85R Top End Rebuild and Upgrades

[Dirtcrasher]

^ Bingo.....

[Samjp22]

Came outta the box like that

[El Camexican]

Okay thanks for the input guys and yeah it's always warm before I go ride, stays in a heated shop.

That isn’t the kind of warm they mean. Your engine should be warm enough to open a thermostat before you rip on it, say 160F. That’s called operating temperature.

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.

The cylinder actually gets larger when it’s hot. The problem is that the piston gets even larger. When an engine has the proper tolerances and is run hard the piston gets so big it doesn’t need the rings to seal. The problem with yours as many have pointed out is that the piston and rings were too big for the bore of your cylinder to start with, so when it got hot the ring gaps closed and the piston became bigger than the bore. When that happened there was no space for oil and metal to metal contact occurred and that is why your engine seized.

As MTS pointed out you want uniform heat in your cylinder. If you suddenly subject one part of your cylinder to a temperature change, be it due to crashing into a creek, or charging up to 100km in minus 40C weather with open rads the cylinder bore will distort, but the piston wont. Again a seizure can occur.

Non-synthetic oil creates a little more friction for seating in the rings better.

I believe that only applies to 4 strokes. His engine is a two stroke.

Thanks guys and I didn't re-jet it for the colder weather and I'm still confused why multiple people say to go up in size. I know colder air is denser therefore more air into the carb but the plug was super brown. Is the summer it runs pretty rich, fouls plugs now and again but the plug looked great!

Better safe than sorry. You can always go down later. At -20C air density is way below sea level. Unless you’re racing for money you want to be jetted rich when you take off across a frozen lake.

Also make sure your water pump is working before you run the new engine too long.

[Samjp22]

The engine gets warmed up good before I go riding it, and I pulled the water pump cover off and it's good, not stripped or anything. I don't know what to say about the riding in the cold part, basically seems like if I ride in the cold and snow just going to hurt the motor

[El Camexican]

The engine gets warmed up good before I go riding it, and I pulled the water pump cover off and it's good, not stripped or anything. I don't know what to say about the riding in the cold part, basically seems like if I ride in the cold and snow just going to hurt the motor

Look at it this way. You've seen the diesel trucks running down the roads with a cover snapped onto the grill right? Same idea. You don't want -40 air rushing directly through your rad fins at 100kph as the wind chill in those conditions is about -90F. At that temperature even pure antifreeze can congeal or even solidify. I think most new sleds now use heat exchangers rather than rads to solve this problem.

The problem with open rads like yours is that long before the antifreeze stops flowing it becomes so cold its entering the cylinder at sub-freezing temps. The effect is the same as if you fired the engine up stone cold and pinned the throttle. The piston is hot and the cylinder is cold and metal starts smearing. Putting a cardboard cut out in front of the rads stops the wind-chill effect and keeps the coolant warm. At -40 you could likely run your trike with no fluid in it and be fine all day like an air cooled engine (don't try it!)

The next issue is your intake. The carb is subject to wind-chill effects as well. In a sled the carbs are inside the shroud and getting some ambient heat, as are the cases, but your trike was never designed for use in the extremes of northern Canada. Everything is exposed to the wind. Being jetted a little rich is good insurance, but not a guarantee. If it was me I'd avoid top end runs in -20C conditions. Also if you've perforated your air box you may want to duct tape the holes shut for winter riding. You can ride your trike all winter, just be smart about it.

[Jason125m]

I don't know what to say about the riding in the cold part, basically seems like if I ride in the cold and snow just going to hurt the motor

I disagree, I have been riding in -30 weather for years, i have never hurt any of my engines. Aslong as the engine is warm'd to operating pressure before riding, you will not have an issue. I've heard lots about covering a rad, but I never have, and it has always been fine. I run ice studs in the winter and play around all day out on the ice, lots of WOT. No issues. Just make sure you are jetted properly.

[Samjp22]

I'm definitely going to jet up for winter riding as there's more WOT trying to get through the snow, just gotta figure out what size I have in there right now.. And I think I might make a "winter front" for my rads. Mostly concerned about this piston as of right now. Anyone else think I should just run it or if the seller says he'll refund it wait another two weeks fora new one?

[Bren_downe]

I'm definitely going to jet up for winter riding as there's more WOT trying to get through the snow, just gotta figure out what size I have in there right now.. And I think I might make a "winter front" for my rads. Mostly concerned about this piston as of right now. Anyone else think I should just run it or if the seller says he'll refund it wait another two weeks fora new one?

How anxious are you to ride your R? As others said you could clean it up and probably fine. If your the type of person that will be bothered by it and always wondering, then I would wait for a new one.
Ultimately it's your decision.
Personally I would get a new one. If I pay for a new piston I would want it in NEW condition.

[3wheelrider]

That dent should be fine- as stated before. I wouldnt worry about it as it is if it was mine. Rub it just a little with scotchbrite or stone to get the high spots off the dented edges & run it. That dent wont cause you no issues really....IMO

[Samjp22]

Pretty anxious lol, going to wait for the seller to message me back first then I'll go from there, just looking for some opinions in case he tells me to jam it.

[El Camexican]

Pretty anxious lol, going to wait for the seller to message me back first then I'll go from there, just looking for some opinions in case he tells me to jam it.

Sucks, but should not be an issue. I've received worse and lived with it.

[Samjp22]

Camexican I was just thinking about the "winter front" for the rads and that'll just cause it to overheat quicker, I say this because it did overheat and I had coolant coming out everywhere basically lol

[El Camexican]

Camexican I was just thinking about the "winter front" for the rads and that'll just cause it to overheat quicker, I say this because it did overheat and I had coolant coming out everywhere basically lol

If they are solid and stuck tight to the rads then yes it will overheat. If you leave an inch or two of space, or better yet pop some holes in the cardboard and stick em tight then no. If you wanted to just reduce the air flow by say 50% it's just a matter of making some holes. The likely reason it over heated last time is that you were either jetted too lean, or your rads froze up. Have you been in a car or truck that the rad or hoses was frozen on, or owned a winter beater that didn't blow good heat? Your tag says Alberta, but I'm starting to wonder

[Samjp22]

Never owned a winter beater lol, drive my truck all year round and have a change of plans possibly for this rebuild.. Stay tuned

[Samjp22]

Just got this from my girlfriends brother as a late christmas gift! Its for an 86trx250r but I'm assuming it'll work for an 85atc250r. Fully ported and polished by "A", MTS maybe you know of this company/person as were from the same area? Going to measure it tomorrow and he may even have a spare piston for it!