1985-6 ATC 250r jug on 84 250r

[plevib]

They tell me i'm crazy! But i'm pretty sure it can be done. I'm sick of my 84 240r melting. I have spent many weekends trying to jet it. I have a beautifully golden plug, but it still melts itself down. I'm sick of rebuilding it, so i'm thinking of converting it into a water cooled beast. Judging from pictures, it appears that it is possible. The intake and exhaust seem identical, bolt patterns are the same....

So my question is, If you ignore the other issues (radiator, water pump, ect...) will a stock 1985-6 jug bolt on a 84 motor without any issues?

My goal is not to make it a hot rod. I just want my machine to stay cool without having to run 186 main jet! Thanks guys

[NETRA3]

I would say no because you have no way to run the water pump and no cooling fins..The '84 is completely different from the '85 .You need to find the root of the problem with the one you have...IMHO,,Good luck.

[yaegerb]

It will not fit. Even if you could get it to fit you would melt it down again because of the lack of cooling fins. Those cylinders are made to have water pumped through to cool them. My guess is you have an air leak on your 84. I would perform a pressure test immediately and yes your plug will look perfect with an air leak.

[plevib]

I do appreciate the response and the input. What I mean is I will sort out the water pump and radiator later. My goal is to convert it to a water cooled.

So yaegerb, Do you know for a fact that the jug will not fit?

I know they changed a great many things from 84 to 85, but I'm pretty sure the stroke and the basic shape of the cylinder is the same (obviously excepting the fins being replaced with the water veins) not trying to be rude, I'm just trying to clarify things.

I'm new to two strokes but I have a good deal of experience with engines big and small.

[atc300r]

The 85-89 cylinder will not as far as a direct bolt on different bolt patttern. The 81-84 cylinders are the same . The 81-84 motors are 70 bore 64.4 stroke. 85-89 are 66 bore 72 stroke. Your best bet is to sort out your carb and jetting . I agree with yaegerb you have an air leak some where.Did you rebuild your bottom end. Check your fuel flow. Check your gas cap vent to be sure its not clogged. On the aircooled motors you want more of a chocolate brown.These motors where tested by Honda at the big Desert races and passed with flying colors.

[manbearpig]

you have 2 options as i see it.

option 1: find your air leak (likely a crank seal) and fix it

Option 2: quit trying to reinvent the wheel and buy an 85/86 250R

[atc007]

Who is Martin Chaisson? I know you well enough to know he must be a real class act lol!

[plevib]

Ok thanks guys. Btw good luck trying to find a 85-6 anywhere around ND haha. .... they don't really exist. I've been looking for many Years.

[DohcBikes]

Closest one i found on cl https://montana.craigslist.org/snw/5372680598.html

[oldskool83]

your melting because its not built right. call an engine builder to get it ported and set up properly...this is why every YZ490 blows up after rebuilds. Just not made right.

www.eric-gorr.com

[NETRA3]

They're around, you might have to have one shipped if you want it bad enough.....This is what the're going for in my neck of the woods........ may not help you much unless your willing to ship. what's your budget?

Ok thanks guys. Btw good luck trying to find a 85-6 anywhere around ND haha. .... they don't really exist. I've been looking for many Years.

https://boston.craigslist.org/nos/snw/5362479161.html

[bkm]

You need one of these if you want a water cooled second gen.

I sold this one a few years back.

[plevib]

That's a sweet jug! Where the heck did you find that? Well anyways, I've decided my 2-stroke days are over. They're TONS of fun but I would rather have a reliable 4 stroke with the climate I live in. Plus the high end is fun, but i miss my low end power

Maybe I'll get chastised for this.... but I'm going to pull the 250r motor out of mine. I just bought a xl500r motor and I'm going to convert it. I'll make a detailed post when I actually start the project. but here's the before picture


And please don't try to lecture me on the error of my ways. I do realize the large scope of the project (frame modification, axle flip including brakes, custom exhaust, ect...) But I think it'll be a one of a kind and a monster of a machine when I'm done!

[hatc200x1]

I run an 84 ATC 250r as my main rider and have 2 82's and another 83r. Air cooled r's are plenty reliable when built right. I live in Minnesota and climate is not a problem for me... IMO converting it to the xl500r engine is going to be way more work than getting your r motor dialed in. If I were you I would follow the great advice that was posted above and do a leak down test, If its leaking somewhere, find out where, and fix it. Then pick a good oil(I use klotz benol in my air cooled 2 stroke engines and klotz supertechniplate in my liquid cooled 2 strokes) , and oil ratio, 32:1 is recommended. Then start from their with jetting. I have ran my 84r into the ground after I got my air leak figured out and have put around 75-100 hours on it, still runs good. It is now getting lower on compression due to high hours and going to have the cylinder bored to my next size over new piston. I will not be surprised when I get another 75-100 hours on it with the new top end that it will still be running good without any seizures or melt downs... Here is a good write up on leak down testing 2 stroke engines. https://www.duncanracing.com/TechCen..._presstest.pdf Also a link to an ATC shop manual website to help with engine disassembly/ assembly. http://www.oscarmayer.net/atc/manuals/

[plevib]

Thanks for the advice, but I've been through all of that. And i get that it'll cost a little more and probably be more work, but after that I'll never have mess with it again (besides maybe carb work) I'll have gobs of low end power and won't have to worry myself about fuel mixture and jetting and making sure my air filter is perfectly clean.... What part of Minnesota are you from? I'm in grand forks. Wanna buy a 250r motor?