Piston Slap?

[FXGTV]

I've discovered that what I thought was pinking is in fact piston slap in my gt-s sw20.
Can someone please explain this term as I have no fricken idea what it refers to. Is it serious? My mechanic seems to think its not a huge deal, but getting a second opinion from the boffins on here is always a good way to go I might be joing the blown 3S club earlier than i expected

[Distrb]

are you sure you don't mean piston slap which = pistons hitting valves?

which is not good

[FXGTV]

Yeah - you're right. I must have heard him wrong - i've changed the title to suit. I've done a bit of research and it looks like I dont have to worry about it till the rings wear - the noise still pisses me off though.

[Skin]

are you sure you don't mean piston slap which = pistons hitting valves?

which is not good

I would of thought that would be near on impossible for a 3sgte, being a non interferance engine and all.

[Jdawg]

I've always known piston slap to be worn cylinder/piston. Piston wobbles about, making knocking noise, until the engine warms up. Eventually you will either rebuild the engine or replace it.

[fivebob]

are you sure you don't mean piston slap which = pistons hitting valves?

Never heard of that being called piston slap before

Piston slap is the sound made when the piston is loose in the bore and rocks around the wristpin axis slapping against the bore. Most usually the sound made at startup when you have low silicon forged pistons with a large piston to bore clearance.

[FXGTV]

Is it usually made at start up because the metal is cold and therefore smaller than after heat causes it to expand?

[Adydas]

If that theory is right, wouldnt it be the other way around? as the metal expands it expandes closer toward a point of touching..

[Distrb]

are you sure you don't mean piston slap which = pistons hitting valves?

Never heard of that being called piston slap before

I must have got the wrong end of the stick on that one back in time

[Quint]

Easy tiger, there we go, fixed for your pleasure.

[d1 mule]

piston slap = side to side motion, piston slopping around in bore.

[Lloyd]

As Fivebob has said, and usually associated with forged pistons when they're cold

[fivebob]

If that theory is right, wouldnt it be the other way around? as the metal expands it expandes closer toward a point of touching..

No, it because of the excess clearance allowing the piston to rock in the bore before the skirt can do it's job of controlling piston rock. So, unless it's in close proximity to the cylinder, then the piston movement about the pin axis will accelerate such that the skirt is able to displace any oil film on the bore and you get metal to metal contact.

[fivebob]

i thought (best starter ever)

Piston slap was after the piston had travelled many many kms in the same area it hones itself a 'travel area' inside the cylinder. Once wear starts happening and the piston head becomes a little loose on its wrist pin it travels further up than it used to, there is then a little tiny intsy wincy lip made by the piston at the top of its travel, the piston ring then trys to travel further than it used to and catchs on the lip and goes, donk. You then have to bore out the cylinders to the factory max limit and replace the rings. Makes the knock go away, though this usually causes blow back. (breather sucking oil past the rings as its now at its limit due to the boreing and putting it back into ur intake... yay for emission control )

Other solution is to bore it out and use slightly bigger rings, but thats lots of work.

This get my award for the biggest BS of the year, though it's early days so no doubt it will be surpassed by another Toyspeeder

FYI the lip is made by the rings not the piston and any play in the wristpin is likely to cause the piston to hit the head, just before it fails spectacularly.

No way could you bore the engine out and fit bigger rings and fix anything, f**k it... Yes, fix it...NO.

There's good reason why piston manufacturers specify a tight range for piston to bore clearance, and exceeding this by doing stupid things such as you describe can only lead to failure.

[jondee86]

I would have thought that if the pistons were getting intimate
with the valves, a slap would be in order

Cheers... jondee86

[Quint]

Easy tiger, i said thought.

and i did mean the lip was made by the rings, not the piston. But thats cool i'll show u a trick!

[ChaosAD]

I remember reading something about piston slap being assosiated with big ends on their way out.

But yea its the piston skirt slapping on the side of the cylinder wall. Like the old school forged pistons when they were cold.

[Akane]

When my big end went, my pistons was hitting the top of the cylinder head, is that called piston slap as well?

When I had forged pistons, which I was told it was the low silica content JE's (huge clearance), it didn't make any slapping sound neither.

Break the engine open, let us know what it really is.

[Lloyd]

When my big end went, my pistons was hitting the top of the cylinder head, is that called piston slap as well?

Thats either called "being broken", or "rooted big end"

[FXGTV]

When my big end went, my pistons was hitting the top of the cylinder head, is that called piston slap as well?

Thats either called "being broken", or "rooted big end"

Hahaha, good call. I just found out my Dad used to be some sort of mechanical engineer lol. (good thing to tell me after all these years ) He seems to think most if not every car gets psiton slap eventually, even if it is only minor, so its put my mind at ease somewhat. Thanks for the help folks.