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Discussion Starter #1
A little bit off topic, but is anyone here good with 2 strokes?
I had a blown crank seal on the stator/rotor side. The bike started right up before I replaced the seal, but it has to be push started as the starter stopped working after I modified the bike a couple of years ago.
Anyway, I removed the flywheel and the stator, changed the seal and put everything back together.
Now I can't get the bike to run. Used to be able to push start on flat ground within 2 bike lengths, but now the rear wheel just locks up no matter what. It does this in all gears. I can rotate the engine by hand, the transmission works fine and I can turn the wheel by hand while the bike is in high gear (barley) and the compression is good.
I am not a small guy so the weight is not the problem.
I went to the biggest downhill in close proximity and just left 20ft skidmarks everywhere.
The bike is a heavily modified Yamaha TZR 50 2008
 

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Seems to me as if the clutch isn't disengaging.

Have you tried sitting on the bike, putting it in, say, 2nd or 3rd gear, and then rocking the bike backwards while letting the clutch out?

You will at first feel the wheel lock, but with a few attempts it should break free and roll without resistance. Can tend to happen with bikes that sit for a while.
 

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Discussion Starter #4
Yeah, I thought it might be clutch drag so I took it apart to split the clutch discs, but that did not help either.
I am able to switch between gears with no problem.
But the wierdest part is that I had the bike running 30 minutes before I changed the seal.
I have removed the clutch and the flywheel/stator sevral times to see if it was reassembeled correctly, but can’t find anything wrong.
I also tried to roll the bike without the plug to check if the compression made it lock up, and it locked up even without the spark plug.
 

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This is probably little help, but logic states that if it worked okay before the seal change, SOMETHING has happened during the seal replacement. Could you have crushed a wire or left something undone? I would undo everything and then reassemble.
 

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Discussion Starter #6
The problem is that I have done exactly that multiple times and cannot find anything wrong with it.
The only thing that I can think of is that under the installation of the seal it came in a little crooked, but I straightened it and the crank turns fine manually.
 

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Okay. I hope someone wiser than me comes along to help - and there are many!!:)

I truly understand you have a frustrating situation.:(
 

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Discussion Starter #9
And the wierdest thing of all is that if I put the bike in gear, lift up the backwheel and rotate the crank.
Then the f** backwheel turns
 

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. . . I also tried to roll the bike without the plug to check if the compression made it lock up, and it locked up even without the spark plug.

And the wierdest thing of all is that if I put the bike in gear, lift up the backwheel and rotate the crank.
Then the f** backwheel turns
Two contradictory and totally opposite reactions here. Perhaps it's not related to anything that you've done but is a totally different problem.
 

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Got any pictures of this thing? And to revisit - it wont start, won't freely roll when the clutch is dumped for a pop start, and also locks up the rear wheel even with the spark plug out?

Then, when you put it in gear and lift up the rear wheel off the ground you can spin the wheel by turning the crank?

Is there a rear brake pedal you're accidentally mashing when trying to bump start it?
 

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Discussion Starter #13
Yes, exactly.
I can try to upload something tomorrow, but there is just no way I am braking without noticing it:LOL:
 

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Discussion Starter #14
I was having a hard time uploading videos on here so I just put them on Youtube. Anyway as you can see the clutch works ok and I am also able to switch gears an roll the bike with the clutch pulled in.
I used to be able to push start it with minimal effort on flat ground.




 

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This has me bamboozled. Just a short while ago I had an aprilia RS50 that I would push start. I therefore know that the compression of these things - even in first gear - is not enough to lock a wheel.

What I now wonder, is if the clutch cable is routed in such manner that it's actually fouling and activating the rear brake? I know @IanDoohan touched on the possibility of a brake problem but this seems so 'rear related'. Also, unless it's my desktop screen, the exhaust chamber looks loose so might that also be contributing to something in the rear when you're on the bike. I do think it's weight related. Get your wife/partner to sit on the bike and check the rear as she slowly goes down the drive.

Could be 'clutching':) at straws here, but important to isolate this as a possible issue.
 

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Discussion Starter #16
Yeah, I’m trying to rule out every possibilty. It does have slightly more compression than a 50 since it is a 88?, but not much.
We tried to roll it down, but it does not seem like something is hanging. I just pulled the head off to see if the rings are fried or something, but it’s all smooth in the cylinder. On the picture you can see the clutch cable is far away from anything else just rooted under the carb.
I came across one of these motorized bicycle forums and there was this one dude that had misaligned the drive sprockets and had a similar issue, but I do not think that this is whats happening. I was thinking of trying to get a new starter and try to start it like it is supposed to, but this is a really wierd issue and I am starting to think that there is a big problem somewhere.
Also the exhaust is not loose I just use an adapter since it does not fit in the exhaust port.
The mods om the bike are:
Doppler enhaced crankshaft
polini 88cc cylinde/piston
Some kevlar clutch i don’t remeber the brand of.
Everything is assembeled correctly since it used to run fine before it blew the seal, but perhaps something has come loose?
 

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Discussion Starter #17 (Edited)
Update:
I managed to get 2/3 revolutions of the engine rolling down the hill with my feet and ass on the passenger pegs/seat but it locked up right after.
 

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Discussion Starter #20
Yes the starter is still hooked up just so shit does not fly into the the flywheel, but it is disengaded. You can see ut right under the flywheel on the «crankshaft» video.
Could you please explain what sprag clutch grab is? ?
 
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