cossie*mad!

Have 7.5:1 low comp accralite pistons and sounds like i have piston slap that doesn't go away. Had it checked and they fit perfectly in the bore, and have been told by different people that this is typical short skirt pistons...is this right?

The DIVA

iTrader: (3)

Depends on piston/bore clearance and wether or not they are offset gudgeon pin....

Pistons with a central gudgeon pin in a turbo engine with large clearance tolerances do tend to slap from cold, but this will usually subside a fair bit once they are warm...

Ebonycossie4x4

iTrader: (4)

its not about the comp its how the block has been machined to take the pistons...

The tolerance etc etc. Thats how i beleive it anyway

Piston slap is caused by wear to the bore over time. therefore if the bore is not machined to the correct tolelerances of the piston it will slap from the beginning.

people that do home builds and just hand it all to the machine shop without giving tried and tested diameters etc etc generally experience piston slap more...

Im sure people will come and shoot me down but im always trying to learn so dont abuse me too much lol.

cossie*mad!

It is a fairly recent rebuild, 450 bhp, no smoke etc and apart from that, goes well. Is it dangerous / detrimental for the engine?

STUCOS

iTrader: (8)

have genuine cosworth lc pistons,on a home built big spec engine.and it.s really quiet.

cheeRS stu

Rick

They are central pin, and do slap - it's not detrimental,don't worry.

Martin Hadland

What piston to bore clearance do you have? There should be no noise when its warmed up, I run lots of pistons with central pins and they are not noisy.

OldDan

Read a few places that slipper pistons make some noise - mine do, nothing too loud though.

lee2cossies

iTrader: (2)

Got accrilite low comp pistons in mine,checked all tolerances to workshop manual after machining and it rattles when cold but clears after a few minutes was told the same not to worry.

Red16

My mate had Arias pistons with Eagle rods in his Pulsar GTiR and they rattled from cold, sounded a little bit like a diesel does, but once the engine warmed up they quietened down.

B13 JUS

iTrader: (24)

What piston to bore clearance do people use with mahle 4x4 pistons

vroooom ptssssh

I think you usually find piston slap on new engines running Forged pistons. They need a fairly big bore clearance.

cossie*mad!

Hope you're right mate...I feel a better now

admanrs

I thought they required a smaller bore clearance?

OldDan

Mine rattled from cold, took it out for a spin and they were quiet when I got back

vroooom ptssssh

What makes you think that?

Alloy (forged) pistons expand a fair bit, so therefore need a bigger bore clearance than say a cast piston.

Im sure that's why manufacturors dont use forged pistons (as far as im aware?)