what exactly causes piston slap??

Foxfan88 · Jul 11, 2005

I know the cyl wall expands and all that, but does just abuse cause it?
I have some piston slap, its noticable, but not too bad. i dont abuse the car so maybe the people before me????

bluevenom867 · Jul 11, 2005

Foxfan88 said:
I know the cyl wall expands and all that, but does just abuse cause it?
I have some piston slap, its noticable, but not too bad. i dont abuse the car so maybe the people before me????

The pistons expand to,so expansion rates dont have TOO much to do with it.

Could be worn rings...maybe a hard turning wristpin.

Just deal with it I guess.

HISSIN50 · Jul 11, 2005

It depends upon what kind of slugs are used. Guys, remember that dissimilar metals have different rates of expansion.

Forged slugs are more likely to have cold (start up) slap since they fit looser in the bores when cold, because of this (hypereutectic pistons fit tighter than forged, so no slap).

bluevenom867 · Jul 11, 2005

HISSIN50 said:
It depends upon what kind of slugs are used. Guys, remember that dissimilar metals have different rates of expansion.

Forged slugs are more likely to have cold (start up) slap since they fit looser in the bores when cold, because of this (hypereutectic pistons fit tighter than forged, so no slap).

Yes,but once its warmed up it shouldnt make any piston noise.

Foxfan88 · Jul 11, 2005

Its a 91 so they are forged (unless the motor isnt the stock one, i doubt it)

I dont really hear it much, but i take it easy b/c i KNOW its there, if i beat the car until it starts getting really hot, then a KNOCK starts i mean loud and unhealthy sounding.

This isnt a cold start issue. Its there, it just usually doesnt get hot enough to hear it well, since i've been babying the car recently. The sound is from the same part of the motor, we had a guy listen to it a while back and he said he heard some piston slap from the left side. And this guy knows his stuff so yeah. I am guessing its a worn ring??

DMAN302 · Jul 11, 2005

Guys who "know there stuff" are often quite far off base when they diagnose by ear..your not hearing Piston slap if the motor is at temp...that knocking sound is likely a more serious issue making itself known. Worn rings are not going to be heard..but seen when the throttle is applied and smoke is leaving the tail pipes. Sorry to sound grim..but any knocking when at temp is something you really don't want to hear..cold start up..ok..warm..um not a good thing at all. My 88's original motor had 200,000 miles and some SERIOUS blowby issues near the end (bless her soul)..but she was quite and polite right up to the day I pulled her (ran like a raped ape but used a quart every 100-200 miles ). Get an oil pressure gauge on that thing and FIND out what that knocking sound really is. Or just leave it and sell her like you indicated you were going to do on another thread.

bluevenom867 · Jul 11, 2005

DMAN302 said:
Guys who "know there stuff" are often quite far off base when they diagnose by ear..your not hearing Piston slap if the motor is at temp...that knocking sound is likely a more serious issue making itself known. Worn rings are not going to be heard..but seen when the throttle is applied and smoke is leaving the tail pipes. Sorry to sound grim..but any knocking when at temp is something you really don't want to hear..cold start up..ok..warm..um not a good thing at all. My 88's original motor had 200,000 miles and some SERIOUS blowby issues near the end (bless her soul)..but she was quite and polite right up to the day I pulled her (ran like a raped ape but used a quart every 100-200 miles ). Get an oil pressure gauge on that thing and FIND out what that knocking sound really is. Or just leave it and sell her like you indicated you were going to do on another thread.

Worn rings CAN make noise,he never said it was making somke thou,so probably not.

Valvetrain.

Did you take the valve covers off?

Try that and start the motor (if you can).

TC93 · Jul 12, 2005

The knock you here at temp maybe the rocker noise. The motor may have some clearance issue's with the bearings. When the oil is up to temp and thinned out, and pressure drops, starving the rockers.

Do you have an oil pressure gauge hooked up? (beter than stock) If so what are the readings??

Foxfan88 · Jul 12, 2005

were trying to get my guage problem fixed shortly, i dont have a good oil pressure guage at all, i havent had a guage since i've had the car

There isnt a knock at temp there is a knock when overheating, now i dont think its a bearing, or it should do it all the time.

This sound i hear all the time is probably just some rocker noise thats normal. My mind may be playing tricks on me. Or it could be some slight detonation since i think my balancer might be bad.

But i still think its a some piston slap, when overheating the oil's visocity is reduced, so there is more room for piston movement, am i correct?

Now right now i am running a tad thicker oil than normal on my last change, i am due for a change here in the next week so what type of oil, thickness? and are there any additives i could use???

bluevenom867 · Jul 12, 2005

Foxfan88 said:
were trying to get my guage problem fixed shortly, i dont have a good oil pressure guage at all, i havent had a guage since i've had the car

There isnt a knock at temp there is a knock when overheating, now i dont think its a bearing, or it should do it all the time.

This sound i hear all the time is probably just some rocker noise thats normal. My mind may be playing tricks on me. Or it could be some slight detonation since i think my balancer might be bad.

But i still think its a some piston slap, when overheating the oil's visocity is reduced, so there is more room for piston movement, am i correct?

Now right now i am running a tad thicker oil than normal on my last change, i am due for a change here in the next week so what type of oil, thickness? and are there any additives i could use???

Well you should have a good oil gauge befor you run any test.

An detonation would probably affect more than just one cylinder.

Maybe a bad fuel injector,that could cause detonation in just one cylinder....but I doubt it.

I uses to run 20W-50 in the 302,could try that.Never made any noise for me.

Then again,it could just be a normal noise.

what exactly causes piston slap??

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