What Causes Piston Slap?

Is it high mileage, worn out cylinder wall, or something?
And what's the remedy? Thanks.

 

Yes, worn cylinder wall. The remedy is to re-sleeve or buy bigger pistons.

 

What car has piston slap?

It is often not a matter of wear so much as a skirt collapse due to an overheat. Pretty unusual in a Ferrari motor is why I ask. At least with OE pistons. Years ago when many people were replacing OE pistons with Venolias it was a big problem.

Many mistake an early manifestation of a failing rod bearing or bad wrist pin bushings for a piston slap.

 

Or, if the piston is asymmetrical (axial offset of the small end of the conrod), having been mounted the wrong way around . Asymmetric pistons have marks on top for avoiding this.

 

Forgot about that one but you are right. We call it "off set wrist pin".

 

Thanks, I was just searching for a proper English term

 

It's OK. Your English is much better than my German. Ich spreche scheisse Deutsche.

 

Brian, I'm speaking about my wife's VOLVO which indeed overheated. VOLVO shop R&R the head gasket and new water pump. Car runs smooth and normal now but the piston slap sound is always there now.

 

I get it with my Tacoma but it is only in the colder months and only the first minute or so of start-up. It has done it since I bought the truck used with 16,000 miles on it in 2006 never had any motor issues and currently has over 100k.

 

Was a broken wrist pin on my 1965 Harley FLH w/Sidecar. I had a few more miles to go and nursed it home and upon disassembly saw that the wall had been scored. I learned all about boring/honing and compressing .10 over rings and all that internal stuff. The coolest part was the local Harley Davidson dealer (J.C. Little) loaned me their tool to remove/insert the new wrist pin. Not sure that would happen today.

 

Your Volvo sounds like it has piston slap as the problem. I call it being caused from collapsed pistons which can happen from the engine being overheated. Sometimes you can get away with just replacing the pistons and rings without boring the cylinders.

 

That's true.

Might do it for another 100,000 miles too.

 

My BMW e36 M3 had a slight case of this when cold that the factory claimed was normal due to the high heat generated in the engine. I know of many e36 M3 engines replaced by excessive slap due to failure of the cylinder lining material and an alleged failure of a subcontractor in the assembly - not sure what it was that failed. I sold my car with 120,000 miles with no issues.

 

The VOLVO tech told me it should be ok as lots of the VOLVO they work on all sounded like that and that my wife's Volvo should last at least 200K miles as long as I'm religious with the maintenance.

 

There is current issues with the Subaru just google Piston slap subaru and it will pop up. Also caused by long factory oil change intervals. Causing rebuilt engines at 60,000

 

The Chevy Z/28 Camaro 302, forged pistons, solid lifters etc. when cold sounded like a diesel.

 

My wife's 89 Volvo 740 with 357K on the orig. motor picked up what was always called piston slap at about 150K miles. It was typical for the old 4Cyl. motors but it is wrist pin wear causing the noise. Sounds a little like a quiet diesel at idle. She is trying to do 500K miles. Just can't convince her to get a new car.

 

What a coincidence, my wife's Volvo is also an 89 740 Turbo 4 cyl. with 189K miles, she bought it brand new, in fact we still have the original sticker/window price.

 

Yep she bought it new and we have every record. It's a GL and I just had the front seats redone with new leather and a new set of carpets. Just can't get her to get rid of it. She has had a green light for the last xx years to go buy anything she would like but she won't do it. Just did another exhaust system yesterday .

 

A) all pistons with wrist pins slap ,
B) pistons with small clearances have less noticeable slap than pistons with large clearances.
C) pistons with offset wrist pins make a different slapping noise than pistons with centered wrist pins.
D) pistons supported on a scotch yoke (and similar) do not slap

 

What is a scotch yoke? Is this used on an IC gasoline engine?

 

Not practical ones -- too much wear (see the wiki article)...

The same idea (eliminating sideways forces on the piston) is done on crosshead engines -- but these are typically only used on very large marine engines as the extra mechanism makes the whole package bigger an ups the reciprocating inertia.

 

It's not an uncommon 4 cyl turbo problem. Back when they were more of those on the road I took a few apart that were really loud and found cyl #1 piston had shrunk. Always seemed to have followed an overheating episode. I never saw one break a piston but there were some that made me very nervous.

Distinctly different noise than a lose wrist pin.

 

As it should have sounded then, all systems normal.
Built many of those, love the noise.

 

Piston slap as noted above is caused by excessive clearance between the cylinder and the wall. Different piston materials expand differently and require different cold clearances. Forged pistons (like the afore mentioned Venolia's) expand more when hot and need bigger cold clearances. As a result you can have a good bit of slap when cold and it will go away when the engine warms and the pistons expand. I had a 2 liter BMW motor that I build with forged Venolia racing pistons and it sounded like a diesel for the first couple of minutes when cold.

If you have a highly supercharged or turbocharged motor then the pistons will get hotter at high power and to avoid sticking, engines like this are commonly built with more clearance, and can slap a bit when cold too, but that is the price for higher cylinder pressures and hotter temperatures.