Hi,

I know that the 4wd pistons in a 2wd motor will give you lower compression (7.8:1 i think).

I've got a 2wd motor that supposedly has 4wd pistons in it, although one of the pistons has copped a flogging from a valve, so ive bought a set of 2wd pistons to replace them.. although looking at the pistons i cant tell the difference between the supposed 4wd ones and the 2wd ones??

the '4wd' ones are still in the block. Is there an obvious difference between the two pistons ?

How do i tell the difference between them ?

If they are the same (both 2wd) i could get away with just replacing one piston.

I quickly measured the distance between the crown and the middle of the piston on both sets and i came out with 8.3mm depth for both (if i remember correctly )

I will try to get out there tomorrow and do a better measuring job.

Any help would be appreciated.
Thanks,
Damion.

 

2wd pistons have a central piston pin. this is why you have (piston slap) on these engines

4wd pistons have a pin offset (thrust side) this stops the slap noise

All race pistons usually have a central pin design cos noise is not a problem!!!

Its due to the expansion of the piston when hot i think

hope this info helps

 

All pistons should measured at skirt 90 degrees to pin

as long as there the same size and your bores are good just deglaze bores and fit

 

Thanks.

Do you know if the depth is different on the pistons or the shape of the concave ?

 

the pistons recieve oil by 2 different means

The 2wd ones have holes just under the lowest ring which go right through the piston to the rod

The 4x4 ones have a notch cut out just under the lowest ring but this is not drilled through to the inner part of the piston, so no holes present at all.

Hope this helps

 

if you look at the bowl in the centre of the piston from above, 4x4 have a much larger surface area than 2wd (there is a circular flat section in the centre)

 

Hi just did a quick search on the net and ...





The bottom ones are what both mine are like.. so both sets are 2wd pistons i guess.

Just confirming that the top ones are 4x4 and the bottom ones are 2wd ?

Thanks fellas

 

correct,bottom ones are 2wd

 

Sweet looks as tho I'll only be replacing one piston then

 

what piston's this then?!!



its got a thin layer of oil over it after a wet compression test... (its the only pic ive got i'm afraid!)

 

No idea Simmo

Is it ok to just replace one piston ? (the bottom end was rebuilt not long before the valve let go ) As i have been told that its best to keep pistons as a set. Is this true, i wouldn't think so as all of the pistons are made the same ???

Thanks.

 

thats a 4x4 piston mate

i had mine machied to this and then machined further to wrc spec with big valve cut outs

 

ok... so this is a 4x4 piston machined slightly for lower comp?...

...suppose the only real way of knowing for definate is to burette it?

 

So the top of the piston is machined down and the piston sits down in the block at TDC ??

Who's the best person to talk to about doing this for info ? As i would need to get someone here in Aus to do it for me.

Thanks

 

i lowered the comp on my 4x4 too