piston bore clearance
Turbo Mini Forums

Hi fellas I've just had a phone call from the firm boring my engine wants to know what piston bore clearance my engine needs to be. He says the book states 4 thou but he thinks that may be to much and it should be about 2 thou . He wondered if the extra was with it being a turbo can anyone help.

standard block being bored 40 thou not sure what else you boys need to help with the answer

cheers Tony

tony what pistons are they ?

@ 4 thou it will slap its tits off.

Found this

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=509971

I found my notes. I went for 2.5 thou at the piston skirt.

Edited by mossy2a on 14th Jan, 2015.

Hi ben the piston are omega +40's. i bought a engine in bits with a brand new set of pistons and was told they were +20's so was a wee bit shocked when he told me today they were 40's. I dont have any other info on them and there at the engine builders so cant look for any numbers so hope thats enough.

Cheers david for the info i have read this thread but it didn't seem to come out with a definite answer it was more like 50% for 4 thou and 50% against lol

Cheers Tony

My accralites slap like crazy for the first minute or two,then go quiet. Better too loose than too tight.

'Where does the engine go?'

what did you go for mate 2 or 4 thou

My engine builder did say he though 4 was to much and he said 2 was more realisic he was just worried he was missing something and I suppose also covering his back which you can't blame him for can you

Cheers Tony

Edited by tony 69 on 14th Jan, 2015.

What did the piston manufacture say

I run a supercharger and I don't care the TB is on the wrong side.
VEMS + 12 PSI + Liquid Intercooler = Small Bore FUN!

I ran 5 though after honing a block out to take standard MT pistons and they ran silently when cold. Obviously less clearance now leaves options to hone out for new rings at a later stage.

I got them new but second hand with no paper work. I have read that omega don't give out piston bore clearence due to ovaling

tell your pet machinist on those pistons with it been a turbo engine to put 0.002.5" thou "overall" on the skirt clearance and all will be well for many years

Hi ben is that overall honing incuded

cheers tony

"OVERALL" honing on the diameter of the bore

he will know what you advise him if hese been at it a while, which seems that way on your above post tony.

Yeh hes been at it a while he was telling me he did lots of these years ago.

Thanks for your help ben i really appreciate it

Tonyy

Don't know exactly Steve it was so long ago,but they are about a thou oversize from standard on the bore. Like you I've had these out numerous times with no sign of piston, ring or bore distress. Must have done at least 5000 very hard miles now including a lot of RWYB and much of that with NOS.

'Where does the engine go?'