jackhammer

If I were a betting man I'd say piston slap coming from #3 or #5... but I'm hoping it's something on top.

Both engines were rebuilt by the same shop. They have about 2-4 no-load hours on them (trying to tune carbs on land). Only one with the knock.

It doesn't start knocking right away... worst part is that it comes and goes. Sometimes it purrs perfectly. When it starts knocking the exhaust changes pitch a bit. It's loud at idle... enough to make a grown man cry. At about 2500-3000 RPM it's more a faint tick, it also changes the exhaust tone pitch and also comes and goes.

Is there anything I can try before tearing it back down?

Thanks!

cuda

Sounds like a lifter.

JTS357

I agree with cuda. It's gotta be in the top end, bottom end problems dont come and go. hows your oil press.

jackhammer

Oil pressure reads 60+

The knock at idle sounds pretty deep... do you think it could be a collapsed lifter or something? When it's collapsed it knocks the crap out of the lifter/rod/rocker/valve?

A new set of lifters is quick and cheap so I'll give it a shot. Do you think I'll be able to see any signs from the old lifters?

Thanks for the input!!

cuda

The main reason I suspect a lifter is that it is intermittant. Sometimes, a lifter will get a piece of crap that blocks the oil hole.

JTS357

JH,
When you remove the intake manifold, pull the sparks have someone crank the engine and watch the lifter and valve action you should be able to see a failed lifter pretty easily.

MitchStellin

I assume you broke the cam in and soaked the lifters in oil to prime them. You need to do this quick before you take out a lobe on the cam, I bet it is a lifter also, oil may be coming and going and causing the inheritance. I would check the rockers also. The fact it sounds deep would lead to a lifter, they are down there a ways and would radiate down also.

jackhammer

Thanks for the input guys!!!

Got it apart... Well at least the side where I thought the sound is coming from. I can't get the other valve cover off because of the exhaust manifold is in the way (can't get it off cause the other engine is in the way).

Looks like some strange wear on the cam (not that I'm an expert). It's not even. I was also surprised to see the lifters not being centered on the cam lobes... last engine I had they were dead center, but it was a roller cam so I figured it was normal to have flat lifters off center this way. Is it normal?

The lifters are shiny and actually look pretty good. I was cranking and watching closely... all lifters were rotating and lifting normally. Rockers looked good, rods look new.

Do I cross my fingers, put new lifters on 1,3,5,7 (suspect side), and fire it back up? or do I put the forklift back on it for the second time in a month? decisions decisions...

Lmarth

Jackhammer-- Based on what you said, I'd try changing the lifters. Piston slap typically is worst at startup when very cold and quiets down or goes away when the engine is hot. If the problem comes/goes and the tone of the exhaust changes, then I'd suspect something in the valve train. Lots of things can cause knocking (Excessive bearing clearance, loose wrist pins, exhaust leak at head,etc.) but they usually don't change the tone of the motor. My experience with wiped out cam lobes is that they go almost immediately and give you either a miss (intake) or backfire (exhaust). As I recall, the lifter bores with a flat tappet cam are off center so the lifter rotates. As for the strange wear on the cam, if the lobe isn't wiped, I can recall years ago where the cam lobe was shiny for part of the surface and darker on the rest. If the lobes were wiped, you'd see it the way the rocker arms went up/down. I'd try the lifter route, you've got nothing to lose.--Lou

Go Big

You may want to check for an exhaust leak. I had the similar symptoms and it turned out to be an exhaust leak.