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Post subject: Mechanical Question: Power Valve Problem
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trumptonriot  Find me a Road! Joined: 30 Sep 2007 Total posts: 11 |
Bike stalled going very slowly as I go to restart it, the kicker won't budge. I got it into 4th and rocked it back and forth and true enough it seemed as if it had locked up.
However I wasn't going nearly fast or hard enough to cause even a soft seize. Also the power valve servo motor, as it cycles thru when I turn it on, seems to want to finish its cycle but can't. So much so that it drained the battery trying.
I got the head off (to be sure it wasn't hydraulic lock or something) and the piston crowns are just below the start of the exhaust port. No scoring on the jugs. I'm tending to believe that its not seized but rather something is going on with the power valves. All my other bikes have been without power valves so before further taking it apart I want to get some advice.
Any way the valves could stop the travel of the piston? The two problems (seemingly seized and valves not cycling properly) must be related as they both occured at the same time.
thanks in advance for any advice
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Posted: Thu Jun 26, 2008 2:02 pm
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gavin RD/RZ Jedi Master Joined: 03 Aug 2003 Total posts: 6423 Location: cheshunt, herts, uk |
take the exhausts off and have a look up the exhaust ports, if all looks ok you may have a problem with the crank...
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Posted: Thu Jun 26, 2008 3:10 pm
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Thrasherg Powerband Master Joined: 18 May 2007 Total posts: 881 Location: Austin, Texas |
If he has the heads off, he won't see much else from the exhaust port. If the kick start has locked up, he either has a problem with the crank/pistons or the drive chain from the kickstart to the crank. I would remove the right hand engine cover (can be done with the engine in the frame) and start looking at the kickstart gears, the clutch and the drive to the crank. Then see if the crank can be rotated using the bolt on the end of the crank or if it is locked up. I don't know why the power valves are jamming, maybe a ring broke and got jammed in the exhaust port locking the engine and power valve, but I would expect to see some damage to the bores and piston (visible with the head removed). If you were not riding very hard, I would expect the problem to be a failed bearing or something in the transmission rather than a seized piston. I could easily be wrong, but the right hand engine casing is quick and easy to remove so I would start there.
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Posted: Thu Jun 26, 2008 4:39 pm
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| Rich |
Even easier to remove the left (flywheel) side as you don't have to drain oil and coolant. It may even be something like a loose flywheel rotor.
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Posted: Thu Jun 26, 2008 4:54 pm
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ThrashergPowerband Master Joined: 18 May 2007 Total posts: 881 Location: Austin, Texas |
That's true, but I suspect it would be more complicated than a loose flywheel and the right hand cover gives access to everything..
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Posted: Thu Jun 26, 2008 5:00 pm
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gavinRD/RZ Jedi Master Joined: 03 Aug 2003 Total posts: 6423 Location: cheshunt, herts, uk |
cant see the point of making large assumptions and looking at the worst case first.  its more likely to be pistons than crank, and more likely to be crank than gearbox. eliminate the obvious and easy to check things first.
undo six bolts and take off the exhausts, see if your problem is there.
undo eight case screws and the gearchange linkage, see if the problem is the flywheel.
and if it is the gearbox, you'll need to take the exhausts and lh cover off anyway... 
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Posted: Thu Jun 26, 2008 5:45 pm
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trumptonriotFind me a Road! Joined: 30 Sep 2007 Total posts: 11 |
All good suggestions. I'm at work know so when I get home I'll start tearing into it.
More info: everything spins freely in neutral
power valves don't complete their cycle when you turn the key
I think I'll undo the bolts that hold the jugs down to the case and rock it in 4th... if the jugs and pistons move then I can rule out transmission, stator etc. yes?
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Posted: Thu Jun 26, 2008 5:54 pm
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Trig One-handed Stoppie! Joined: 04 Aug 2003 Total posts: 2499 Location: On Cloud 9 |
| trumptonriot wrote: |
All good suggestions. I'm at work know so when I get home I'll start tearing into it.
More info: everything spins freely in neutral
power valves don't complete their cycle when you turn the key
I think I'll undo the bolts that hold the jugs down to the case and rock it in 4th... if the jugs and pistons move then I can rule out transmission, stator etc. yes? |
Pistons rings snagged on exhaust port, bent the bore liner and trapped power valves I reckon.
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Posted: Fri Jun 27, 2008 7:57 am
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ThrashergPowerband Master Joined: 18 May 2007 Total posts: 881 Location: Austin, Texas |
If everything spins freely, that's good news but just tells you the gearbox is okay. If any debris has fallen into the gears on the clutch and the crank shaft, it will still be jammed.. As suggested, check the flywheel has not come loose, then either loosen the jugs or remove the right hand engine cover and look for whatever is locking up the crank.
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Posted: Fri Jun 27, 2008 2:02 pm
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Bare All-gear Wheelie! Joined: 28 Jan 2006 Total posts: 1986 Location: Vancouver Canada |
[quote=
Pistons rings snagged on exhaust port, bent the bore liner and trapped power valves I reckon.[/quote]
uuugh ..thats' ugly.. and quite possible/ likely. yer Good 
I have an old trashed cyl that suffered that exact problem ..so it has happened before.
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Posted: Fri Jun 27, 2008 3:47 pm
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TrigOne-handed Stoppie! Joined: 04 Aug 2003 Total posts: 2499 Location: On Cloud 9 |
| Trig wrote: |
| trumptonriot wrote: |
All good suggestions. I'm at work know so when I get home I'll start tearing into it.
More info: everything spins freely in neutral
power valves don't complete their cycle when you turn the key
I think I'll undo the bolts that hold the jugs down to the case and rock it in 4th... if the jugs and pistons move then I can rule out transmission, stator etc. yes? |
Pistons rings snagged on exhaust port, bent the bore liner and trapped power valves I reckon. |
Take the pipes off and look up the exhaust port, this will tell you all you have to know!!
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Posted: Sat Jun 28, 2008 7:40 am
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