Jammed Chain

[Rudie]

aloha Rudie:
I hope you are doing well and life is good for all!
I have another issue; I don’t know how, but my chain is jammed in front of the forward sprocket and I’ve tried everything, short of taking everything apart (not in my wheelhouse). Do you have any suggestions
thanks,
Lanny

Sorry to read this.

Guessing the chain either broke or jumped the front sprocket, at least one link is jammed between a front sprocket tooth and the crankcase?

If it is only one link jammed and the chain has not broken, it could be possible to loosen the chain by turning the rear wheel backwards very hard until the chain link comes off the sprocket?

However, without removing the primary drive and the access to the front sprocket, you will not know if the jammed chain has damaged the crankcase, and you might have to do this anyway if you cannot unjam the chain with the rear wheel.

short of taking everything apart (not in my wheelhouse).

Smaller deal than the electrics ...

 

[LannyDaise]

Sorry to read this.

Guessing the chain either broke or jumped the front sprocket, at least one link is jammed between a front sprocket tooth and the crankcase?

If it is only one link jammed and the chain has not broken, it could be possible to loosen the chain by turning the rear wheel backwards very hard until the chain link comes off the sprocket?

However, without removing the primary drive and the access to the front sprocket, you will not know if the jammed chain has damaged the crankcase, and you might have to do this anyway if you cannot unjam the chain with the rear wheel.


Smaller deal than the electrics ...

Good Morning Rudie:
Thanks for getting right back with me. I got it unjammed yesterday, but you probably would be upset with me on my technique! I had to remove the rear wheel as i couldn’t get the chain on the rear sprocket anyway, and could barley get my longest screwdriver up to the sprocket. Then I took a hammer and tapped the sproket in reverse and that freed it up! I bet I worked on that for over five-hours!

Now I need to wait for parts, as when this happend, it broke the left rear adjuster (or maybe the adjuster broke which caused the chain to skip)?

Either way, I’m going to have to be more careful on installing the rear wheel. I thought I had the recommended 1/2” play in the chain, but I hadn’t checked it after I last installed the rear wheel.

Thanks so much, and if you have any advice on this, I’ll always be grateful.

Lanny

 

[Rudie]

I got it unjammed yesterday, but you probably would be upset with me on my technique!

Whatever works.

recommended 1/2” play in the chain

I hope "1/2”" is a misprint, the slack in the bottom run of the (rear) chain should be:-

. either 3/4" with the bike on both wheels;

. or 1-3/4" (one and three-quarter inches) with the bike on its centrestand;

. http://www.classicbike.biz/Triumph/OwnersManuals/1970s/1978-Bonneville-750-T140E-Owners-Handbook.pdf, pdf page 21 or handbook page 19.

That said, ime Triumph handbook measurements are not always super accurate:-

. If you have a tall and heavy friend - tall so he/she can hold the the bike up sitting on the rear seat, heavy so he/she can compress the rear suspension until you can see the clutch adjustment plug, the swinging arm spindle and the rear wheel spindle are in a line.

. Then the chain is at its tightest point. Renold (the original chain maker) say a roller chain should still have up-down slack equivalent to the pitch - i.e. because it is a 5/8" x 3/8" chain, it should still have 5/8" up-down slack - when the chain's tightest in the rear wheel's arc.

I have checked/adjusted my bikes' rear chains to the Renold advice then put them on their centrestands and measured the chain slack again. Not always what the handbook or manual says but, once I have done this double-check, I know what each bike's chain slack should be when it is on its centrestand.

 

[LannyDaise]

Whatever works.


I hope "1/2”" is a misprint, the slack in the bottom run of the (rear) chain should be:-

. either 3/4" with the bike on both wheels;

. or 1-3/4" (one and three-quarter inches) with the bike on its centrestand;

. http://www.classicbike.biz/Triumph/OwnersManuals/1970s/1978-Bonneville-750-T140E-Owners-Handbook.pdf, pdf page 21 or handbook page 19.

That said, ime Triumph handbook measurements are not always super accurate:-

. If you have a tall and heavy friend - tall so he/she can hold the the bike up sitting on the rear seat, heavy so he/she can compress the rear suspension until you can see the clutch adjustment plug, the swinging arm spindle and the rear wheel spindle are in a line.

