piston clearance

[5banger]

hello friend

my friend is building a I5 motor with some forge wiseco piston he has and the engine builder has bore to .006" wall clearances is this too much for forge piston. He's not sure if to assemble or get new piston. spec was for .0035"

[mcandmar]

Have a look at the end of the thread here http://www.s2forum.com/forum/showthread.php?t=24560

[QuattroFever]

In a similar situation. Just over 5.5 thou On number 5 the rest are around 4.5.
So over 4 thou would need work??

.0005 or even .001 as a sheet of metal would prob be see thru. The heat from your hand on a micrometer could poss throw it out. Is it really that critical?

[QuattroFever]

If the max recommended is 0.004 and you have 0.006 then your difference from ideal in mm is 0.0508mm or half of a 1/10th of a millimeter. That's frikkin small and mine is even smaller at half that.

[GazzaG60]

its necessary to measure each piston and bore each out in relation to piston size. the bore size is sometimes dictated by pressures applied also.

to tight or too loose and yuor not on a winner.

[caterpillar]

7.5-10/100 mm clarence... are ok. high effect ; more than 5-6oo HP, more clarence for the audi engines

[JP]

I'm running JE pistons spec'd for 900+. And the gap is 4thou because as the piston expands so does the bore. So at a certain point to go larger becomes pointless unless you wish to suffer from piston slap, shorter ring life, oil consumption, less power and potential smoking under load.

To put it into perspective take a piston ring and measure the ring gap in two bores that are one thou difference in size.
note the difference in the gap it is shockingly significant.
Obviously if you've overbored and are gapping the rings its not an issue, however if re using stock pistons it is as the rings come pre gapped from factory on the large side to drop straight in. With a bore with no wear showing ring gaps as large as 20-22thou add a couple of thou to it and you can see gaps close to 30. With 36 being considered the upper wear limit.........

Just my 2p

[UrS4boy]

my friend is building a I5 motor with some forge wiseco piston he has and the engine builder has bore to .006" wall clearances is this too much for forge piston. He's not sure if to assemble or get new piston. spec was for .0035"

Just for context, the AAN engine manual says that the basic measurements for the piston bore is 81.01 mm and the piston diameter is 80.98 mm, i.e. 0.03 mm difference. My math says this is 0.001 inches.

[caterpillar]

if you got more than 12-20/100 mm clarence; you WILL get some nasty ratlle in the engine,when its cold... and some bad blowby( and oileak engine).. the ringland will suffer too...
other issue to think about are the gap between the ringends... tooo tight=wrecked engine