Engine knock fades once warm.
Thread Starter
Melting Slicks
Joined: Sep 2004
Posts: 2,412
Likes: 3
Engine knock fades once warm.
Sounds like I have a slight knock, but it goes away after a minute once the engine starts to heat. Is this normal?
Engine knock means too much compression and timing, not enough octane right? Should I be worried?
Engine knock means too much compression and timing, not enough octane right? Should I be worried?
Thread Starter
Melting Slicks
Joined: Sep 2004
Posts: 2,412
Likes: 3
Piston slap? Eeek 
I don't know. Sounds like someone is lightly tapping on the valve cover from inside. Could be the new distributor, it started once I put it in. But then again, it could be because of the adjusted timing...
I don't know. Sounds like someone is lightly tapping on the valve cover from inside. Could be the new distributor, it started once I put it in. But then again, it could be because of the adjusted timing...
Le Mans Master
Joined: Jul 2001
Posts: 9,622
Likes: 16
From: absecon nj
Without hearing it its hard to say,i was thinking if it had forged pistons they sometimes give a slight knock when cold till they heat up.So it wasnt making this noise till after you put the new dist. in?
Thread Starter
Melting Slicks
Joined: Sep 2004
Posts: 2,412
Likes: 3
I do have forged pistons. The knock may or may not be distributor related. I might not have noticed it till after I put the new distributor in, or the advanced timing with the new distributor might play a role.
But you say that this is common with forged pistons?
But you say that this is common with forged pistons?
Melting Slicks
Joined: Apr 1999
Posts: 2,675
Likes: 13
From: Sudbury MA
I had a similar problem when I installed my new engine. Called the machine shop, guy came to the house and when he put his hand on the distributor the slight pressure of him leaning on it made the noise go away.
The noise was caused by excessive end play in the distributor gear on the bottom of the distributor. I rebuilt it to factory specs (shimmed the gear on the bottom) noise went away. It wasn't my engine after all, it was the distributor but I almost had a heart attack thinking it was my new engine.
You might get lucky and have similar problem, sounded like a faint tapping but it was really the distributor riding up and down slightly and causing the tapping sound.
The noise was caused by excessive end play in the distributor gear on the bottom of the distributor. I rebuilt it to factory specs (shimmed the gear on the bottom) noise went away. It wasn't my engine after all, it was the distributor but I almost had a heart attack thinking it was my new engine.
You might get lucky and have similar problem, sounded like a faint tapping but it was really the distributor riding up and down slightly and causing the tapping sound.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Originally Posted by shafrs3
Piston slap was the first thing that came to my mind.
The forged pistons expand more and require larger piston to wall clearances when the engine is built. They will slap when cold. Once it warms up the piston expands and the knock goes away. Let the car warm up good before driving it hard with forged pistons. I went with the high silicone forged pistons from Mahle for this reason. Recommended wall to piston clearance .003 with a forged piston.
