Hi Guys,
what is the bore size for a JE 85.5mm piston to a stock Evo 85mm block?
1) 85.75mm?
2) 85.8mm?
3) 86mm?

Thanks

 

Well it sounds like the JE you are refering to is .5mm larger then the stock 85mm bore , so the bore would need to be the .5mm lager + the differance the piston manufacture ( being JE in this case ) requires as clearance some piston makers require differant clearances basssed upon the exspasion of how different piston react to heat and such , also pay close attention as to how you gap the rings make sure you follw the guidline the manufacture recomends , there is usaly a range in which to follow from a street motor to a race motor the tighter of the spectrum being a street motor and and the looser bering a race motor , and when you do the build please break the motor in correctly with a good break in oil or conventional oil , do not use synthetics to break in as it is in a lot of cases to slick and will not allow the rings to seat correctly and could cause cylinder glazing , or so I have read , and heard from some old school engine builders .... I hope this helps ..

 

I just bought a set of 86mm JE pistons, and measured all of them to 85,90mm. According to the sheet, clearance must be 0,10mm, so it means the pistons already came machined to the specified bore minus clearance.

 

Dont use any of the measurments provided. 85.5mm is not the actual diameter of the piston as it will vary per piston set.
measure the actual diameter of the piston, and then add the recommended piston to wall clearance for that piston. for example, 0.0045" clerance. the a machine shop should bore out the cylinder to that value.

 

Hi Guys,
my mech did measured the piston and overall its 85.5mm so just wonder what is the minimum clearance onto the block? 85.75mm?

 

The 85.5mm are 20 over bore.

.020" = .5mm

 

Why donīt you just take the block and pistons to the machinist? The clearance is informed by the manufacturer. There should be some data sheet in the pistons box.

 

This is correct. If the pistons are for an 85.50mm bore, they will already have the clearance built in the design. Bore/hone the block to a finished bore size of 85.50mm and the piston should already provide the proper clearance. Some engine builders may measure each piston individually then hone each cylinder to match to make up for small variations in piston size. You should not have to do this with JE Pistons since their sizing is spot on.

 

x2 take to the machinist he should be able to determine all the clearances, tolerances to get them perfect.