piston and rod set ups

[LONG-ROD]

I need to understand this a little better tHen I do. I have a long rod and a stock cylinder 87 I beleive. no spacer plate so what piston do I have? I am going to to do a rebuild soon, what should I run with my long rod, seems all my friends bikes that have work done have the spacer plate I am guessing my cylinder is an 87 and is diffrent from the 88 89 and if I put what ever piston I do not have in there I will need a spacer plate.

[C-LEIGH RACING]

87/88/89 model cylinders use the same piston.
Only reason you would need to use the 85/86 model piston in your cylinder, would be if it needs boring higher than a 68mm.
87/88/89 model pistons only go up to 68mm
If you have a long rod crank & need to bore the cylinder higher than 68mm, you can use the 85/86 model piston, but will need a 3mm spacer plate to go under the cylinder.
Neil

[LONG-ROD]

o k i have a 67.50 now if I go say70.00 I will need a spacer plate cause I have to use a diffrent year piston

[trx250rider]

im also wondering the same thing...my engine has an 87 style piston and no spacer...how do i know if its a long rod or short?

[C-LEIGH RACING]

LONG-ROD,
Heres where it can get confusing.
Your at 67.50mm, 87/88/89 model piston & long rod crank, well, only way you can go to a 70.00mm size, is if you use the 1986 YZ250 Yamaha piston along with a 2.5mm spacer plate & 2 base gaskets.

The old 85/86 model TRX250R pistons only goes up to 69.50mm in size, not up to 70.00mm.


rider,
If you have a 87 year piston in your engine & no spacer plate under the cylinder, thats saying you have a long rod crank in the bottom end.
If you had a short rod crank, that 87/88/89 model piston skirt would hit the crank webs before it ever got to BDC.
Reason why, because of where the wrist pin hole is machined in the piston.
Now, it could be done, if someone was to machine the skirts of the piston to clear the crank webs, but thats realy not normal to be done.
Neil

[chamberlain31c]

just curious, why to people run an 86 style piston(66mm-68mm)and spacer for the long rod when you can just run no spacer an an 87 style piston? is there an advantage?

[LONG-ROD]

Ok wellm I have a 310 sleeve so if I goall the way what mm am i at and what piston do i use

[Honda 250r 001]

Originally posted by chamberlain31c
just curious, why to people run an 86 style piston(66mm-68mm)and spacer for the long rod when you can just run no spacer an an 87 style piston? is there an advantage?

you can run a bigger piston. they only made the 87 pistons to like 68. and they made the 86 pistons all the way yo 69.50 i think.

[jhtrx250r]

If you have a big bore 72mm and up, you can get a piston from LA sleeve to run on a long rod with no spacer plate.
the reason people run the 86 style piston is, as neil said more bore size choices ,and also it has a large cut out at the rear, CR style and is lighter (my opinion and many others agree a much better piston design)
If it is time for a replacement piston you can alaways clean off the done wiesco puts a part # on top I think others do as well.

[jas250r]

what about the wrist pin flats on the side of the piston. i think the 86 style on has it on the intake side, and the 87-89 style have on both so you can widen the exhaust port for so more peformance