My '98 Turbo is in the garage at the moment about to get the piston slap sorted, new piston, done under the 2 year extended warranty. A question for the more mechanically minded, does the over sized piston that I have been told they are fitting cause any form of engine im-balance, or is it so small a correction as to not be an issue. While we are on the subject, the garage is a dealer in Carlisle, and up 'till now the service has been excellent, giving me brand new cars for use when mine has been in their workshops, a refreshing change from the cr***y fords my previous garage used to dole out.

 

Hi,

Although the piston is slightly bigger, it doesn't necessarily weigh any more than what it is replacing.

All pistons on non STI cars (and probably those too) aren't likely to be balanced other than within normal production tolerences, so the revised piston only has to be within the same specs for weight and tolerences to be a 'match'.

My own car has been fine since the piston was replaced (even in the recent cold weather), so I'm sure this fix is quite legitimate.

Cheers,

Alex

 

Here in Sweden they rebore all the cylinders 0.25mm
And put bigger pistons when you got pistonslap.

In the UK do they check if the cylnders are oval?
My #4 cylnder was oval and that was why I got pistonslap.

 

slap on number four is normaly because they have put the wrong grade piston in the car or a piston that is not quite graded right you will find it is number 4 and you will find it is prob a grade b piston we have done loads of this and have no probs with the new ones in fact people dont even no it has been done apart from the noise has gone

 

Yikes. Im a bit thick so could someone explain this piston slap to me? what are the signs?

 

Turbo,

Have a listen to this recording of piston slap, provided by AJ Leslie, to hear what it's like.

http://homepage.ntlworld.com/alan.leslie/

Piston slap is when the bore is too big for the piston, or the piston is too small for the bore and the piston hits the bore. A very simple explanation of it.

With the Scoobs that have piston slap, you hear it when the engine is cold when first started. It goes away when warm coz the piston expands and the clearance becomes smaller.

Cheers,

Wrexy.

 

Silly question perhaps...

But talk of this slap and that STIs are treated differently in their engine build (more care/strengthening/balancing etc) leads me to ask wheter STIs are known to suffer from this..

I have a STI 4 and I dont think it suffers frm it..

cheerio

 

STi`s, I believe have forged pistons? Theoretically more likely to slap a little when cold (e.g. early Cossies, RS turbo`s)
Slap in the Cossie was cured by offsetting the gudgeon pin a tiny amount from centre. You would be surprised by the number of production cars which, without crafty little gizmos such as temp. controlled ignition dampers, oval pistons, offset gudgeon pins etc., would have slap when cold.
JohnD

 

So is it usually no.4 that needs a new piston to cure the noise and does anybody know whether aftermarket warranties will foot the bill ?

cheers

Daz