Mikes XS bore kit

JRay77

JRay77

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Question, maybe I'm tired and having a brain fart. I have the Mikes XS 650 replacement big fin bore kit. I have the rings installed on the Pistons and cam chain shit on the jugs/block. I'm ready to install Pistons into jugs. I know the arrows face forwards. Does it matter what piston goes on which side? I noticed a #1 and a #2 on the other. (Stamped) No instructions in the box. You'd think for the price you'd get some but nah, just a freakin Mikes XS sticker. How much do I have to spend for a fuckin' tshirt? Haha!

Thanks in advance guys, Off to work soon.
 
There are no left right on pistons. I'm not an engine guy but my engine guy found the crusin image pistons to be dimensionally exact twins, as might be expected on modern machine tooling.
#1 #2 on the other, what????
 
Good question. Long ago, I've run into the occasional mismatched piston sets, twins and fours. Anywhere from a half to a full mil difference. I always either marked pistons and matching cylinder(for the customer), or placed the matching pistons in their respective cylinders (for the shop guys).

If you can, measure the pistons and bores just to be sure...

Edit: I suppose you could use a ring to compare bores. Check ring gap with one ring in one cylinder, then, with same ring, do again in other cylinder. A 0.003" difference in ring gap would be a 0.001" difference in bore...
 
Last edited:
Needless to say if you sent the cylinders out to be bored to 750cc then they should both be exactly the same so it shouldn't matter which piston goes where.... BUT it never hurts to be sure......and that is where measuring comes in at
I suspect both pistons are identical in size, so the holes better be too !
......my 2 coppers
Bob........
 
No bore job involved, Bob; the man bought the manufactured 750 package from Mike's XS. But yeah, measure twice, assemble once.

JRay, take nothing for granted in motor assembly, especially when it involves parts from Mike's XS; but for the record, Yamaha identified the right as the #1 cylinder.
 
Production tooling in the 70s was nowhere near as precise and repeatable as what is available today. Yamaha used a sizing system and measured - matched pistons, as machined, to bores, as machined, the pistons were marked over under size on the top. Quality manufacturing today needs no Kludge sizing system for these parts. Some backwater manufacturer in rural china, or ancient, worn out machines in some local engine machine shop run by???? may not match those tolerances.
Somewhat along those lines; a local engine shop had an old crank grinding machine, the "old man" could grind very accurate bearing surfaces with it. Decades of use gave him the skills to do it. When he retired the shop HAD to upgrade the equipment, no one else could get a decent result out of it.
 
Ahh I see now, had to re read it , missed the big fin Kit, ....yup best to measure if in doubt !
.....
Bob.......
 
grizld1 said:
... take nothing for granted in motor assembly...

... Yamaha identified the right as the #1 cylinder...
Click to expand...

The guy who cooked-up #1 and #2 for cylinder ID should be shot...

CylNum1.jpg
 
Hmmm, looks like Mama Yama changed her mind. "Timing plate" and the U-shaped mark seem to refer to the TCI system (80 and forward) where both plugs fire at the same time anyway. Shooting would be too good for that rascal, 2M; save the ammunition and stake him out for the buzzards!
 
Thanks fellas! Just left the garage and I'll be ready for the top end assembly soon. I have the link in the cam chain but no tool to mushroom the rivets. I thought about MacGyvering a tool out of a Clovis clamp but stopped. Don't wanna fuck this up. It appears (Whose name that rhymes with dike) sent me a bad base gasket. It appears the dowel holes are punched after the perimeter. This gasket is not gonna work. Fortunately I had another. How does that corksucker sleep at night?! Bawhahaha!
 
BTW I measured and the difference wasn't bad so I put the #1 on the right side. I put the pistons in the cylinders and guided the assembly down to the rods. Held it up with a block while putting pins thru pistons into rods. I had the inner clips already installed on the pistons.
 
put some rags around the Rods tightly so if something does try to fall in there the rags will catch it.....
I used a center Punch om my cam chain link it flared nicely holding the backing bar ( another big hammer) while holding the punch and hammer is a bit tricky with only 2 arms though ...hehehehehe ! one to two good whacks is all it took, make sure your straight when doing this !
.....the manual said L.H. side not the right Btw...... for #1
....
Bob......
 
I said the numbers were stamped. They are cast in the part. So does it matter? I'm thinking not. I don't recall, are the piston oil holes even/symmetrical? I know the arrows are facing right, the rings are right with the letters up. Indexed right. So what side the 1 or 2 is on is insignificant right? I'm nervous. Shits expensive and I didn't go all the Bog Bore way....
 
yes, put No# 1 on the Left hand side and #2 on the right hand side like the manual said... even if you have to take them out again
it's worth it for the piece of mind !
.....
Bob.........
 
Bob Kelly III said:
yes, put No# 1 on the Left hand side and #2 on the right hand side like the manual said... even if you have to take them out again
it's worth it for the piece of mind !
.....
Bob.........
Click to expand...
Will do. Thanks Bob. You are right, I need the piece of mind.
 
Casting marks like that would be for the fellow who does the casting. Let's him know if a mold is degrading. The machining process occurs after the casting process.

If the numbers were stamped, then I'd take a closer look.

The important thing is the piston to cylinder clearance. If the pistons and/or cylinders are different diameters, they must be properly matched. If they are the same, and show equal skirt clearances, put whichever one you like into any cylinder.
 

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