MTFCA Forum

if anyone has a standard aluminum piston laying around could you measure the skirt dia.
for me? not going to start that whole clearance argument im sure i have plenty maybe too much.
thanks philip

Phillip, If you are going to replace std. aluminum pistons where cast iron have ran they will rattle coming down a hill, the original cast iron have the oil ring on the bottom, that stops the piston rattle. The aluminum ones have all the rings on the top, unless you have a narrower that will stretch the piston skirts to take up the play. I have been down this road many years ago when I could not afford to do it right. If you do not want to have it bored run the cast iron ones so it will not rattle.

Yes, it's a big ask for a T std bore to be good enough to fit an aluminum piston. They even very rarely clean up to the next size, the last one I just bored was std and took to .060" before it was 100% clean.

I just bought a set of Standard Aluminum pistons.

Trying one without rings they seem to fit OK.

The cylinder diameter was 3.77 and the piston measured 3.73 with my caliper.

Trying a ring in the cylinder, it appears to have too much gap and is close to .100 so I may use the originals with the large ring at the bottom.

I'm not sure how much it will stretch when hot, but I suspect that is too much.

Jim, According to your measurements, you have .040” clearance between the pistons and bore... Ideally, you should have .004”... 3.750” would be about standard. Something doesn’t make sense...

It depends on where he measured the Aluminum piston, weather it was measured at the piston head (where the ring lands are), the skirt across the skirt & across the pin??? He has a new set of standard aluminum pistons, the bore needs to be checked for bore taper, cylinder wall ware will not be constant in a used cylinder. Jim had removed Std. size cast iron pistons. George

Using calipers for such measurements is not usual practice. To accurately measure both pistons and cylinder bores, you need internal and external micrometers. There is no way a bore can be measured with calipers, other than at the deck.

Allan from down under.