contact the block at idle - clunk. Under acceleration there was tension on the chain to pull it true. I'm thinking "I got it". Also was missing the timing chain guide.

I put a new roller chain set and chain guide on - nice and snug. Also installed a high volume oil pump while I was in there. Put it back in; now I have a continuous knock of the same pitch.

It could still be the cam floating, but I am running out of ideas. I don't have the veteran eye to spot the problem. I think I am just overlooking something. Maybe something that is used to hold the cam in place?

BTW oil pressure is still a little low at warm idle.

Could really use some advice.

Thanks,
Bob T.

[paxter]

If you meant .008" on the bearing clearance that is most likely the problem. Max is .003".

[fyrebird68]

If you meant .008" on the bearing clearance that is most likely the problem. Max is .003".

Sorry - that was my typo. I meant .008 in. I am having trouble getting consistent information on needed bearing clearances.
I'll change these out and post with results.

Thanks,
bob T.

[pocket-rocket]

While you have the old ones out, you should probably check journal measurements as well to rule out (hopefully) a reused worn out crank. If it's too worn you can get a remanufactured crank that will come with the correct bearings for it.

[fyrebird68]

While you have the old ones out, you should probably check journal measurements as well to rule out (hopefully) a reused worn out crank. If it's too worn you can get a remanufactured crank that will come with the correct bearings for it.

Should I be able to buy oversize bearings to compensate for a turned crank?

[pocket-rocket]

If the one who rebuilt it turned it, yes. If it's out of standard specs but not within turned specs, then you could either have it turned or get a reman'd (turned) crank with a warranty and the correct bearings.

[fyrebird68]

If the one who rebuilt it turned it, yes. If it's out of standard specs but not within turned specs, then you could either have it turned or get a reman'd (turned) crank with a warranty and the correct bearings.

This is uncharted territory for me; sorry if these questions seem obvious. If I measure the crank journal would I be able to go the the auto parts store and buy bearings that would work for that journal size?

[pocket-rocket]

If it is in the specifications range for your engine, yes. If it is not within the spec range, then the crank needs turned or replaced. Otherwise your oil clearances will be too large and you will be back to this same situation not too far down the road (low oil pressure and eventually possible engine failure). When the clearance between the crank and the bearings gets too large, oil will flow out from between them faster- reducing your oil film that the parts actually ride on. Thinner film means more room for metal to metal contact which leads to damage/failure.

[SappySE107]

The high output oil pump is only going to waste HP. There is no advantage to it other than being new at this point.