Hey Gang, Just received .060 pistons and rings from SRM Engineering. They are 7.5:1 compression. My engine is a DA10R (Super Rocket) I just want to confirm, what I want as far as clearance goes, when I talk to the engine borer. It has .040 in there now. The Haynes manual states .004-.0055 piston clearance for a Super Rocket with 8.5:1 pistons. Setting them to .0045" would be good then? States the comp. rings at .013" and the oil ring at .011". Do you ALL agree with those specs? Would appreciate your thoughts. I don't want to screw this up. LOL Thanks, Wyn
Wyn, you need to know the type of alloy they are cast from. (Talk to manf.),some low expansion stock could safely have you running .003 and some drop forged jobs may have you needing near .005. From reading here it's better to set the ring gaps to the larger sizes given again talk to the Manf.,no pat answerers sorry.
norbsa 1960 TR6 1963 Super Rocket 1965 650 Star 1966 441 1968 Thunderbolt 1969 Twinkle 250 1972 Fastback 1974 Roadster 1970 S.S Way too many BSA's not named http://decentcycles.com
There is absolutely NO mfg. markings on the pistons at all. The only markings are on the top of the piston and show 060. I've emailed SRM twice about any specs they might have, and have gotten no answer since thrs. These damn pistons aren't cheap, but even more, I just want to do it right the first time. The two pistons just came in two plain brown boxes with no markings at all.
Thanks for the input guys. I just received a reply from SRM on fitting the pistons to the bore. I'm going to take this email reply, along with the spec sheet from Haynes, give it to the machine shop, and hope for the best. Thanks again, Wyn
Here's their reply:
Hi, Pistons are of Euro origin, but we always fit Hepolite or equivalent rings, just to make sure.
If bore is finished honed to the correct size, clearance and ring gaps will be correct, just fit and go.
Bore and plateau hone to exactly 71.50mm thats 2.8150" +/- 2 tenths.
Bore size is standard BSA, if bore is finished to this size, whatever make piston you fit, will have the correct clearance, piston manufacturers use different alloys, different thickness alloys, so they know the expansion rates for their piston, so they are all made to suit the stock BSA bore sizes. It is dangerous to deviate from the BSA bore size and go only for clearances, BSA clearances are for BSA pistons only, and do not apply to any other piston.