The Cal-look Lounge

I need to get the pistons dished for my dads very mild 1915 to lower the compression. How deep can I go?? Thanks!

My 94 Bs have a crown thickness of .210"(actually measured) I wouldn't want to go any thinner than .150. A pistons may be thicker.

send them to bergs and just tell them how many ccs you want? 7cc is plenty safe still

cheers richie

I can get them taken care of here, no need to send them off. I just need some figures to get me in the ballpark. Thanks guys-

I can tell you the crown thickness as well as the thickness under the wrist pin support has become smaller over the years. Back in the late 80's Gene Berg sat with us at a meeting with the Cima/Mahle company. Gene had (I beleive) every generation that the company had produced over many years. They (Cima/Mahle) could not refute Gene's information and promised to return to the original design as best they could. This did not happen in it's intireity but they did improve. Measure your pistons first to see which generation you have,

Been a while since I had to dish a set of pistons but have done it many times in the past....

I limit depth of dish to .060" (1.5mm) max
Max dish diameter: 20mm less than piston diam
Better squish with smaller diameter dish
Juggle diameter and depth to arrive at target cc using formula below

Never had any problems with a .060" deep dish (Mahle pistons).... even after 100,000+ miles but only recommend the mod for mild-ish n/a motors

It's easy to target specific volume increase via the formula:
dish diameter (mm) squared x depth (thou") x .01996

eg for 94mm piston, 70mm wide dish, .040" deep.....

70 x 70 x .040 x .01996 = 3.9cc

Need to allow a little for angle of cut into OD of dish
i.e. dish volume will be slightly less than above, assuming outer edge of dish isn't a vertical plunge cut, but above calc will get you close.
Measure cc with burette etc for exact figure

John Maher

That's exactly what I was looking for. THANKS! :)