Cold seize?

[averysdad]

After a long thread on jeting and one on cleaning out the stock pipe and silencer. I burnt out the pipe with a torch and painted it left the spark arrester out bike was running good after that. Then After a 1/8 mile at W.O.T it starts bogging down and died poped the clutch to crank it back up made it home bogging running like crap. Next day I cleaned the carb runs good for an hour I'm happy. Later that day I cranked it up gave it a little gas and it locks up kick start will not move. Why did this happen? Is the piston stuck or is it something in the bottom end?

84 250r all stock
132 main 1 size up from stock
50 pilot
Aftermarket reeds

[yaegerb]

Maybe crank bearings or big end Conrod bearing finally gave out or you could have a ring stuck in a port. Pull the head and stator cover and see if you can turn the engine over by hand using the flywheel. If not, sorry to say you need to pull the cylinder.

You sure it's not something wrong with Kickstarter? Long shot, but maybe....

[averysdad]

Rocked it back and forth in gear and the piston will move up and down but won't make a full revolution stops at top then at bottom What's that mean? Aluminum every where in exhaust on spark plug piston looks ugly

The bad thing is I can't get the head off. And I broke one of the fins of the cylinder prying on it I'm really pissed about that right now.

Any tips on getting the head off?

[loganm]

Whack it with a dead blow a couple times, in a way that won't break fins. Looks like you fuckered it up pretty good there boss. If it won't turn all the way over the whole things probably trashed.

[averysdad]

All the Bottom end bearings all trashed ???

[loganm]

Well not in the transmission, but I would definitely do crank bearings crank rebuild or rebuild another crank if the center pin is snapped and a top end refresh, for starters.

[atc007]

That is aluminum,molten aluminum, that USED to be your piston.It melted from all of the heat. While some have torn an engine that bad apart and "cleaned" the cases and crank bearings. The only correct way is a full split the cases,and start from the ground up now. After rebuilding, you will have to pull a leak test to ensure this doesn't repeat itself. You will need a clean/correctly jetted carb,clean fuel tank,cleaned petcock,and good parts in that new carb to ensure it is getting fed what it needs.Yes, you will need crank bearings/seals, complete top end and very probably a fresh bore. We can walk you through it if you dive in. Good luck and sorry

[yaegerb]

Piston has eroded on the top edge. That much is evident. That motor is a paperweight for now. Send me a PM if you want a full rebuild. I don't cut corners and I will set you straight again.

[fieldy]

Doesn't really qualify as a cold sieze if it was warmed up good. Maybe an air leak and worn parts like others have suggested.
I saw a liquid cooled rm125 cold sieze in colder weather by a kick start and then went directly to ing through the gears. Thats how i understand that happening. Not enough warm up time. Piston and cylinder warm up at seperate rates.
Would like to find your previous thread about jetting.

[nstyle73]

When a piston erodes on top like that, especially the exhaust side, isn't it often due to detonation, possibly from a lean mixture ?

[fieldy]

What octane, oil and ratio. Be interesting to know.

[loganm]

Wasn't this the bike with like 120 psi compression? Maybe a crank seal went, I thought detonation also.

[fieldy]

Maybe a seal went at wot the day before? Any reving at idle before your last good ride? What was the last compression test and when? We've got a lot of questions here tonight! Thank you, Blown Motor Patrol.

[atc007]

If I did drink coffee,it would be all over the screen. Shook it till it's dead!! Indeed! Averysdad,if you can come up with the change, Yaeger will make her just as good as she was when new,and I suspect for a very reasonable price. Many with far less problems have also sold the scrap metal off on cl also. Let us know how you make out.

[yaegerb]

I wouldn't be able to tell if it's a cold or four corner seize until he posts pictures of the piston. Cold seizure happens because the motor isn't sufficiently warmed up and you begin flogging it immediately. What happens is the piston skirt which is actually an increase in diameter from the crown heats up to fast and locks itself in the bore.

What I can barely make out from that pic (this is only a guess) is one of two things. Exhaust side seizure which is caused by air leaks. I think this one is more likely because averysdad was complaining of a low speed bog and that's usually a sign of airleak on the flywheel side of the crankcase.

The other thought I had was either blown head gasket or squish band velocity was too high.

Either way man, take a deep breath and we can get you moving again. Just need a few parts and some time.

And I highly doubt your carb jetting was off if the specs you gave above are the ones you are running. If I remember correctly you are running 32:1 oil ratio. My bet is that it was just time for the seals to be replaced.