NEW OLD STOCK 850 PISTONS AND CYLINDER

I purchased NOS pistons and cylinder (standard size) for use on an 850 Commando engine I'm building. However, something tells me that the original "factory" 850 pistons were prone to early failure.

Can anyone substantiate this?

Jason

Jason,
I'm not aware of any problem with the 850 pistons. It was the early 750 Commando pistons (Hepolite) which had a slot running below the oil control ring that often broke. A later design was better which eliminated the slot under the oil ring, but retained the slots in the skirt near the piston pin. The final design was identical to the 850 piston, with no slots but holes in the oil control ring land.

This being said, I have seen many high mileage 750 engines with the early style pistons which did not fail. I would surmise this is another case where abuse by over-reving probably caused the failure. Engines which were kept under normal redline probably survived.

Your OEM 850 pistons should be fine.

Ron,

Thank you for the good news and the prompt, well thought out reply.

Jason

I've run 850's since 1974, with one over 80,000 miles. Never any piston problem. Currently run an 850 in my 64 featherlastic and often run it hard. Still no problems.

Randy

piston failure

Hi Ron,

I know I abused my '72 combat when it was new. What can you expect from a 20 year old on the fasted production road bike available? Still I didn't damage the pistons. It was the tune going out all the time due to the defective '72 auto advance unit, cracked muffler, broken oil ring slipping clutch, you know all the normal stuff. After moving from a '64 Superhawk to the '72 Commando, I didn't think much about 10,000 rpms and man did it launch from redline on up! I'm old now and don't do that anymore...not.