Something that's confusing me...

Advertised piston specs for a std LSJ:

Piston specs stroke = 3.386
Piston bore = 3.385
Clearance = 0.004 measured 90* to pin hole diameter, 0.850 down from oil ring.

Std LSJ bore = 3.3855-3.3861, so do these pistons need the bore enlarged to 3.3895-3.3901?
Or are the pistons made already with the 0.004 clearance and measure actually 3.3815-3.3821? (3.3845-3.3851 std LSJ piston specs, so these have 0.0010 clearance)


The actual piston diameters should be measured off course and bore adjusted accordingly, but like to know up front what is what as I have a good block but it has some 3.388 bores... :-/

 

the clearance should be made into the piston but you also need to check the taper and roundness of the bore

stock piston clearance is less then .002 total(.001 each side) general clearance for forged pistons are .004 total (.002 each side)

 

OP are u asking about stock pistons or aftermarket forged pistons? cast pistons dont have as much thermal expansion as forged hence what belvedere said above. when u buy after market pistons marked as .020" or .040" over, that is what the bore should be set to its not the actual diameter of the pistons. if u want the wall clearance set to more or less what the manufacturer suggest then u tell ur machinist when u drop ur stuff off to get machined.


mike

 

yeah, I know the overbore sizes. (not a very good idea on the thin walled Ecotec sleeves..)

Just a bit in doubt if I'm going to order some custom forged (like to get 4032) LSJ pistons for my 3.388 re-sleeved block or simply run stockers with 0.003 clearance. Which is a bit much...

 

Oh ok, I reread ur first post.


Mike

 

just call with your bore size and then they can make the clearance in the piston or get some sleeves that made undersized so you can bore and hone to size

 

You can simply buy the GM sleeves that are already honed to the correct size. But this block has new Melling Ecotec replacement sleeves that turned out to be 3.388 bore, not the stock 3.385 size. :-/

Custom sized pistons are my escape route, but like to run 4032 pistons in this street engine and those are not easy available.

 

I have the Weiscos and they call for a minimum of 3 thousanths being 2618 forgings . I went with 3.5 thousanths for EFR

 

have you tried diamond pistons