85 Atc250r Motor Help

[anthony250]

Alright so I'm working on my good friends 85' 250R it has all stock besides over bore 2.00 "68.00mm" using a Wiesco Piston and supposedly the carb may be slightly bored too it was claimed to be and has a Eddie Sanders Racing sticker on it. So my buddy took it out two years back and overheated it pretty good. And I didn't think anything of it and recently put a new headgasket, coolant and ran it again. Bad Mistake. He took it out again and it died and puked the coolant. I'm pretty sure the head or cylinder is warped. But this last trip it also melted a portion of the front of the piston off. Nearest to the exhaust port. So I assume I got too hot and lean. Pictures below. So now am I wondering do I fix this by a new piston and rings and have the cylinder and head resurfaced ? Or have it both resurfaced and get a stock cylinder and run a oem bore? My buddy loves this thing and really wants reliability over power. And for additional details he was running castor 927 a liter to 5 gallons of 91. I cannot recall correctly but slight chance he may have ran the smaller bottle to same 5 gallons on that last trip it failed. And also jetting I'm not sure how far it was but it on the lean side, running a br8eix spark plug, aftermarket pipe and silencer, and a k and n filter.

http://i70.photobucket.com/albums/i109/anthonyspic/atc_zpsmeggclns.jpg (http://s70.photobucket.com/user/anthonyspic/media/atc_zpsmeggclns.jpg.html)

[yaegerb]

Likely your squish is tight and you aren't running the correct fuel or your rings are so bad the piston is hopping around and broke a section off the crown. Also could be worn small end or large conrod bearings making the whole assembly hop around. Hard to tell by that picture alone.

1. Pull the circlips, small end conrod pin, bearing and remove piston. Pull up/down on conrod. Should be zero play. Stick a feeler gauge in between the thrust washer and flywheel on the big end conrod bearing. Service limit is .04"
2. Check small end conrod ID with a set of calipers. Service limit is .8670"
3. Take your cylinder in for a bore, have it mic'd and get the next size piston/rings.
4. While the cylinder is off lay a straight edge (metal carpenters square) across the top of the cylinder at 0, 90 and 45 degrees while holding up to a light. If you see light peeking under the straight edge at any of those measurements its time to mill the top of your cylinder. Do the same with your head.
5. When reassembling try and find an OEM head gasket, those seal the best IMO. You can get away with a .020" cometic base gasket. Those are actually pretty good.
6. After you have torqued your head nuts down, perform a solder squish test. Aim to be around .090". If you are less then get your head cut for increased CC's.

Other helpful hints.....I have never had good luck with a K&N. I would run a oiled uni with a full airbox/lid. 1 liter to 5 gallons of gas is incredibly leaning out the motor. 1 liter to 5 gallons of gas is 19:1...way too much oil. You may want to start running 17 ounces of oil which puts you at 36.1. Stick with a stock sparkplug. No need to run a hotter plug, just stick with OEM NGK. Lastly, you need to really do your homework on what carb he is running. If you find out the carb size and jets, post it up here.

[atc007]

And do a leak down test before you start it,and preferrably again after a few heat cycles,, given this engines history..

[barnett468]

Did he ride it much before with no problem?

How hot out was it when he rode it last?

How hot out was it when you rode it last?

Were either rides in heavy sand or steep uphills etc that would put a lot of load on the engine?

Did you use the same fuel mix he used or did you mix new fuel?

What oil did you use?

What ratio did you mix it at?

Did you ever hear any detonation like a slight rattling upon acceleration?

Is the cylinder ported?

What octane gas did you use?


If the head and/or top of the cylinder were warped bad enough to be a problem, it would leak coolant inside or outside the engine.

You can get a temp gauge pretty cheap so he might consider getting one of those.

https://www.ebay.com/sch/sis.html?_nkw=TEMPERATURE+GUAGE+BANSHEE+250R+ATC+T RX250R+TRX+YFZ450+&_itemId=320207823624

http://www.trailtech.net/digital-gauges


Post a couple close up photos of the end of your spark plug from different angles.

If you are certain it is lean, I would go up 2 sizes on the main jet and raise the needle by lowering the clip 1 position.

Your piston most likely broke from detonation and/or a worn top ring land.

One of the most accurate ways to tell if your head or top of your cylinder is warped is to simply put a piece of 220 or 280 grit sand paper on a granite counter top then color the head and cylinder sealing areas with a black felt pen after they have been thoroughly cleaned then place them on the sand paper and press down lightly as you rotate them around 10 times then look at the surfaces. If there is any heavy felt pen color left on part of the surface, it is warped.

Look inside the radiators the best you can to see if there is any debris in the top of the tubes.

Check the water pump impeller to make sure it is no spinning freely on the shaft or something . Also make sure it is not leaking.

Unless it will be ridden in sub 20 degree weather, I would try 20% Prestone green antifreeze, 4 ounces of DEI radiator relief (available at most auto parts stores) and the rest water. You might also try a higher pressure rad cap in addition. Rocky Mountain ATV sells them.

In addition to the leak test 007 mentioned, I would also do a compression test after it has run for a few minutes.



PREVIOUS KAWASAKI INTERNATIONAL R & D PROJECT ENGINEER AND ATV DEPARTMENT SUPERVISOR AND THE ONLY PERSON ON 3WW WITHOUT AN EDIT BUTTON OR A STAR :lol:

[350for350]

Just tell him that it's cursed and you'll take it off his hands for $200.

[anthony250]

Motor is all apart currently , But it did have 180psi for compression holding great. Will post pictures soon. He did not ride it much before he had issues with overheating, it was last rode at glamis on a rainy day so not that hot probably in the 70's ... He is a big guy and rode it pretty heavy. He supposedly always used that same mix Maxima castor 927 one liter to 5 gallons of gas but that last ride I think he accidently purchased the smaller bottle 16oz and mixed it to 5 gallons. Don't recall hearing any detonation but I'm not aware of the sound haha. Used 91 octane. It was leaking coolant on top of the head outside. Using engine ice coolant.