OK, time for another of my soon-to-be-famous ignorant questions designed to make the technically-capable amongst us feel smug.

I was just wondering about the replacement piston used to cure piston slap. I’m sure I’m wrong but I think several posts have said that it’s a ‘bigger’ piston, not just rings?

If this is correct, my question is – what does this do to the balance of the engine?

In my limited technical ability (soon to become obvious how limited ), I’d assume that having two different size (and hence weight) pistons on opposite sides of a boxer engine would play hell with the balance? I mean, isn’t this one of the things that blueprinters strive for – equal weights for balance?

Of course, you could assume that the design engineers would have taken this into account and the new piston is shorter as well as wider, or some such, but then, you’d assume their testing would identify the piston-slap problem too before mass-production started?!

Please feel free to gently educate me on why I’m wrong!

Cheers,
Steve

 

I'm not a techy, but I've read that the difference in the weight of the replacement piston is so small that it does not cause any problems with the balance of the engine.

Can anyone tell me if only one piston has the easy access hole. If so, what number or location? - I take it that it's the one always effected by piston slap (no 3 or 4?)

 

the difference in size is 60 microns so it won't effect the balance of the engine. as for the spy hole for each piston there is 2 bungs in the timing belt side of the engine which have an allen key fitting and behind the flywheel there are 2 plates which when removed give access to the other 2 pistons

 

As Scoobyboy says the new piston is only a tiny bit bigger than the old one.Not enough to make any difference especially when you consider this next bit of techy stuff.

There are two types of balance used to describe car engines.
They are primary and secondary balance.
Most types of engines have perfect primary balance but very few have perfect secondary balance.Flat four engines are one of the few that do along with straight sixes and v12s.

So the Scooby engine has perfect balance to start with due to its design.

By the way I had no4 piston replaced 1K miles ago on my my98 and it has NOT cured the piston slap but merely reduced it.I'm not happy.

Andy

 

Damn, you guys are good - thanks for the info!

Now all I have to do is get my dealer to confirm if my MY98 is a slapper

Maybe they can do so at the same time as changing the clutch & flywheel!

Cheers,
Steve

 

spider,
Had my MY98 done about 500 miles ago. Engine still running fine, no balance problems. In fact, I didn't realise just how much engine noise was due to the slap problem - unbelievably quiet now (for a scoob).

Andrew

 

Does anyone know if they have to take the engine out to perform the piston replacement? and/or do they have to disconnect the downpipe from the turbo?

(You can guess where this line of questions is going)

Andrew - soon to be SS downpipe owner.

 

yes the engine comes out and if it is no.4 piston being changed which it could also be no.2 or both then the flywheel comes off the n/s head comes off and the modded piston is fitted with new rings and the whole thing reassembled. and the exhaust is usually taken off at the turbo down pipe and then removed from the engine completely when the engine is out of the car