long rod or short rod 250r motor?

[dizasterzrfun69]

Hey guys im redoing an 85 R and i have an 89 engine and an 85 engine im going to put together for one engine do to the cases being cracked. whats better? the long rod setup or the short rod? its going to have a cool head, maybe reeds, paul turner pipe, and not sure if it'll be a stock size carb or not

[jason85atc250r]

run the long rod 89 crank with a 85-86 piston and a spacer plate.

[X2guy]

If you gotta run a new piston get a 87+ piston. The 87-89 pistons had a 5mm higher piston pin hole to compensate for the 5mm longer rod length. I don't see why people use a spacer plate with an 86 piston unless they add the long rod to an existing top end.
I built an 86 with a long rod crank and 87+ piston...It works great. If piston dwell time is understood then you will see why the long rod is better for top end. With a long rod the piston spends more time around top dead center allowing more time for the fuel to burn in turn giving you more bottom end.

[Yamahondaman]

some people like MORE Crank Case Volume with the ATC Piston and the Spacer Plate.......... Plus when People see the "plate"...they won't race you..... :naughty:

[dizasterzrfun69]

some people like MORE Crank Case Volume with the ATC Piston and the Spacer Plate.......... Plus when People see the "plate"...they won't race you..... :naughty:


so are you thinking the 89 jug? what piston then? I'll have to check the jugs/cranks and see whats good. I was thinking one of them has some porting done to them.

[phil53]

the cylinders are all the same pretty much other than a bridged intake and a bit better clean-up of the ports through the years.

The 85-86 pistons are available in more oversizes, to allow more bores of the cylinder. Ran into this when I rebuilt my engine & crank a few years ago.

[InPiEcEs]

Stick with the 85-86 piston if you're gonna use and 85-86 crank.
If you wanna use the long-rod crank, then use 87-89 piston.
Some people like using 85-86 pistons w/a long-rod crank and spacer plate, but you tend to lose a little crankcase vaccuum/pressure with them.
Most of the guys that run them here say you gain a little top, and lose a little bottom with a spacer.

[dizasterzrfun69]

ok guys so are ALL the jugs the same and just the rods and pistons are different?

I have an 85-86 piston and a long rod /crank. Now what do i need to do to use them together? Im making this whole thing a LOT harder than i think it really is.:lol:

[3leggeddog]

use the 85-86 piston,and 85-86 cylinder.then use the 88-89 crank,and buy the 5mm spacer plate from esr.throw it together,and rip it up

[InPiEcEs]

The cylinders are all pretty much the same, the only differences being porting, and intake bridges are on the later ones.
The pistons and cranks are different.
As long as you use an 85/86 piston, and 85/86 crank together, you can use any cylinder you want.
Also, as long as you use an 87-up piston, and an 87-up crank together, you can use any cylinder you want.
When you use a long-rod (87-up) crank with an 85/86 piston, you need the spacer plate.
The piston pin hole is about 5 mm lower on the 85/86 pistons than it is on the 87-up pistons.
You cannot use an 87-up piston with an 86 crank.
To sum it up.......the jugs are all the same besides porting, and you will need a spacer plate using 85/86 pistons with the 87-up crank.
Otherwise, you will be fine.

[dizasterzrfun69]

thanks guys i finally learned something and it didnt go in one ear and out the other :D I also already have a spacer plate that came on my 89 motor so it must have an 85-86 piston in it. I have a brand new 1.00 over piston im going to use. :w00t:

[max]

Stick with the 85-86 piston if you're gonna use and 85-86 crank.
If you wanna use the long-rod crank, then use 87-89 piston.
Some people like using 85-86 pistons w/a long-rod crank and spacer plate, but you tend to lose a little crankcase vaccuum/pressure with them.
Most of the guys that run them here say you gain a little top, and lose a little bottom with a spacer.

This guy is right on the money. I have an 86 motor, long rod, later style piston. Using the space just gives it one more place to leak also.