2 Stroke New Top End Problems

Harfend

Harfend

Greetings all,

I am new to the forum and seeking help. I have a 1986 KTM 250 MX. I replaced the piston, ring and had the cylinder recoated. The new piston went along with the cylinder to the machine shop so the parts were fitted. I reinstalled everything according to the factory manual, set all the clearances and had excellent compression. The bike started and ran. I let it idle for a few minutes and let it cool. I started the bike again and went for a short ride then let it cool. I started the bike a third time and rode a bit longer and the engine quit, locking the rear wheel. I was not hammering on the bike at all. Now I can not turn the motor over with the kick starter. I was using super oily gas as well. Have I ruined my engine and threw away all that money??!! Any help appreciated as well as ideas on how to unstick the piston if it is frozen....

Thanks,
HARFEND
 
2strokesteve89

2strokesteve89

Harfend:
Greetings all,

I am new to the forum and seeking help. I have a 1986 KTM 250 MX. I replaced the piston, ring and had the cylinder recoated. The new piston went along with the cylinder to the machine shop so the parts were fitted. I reinstalled everything according to the factory manual, set all the clearances and had excellent compression. The bike started and ran. I let it idle for a few minutes and let it cool. I started the bike again and went for a short ride then let it cool. I started the bike a third time and rode a bit longer and the engine quit, locking the rear wheel. I was not hammering on the bike at all. Now I can not turn the motor over with the kick starter. I was using super oily gas as well. Have I ruined my engine and threw away all that money??!! Any help appreciated as well as ideas on how to unstick the piston if it is frozen....

Thanks,
HARFEND
Click to expand...
Welcome to the forum.....Well as far as your problem goes, you are going to end up pulling it back apart. you might have had a cold seize, its possible it could be another problem such as a crank bearing but if it didnt make any noise prior to the engine lock my money is on a piston seize. but you wont know till it comes apart. you stated you were using "super oily gas" as well. any idea what the actual ratio was? should have been in the 32:1 ball park.
 
SRAD97750

SRAD97750

Moderator
Staff member
Welcome to the forum, despite it being under less than desirable circumstances.:wave:
You're going to need to tear down and inspect for damage, spec everything again and re-assemble. -BIG DAN:thumb:

I had the same thing happen to me on my 1989 KTM 250. Seized shortly after warm up, then again after a full rebuild sent off to millennium for plating. Sold it locked up and never rode another KTM. Still to this day I don't know what I did wrong. I have rebuilt MANY engines with excellent results.
 
Redordead89

Redordead89

SRAD97750:
Welcome to the forum, despite it being under less than desirable circumstances.:wave:
You're going to need to tear down and inspect for damage, spec everything again and re-assemble. -BIG DAN:thumb:

I had the same thing happen to me on my 1989 KTM 250. Seized shortly after warm up, then again after a full rebuild sent off to millennium for plating. Sold it locked up and never rode another KTM. Still to this day I don't know what I did wrong. I have rebuilt MANY engines with excellent results.
Click to expand...
Nice spoiler button Big Dan:thumb: mod only tool:noidea:
 
Harfend

Harfend

Thanks for your replies! I was at a few ounces over 32-1 hoping to avoid any crank issues. There were no clanking or banging noise before the engine quit. It just stopped running and the rear wheel locked. This is my first water cooled dirt bike and I have rebuilt several air cooled two strokes in the past with out break-in issues and locked engines so soon after an overhaul. Is this "cold seize" an issue with water cooled bikes? Can it happen at any time or only after a topend rebuild? Any replies and ideas are welcome. Thanks again!
 
Mihylo33

Mihylo33

Did you check your ring end gap?
Did you check your wall clearance?
Do you have a powervalve bridge requiring that you drill a lubrication hole?

Mixing gas too oil rich will actually lean out the jetting creating a lean condition. This lean condition will over heat engine components like a piston and ring.
 
Harfend

Harfend

Thanks for the reply. I did check the end gap and found it was in the specs listed in the factory manual; however it was on the tighter side of the allowable amount. If I get to that point again, I will certainty go to the bigger gap... I did not find a spec for "wall clearance" but I did send the piston along with the cylinder to the coating specialist. I have no power valve. That came on an 87 bike.

At this point I am assuming the piston is stuck to the wall of the cylinder. Any ideas on how to free it? I am able to remove the cylinder head and am thinking of rapping the piston with a piece of wood and a hammer to break it free. Any thoughts.....? I am hoping to not damage the piston and reuse it if possible. The last time I took the top end apart the motor would turn over, but the ring was stuck to the piston and I had no compression. Now the engine is stuck.

Thanks!
HARFEND
 
2strokesteve89

2strokesteve89

Harfend:
Thanks for the reply. I did check the end gap and found it was in the specs listed in the factory manual; however it was on the tighter side of the allowable amount. If I get to that point again, I will certainty go to the bigger gap... I did not find a spec for "wall clearance" but I did send the piston along with the cylinder to the coating specialist. I have no power valve. That came on an 87 bike.

At this point I am assuming the piston is stuck to the wall of the cylinder. Any ideas on how to free it? I am able to remove the cylinder head and am thinking of rapping the piston with a piece of wood and a hammer to break it free. Any thoughts.....? I am hoping to not damage the piston and reuse it if possible. The last time I took the top end apart the motor would turn over, but the ring was stuck to the piston and I had no compression. Now the engine is stuck.

Thanks!
HARFEND
Click to expand...

Before I pulled it apart I'd shoot some kind of lubricant thru the top of the cylinder it can't hurt. remove the cylinder mounting studs if possible so instead of just pulling straight off with the cylinder you could rotate and lift. also keep in mind that you can use heat. Obviously not to much since you are going to be grasping the part with your hands but if your able to heat the cylinder and not so much the piston it may gain you an edge.
 
Mihylo33

Mihylo33

2strokesteve89:
Before I pulled it apart I'd shoot some kind of lubricant thru the top of the cylinder it can't hurt. remove the cylinder mounting studs if possible so instead of just pulling straight off with the cylinder you could rotate and lift. also keep in mind that you can use heat. Obviously not to much since you are going to be grasping the part with your hands but if your able to heat the cylinder and not so much the piston it may gain you an edge.
Click to expand...

I'm wondering if he snagged a port
 
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