Piston Clearances
Turbo Mini Forums

Hello, im currently building a new engine for my turbo since the last one fooked up on me.

it will be used as a weekend car/track days... so a lot of high reving will be going on, more than likely be running somewhere between 10-16psi of boost, ive bought the 14cc acralites from avonbar (+40) and im wondering what the bore clearances will be for this type of engine? i looked in the box they came in but no info on what clearances i should use for this application? Cheers Johnny.

Well if the pistons don't specify, you'll have to resort to the Haynes manual.

I did mine 2.5 thou on the road car and 4 thou on the racer.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

thats on the piston skirt to the bore overall!
tell the machine shop ............
bored & honed, my engines are done at 0.002" nice and tight OVERALL Diamiter 0.002"

if you are REALY cooking the motor make it 0.004" as will says

i had to do a bit of ringing around for mine, each piston/size type is different, but forged need a larger clearance due to the higher expansion rate
phone avonbar? or even acralite, they was happy to help me

Yes i moved to the darkside

Instagram @jdm_brett

i have just built 2 engines using accralights 14cc dish +20 i have CNC bored and honed them, i have gave them 0.002" skirt clearence overall and built dozen more! in the past NO trouble to date bret

there nice and tight ish so the rings have a chance to bed in correctley without any! detrement to the running of the engine in the future!

but i suppose it youre using them in a track balls out motor ad that little more like i said

Edited by BENROSS on 20th Jul, 2010.

thanks for the replys guys, i remember someone saying 0.002" and when i said that to them they disagreed and said isnt that a bit tight? i think i will go for 0.004" just to be safe and it will give it more room for error. dont want it to sieze on me. i will be driving it every weekend normally with a bit of welly, and a couple of track days and the nurburg every year plus the drag days too.

Thank you, Johnny.

Why not either phone Avonbar or Accralite and ask?

Simples

I left mine with my machinist and he phoned Accralite.

You have to be careful witrh forged pistons as they sometimes have a larger clearance as they tend to expand more.

you will only get the same answer
like i said sprocket .......

mine ended going to 2.800 inch ( 18thou by my calcs)

all piston makes/types/sizes require different skirt clearance's

Edited by Brett on 21st Jul, 2010.

Yes i moved to the darkside

Instagram @jdm_brett

18thou, fuck off is it (sorry), that's like a 15thou overbore using standard pistons and rings!!!

I suspect you mean 2.8 thou, or 0.0028 inches.

No offence taken I hope Brett!!

Edited by wil_h on 21st Jul, 2010.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Yet more superb observations from mowog! I do feel I am on a personal crusade here. Is it just me?

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

Yes i moved to the darkside

Instagram @jdm_brett

Your not the only one Ben. Personally I have just installed a "inane ramblings filter" on my PC which seems to get rid of his posts quite effectivly. However I have to turn it off or I can't post or see my own posts

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

Piston to bore clearance is a personal choice in our kind of applications depending on how you intend to use the engine.

I think most high level piston manufacturers realise this so don't state a specific "one-off" clearance but you can ask them for advice based on a specific application.

Otherwise just use the OEM clearance available in Haynes or Rover Manuals.

I used 0.06mm (about 2 1/2 thou for the older members) with 73mm Hypatechs.

EDIT - missed zero in my 0.06mm......

Edited by Rod S on 22nd Jul, 2010.

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

On 21st Jul, 2010 Sprocket said:


Did the hypatecs come with instructions? If not, Minispares Aus are selling shit pistons

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

I use 0.06mm with Megas and Omegas.

If it's 0.20 bore it 71.12mm.

My pants didn't come with instructions, are they crap? :(

Use the piston and guess your piston to bore clearance, not my engine..........





That was exatctly what this 'professional' fucken genius engine builder did. Wow, it lasted a whole 1100 km.........fucken awesome....

If you expect me to believe that a cracked liner/bore on whatever engine that is, is down to wrong piston/bore clearance.....

I'm obviously on the wrong forum.

Just look at your own photos and you "might" be able to see the cause of that failure.

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

I don't see any guessing going on. Although I am guessing some people are getting a little tired of you typing skills.

On 22nd Jul, 2010 mowog said:
Use the piston and guess your piston to bore clearance, not my engine..........





That was exatctly what this 'professional' fucken genius engine builder did. Wow, it lasted a whole 1100 km.........fucken awesome....

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.