aluminum pistons

[Philip]

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

[Joe Bell]

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.

[Kerry]

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.

[J1MGOLDEN]

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.

[Adam]

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...

[George Hand]

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

[Allan]

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.