L82, Forged piston "slap"
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,139
Likes: 109
From: B'ham Alabama
L82, Forged piston "slap"
I would like some input. I recently purchased a 1975 L82. It runs great,..but has the "forged piston slap". While most of the engines with forged pistons usually have a slight "slap" effect,..this one is a little louder than most.
It has great compression, runs very smooth, does not burn oil and no "blow-by". However, the "piston slap" is a little concrning.
What is everyones take on this?
How can it be remedied?
It has great compression, runs very smooth, does not burn oil and no "blow-by". However, the "piston slap" is a little concrning.
What is everyones take on this?
How can it be remedied?
Instructor
Joined: Nov 2012
Posts: 219
Likes: 0
From: Irma Northern WI
I ran an L-82 with piston slap for nearly 40,000 miles without issues. I certainly do not like listening to it though. Forged pistons are installed with a little more clearance than cast pistons as they are not as thermodynamically stable. The slap should go away after a short warm up period. If it does not go away, you should address the issue. Forged pistons can take that abuse but, there are limits.
Le Mans Master
Joined: Oct 2007
Posts: 7,454
Likes: 977
From: RI, Now Franklin/Nashville TN
My L-82 has had piston slap when cold since I bought the car in 1983 with 25,000-Now has 66,000 miles. The slap always goes away once the car warms up and is very normal for these and many other GM engines as long as it goes away after warm up. My 2001 Pontiac Grand Prix 3.1 V6 also piston slap when cold and ALWAYS has since day 1 new-140,000 miles on the engine now and runs like the engine was new.
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,139
Likes: 109
From: B'ham Alabama
She runs right around 190 when full warm. Never gets any hotter. Oil pressure is slightly over 40lbs, (half way point on the gauge), when full warm abd idling. The rattle, (slap), never goes completely away.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
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
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,139
Likes: 109
From: B'ham Alabama
No blow by, no leaks, no smoke and no oil consumption yet. It holds very good oil pressure and runs out oerfectly. Just sounds like a diesel running.
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,139
Likes: 109
From: B'ham Alabama
It runs just over 190 when fully warmed up.
I am running 20w50 oil right now.
It holds just over 40lbs oil pressure wen hot idiling.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
Dont worry about it.
My 02 Silverado sounds like a diesel the slap is bad it doesnt hurt a thing.
There isnothing you can do about it except rebuild and use a piston with a tigheter piston to wall clearance.
These are performance motors youre going to hear a little something.
My 02 Silverado sounds like a diesel the slap is bad it doesnt hurt a thing.
There isnothing you can do about it except rebuild and use a piston with a tigheter piston to wall clearance.
These are performance motors youre going to hear a little something.
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
From my experience that oil pressure is a little high for a stock engine. Nothing wrong with it though. Mine is only about 25lbs. at warm idle. Original L82 with 40,000 miles. Perhaps someone has changed the oil pump in the past? I would stick to 10w-30 oil. This of course has nothing to do with the noise. Just wondering if the engine is stock. I have verified that I have TRW pistons by removing the pan in the past but mainly to change the pan gasket. What is the history of the cars engine? mike...
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 1,139
Likes: 109
From: B'ham Alabama
It is VERY peppy,...runs out very strong.
I came from a classic car auction,...so I have no prior history on the car.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Try and google that for yourself. But i read a lot of posts saying it could be carbon on the pistons and a good fuel cleaner like SeaFoam will help. Others say stay away from SeaFoam. And others say use different oil additives or oils or even synthetic.
I leave it up to u to straighten it all out.
Please report back what works and what doesn't,
cardo
I leave it up to u to straighten it all out.
Please report back what works and what doesn't,
cardo
Burning Brakes
Joined: Mar 2005
Posts: 1,231
Likes: 34
From: Ontario
Change the oil and put in some 10 x 30 Ritella T or similar diesel type ans see what the results are .
Since you purchased it at an auction the seller may have put heavy oil in to reduce engine noise .
The idol oil pressure is high for a used engine and leads me to suspect heavy oil in the crankcase to reduce piston slap . You may not have forged pistons just collapsed skirts .
Bill
Since you purchased it at an auction the seller may have put heavy oil in to reduce engine noise .
The idol oil pressure is high for a used engine and leads me to suspect heavy oil in the crankcase to reduce piston slap . You may not have forged pistons just collapsed skirts .
Bill