250r piston / cylinder / head interchangeability

[MathGSR98]

Hi there,
I made some search but I need someone to clarify the things. I have a 85 trike with a 86 trx engine. Which top end combo can I use. I think that it doesn't matter the cylinder year you put, you just have to match the piston year with the rod length? What about the bridged intake?
Would this setup works: 86 base with shortrod, 86 piston and 87+ cylinder? What about the bridged intake? 87+ pistons are made to match with the bridged intake?
Should rather use: 86 base with shortrod, 87+ pistons, 87+ cylinder and a spacer plate?
I know that the 88+ head are cooler and maybe make more compression?

Thank u folks

[deathman53]

the following works:

85/86 crank, any year clyinder, 85/86 piston
87-89 crank, any year clyinder, 87-89 piston
87-89 crank, any year clyinder, 85/86 piston, 5mm sapcer plate

[MathGSR98]

So it doesn't matter putting a 86 non bridged piston with a bridged cylinder?

[Pete]

nope, doesn't matter a bit. I would stay away from the space plate, they add volume to the crankcase and soften power delivery.

[deathman53]

I like the spacer plate setup, doesn't snap so much. It makes mx riding less tiring, while keeping the same power.

[rich250rracer]

So it doesn't matter putting a 86 non bridged piston with a bridged cylinder?

An 85-86 non-bridged piston will work in 87-89 cylinders with no problem, but I would try to avoid running an 87-89 piston in the non-bridged cylinders. The 87-89 piston is full skirted with a window on the intake side. When this type of piston is run with the non-bridged cylinder, the piston can "cock" slightly on the downward stroke and possibly snag on the bottom of the intake port, especially if there's larger piston to wall clearance.