Aircooled 250R Siezing and then Unsiezing

[leetwanker]

This has happened two or three times since I had my topend redone (which I had to re-do because I siezed the piston). Anyway, I put a new sleeve in my cylinder, replaced the piston and rings and put a new gasket kit on it. Don't worry, I had an engine builder put the sleeve in and bore it.

What's happening now is when I'm riding, If I'm steady on the throttle at medium speeds my rear tires will lock up, the bike will come to a stop, the kickstart won't move, etc. I sit there a minute and then it starts right back up. What the hell would cause a piston to sieze up and then unsieze a minute later? Heat is the only thing I can think of. How do you get an aircooled engine to stop overheating though?

I was paying close attention to the engine this time and before it siezed it sounded like it was misfiring and I could feel it momentarily losing power while it was doing that, then I'd change the throttle position a bit and it would stop. What causes a 2-stroke to fire too early or too late and could that be a reason for it to overheat?

Thanks guys.
Justin

[slothminx]

I think that its been built with too tight tolerences, when the piston heats up it gets larger, sticking in the bore then when you let it sit, cools down and frees up. You need to get your engine builder to hone it out a little to give it the clearence it needs, remember if you used a forged piston like a wiseco, they need bigger clearences then a cast piston.

[SYKO]

could also be running a bit lean to that will cause alot of extra heat, did you put in a wiscoe forges piston or some other cast piston? how big is the bore?

[Unclediezel]

Piston siezing in the Bore? While your riding it? At mediumm Throttle?---Your sleeve would be TRASHED.......

Im not saying it isnt possible.... But I would look more towards something in the Geartrain, Or transmission.....

[leetwanker]

I'll pull the cylinder off tomorrow if I'm not too hung over and see if it's taken any damage since the last time I looked at it. I'd really think that an engine builder would know what kind of tolerances to give with different types of pistons but I guess it's possible.

[TRI-Zbrian]

lol i used to have a blaster back in the day that was 80 over when i got it... and i tried to ride it like my tri z.... welll lol it locked up a couple times on me also.. and i just pulled the clutch in wated for like 5 mins and kicked it over and it fired back up again... i didnt pay to much attention to it cause it was just a beater at the time for me.... and at 80 over theer was no help for that sleive any way... it would only do it if i held it wide open for longer then i should... you cant hold a 2 stroke wide open all day like you can a 4 stroke... the blaster is the only 2 stroke i did that too just cause i hate them...but any way hang in there dude you figure it out... and like said it may be starting back up but if you keep seizing that thing like that that sleive is going to be garbage soon if you dont figure out the problem...

[PowerTech]

the jug is to tight.

what does the spark plug look like? can you raise the needle up and if you do does it still run ok?

[leetwanker]

the jug is to tight.

what does the spark plug look like? can you raise the needle up and if you do does it still run ok?

From the looks of the plug it's definitely running rich and I don't want to lean it out until it stops siezing up on me.

[leetwanker]

Should I call Wiseco and ask them what the exact bore size should be?

[Billy Golightly]

What kind of machine shop did you have do the work? I'd almost bet the farm that they not only have the clearence to tight that they didn't bevel any of the window edges either.

[PowerTech]

From the looks of the plug it's definitely running rich and I don't want to lean it out until it stops siezing up on me.


when i say raise the needle i mean raise the needle. not the clip.

lower the clip to raise teh needle but regaudless of that the thing is built to tight anyway. dont ride it.

or you could put a cast piston in it and it would probably be OK.

for real though down load the booring directions for your piston and take it back to teh dude and have him hog on it some more.

[TimSr]

What kind of machine shop did you have do the work? I'd almost bet the farm that they not only have the clearence to tight that they didn't bevel any of the window edges either.

I can almost guarantee this is the problem. Most "discount machine shops" dont even ask what kind of piston you will be using, which should be a clue not to let them bore your cylinder. I ran into this problem once with a TriZ cylinder. Get hot, swell, seize, cool down, and start again. Wiseco had bored it, and they fixed it and gave me new piston and rings at no charge. They did not have to bore to teh next overbore size. Your cylinder will have piston scuff marks all the way up and dow, but it rarely trashes the cylinder. Piston is much softer than cylinder, and they can usually clean it out without boring again. (other than boring out enough for the correct tolerance for YOUR piston)

This is NOT a jetting or carb problem. Jetting rarely will cause a piston to swell and seize. Most often it melts the piston instead of causing it to seize.

