scoobysnacks

I have read on this board that this is the case so you can replace a dodgy piston for the piston slap cure for example. However I have also heard lot's of comments like 'if you replace one you may as well replace them all' which to my mind contradicts this as it sounds like you have to take the whole engine apart. What's the truth then?

AlexM

There are covers on the block that allow you to drive out the gudgeon pin joining the connecting rod and the piston. This allows you to remove the pistons through the top of the block once the heads have been removed.

This removes the requirement to disturb the bottom end while working on the pistons (splitting the block, opening big ends etc).

Cheers,

Alex

scoobysnacks

How big a job is this compared to the 'usual piston replacement on a car' scenario? It's just that I asked a local garage (Porsche specialist) about the costs and was quoted about a grand off the top of their heads. They probably would not know about what you've expalained above and said I might as well do all the pistons... Is there any logic in doing all 4 using the method you've described or is it 4x the work (and cost)?

AlexM

If you are just doing the pistons/rings, it will always be cheaper to take the head off and extract the piston through the top of the block because it involves less disassembly / re-assembly time (labour costs).

Piston slap tends to affect one cylinder more than others - which one depends on the date of manufacture of your car.

Once the pistons have been extracted it should be possible to tell if one or all of them need to be replaced by checking the pistons and bores for clearance, ovality or other signs of wear. It is ok to replace them on condition, i.e. only if required.

A complete piston set would be the most 'correct' engineering solution, but then you would probably be into having the block bored, or at least honed. While you're at it, you should also replace the bottom end bearings, oil pump, rods.. yada yada.

If it is restricted to one piston, then just do that. They should be able to tell by disconnecting the fuel injector for each cylinder in turn.

Cheers,

Alex

scoobysnacks

Thanks Alex,

I've got the classic MY98 piston slap problem (mines a Jap WRX)effecting the one piston, whose number escapes me. I've done the disconnect spark plugs one by one routine and it's only one piston from which I get the noise. I know I can leave things as they are but am a bit concerned about increasing damage to the bore and costs in the future. What's you personal recommendation on this matter as you sound like you're in the know? I'll be able to afford it more easily in a year or so but would it be a disaster to wait? It's had the slap for at least a year and is on 57000 miles. Do you carry out such work and who else do you recommend? Obviously I'd like a good job but don't want to pay any more than I need to. Thanks again for any help.

Leeroy

I too have a case of piston slap on MY97 turbo. Found it to be only coming from number 4 piston (passenger side rear) on removal of HT lead.
Car has 65k and the noise only lasts for a few minutes on a morning. It has been a bit better on SUL fuel, and also isn't too bad on mild mornings. Thoroughly bloody annoying though!
IMHO no major detriment to engine life will occur, so long as the engine is not revved hard when cold and if the noise goes when hot, as all pistons expand considerably when warm and up to their designed operating temperature.
I have heard of one or two cases of piston skirts coming away (very bad!), although not on Subaru engines.
GGR website have a price list for standard pistons and rings which seem pretty reasonable, and can also supply all gaskets etc. required.
I have been quoted around 600 quid from Scoobysport and Power Engineering, and am generally a bit reluctant to spend this cash unless absolutely necessary. If it gets much worse i will do it myself (when i get time), and hope only one piston is needed.
Bloody annoying how a 4 year old car needs a new piston though!

AlexM

Hi,

I would tend to agree with Leeroy - it is annoying, but isn't worth getting too worried about as long as it goes away when the engine is warmed up. If so, you won't really get more engine wear than normal.. just monitor it - it will probably plateau and carry on like that forever.

My car UK MY98 had the single piston job done under warranty by Cheam motors. If I were spending my own money I would probalby have lived with it as it wasn't very pronounced.

Having said that, it did completely eradicate the problem, and the car has been nicer to live with since then. I'm probably hypersensitive when it comes to unwanted noises, benign or not.

Cheers,

Alex

scoobysnacks

Thanks for all the replys. One more thing though... If there is increasing ovalling of the bore where the affected piston resides (how likely is this?) will it greatly increase the repair costs in the future? Also, what exactly is involved when repairing an ovalled bore?

[Edited by scoobysnacks - 3/20/2002 9:37:01 AM]

AlexM

If any of the cylinders is rebored, you really should do all four to equalise the combustion chamber volumes, and keep everything in balance.

My piston was replaced at about 20k, and the cylinders were perfect... even the honing marks were like new, so I don't think this is too much of a factor. You won't really know for sure until you get the heads off and can measure up.

Regards,

Alex

AlexM

If any of the cylinders is rebored, you really should do all four to equalise the combustion chamber volumes, and keep everything in balance.

My piston was replaced at about 20k, and the cylinders were perfect... even the honing marks were like new, so I don't think this is too much of a factor. You won't really know for sure until you get the heads off and can measure up.

Regards,

Alex

Leeroy

Can piston slap cause inadvertent knock sensor switching? If this is the case, the timing will be fully retarded on affected cars, any ideas people?