pistons

[2scooters]

I finally started the rebuild of my 78 xs1100 . I got the heads off and found 5 - 5 or S - S marked on top of my pistons. What does this mean ? I found 1 weak cyl. and my cam chain stretched so far. Can you tell me the things to look for and where to get the parts. I want to do this right the first time . Thanks for your help.

[Do Lee]

the "S" on top of the pistons means that they are still standard size pistons and not over sized pistons which would have 0.25 for 1st over, 0.50 for 2nd over, 0.75 for 3rd over and 1.0 for 4th over. Unfortunately pistons for our bikes are a discontinued item. Rings are still availiable at $40.00 a set but for how long is the question. I have read on the site where other XSers have purchased the Big Bore Kits for their bikes ($300-400 plus the price of boring out your cylinders)

To check your existing pistons rings and cylinders for wear limits and out of roundness.
to check cylinders for out of round you will need a bore mic.
measure at the top, middle and bottom of the cylinder at 12 to
6 o'clock position and also at 3 to 9 o'clock position. If the
cylinder out of round is more than (0.01mm) (0.0004in.) the
cylinder should be bored out.

Piston/cylinder clearance is between (0.040-0.045mm)
(0.0016-0.0018in.)
Ring end gap for both compression rings (0.2-0.4mm)
Oil scraper rails (0.2-0.9mm)

If you look on the site you can find alot of helpful information and the people on this site can will be very helpful with all their info.
hope this will get you going in the right direction.

[2scooters]

pistons

Thanks for all the helpful info.