Tolerances for boring barrels

[obrut]

Hi all,

I'm planning on having some 80.0mm 2 litre barrels from a 67 911 bored out to 81.5mm.

Does anyone know the tolerances I should provide to the machinist?

[Steve@Rennsport]

Clearances depend on what pistons you will use,... .

[obrut]

Thanks Steve - pistons are 9.8:1 JE's.

[Henry Schmidt]

Bore to 81.47mm and hone to the desired tolerance. If 81.5mm if the pistons are perfect. We like to size each piston.
All piston manufacturers build their desired clearance into the piston.
If everything was exact you would bore to 81.5mm. Then the JE would fit perfectly but nothing is exact. Each piston and each cylinder will have a tolerance. If your machinist can hold a .0005 that's about as good as you could hope for.

JE uses a .0015-0025" depending on the diameter and cylinder material.

[obrut]

Originally Posted by Henry Schmidt

Bore to 81.47mm and hone to the desired tolerance. If 81.5mm if the pistons are perfect. We like to size each piston.
All piston manufacturers build their desired clearance into the piston.
If everything was exact you would bore to 81.5mm. Then the JE would fit perfectly but nothing is exact. Each piston and each cylinder will have a tolerance. If your machinist can hold a .0005 that's about as good as you could hope for.

JE uses a .0015-0025" depending on the diameter and cylinder material.

Thanks Henry, much appreciated.

[ajwans]

What's the opinion on clearance for Mahle forged pistons? 80.5mm diameter.

andy

[304065]

Of course you must measure.

Jugs and Slugs: Confessions of a JE Piston owner