Topic: Chain Stuck between front sprocket and Engine casing

[BlissMX]

Hello SOHC4.

I was out riding the other day on my 76 CB750F and the chain link that connects to the master link broke. The chain the proceeded to pull through the bike until it became jammed between the front sprocket and the engine casing. The chain now makes a U shape in from of the sprocket and there is no play in the sprocket what so ever. I can’t seem to shift the bike into natural (I’m thinking/hoping this is because of the pressure on the gears from the jammed sprocket). I can’t pull the chain out backwards so I’ve started taking the dremel to the U section of the chain to try and free it.

I was wondering if anyone else has ever come across this issue and if so, what they may have done to free the chain. I’ve already succumb to buying a new chain; I just want to get the old one out.

Any Ideas/suggestions?

BlissMX

[Duke McDukiedook]

Take the sprocket off and cut the chain?
Hopefully you didn't gnaw through the crankcase.

[BlissMX]

hopefully you are right, I hope the crank case is still good.

The chain is so stuck I can't get the sprocket off. I just took some picture of the situation.

[MCRider]

I would say do not try to shift it till this is fixed. It is as you sy, pressure on the gears and working aginst that you can only damage something.

As to the problem, you have a snapshot in time of what so many have seen, in the frames that come after. A broken chain that breaks the crankcases. If the case were broken the chain would be free and thats where most end up.

Consider yourself lucky (I hope) and proceed to cut it out.

[BlissMX]

If there case is/were broken, would I be seeing leaking oil?

[MCRider]

If there case is/were broken, would I be seeing leaking oil?

Good question, not much is my guess. The engine didn't run much after the break? There is not a pool of oil in that area to drip. The shafts are all pressure fed and it drips back to the sump. I've seen several broken ones, but always sometime after the fact.

So maybe not.

[BlissMX]

Any suggestion for a cutting method? I was able to get the side of one link off with the dremel, but i'm working in a pretty tight space and I can't get the dremel on the other side of the chain.

Thoughts?

[Johnie]

Gosh, I hope your case is OK. In some of the pics it looks like the edge of the link is embedded into the case. I hope that is only grease and dirt build up and not the case. Good luck with it.

[2wheels]

I think the dremel and cutting wheel are the best tool for the job.
Both the chain and spocket are done.  So I would be cutting away at them, one small chunk at a time.  just my thoughts

[Cuts Crooked]

..and figure on replacing the seal on the output shaft once you get it all apart.

[CB750F2]

I would try removing the two bolts that hold the sprocket holding plate and then remove the plate. You will probably have to use a punch to rotate the sprocket holding plate until it lines up with the output shaft spline so that it can be removed. Doing this may allow some movement in the sprocket and loosen the jammed chain. If this doesn't continue with cutting the chain. Pat

[BlissMX]

Hello all,

An update on my stuck chain. I was able to get it off but discovered bigger problems. here is a picture of where I sit now. My question to the forum, what are my options now?

Thanks everyone, your input is appreciated.

[MCRider]

The real fix is to disassemble and weld repair.

But many here have done a temporarily permanent fix with JB Weld. I'm sure they will chime in.

I would do that if I was never leaving the state on a long trip. Even though its probably fine, I would be so paranoid 500 miles from home I couldn't enjoy the ride.

[BlissMX]

It also seems as thought I can't shift the bike. I'm not sure if the case has pushed into the gears, or if the chain jamming in the first place has broken on the inside or not. the engine still starts and runs fine, i just can't seem to shift it.

[Johnie]

On a bike with the chain on & stuck in gear, we usually rock the bike in gear to unlock it. In your case with the chain off, I would put the sprocket back on and try to rotate the shaft and and move the shift lever. See if that will free it up. Hard to tell, but from the pic it does not look like it is indented enough to contact the guts.

[HedNut]

I've been thru this... well...kinda.... the previous owner sold me the bike with this condition "covered" with some type of pasty patch. 
   I had a chunk broke from the same type of thing...and he "pasty patched" it right up against the gears in the tranny.  I would say there's probably only about 3/16 inch of clearance behind the case and gears at the MOST...

You could tell he fired up the bike and forced the tranny to turn....as there was shards of case and slivers of aluminum all over the oil pan. 

That said...I believe that if the sprocket shaft isn't turning....you can't manually twist it back n' forth and shift gears....or kick it over gently....then the case is more than likely pressed against the gears.... 

http://forums.sohc4.net/index.php?topic=57699.225
my experience...about 3/4 way down the page (reply #243)...Is when I found my hole...

Otherwise...IF everything moves nicely again...there really isn't any "pressure" in there...and as long as you can patch it VERY WELL and be good'n CLEAN with the JB...it'll probably carry you a long way without having to split the cases.  If you go that route...I'd just keep a truely keen eye on the fix and like MCRider said....no long trips....at least until it's been Proven.

GOOD LUCK!! And let me know if I can help in any way!??....

[BlissMX]

Thanks HedNut, you've givin me some hope. I'm going to see if I can't free up the tranny and clean up the gunk and go the JB Weld route. Fingers crossed, My biggest concern now is the jammed tranny.

[CycleRanger]

http://forums.sohc4.net/index.php?topic=60825.0

JB weld can work....for a while.

[eshumaker]

Had a much more minor crack on the upper crank case. I took it to a guy in Livermore, he specializes in aircraft. It's a perfect job, $40! I could see him going double per case, mine wasn't missing any material...

[HedNut]

Yes JB weld is touchy...can be superfantastic if the area is prepped properly and it's done right.... can be a turd job if it's not.    I paid $60 to get my gaping hole welded up....which was a GREAT deal...but it looked like snot...most of the time you get what you pay for. (eshumaker...YOU got a good deal...perfect welds for $40...nice!)  Quotes for me ran $60-$260 to weld my case...and it had to be completely torn down and thoroughly cleaned before they touched it.     Good Luck BLiss!  Hope this all works out good for you.... let us know how you're doing with the tranny.

Cheers!

[BobbyR]

There are alinum welding rods you can buy online or at Home Depot. You have to really clean the area well. The stuff is pretty hard. You can grind it down to make it look nice and get clearence.

[ianadams86]

Hi all!
Pretty excited to reopen this 12-year-old thread.

So, I had this exact same problem, but when I cut out the chain, I found the crankcase behind it basically shattered. I cleared the pieces out and now I'm left with a gaping chain link sized hole in my crankcase.

Luckily, the sprocket shaft still spins free and the transmission shifts through all 5 gears and neutral cleanly, so there was no (*significant*) internal damage.

I just need to figure out how to patch this giant window into my bike's guts. Thoughts and prayers appreciated!

[grcamna2]

subscribed

[Don R]

  The choices are find a new crankcase and swap in your internals, take that one apart and give the cases to a great aluminum welder, or swap engines. I recently scrapped a pair of cases that were like that. 
  There will be scrap metal inside that the trans gears will chew up and then use to destroy itself so even if you glued metal over the hole it wouldn't last. Zoom in on the picture and you can see some chain damage on the gear teeth, they may wear in or wear out. I would look for a good engine and get riding again.

[grcamna2]

  The choices are find a new crankcase and swap in your internals, take that one apart and give the cases to a great aluminum welder, or swap engines. I recently scrapped a pair of cases that were like that. 
  There will be scrap metal inside that the trans gears will chew up and then use to destroy itself so even if you glued metal over the hole it wouldn't last. Zoom in on the picture and you can see some chain damage on the gear teeth, they may wear in or wear out. I would look for a good engine and get riding again.

A parts engine/bottom-end could be located just for the cases;one which hasn't had the cases damaged yet,you would have all the spares within.