Topic: Chain Stuck between front sprocket and Engine casing

[newday777]

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!

Welcome aboard Ianadams86
Bummer about your motor lunched. What year is your bike? How long have you had it, do you or family have a history with the bike?
As has been said, the quickest way will be to find another motor or complete bottom end as you have a big hole to fill, doable, but time wise, extended loss of riding time.

[ianadams86]

Welcome aboard Ianadams86
Bummer about your motor lunched. What year is your bike? How long have you had it, do you or family have a history with the bike?
As has been said, the quickest way will be to find another motor or complete bottom end as you have a big hole to fill, doable, but time wise, extended loss of riding time.

Thanks newday!
This is my '77 CB750F with a 1978 engine I swapped in a decade ago when I bought the bike as a project. It has since become my daily rider (and perpetual passion project). She is nowhere near cherry stock, more of a utilitarian zombie assemblage of OEM and aftermarket parts and I'd have it no other way.

I can't stand being grounded, so I want to get her back up and running as soon as possible and I'm weighing my options in practical terms.

Sounds like patching will be tedious and temporary unless I can find a brilliant welder in my neighborhood. Sourcing a replacement engine could also take time, though it's the most straightforward option. Finding a parts engine to swap out just the bottom end or the cases themselves sounds like the most labor intensive option.

I'm stumped for now.

[newday777]

You could put in a 77/78 k model motor as a temporary solution to get you back on the road while looking for a F2/3 motor.  You are in the bay area? Probably lots to choose from finding someone that has a boatload of them in your area.

[craz1]

Sorry that has happened to you. Looks like a learning experience. To me it looks like a little bit of chain maintenance may have prevented that situation. Things look a bit rusty/dirty on that chain and sprocket. Oh ya dump those clip links next time and use a rivet type link.

[BenelliSEI]

  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.

Don is absolutely correct and gives solid advice. Having said that, I know a local guy who calls his bike “Patch”. He punched a hole, just like yours. Removed the sump and flushed all around the area with a garden hose! Made an well filling patch from thin aluminum sheet, the locked it in place with 3-4 well placed pop rivets. Cleaned the area really well and painted it over with JBWeld..... he’s been riding it for +15 years! NOT a recommendation, but there you are.