Cold start, sounds like a piston slapping. Once the motor warms, 2-3 minutes it goes away. Oil pressure is high and remains that way. 60 during warm up, 20 at idle. I let the engine run for about an hour yesterday and never heard it again. So I'm guessing pull the motor and fix.... I guess I'm looking for assurance. Anybody ever have this? Not many miles on the rebuild, about 5000. Wah
Forged pistons? What clearance? May have just been setup on loose side piston to wall. I had an old school race motor setup loose....noisy for first few minutes....ran strong being a little loose....no breakin needed.
more of a knock, ive heard noisy lifters, its not that. stock pistons, i was hopping for the exhaust/intake leak. not sure. ill record andtry to post.
So once it warms up the noise is gone. Do I just drive like it is ? Is this like a hand grenade, waiting to blow? Its not a race car.... it will bark tires though. Thanks for all the comments. Paul
If it is piston slap, how would you fix it? You might need a slightly bigger piston in that hole. Some LS engines are famous for this, and other than the noise when cold, they are fine. One of the guys here on Long Island mentioned to me his engine does that with the Wiseco pistons. AFAIK, he isn't planning on pulling it apart. If that is the definite diagnosis, you might be better off just leaving it alone. Maybe have the engine builder listen to it?
I had the sides of cast pistons knurled to decrease clearance and noise. Machine shop screwed up and ordered cast pistons rather than forged after prepping block for the looser clearances for forged. Got rid of the cold piston slap.....
Had a 70 GS350 that had some piston slap when cold. Ran the hell out of it, beat on it unmercifully and it took it all. Unless the noise REALLY bothers you, just drive it and enjoy the car.
A bit of history Paul, back in 1975 my dad bought a new LeSabre with the standard 350 4 bbl, that thing knocked when cold, went away when warmed up, everybody told him it’s “probably “ piston slap, well that car went 185,000 miles before it went to the junkyard. That engine WAS NEVER opened up, just a pair of valve cover gaskets. It sounds like you’ll be ok, just drive it gently till it’s warmed up. Piston slap is pretty common in engines, my wife’s 5.3 does it (230.000 miles) when it’s 20 degs out or colder. My 4.3 Safari does it too 240.000 miles, My 2000 Monte Carlo 3.4 did it too. If your oil pressure is good I wouldn’t worry, it’s more of an annoyance
I believe a pretty common problem on Buick 350's with an auto trans is for the flywheel to crack. Sounds a lot like a rod knocking at times and sometimes is more audible than other times.
I started my car today and the noise is there just when the engine is cranking, I think you are right, cracked flywheel. Should be easy fix. It goes away quickly now that its warm out. Hew