Jackshaft Chain falling off

MinimumVK

Member
Local time
10:30 PM
Joined
May 19, 2023
Messages
57
Location
Slovenia
Hello all so as i may have thought i have issues with my jackshaft project... a lot of problems. So i bought a chinese 3 piece Jackshaft kit because i found it for only 50 euros (a few months ago the cheapest one was 130) and see if i could make it work. I took my time and put it together but even on my bike stand it kept jumping out of alignment and it didnt last a meter until it didnt bend every bracket bolted to the engine.
Next i made my own 1 piece jackshaft mount and put it on the bike. It now at least stayed in place. I made a tensioner for the right jackshaft chain. Also used an old front derailleur to use as a chain limiter for the actual drive chain. Took it out for a test drive and as soon as i engage the clutch the right jackshaft chain jumps off the sprocket freewheel (its on the second cog and jumps onto the first one) The chain is tight and also runs as straight as i can get it... Could it be that i would need to make my own cog out of an old crankarm? I had to grind the sprocket teeth a little bit on the original cog to get my 8 speed chain to mesh with it.
 

Attachments

  • 20231013_203738.jpg
    20231013_203738.jpg
    156.6 KB · Views: 91
The first immediate thing I notice is your tensioner is on the load side of the chain instead of the slack side.
This. I second this.

You want to tension the slack side in order to Keep a chain in place. You would be impressed with how much a chain moves under load even when it seems tight to us sitting still.

Are you able to shorten that chain any more or does it get too tight?
 
If I understand it right you're using 408 chain on what were once 410 sprockets. Are the teeth consistent? Multi Speed bike sprockets are intentionally machined with irregular teeth to aid in shifting with derailleurs.

Is the chain angularly misaligned?
 
The first immediate thing I notice is your tensioner is on the load side of the chain instead of the slack side.
Hmm i will check but without the tensioner the left side od the chain (where the tensioner is) gets alot of slack while the right side gets tight when i spin crank.
 
If I understand it right you're using 408 chain on what were once 410 sprockets. Are the teeth consistent? Multi Speed bike sprockets are intentionally machined with irregular teeth to aid in shifting with derailleurs.

Is the chain angularly misaligned?
I am using a 410 chain for the left jackshaft side (from engine to the big jackshaft gear). A BMX chain for the right jackshaft side (from small jackshaft gear to big crankarm gear) and a 7/8 speed drive chain from the small crank gear to my rear 7 speed freewheel. I had to grind down the small gear on the crankarm freewheel and have no problems with this chain only the BMX one... yes the links mesh perfectly.
 
Hmm i will check but without the tensioner the left side od the chain (where the tensioner is) gets alot of slack while the right side gets tight when i spin crank.
Of course it will. When you spin the crank the load will be on the right side. However when the engine is turning over the load will be on the left side. Here's a picture of where my tension sprocket is.

20230903_185721.jpg
20230903_185646.jpg
20230803_193949.jpg
 
Of course it will. When you spin the crank the load will be on the right side. However when the engine is turning over the load will be on the left side. Here's a picture of where my tension sprocket is.

View attachment 200741View attachment 200742View attachment 200743
Ohhh okay i get it... I will try flipping the tensioner and see if it helps. If not i will abandon the project since i spent way too much money and time on it. Wish i could get a SickBikeParts shift kit (i hear good things about them)
 
Ohhh okay i get it... I will try flipping the tensioner and see if it helps. If not i will abandon the project since i spent way too much money and time on it. Wish i could get a SickBikeParts shift kit (i hear good things about them)
If you get a sprocket instead of that little roller it'll help too. I have mine in a fixed position instead of something that's spring loaded.
 
Back
Top