extra PTW clearance for furthest from pump.

[QuattroFever]

my machinist has just told me hes going to hone a half a thou more piston to wall clearance for the pistons on the opposite end of the engine to the water pump?

That sound right? Ive never heard of anyone else doing this.

[Flat on my back]

.

Each bore needs to be honed to match the piston in that position...so he should be matching pistons/bores to get the same wall clearance all round.

Make sense...

[QuattroFever]

he says the piston furthest away sees more heat than the rest and so will expand more.

[Jamo]

he says the piston furthest away sees more heat than the rest and so will expand more.

Err wtf, he should be boring them to the piston sizes nothing else IMO

[GazzaG60]

slightly bigger than the piston sizes jamo or they wont go in. i know what you mean though.

basically each piston should be measured and labelled. then each bore should be machined for a that piston with the clearence specified by the manufacturer of said piston who knows the expansion properties of each piston.

[GazzaG60]

usually most heat is the farest one from the TB. best airflow so weakest AF and most heat.

maybe audi did the inlet this way to avoid high temp differences?

[QuattroFever]

ive never heard of allowing a little more. Maybe for an endurance racer? Wanted to see if anyone thinks his theory rings true.
Seems hes fluent in the ancient language of "******"

In two minds to let him bore the engine now.

[GazzaG60]

id not be going there i dont think.

i use impulse engines on rochdale.

myself and my mate have had things like block bores, sleeves, piston skims, rod balance and weight match, polishing, head ports/rebuilds, custom cams profiled. re shimming on solid lifters. never an issue.

if you are assembling yourself then you want everything clearly labelled. most shiops will give you the exact measurement they have taken things to also.

[QuattroFever]

this guy is a friend of a friend who works in a machine shop. Alot of ppl round sth london swear by him. I have wagner IM now so furthest from TB would be furthest from pump too. Maybe some sense there

[Jamo]

Do a poll of how many engines have been bored like this..........

[GazzaG60]

on motec you can tune each individual injector so that lean spots are avoided. they dont bore the block different to compensate.

bored bigger at the far end will result in slappy no5.

[Jamo]

And big big blow by on that cylinder, how would you gap the piston rings so they were equal across the cylinders?

[GazzaG60]

basically you would need a custom ring set for 1 piston lol.

or 5l of oil in the boot.

all i can say is if you dont want to upset your friend then have it done there. what i would try to do is instruct in a advisory type of way the bore/piston tolerence from the supplier to be applied to all pistons/bores and that youll take your chances without the bigger bore at the far end..

[G60Rallye]

And big big blow by on that cylinder, how would you gap the piston rings so they were equal across the cylinders?

Its not go to get big big blow by from half a thou more clearance! Same goes for piston slap which has been mentioned. The rings wouldn't be a problem to gap either not realy sure what you are getting at there?

If the guy has got a good repuation then it would be for a reason?

[QuattroFever]

basically you would need a custom ring set for 1 piston lol.

or 5l of oil in the boot.

all i can say is if you dont want to upset your friend then have it done there. what i would try to do is instruct in a advisory type of way the bore/piston tolerence from the supplier to be applied to all pistons/bores and that youll take your chances without the bigger bore at the far end..

spoke to the guy today. he said (you'll like this) "you're worrying about tolerances thinner than half a human hair, if you want to worry about something...apparently theres a bread crysis in outer mongolia"

I'll give it to him...he's quite the character and with some wacky theories too. He'll be boring them all the same now and labelling each piston for each bore.