StandupKing1186

I'm in the process of rebuilding the engine in my 87 js550. I'm going to put a fresh bore on my cylinders but I'm not usre whether to do .25mm over or .5mm over. The cylinders look great, .25 will probably do. Any reason to go .5 over?

Thanks!

bkoche

piston availability

__________________
2004 SXR - FPP Wetpipe, Blowsion railcaps, 4deg bars, billet clamps
1994 750sx - Loaded -FOR SALE
1983 JS550 - WC RC520 reed cylinder, WC Head, PJS WB, Dual 38SBNs, WC 750 reed stuffers, WC Stacks, WC 6.5gal tank, FPP Halfpipe, SBT High torque starter, 16.5 Skat, Blueprinted 440 pump, lightened driveshaft, 76mm OP nozzle, Jetsport bulkhead brace, 90wt mod, WC scoop, Rend plate, Rear exhaust, Carbon Fiber

1991 Honda CB750
1976 Suzuki RE5A
1976 Suzuki GT750A
1975 Suzuki GT550M

StandupKing1186

I can get either size. I'm guess if I do .25 over, I'll have room to bore again later if needed.?

550/440

If you can get away with .25 over, do it. The only reason to go to the .5 over would be to gain more displacement - as minimal a gain as that would be... or if the gouges (if you have any) in your cylinder walls are too deep!

__________________
1991 550sx, 1993 750sx, 1993 750sx (Wife's ski), 1998STX, 1994 Waveblaster, 1983 550

Big thanks to Newmiller Machine in Oregon for the great work! (Mcn6 on PWCtoday)

"The number of ways of playing footsie with detonation is endless, but nothing works every time. This guarantees that we will never be bored, and will never run out of seized pistons. " - Kevin Cameron

bkoche

you have a lot of room either way. ive seen pistons as large as +1.75

__________________
2004 SXR - FPP Wetpipe, Blowsion railcaps, 4deg bars, billet clamps
1994 750sx - Loaded -FOR SALE
1983 JS550 - WC RC520 reed cylinder, WC Head, PJS WB, Dual 38SBNs, WC 750 reed stuffers, WC Stacks, WC 6.5gal tank, FPP Halfpipe, SBT High torque starter, 16.5 Skat, Blueprinted 440 pump, lightened driveshaft, 76mm OP nozzle, Jetsport bulkhead brace, 90wt mod, WC scoop, Rend plate, Rear exhaust, Carbon Fiber

1991 Honda CB750
1976 Suzuki RE5A
1976 Suzuki GT750A
1975 Suzuki GT550M

StandupKing1186

Yeah...I didnt think a .25mm more would give me that much more performance. I mean what are we talkin about...a few cc. Guess I'll go with the .25 if I can.

jural

If they look great, then you may want to have them checked to see if they would be in spec after a hone. May not have to bore at all. Not likely, but possible.

StandupKing1186

I took them to a machine shop today and they said they were out of around enough where they would have to do .5mm over.

MrSki

Surprised you can find any quarter mm oversized anymore. Most go by 1/2 mm. WSM only goes to 76mm. 77mm is the biggest that was made commercially available.

__________________
1995 PJS VHP7000, stock but darn fun.
1992 550 SX - R&R port Kawi Reed, Kind of fast.
1989 JS 550 - PJS motor Dual 46's, 50 MPH on GPS.
1986 JS 550 - Pile of parts at the moment.
1976 JS 400 - Pretty much just a shell.

StandupKing1186

The guy I bought them from said he could get .25mm over....don't really know though. I went ahead with the .5mm