85R Top End Rebuild and Upgrades

[Samjp22]

So at the title states my R has barely any compression. Was going on her pretty hard today in about a foot of fresh snow. Was ripping up this one hill when it overheated and shut off. Motor didn't seize (thank god) and i didn't try starting it. Brought it home and hooked up the compression tester and it only made about 50PSI. The cylinder looks pretty good (little bit of scoring by the exhaust port), head isn't warped and head gasket looks good. Going to head out right now and pull the jug off and look at the rings.

Ill post some more picks in a couple hours after I'm done in the shop. I guess my question is if it is the rings should i replace the piston, rings and head gasket since its all apart and what kind of piston and ring sets do you guys recommend?

[3wheelrider]

Doesnt look like the rings came apart? -Check that rod/bearings carefully when you get the jug off. You got plenty of bores left there. Stick with Wiesco piston/rings(85/86 style)- which is what you have in there now. Use OEM ATC/TRX gaskets.

[Samjp22]

The rings are imbedded and melted into the piston and theres a little bit of scoring on the exhaust side of the cylinder, not too bad though. The current piston is a Wiesco 66.50mm piston, would you recommend boring it or running a hone through it and is there a nickel coating on these cylinders? Rod/bearings seem good and okay thanks for the tip on the gaskets.

[3wheelrider]

OK-I see that now... Looks possibly like insufficient piston to wall clearance/end gaps?? That piston wasnt in there very long -right? Are you letting it warm up well before you rip on it hard?....No nikasil plating there. You would want to bore it/hone only to next size 66.75 (it should be enough to clean up any scaring) Clearance is very important!-get a new piston/rings(matching) first- then take the cyl./ new piston to someone with exp. to check it/bore /hone & set clearances correctly if you want it to run long.

[oscarmayer]

me, i would actually go 2 sizes up with that wall scoring jsut to be 100% sure it will get all the scoring out and allow the rings to seat. as mentioned piston to wall clearances were not right. the piston got warm, swelled up and grabbed the side of ghe cylinder walls. also that head gasket seems to be off on the holes. make sure you use only honda factory headgaskets. the holds should align up perfectly. i am wiondering if water flow was limited due to the holes beign off-set not matchign up properly and it caused the over heating. something to consider looking at next time you put it together. but again if you use factory honda, it will be fine.

[Samjp22]

Okay thanks for the input guys and yeah it's always warm before I go ride, stays in a heated shop. The motor was rebuilt before I bought it so I'm not 100% sure if the clearances were correct but I have a feeling as soon as she over heated the jug got way too hot, swelled and that's when the rings became imbedded. As for boring it I'll probably get it done one size over at the local Honda shop as there's very little scoring on the exhaust port size.

Should I stick with a similar style wiseco piston (same style on top) or something different like a high comp piston or something along those lines

[Dirtcrasher]

Stick with Wiseco.

[Samjp22]

http://www.ebay.ca/itm/361024687191?...84.m1438.l2648 ?

[oscarmayer]

^ agreed.
hi comp is fine as lon as you have an aftermarket reed cage and pipe and carb upgrade. if not it can pose a few minor challanges.

[Samjp22]

Okay I will stick with one similar to stock like the link I posted

[RoscoW]

Before ordering your piston get your cylinder checked for size. Looking at your 2nd pic there seems to be a lot of gap on the intake side just above the #'s on the piston. Verify that the piston in there is the correct size for the bore, if you didn't rebuild it anything is possible. Have someone mic it, top and bottom, front to back and side to side, get the piston size that will clean up any oval-ing or taper. Get the piston and have the machine shop match the bore and clearance to the actual piston your using. I would also bump your main jet up one size, the plug is a little light for me. Head gasket is typical for 250R, more coolant flow on the exhaust side and less flow on the intake side.

Ross..

[Samjp22]

I think why you're seeing a bit of a gap on the intake side of the piston is because the rings got pushed to that side of the piston causing a bit of spacing. Before I go ahead and order a piston I will have someone mic it and if they say it was the proper bore for that piston I will end up boring it up once, thanks

[Samjp22]

And the head is actually a darker brown then the picture looks, flash probably caused that

[crackshot]

Yeah ditto on having a machine shop do the bore, hone and fit the piston. I had a snowmobile/atv machine shop do my 85r back in 2007 and still runs hard.

[MTS]

Make SURE! who ever sets that up relives that exhaust bridge, and set the bore to wiseco spec if you go that rout, if that was set tight i can see why it stuck after watching your riding video...a screaming hot cylinder will cool off FAST when you bust though a snow bank and cover it and the radiators in snow. Might want to put a temp gauge on there and possibly some covers over the rads to keep a more consistent engine temp.