. Then the chain is at its tightest point. Renold (the original chain maker) say a roller chain should still have up-down slack equivalent to the pitch - i.e. because it is a 5/8" x 3/8" chain, it should still have 5/8" up-down slack - when the chain's tightest in the rear wheel's arc.

I have checked/adjusted my bikes' rear chains to the Renold advice then put them on their centrestands and measured the chain slack again. Not always what the handbook or manual says but, once I have done this double-check, I know what each bike's chain slack should be when it is on its centrestand.

Aloha Rudi:
the parts arrived today, and I was able to put it back together, but as I spin the wheel, I’m getting some resistance on one small section of the chain as it passes around the forward sprocket. I appreciate your advice in the slack measurements, but I don’t feel real good this evening with that one section of friction. I cleaned the chain and sprayed some lithium grease, but still have that friction.
Maybe I’ll sleep on it and try again tomorrow.
Mahalo,
Lanny

 

[Rudie]

some resistance on one small section of the chain as it passes around the forward sprocket.

The chain or sprocket could have been damaged when they jammed together.

As you rotate chain and sprocket, can you tell if the resistance is in the same place on the sprocket or in the same place on the chain?

If it is the same place on the chain, replace the chain?

Otoh, if it is the same place on the sprocket, if you rotate it slowly while looking from under the bike between the upper and lower chain runs, damage might be visible?

 

[LannyDaise]

The chain or sprocket could have been damaged when they jammed together.

As you rotate chain and sprocket, can you tell if the resistance is in the same place on the sprocket or in the same place on the chain?

If it is the same place on the chain, replace the chain?

Otoh, if it is the same place on the sprocket, if you rotate it slowly while looking from under the bike between the upper and lower chain runs, damage might be visible?

Aloha Partner:
I believe it’s the chain…it has friction in the exact same spot and the sprocket looks okay, I’ve ordered a new one.

How‘s everything in your worl

The chain or sprocket could have been damaged when they jammed together.

As you rotate chain and sprocket, can you tell if the resistance is in the same place on the sprocket or in the same place on the chain?

If it is the same place on the chain, replace the chain?

Otoh, if it is the same place on the sprocket, if you rotate it slowly while looking from under the bike between the upper and lower chain runs, damage might be visible?

Aloha Rudi:
The chain was slightly binding in the exact same place, and the sprocket appears to be okay. Thanks once again for the advice…I’ve ordered a new chain. I’ll let you know how that turns out.
I’m guessing I’ll need to tie a small line on the last link on my old chain to pull it over the sprocket to feed the new one so it passes over the forward sprocket? Is that how’d you’d get it over it?
The link you sent me from the 1978 Bonniville states I should have the same amount of turns on each side adjuster, however when I do this the tire rubs on the frame. I hope that doesn’t cause any problems if I finally get the wheel lined up and the adjusters are not the same number of turns?
Hopefully everything in your world isn’t too crazy! Covid is really ramping up here! My wife and I got it a month ago, and wasn’t fun for a week, but we’re okay now.
Thanks for everything!
Lanny

 

[Rudie]

guessing I’ll need to tie a small line on the last link on my old chain to pull it over the sprocket to feed the new one so it passes over the forward sprocket? Is that how’d you’d get it over it?

I link the new chain to the old chain with part of the split link and pull on the old chain; as it comes off, it pulls the new chain over the sprocket.

The link you sent me from the 1978 Bonniville states I should have the same amount of turns on each side adjuster, however when I do this the tire rubs on the frame.

Same number of turns assumes Meriden machined the ends of both axle slots exactly parallel to the swinging arm spindle axis ...

The most important thing is the wheel centrelines are the same. For complete accuracy, this should be checked with two long straight edges, clamped either side of the rear rim (not the tyre as sidewall mouldings can cause inaccuracy in the straight edges). As the front rim is narrower than the rear rim, there will (should) be gaps between both straight edges and each side of the front rim (again, not tyre) in two places. If the wheel centrelines are the same, all four gaps should be the same.

The common practical problem with the previous paragraph and old bikes is the bikes are forty, fifty years old, the accidents they have been in that could bend frame, swinging arm and/or forks have become lost in the mists ...