here's a technical question for you guys. I'm recently in the process of rebuilding a 1995 600ss engine after a top end/piston failure that ruined the bore of my bottom cylinder. After two ebay purchases, I'm still at square one after discovering the different piston designs/weights throughout the 600's production life, I've now got 3 different pistons at 3 different weights. Obviously, I ideally want to match the piston weights of both top and bottom cylinders, and this may mean replacing both pistons with a matched set. However. This is proving to be difficult to source the same pistons as a matched set at a weight the same as the old pistons. So, my question is. Has anyone run different weight matched pistons in their engines without rebalancing their crankshaft? My old pistons weighed in at 375 grams and 374.5 grams for top and bottom respectively. Top was marked with a 'C' on the piston crown, and the bottom with a 'B'. (weights are taken with rings, gudgeon pin and one retaining clip) The ebay purchases have given me two separate bottom pistons, at weights 393 grams with crown mark 'A' and 360 grams, crown mark 'B'. all the pistons differ in design, but their ultimate dimensions remain the same. So, any advice from people who've swapped pistons? Please no "just get a new engine" and "give it a go" comments, please, I'm a student on a £0.00 budget. Regards, Jacques
From what I have learned, and warning I'm not techy by any means, if you try and match a pair as you are describing you could be there forever. The only way to balance exactly is have them machined to match or but a new set of pattern ones which are matched You may get mega lucky of course.
What I really want to know is the bob weight calculation, I can't for the life of me remember what text book I read it in, and the internet has so many different ways of calculating it, I don't know what source to trust. I was hoping someone might know the formula so I can work out to within what weight pistons I could use before the overbalance leads to failure.
A friend and Uni has since helped me out and we've calculated that I can get away with a pistons between the weights of 372 - 378 grams (weights are of pistons with rings, gudgeon pin and one retaining clip) to keep the reciprocating factor at 50% +/- 1%, to keep it smooth as a honey. Now, anyone have anyone have a set of pistons, rings and bores for a carby 600ss with those weight pistons that they want to sell? (worth an ask) regards, Jacques
