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Discussion Starter #1
Took my 84 out for a ride today and was a few miles down the road running in 4th @ 2000 rpm when it made a loud clack, and for a split second, locked the drive line. Not long enough to slide the tire, but enough to cause the front end to dive. It was over before I could grab the clutch.

I stopped and looked it over. It sounded kind of like dropping a valve, but the engine runs and idles fine. I rode it home, hand on the clutch all the way. Every thing seems fine. No issues on the way home. Before I ride it again, I think I'll open the primary up. Make sure there isn't something broken in there. Beyond that, I'm at a loss.
 

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Hi Therm

With your good description but Not being there, I have a theory based on
running in 4th at soo low an Rpm..

You're prob aware of the "bucking" that some guys get when riding slow..
It can be caused by over loose primary chain and/or rear drive chain/belt
but very often, it is from running too slow in too high a gear with the Ign
advance set to too fast and/or too far..

When running slow around a parking lot or slow traffic etc etc in too high a gear,
the Ign may be at Full advance but the sickle speed is low and the piston speed
may also be too slow to get over TDC before the complete burn is done..

At that moment, that completed burn may attempt to drive the piston Backward
down from the direction it just came from,, this is real and simply needs
the right conditions to occur..
It is Not a good thing and will encourage Detonation..
That "clank" you heard coulda been just that..!
Usually setting the advance a wee slower And/OR running in a lower
gear will fix that..

At 2K you're prob at Full Advance but the piston speed May not have been high
enough to get over TDC before the Full burn and for a Nano-second the
motor & sickle tried to go backward..

OR,,,,,,,,, a rock/pebble simply got caught in the rear chain & sprocket
and locked it up before passing on or breaking up..

Either crazy simple or a wee worse..
 

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Swamprat Rider
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Subscribed, curious to see what find ..
 

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I think that is a good safe move to open you primary and make sure all is good. Maybe a piece of the tensioner shoe fell off. Remember that mine was cracked almost all the way through...

http://www.v-twinforum.com/forums/transmission-primary/191877-check-your-primary-chain-pad.html

rkc
@gree:

The front of my OEM primary chain tensioner broke off and locked up the primary while I was doing 80 on the freeway -- and it sounded / acted exactly as described. IMHO it was the cause of my flywheels shifting.

If in fact you find this to be the issue, strongly advise you disassemble everything in the primary to be sure you get all the debris. I found a lot of crap I'd have missed had I not done that.

Finally, recommend you either switch to the old Evo style, as it supports both sides of the shoe, or better yet - Baker and someone else I can't recall makes a beefier shoe.

I would not ride the bike until opening the primary and checking, as a big chunk of the shoe could be laying on the bottom of the primary just waiting to get wedged in the chain. Good luck. Keep us posted.
 

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Discussion Starter #7
Hi Therm

With your good description but Not being there, I have a theory based on
running in 4th at soo low an Rpm..

You're prob aware of the "bucking" that some guys get when riding slow..
It can be caused by over loose primary chain and/or rear drive chain/belt
but very often, it is from running too slow in too high a gear with the Ign
advance set to too fast and/or too far..

When running slow around a parking lot or slow traffic etc etc in too high a gear,
the Ign may be at Full advance but the sickle speed is low and the piston speed
may also be too slow to get over TDC before the complete burn is done..

At that moment, that completed burn may attempt to drive the piston Backward
down from the direction it just came from,, this is real and simply needs
the right conditions to occur..
It is Not a good thing and will encourage Detonation..
That "clank" you heard coulda been just that..!
Usually setting the advance a wee slower And/OR running in a lower
gear will fix that..

At 2K you're prob at Full Advance but the piston speed May not have been high
enough to get over TDC before the Full burn and for a Nano-second the
motor & sickle tried to go backward..

OR,,,,,,,,, a rock/pebble simply got caught in the rear chain & sprocket
and locked it up before passing on or breaking up..

Either crazy simple or a wee worse..
It didn't sound like spark knock and the engine was still way cold. With this scooter, 2 grand is well past where it wants to lug. I considered that it could have been a lean back fire from the cold, with the noise being from the drive line slapping. But I can't really convince myself of it. I need to put some new clutch disks in anyway so I get some reassurance by checking the primary. Only other thing I could come up with is trash in the bottom of the tranny. Cold thick gear oil might have picked it up. Or one of the ratchet springs was cold and brittle enough for a piece to break off. But I never saw a tranny that was able to pass any junk without being permanently damaged.
 

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Discussion Starter #9

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I had something similar, bolt holding the rear wheel drive pully had unwound on a long trip and when it reached the swingarm 'width' sheared off the head of the bolt. Was going fast enough not to lock the rear wheel and surprisingly no damage to the swingarm.
 

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I had something similar, bolt holding the rear wheel drive pully had unwound on a long trip and when it reached the swingarm 'width' sheared off the head of the bolt. Was going fast enough not to lock the rear wheel and surprisingly no damage to the swingarm.
Wow, that sounds crazy. I had one on my rear sprocket (chain drive like the OP) loosen up and it "rubbed" the swingarm and made a racket. I was probably going about 50mph. Yours must have come out real fast...

rkc
 

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Elongated the hole by rubbing on the swingarm and stripped threads, ruined a three spoke cast wheel, expensive learning curve.
 

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^ Same thing happen to me with blue lock tight on the bolt's. I have since then installed bolt's with locking wire to prevent the problem in the future.
 

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Discussion Starter #15
I got around to pulling the cover today, and all looks well. It has an almost new tension shoe, and no trash what so ever in the case. I went around and checked the rotor and sprocket bolts and they too were all good to go. I have some clutch disks coming, so once they get here, I'll put it back together and see what happens.
 

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Your original description sounded exactly like what happened when I had a relay fall into my drive belt. In my case, the belt didn't survive. Have you checked your drive chain closely? Crooked links or anything to indicate something getting into it?
 

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Sua Sponte
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@gree:

The front of my OEM primary chain tensioner broke off and locked up the primary while I was doing 80 on the freeway -- and it sounded / acted exactly as described. IMHO it was the cause of my flywheels shifting.

If in fact you find this to be the issue, strongly advise you disassemble everything in the primary to be sure you get all the debris. I found a lot of crap I'd have missed had I not done that.

Finally, recommend you either switch to the old Evo style, as it supports both sides of the shoe, or better yet - Baker and someone else I can't recall makes a beefier shoe.

I would not ride the bike until opening the primary and checking, as a big chunk of the shoe could be laying on the bottom of the primary just waiting to get wedged in the chain. Good luck. Keep us posted.
+1, that's my guess. tensioner snapped.
 

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Ranger if you read Thermodyne's post #15 you'll see that's not the problem.
 

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I got around to pulling the cover today, and all looks well. It has an almost new tension shoe, and no trash what so ever in the case. I went around and checked the rotor and sprocket bolts and they too were all good to go. I have some clutch disks coming, so once they get here, I'll put it back together and see what happens.
Any news on this too report?
 
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