piston / bore clearance
Turbo Mini Forums

im having a 3 way conversation here but just want to run it past you lot before committing to anything

my engine is in for machining now, but the measurements dont add up to them, the instructions say
bore to the std bore plus 20thu for race use or
reduce the bore down to give 3.5 to 4thu clearance for road

the problem being std bore +20 only give 1.5 thu clearance the pistons being 2.795 inch

i have called med ( who im calling back in 5 mins) med say bore to 2.800 inch but again this will give only 1.5 thu clearance

i say bore to 2.802 solves the problem but my machinists want clarification

im to phone med again but what do you guys think?

Yes i moved to the darkside

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Do they have the pistons ???

No machine shop I've ever used would be prepared to bore a block without having the pistons (or at least one of them) in their hands to check it's actual measurement.

Then all they would want to know is the clearance you want.

Schrödinger's cat - so which one am I ???

Yes i moved to the darkside

Instagram @jdm_brett

I believe maximum standard clearance is 2.5thou.

I guess in a perfomance build you may want to open this up slightly which is why the 3thou figure is quoted.

Edited by John on 24th Feb, 2010.

If something is worth doing, it's worth doing half of.

Search and you will find!!!

http://www.turbominis.co.uk/forums/index.php?p=vt&tid=1920

If something is worth doing, it's worth doing half of.

im calling med back tomorrow and there going to measure a set of pistons for me , mr med thinks either my pistons are 2 thu too big or the machinists calliper is out, there going to bore my block and wait for final honing measurement

Yes i moved to the darkside

Instagram @jdm_brett

I've used 0.6mm (~2.5 thou) but that is on the high side for a non-turbo road car.

Probably about right for a turbo on Mini diameter pistons.

Schrödinger's cat - so which one am I ???

Schrödinger's cat - so which one am I ???

Drakes in Bradford come highly recommended.

If something is worth doing, it's worth doing half of.

I had no ill effects running 5 thou piston to bore clearence on my last engine.

The ring gaps were at the top end of the recommended maximum, but it ran bloody well with no smoke. Its nestling under the bed now as I may use it in the future.

Speak to your piston supplier or manufacturer, different pistons ie material it's made of & piston style ie design of piston require different clearances

Yes i moved to the darkside

Instagram @jdm_brett

i think i am all sorted now, they was using micrometers, 3 to be exact, read by 4 different guys who all came to the same conclusion, the dimensions supplied was wrong. fortunately med was ably to give the skirt clearance's (rather than bore diameter) for the cast omega's at +0.020 inch.
0.0025 - 0.0030 inch

cheers guys

also may i add, MED was very happy to help so thanks to the for that :)

Edited by Brett on 25th Feb, 2010.

Yes i moved to the darkside

Instagram @jdm_brett