Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board A65 Front Sprocket FUBAR

Hey all, I managed a solid screw up the other day.

1970 A65 Thunderbolt. All I wanted to do was put on a new chain.

Took the tip to connect new chain to old chain and pull it through. Gave that a shot but did not work as intended.

Right now the old chain is jammed somewhere in there and I can’t get a drift or pry bar to move the sprocket at all.

It seems like there’s a cover on the interior side by the swing arm but I’m not sure if that gets me anywhere.

I pulled the left side cover but realized you have to pull the whole clutch etc to get all the way in to the sprocket.

I’m wondering if there’s any tips from the gurus to getting better access to to sprocket to see what the jam looks like and if I can pry it out without pulling the clutch.

Are the front sprockets in these things that crazy to get to?

Thanks in advance!!

John

"Are the front sprockets in these things that crazy to get to?" - yes, they are British.
You could try pulling on the top and bottom run of the chain to free it up. Worst case you have to pull the clutch and take the door off to unpack the chain.

Sounds like you didn’t keep some restriction on the feeding side of the chain as well as pulling on the other end, chains seem to like to jump the teeth and put the next link a tooth early if some tension isn’t maintained.

Thanks for the replies guys. I’ll try and track down a good video of the clutch.

Is there a how to anywhere?

Any parts that should be replaced while Un-effing the chain? Reuse/reset the tensioner?

Thanks

John

I've had this a couple of times and the way I got it out was to pull the chain hard in the opposite direction it was fed.

Another way is to use a USB endoscope with mobile phone and see where the chain is kinked and locked against the cases. Then somehow use fingers, screwdrivers etc. to lift the kink off the tooth and pull the chain out.

TRY PUTTING IT IN GEAR AND GENTLY ROCKING THE BIKE FORWARD AND BACKWARDS TO FREE THE CHAIN

John, do check the new chain, if it is not wider than the old one. There is not much place at these Unit engines. Unfortunately there are various widths of these chains around. There is no way to fit an o-ring or x-ring chain on A 65s.
Just saying...

Thanks again for the replies!!

The old chain is stuck at one end, OF COURSE. Rear wheel and chain guard are also off.

One explicit question: It's OK to re-use the tensioner, right?

The endoscope is a great idea, I'll bring mine home from work tomorrow!

Updates coming.

JC

"One explicit question: It's OK to re-use the tensioner, right?"

What tensioner? Do you mean the joining link?

There's a tensioner that pushes up on the triple chain from the bottom of the case in between the rotor and the clutch. Should get a chance to dig in more tomorrow.

Has nothing to do with feeding rear chain onto front sprocket unless you're pulling clutch and primary chain to see what's going on. Confusing me!

"There is no way to fit an o-ring or x-ring chain on A 65s" - except by using narrower sprockets.
Have you thought of downloading a repair manual from classicbritishspares (CBS)? They are free. Might help.

For some great A65 videos I would suggest The Classic Motorcycle Channel on YouTube. The Classic Motorcycle Workshop series (within The Classic Motorcycle Channel) is great, lots of "hands on / how to" information.

Specifically for the A65 look at "Low budget classic motorcycle restoration", a 13 part series which chronicles the host's project 1967 650 Thunderbolt. Part 2 shows the assembly of the drive sprocket and clutch assembly which will help you visualize what's back in that dark hole.



https://www.youtube.com/channel/UCcexUX0sijZDjVpopm7EAjg

Well that certainly is a low budget restoration, "theres no gasket behind there" (re the trapdoor for the sprocket). Well there aught to be one!!

Not too impressed with that honing job either or the state of those rods.