1981 Atc250r

[Brockey]

if you have more numbers like mine you can tell. Sometimes its on the bottom of the piston aswell I believe. Not sure someone here should know. But all you have to do if it is, is take off the jug and look under the piston. You gotta take it off anyways, hey by.

[toocheaptosmoke]

It looks like "1.00" on the piston, probably bored 1mm over stock. Stock is 70.0 mm. Almost looks like someone ran her hot or lean, and maybe had some detonation going on.

[money89tractors]

i think might have predetonated...if you look close at the top of the piston, its not perfectly round anymore and all around the top of the cylinder is a bit rough like bits of it melted to the cylinder.

-Phil

[NINJA]

Hey Phil, tough break man! I'd be pretty pissed at my friend for that one man! Why can't he pay for it, he blew it up? Looks like you only have a filter cage and no air filter also, unless you took it off. Make sure you check the condition of your conrod lower bearing if she was run on straight gas too. Also, if you wanna make er a bigbore since shes blown up, check out Kustom Kraft's 290 kit. It aint cheap at $490 but it's everything you need. Good luck to ya.

[money89tractors]

Thanks NINJA. Ill make sure to check the bearings and everything (i hope to god they arent bad...i dont wanna split the case)

At $500, ill pass on the big bore kit, but it might be a future investment thanks for the heads up.

-Phil

p.s. My friend cant pay for the rebuild since he has no money and no job and i dont feel like letting to bike sit for years before he gives me money so imma bite the bullet and just get it done.

[NINJA]

Yup dude, tough lesson learned. Friends don't let friends without money ride personal trikes.

[money89tractors]

Aint that the truth...ohwell, it should be getting a top end soon.

-Phil

[money89tractors]

Another question for you guys: I just read in a different thread about a 300R kit for the 250R. Granted the engine in the other thread was an 83, what all is included for this kit? There was a picture of the size difference between the 2 cylinders. Will this 300 head be a direct bolt on for my 250R block?

-Phil

[mrtwidster1]

Use the search function at the top of the page and u will find tons of helpful info! I have a 82 and 84 r and I knew very little about them. The guys on this forum are a great help!!

[money89tractors]

Some pictures of the cylinder and the groves...




I also have a few questions:

-What is the largest bore i can get out of the stock sleeve? As of right now i think it is 1 over bore, how much more can i get out of it before it needs resleeved?
-Will a TRX250R clyinder and piston work on my bottom end? If so, will the 250r head work on the TRX cylinder?

-Phil

[Danold]

the largest bore you can go up to is +2.00 which is 72.00mm. It looks like you could get by with the next size up which is 71.25 or 1.25mm overbore.

The trx cylinder will not work with your 250r. trx is liquid cooled and yours is aircooled

[money89tractors]

Thanks Danold.

Heres some more questions:

-I would rather make this a 300R if i can find the kit for the right price. What is the stock bore on the 300R cylinders, where can i get the head and jug gasket for it
-Is the stroke on the 300R the same as the 250R jug?
-What size piston will fit the 300R jug (lets just say it is on stock bore)

Anything else you with to add would be great. thanks

-Phil

[SYKO]

dont have the numbers right off hand, but some members here have some 300 ktis they may part ways with (most need to be resleeved) and they pop up on ebay often (also most needing a resleeve) stroke is the same. Pistons well, forget honda pistons for them, I beleive I was one of the last few who may have gotten a factory 300 honda piston and it came from england. But when you send one off to get resleeved they also update the cyl and use a newer style piston as well. And there is a big bore sleeve I beleive that is avail for your stock cyl that makes it a 295? pm NINJA he seems to know about it more then I do.

[money89tractors]

Alright, small update. I got the news from the mechine shop...he started off by telling me the cylinder was egg shaped and he wasnt sure if it would come out before it would need resleeved.

I called back the next day and he had good news, the cylinder trued up and the bore is now 71.5mm.

Next problem was...$177 piston and rings (wiseco and Honda) :-|
Well, after some looking, i got the piston, rings, wrist pin/clips, and top end gasket set for $147!!

Next set of questions: If this piston doesnt come with break-in instructions, what is the best way to break it in? What oil mixture will be best to run during break-in and afterwards.

Any other tips would be appreciated.

-Phil

[1upfront]

Run at least a tank of fuel through the bike before you decide to run it hard and use 20:1 fuel oil ratio.