Motor question

[bm250r]

I just bought a 86R, which was supposed to be stock. The motor was low on compression, so i picked up a 20 over pro-lite piston for it. When i took it apart, the piston looked nothing like the one i got from wiseco for an 86. I beleive it's a newer style piston in the motor now. How can i tell what year this motor is? I checked the part numbers on the piston with wiseco's website, and i have the correct piston for an 86R. Thanks for the help

[etter696]

check the number stamped on the top of the piston, and try to match it with wiseco's or the oem pistons just a suggestion

[1988R]

you can also look on the underside. If its a pro-x piston it will say pro-x and have a few other marking on it. If so call LA Sleeve and they should be able to help

[RayWilt]

if the pistons look totaly different you might have the newer style piston like out of the 87-89 style that means your crank is just the newer one with the longer rod. The 86 pistons on the intake side have a half moon shape cut out in the botton. The 87-89 has a rectangle port in the side.

[bm250r]

Originally posted by RayWilt
if the pistons look totaly different you might have the newer style piston like out of the 87-89 style that means your crank is just the newer one with the longer rod. The 86 pistons on the intake side have a half moon shape cut out in the botton. The 87-89 has a rectangle port in the side.

This is exactly what the piston looks like. It has a window in the skirt of my old piston. so i guess i'll be lookin for another new piston.

[8dave3]

You can check the #s on the rod to verify if it is a long rod or short rod.It will have HA2 or HA4.I think the 2 is long and the 4 is short.You can run the short rod piston on the long rod if you use a cylinder spacer plate.

[bm250r]

mine is def. a long rod. Is there an advantage to going with a spacer plate and the 86 piston? Or should i just get the 87 up piston? If it is worth the trouble, where can i get a spacer plate?

[8dave3]

Suppose to help on the bottom end power someIDK.There are more bore sizes available in the 86 style piston so thats a good thing.The plates are available from about any place that sells parts.Check some of the guys on here or I see them on ebay sometimes.

[RayWilt]

i have a spacer plate in mine and you can tell a little difference. It gives you more crank case volume. you will have to get a long stud and dowl kit to go with the spacer plate.

[bm250r]

Great guys, thanks for all the help!

[xlr810]

What hasn't been mentioned so far is that the 86 piston has a shorter skirt. The longer skirt on the 87+ pistons prolongs their life. That, and the 5mm extra space affects the position of your head in relation to the headstay. The hardly perceptible increase in performance isn't worth the tradeoff in my opinion-- but is entirely necessary if you go beyond 68mm bore...

[Sanchez]

If you have the cylinder removed from the case there is a date stamp on the bottom of the sleeve. It's located on the part which sticks down into the case and will probably still have the black anodized finish on the face which is stamped.