which piston should i buy?

[polinipower]

hi guys

i have 86 250r with 86/87 piston and 88/89 crank, curtis sparks exhaust, 38mm carb, and cool head n some more goodies.

recently my piston got a hole in it and now im wondering which piston would be the best to buy and where is the best place to buy it?

thanks

[deathman53]

I'm cunfused, 85/86 are one piston and 87-89 are another piston and crank. If you used a 85/86 piston, you need a 4.5mm spacer plate, long studs and long dowels, also your headstay may not line up. With the 87-89 piston, you don't need anything different and headstay lines up.

[polinipower]

yes i have the spacer plate on it so it should be the 86/87 style piston right? forgot to say that.

i was just wondering which piston would be the best to buy and where

[deathman53]

you have a spacer plate, so you have a 85/86 piston, 4.5mm plate, 2 base gaskets and long stud set. 87 was the first year of the long rod crank and that used a different piston w/5mm higher pin height. I'd just get another 85/86 piston and be done, extra base gasket and standard top end gasket set.

the 87 motor was very similar to 85/86 with exception of the long rod crank being the only thing that was a big change. It had stronger gears, but same ratio as 85/86. 87 was kinda like the hybrid year for 250r's, nearly the same as 85/86 motor, but a different crank, cylinder and piston. It still kept the steel swingarm, but the dog bone was shorter(same as 88/89) and shock was slightly shorter also. It had the better a-arm bushings(same as 88/89), got rid of the replaceable ball joint and some say adjustable camber top a-arm. The frame was slightly different, lighter, improved front motor mounts(same as 88/89) and something about the foot pegs. The other change that is noticeable is the resonator on the air tube(same as 88/89). 88 is when the bigger and more noticeable changes happened, but the 87 is 70% 86 and 30% 88, a "testing ground" for more changes.

[polinipower]

oke i understand now thanks a lot for the information. do you know where the best place to buy a piston or is there a specific brand piston i should buy?? thank you your helping me out alot!

[atv fan 28]

Originally posted by deathman53
you have a spacer plate, so you have a 85/86 piston, 4.5mm plate, 2 base gaskets and long stud set. 87 was the first year of the long rod crank and that used a different piston w/5mm higher pin height. I'd just get another 85/86 piston and be done, extra base gasket and standard top end gasket set.

the 87 motor was very similar to 85/86 with exception of the long rod crank being the only thing that was a big change. It had stronger gears, but same ratio as 85/86. 87 was kinda like the hybrid year for 250r's, nearly the same as 85/86 motor, but a different crank, cylinder and piston. It still kept the steel swingarm, but the dog bone was shorter(same as 88/89) and shock was slightly shorter also. It had the better a-arm bushings(same as 88/89), got rid of the replaceable ball joint and some say adjustable camber top a-arm. The frame was slightly different, lighter, improved front motor mounts(same as 88/89) and something about the foot pegs. The other change that is noticeable is the resonator on the air tube(same as 88/89). 88 is when the bigger and more noticeable changes happened, but the 87 is 70% 86 and 30% 88, a "testing ground" for more changes. when you say 2 base gaskets do you mean one under the spacer plate and one on top? thanks

[deathman53]

I also had good results with weisco forged pistons. Rocky Mountain probably is the cheapest place to get what you need. I have used pro-x pistons(cast) on my big bores, but I now have forged pistons for them. The noticeable difference between forged and cast is the warm-up time. A cast doesn't take as long to warm up, where-as a forged expands faster than the cylinder and if doen pre-mature can result in a cold seize. Another thing to throw in, now most of the top end gasket sets come with a thick(86-89 250r) and/or thin 89(cr250r) head gasket. It goes based on how much compression you want thin=more compression. To many the stock trx gasket doesn't make enough and the cr gasket requires race gas use(for the most part), so the middle ground is a 85 or 86 atc250r(very important to make sure) head gasket. Its more compression, but for the most part, safe for pump gas.

Yes, one under the spacer plate and other under the cylinder. Torque values are 35 ft/lb for base nuts and 20 lb/ft for head nuts. You should spray the headgasket with cooper-coat and let it dry until its tacky before installing it and torquing the head. After 2-3 hours, re-torque and after break-in is done, check torque again. Things expand and "seat-in" to place changing the torque values.

[destey]

I have a wiseco 66.50 mm (.020 over) piston brand new in box, bought the wrong size piston. comes with rings, pin and circlips $90 shipped