[leetwanker]

I can almost guarantee this is the problem. Most "discount machine shops" dont even ask what kind of piston you will be using, which should be a clue not to let them bore your cylinder. I ran into this problem once with a TriZ cylinder. Get hot, swell, seize, cool down, and start again. Wiseco had bored it, and they fixed it and gave me new piston and rings at no charge. They did not have to bore to teh next overbore size. Your cylinder will have piston scuff marks all the way up and dow, but it rarely trashes the cylinder. Piston is much softer than cylinder, and they can usually clean it out without boring again. (other than boring out enough for the correct tolerance for YOUR piston)

This is NOT a jetting or carb problem. Jetting rarely will cause a piston to swell and seize. Most often it melts the piston instead of causing it to seize.

You're exactly right, I just pulled my jug and there is very little damage to the sleeve but the piston has siezure marks all the way around it. The thing that gets me is, I didn't take it to a discount machine shop, I took it to a professional engine builder and paid pretty good money for them to resleeve and bore it. They also required the piston before they'd do the job because they wanted to get the tolerances right. These are the same guys that built my 383 Stroker for my IROC and I've never had a problem with it so I had a good deal of trust for this shop.

How did you get Wiseco to bore your cylinder? I didn't know they did that kind of stuff.

Justin

http://i79.photobucket.com/albums/j128/JustinWPB/11-05-06_1512.jpg

http://i79.photobucket.com/albums/j128/JustinWPB/11-05-06_1513.jpg

http://i79.photobucket.com/albums/j128/JustinWPB/11-05-06_1514.jpg

[leetwanker]

What kind of machine shop did you have do the work? I'd almost bet the farm that they not only have the clearence to tight that they didn't bevel any of the window edges either.

Before they did the work I specifically asked them if they would be beveling the ports in the sleeve and they said they never do, and if it needed to be done, Honda would have done it initially, so he told me not to worry about it, which goes back to the trust I mentioned having for them in my last post.

I also asked him if it needed to be broken in and he told me the same thing he told me after he built the engine for my IROC, "Just drive it how you're going to drive it".

[slothminx]

The ports need to be beveled, otherwise they wipe the oil off the ring and can catch and jam up your motor. Sounds like this guy dont know what hes doing with this motor.

[leetwanker]

The ports need to be beveled, otherwise they wipe the oil off the ring and can catch and jam up your motor. Sounds like this guy dont know what hes doing with this motor.

I'm guessing he doesn't work on performance two stroke engines, probably just some marine engines. But his specialty is car and truck engines. I guess that's where I went wrong.

[MTS]

Before they did the work I specifically asked them if they would be beveling the ports in the sleeve and they said they never do, and if it needed to be done, Honda would have done it initially, so he told me not to worry about it, which goes back to the trust I mentioned having for them in my last post.

I also asked him if it needed to be broken in and he told me the same thing he told me after he built the engine for my IROC, "Just drive it how you're going to drive it".
I would take that piston back and Slap him with it, what an idiot, it aint no Car Motor!!!......and honda did bevel the ports from the get-go They Absolutely Have to be.....and broken in properly, Means Heat cyling the Wiseco...,

[leetwanker]

I would take that piston back and Slap him with it, what an idiot, it aint no Car Motor!!!......and honda did bevel the ports from the get-go They Absolutely Have to be.....and broken in properly, Means Heat cyling the Wiseco...,

Heat Cycling?

[Billy Golightly]

crank up, let it warm up go from idle to 3/4 up and down non stop for about 5 minutes and then shut it off let it go completely cold, do the same thing again except go to full throttle, shut it off and let it cool and then it should be ready to ride. Thats how I do it. Don't just hold it open, just stab it and kinda blip it up and down.

And as mentioned...the sleeve most definitely needs to be chamfered/beveled. I mean it aint got to be a 1/4inch or anything like that. .080 around each edge tapered down in towards the opening is plenty.

Heres a quick little scan from the 2 stroke tunders handbook on port chamfering.

[leetwanker]

I think I was kindof doing my own version of Heat Cycling, the first two times I rode it after redoing the top end I wasn't too hard on it but gave it some quick bumps of higher throttle and only rode it for about 10 minutes the first ride and 15 minutes the second. Being that it siezed up on me on my first ride, apparently from not having the right tolerances, that seems to be a mute point.