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Discussion Starter · #1 · (Edited)
Anyone have a suggestion as to why a 2-stroke crank seal could be blown right out of its bore with enough force to bend the seal keepers? I don't want to simply replace the seal and have it repeat the same problem. Can this happen from a backfire? POW.
 

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Anyone have a suggestion as to why a 2-stroke crank seal could be blown right out of its bore with enough force to bend the seal keepers? I don't want to simply replace the seal and have it repeat the same problem. Can this happen from a backfire? POW.
yes, Did it run ??? is the piston in right ???
 

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Discussion Starter · #3 · (Edited)
yes, Did it run ??? is the piston in right ???
It ran, but it never has run right. I never pulled the top end off this bike because it has the highest compression of any 2-stroke I own.
I have been chasing carb issues because the carb that came with it was a mess inside. I rode it with the carb off my 400 but again, it isn't running right. I recently put a smaller carb from a running 250 parts bike. The timing is spot on, and that's no easy task on these old girls. With the 250 carb it started and ran for about 30 seconds and drowned out in a cloud of smoke. Hence the reason I went for the right side crank seal. Bingo! Blown right out of its seat. It has backfired during my many attempts to get this thing running right. The fact that it bent the keepers has me concerned. Those little brackets are pretty robust.
Will it even run with a piston in backwards?
 

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It ran, but it never has run right. I never pulled the top end off this bike because it has the highest compression of any 2-stroke I own.
I have been chasing carb issues because the carb that came with it was a mess inside. I rode it with the carb off my 400 but again, it isn't running right. I recently put a smaller carb from a running 250 parts bike. The timing is spot on, and that's no easy task on these old girls. With the 250 carb it started and ran for about 30 seconds and drowned out in a cloud of smoke. Hence the reason I went for the right side crank seal. Bingo! Blown right out of its seat. It has backfired during my many attempts to get this thing running right. The fact that it bent the keepers has me concerned. Those little brackets are pretty robust.
Will it even run with a piston in backwards?
if there is a window in the skirt it should go toward the carb if i remember right. if it has reed valves. pop off exhaust and look at your piston. maybe its broke too. looks like exhaust in the crankcase.
 

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Discussion Starter · #5 · (Edited)
if there is a window in the skirt it should go toward the carb if i remember right. if it has reed valves. pop off exhaust and look at your piston. maybe its broke too. looks like exhaust in the crankcase.
The residue behind that side cover was black as black can be. It does have a reed valve. I will pull the intake and the exhaust to verify piston orientation. The exhaust pipe will have to be burned clean anyhow since it has been completely fouled with oil.
I have no idea if the previous owner had been into the top end. It wasn't running when I bought it. But I got it running and have probably ridden it for 20 miles or so as I try and sort out the issues. I can't imagine it would run at all if the piston was backwards. But that's easy to check without pulling the jug. I appreciate your input Burke.
 
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Discussion Starter · #7 · (Edited)
also check the reeds if it blew that bad the reeds are probably fuct too.
The reeds look fine, although they are aftermarket Boysen's which I've never used before. There are backing plates that limit the reeds from blowing back too far.
The piston orientation is correct with intake ports toward the carb.
The cyl bore looks ok to me as seen thru the exhaust port. It actually shows some cross hatching, so maybe someone has been in there.
Is it possible I have a "twisted" crankshaft? I believe they are pressed together. Might explain why I cannot seem to make this thing run properly regardless of using 3 different carbs and knowing the timing is set perfectly using a dial indicator and a buzz box.
How the heck would I checked for a twisted crank?
 

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The reeds look fine, although they are aftermarket Boysen's which I've never used before. There are backing plates that limit the reeds from blowing back too far.
The piston orientation is correct with intake ports toward the carb.
The cyl bore looks ok to me as seen thru the exhaust port. It actually shows some cross hatching, so maybe someone has been in there.
Is it possible I have a "twisted" crankshaft? I believe they are pressed together. Might explain why I cannot seem to make this thing run properly regardless of using 3 different carbs and knowing the timing is set perfectly using a dial indicator and a buzz box.
How the heck would I checked for a twisted crank?
dial indicator for radial and axil play. visually by removing cylinder, or splitting the case. maybe there is too much endplay(axil).
 

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Discussion Starter · #9 ·
dial indicator for radial and axil play. visually by removing cylinder, or splitting the case. maybe there is too much endplay(axil).
Well I'm open to popping the top of this thing since I have the gaskets in hand, but I really really don't want to split cases again. Just did that in my Tooth Fairy post with my 400.

Oh well. It's a hobby, right? Can't let this stuff bring me down. I'll let you know how it turns out.
 

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Well I'm open to popping the top of this thing since I have the gaskets in hand, but I really really don't want to split cases again. Just did that in my Tooth Fairy post with my 400.

Oh well. It's a hobby, right? Can't let this stuff bring me down. I'll let you know how it turns out.
if it brings you down, walk away come back fresh another day.
it's cocktail hour !!!
 
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