SOLVED! - Rear chain fouling on the disc thrower behind gearbox sprocket

Helpful information and requests for assitance and advice
56G80S
Member
Posts: 3353
Joined: Wed Oct 12, 2005 10:45 pm
Location: N YORKS UK

SOLVED! - Rear chain fouling on the disc thrower behind gearbox sprocket

Post by 56G80S »

This is infuriating. I'm trying to make as much progress as possible. A fellow Club member (thanks, Jim) donated one of the discs that fit behind the gearbox sprocket to restrict water/mud ingress.

All nicely fitted, primary, dynamo chain and chaincase all fitted; latter not leaking while stationary). The gearbox sprocket has an extra tooth so I used some old chain to check required length with no problems at all or untoward noises. Following some good advice on this Forum, I went for a longer chain but with an odd number of links, leaving the option of reducing to an odd or even number.

Fitted the new chain (reduced from 101 to 99 links) and no tight spots all good EXCEPT for some reason the thrower and the cranked link seem to foul each other. As the barrel's not on yet I can get my head in and see it happening. The chain goes tight, there's a little clonk as the cranked link rides up a little and then falls into place on the sprocket.

So it's looking like chaincase dome off, clutch off, gearbox sprocket off, remove the thrower, and refit everything. I just can't see why. It's Renolds chain and matches the old chain that I was using to get a check on the length.

Any suggestions welcome. Under pressure as the owner of the site where the lock-up is died yesterday. I have to be out by the end of September at the latest. There's a substantial volume of stuff to shift/throw away and I've nowhere for the Matchless.

Johnny B
Last edited by 56G80S on Mon Jun 05, 2023 7:17 pm, edited 1 time in total.
56G80S
Member
Posts: 3353
Joined: Wed Oct 12, 2005 10:45 pm
Location: N YORKS UK

Re: Rear chain fouling on the disc thrower behind gearbox sprocket

Post by 56G80S »

Giving this a bump as I really would welcome positive suggestions/easy solutions.

Johnny B
SPRIDDLER
Member
Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Rear chain fouling on the disc thrower behind gearbox sprocket

Post by SPRIDDLER »

I've no firm idea John, but clutching at straws........

The sliding seal is shown in the '56 parts list only for comp models which have a different rear half of chaincase vs the G80 tourer. The rear forks also have different part numbers for the touring and comp bikes so maybe the comp rear forks result in more clearance between the inner chaincase and the gearbox sprocket?
By how much does the link interfere? Would it make any difference if the split link was inserted from the outside of the chain with the plate and circlip on the inside of the chain? Not that it would give much/any extra clearance.

Ruddy nuisance about your lock-up as you've quite enough on your plate already.
Last edited by SPRIDDLER on Tue May 30, 2023 4:39 am, edited 2 times in total.
'There is a tide in the affairs of men
Which taken at the flood............'
User avatar
Duncan
Member
Posts: 2118
Joined: Thu Jul 10, 2003 1:00 am
Location: HAMPSHIRE UK

Re: Rear chain fouling on the disc thrower behind gearbox sprocket

Post by Duncan »

Hi John, grabbing a spare straw, assuming the chain is the correct size could it be that the half/cranked link is tight/binding and not free to move giving the impression it is hitting on the seal.
56G80S
Member
Posts: 3353
Joined: Wed Oct 12, 2005 10:45 pm
Location: N YORKS UK

Re: Rear chain fouling on the disc thrower behind gearbox sprocket

Post by 56G80S »

EDITED VERSION
Hi and thanks for the responses.

Sprid, it's not the sliding seal but a very large type of dished washer which is fitted behind, outboard of the gearbox sprocket. Rob Swift confirmed these could be fitted on touring models and that he'd stick a leather item to the rear of the chaincase to take up the small gap; I didn't do that. The thrower runs close to the rear of the rear chaincase, maybe a bit less than an eighth of an inch away. It's the standard Renold chain supplied by Steve Surbey at AMC Classic Spares - he knows a thing or two.

Duncan, someone else made the same suggestion by email. Also that while it may seem free when not fitted, a little tension could make a difference and make it sticky.

It's odd as I used the same spec. Renold chain to check the number of links I'd need. No problems. TBH the "old" Renolds chain only has about 1/4" of stretch and I have a new cranked link I could fit to it. I just wanted all new.

Johnny B
Last edited by 56G80S on Sat Jun 03, 2023 11:08 pm, edited 1 time in total.
56G80S
Member
Posts: 3353
Joined: Wed Oct 12, 2005 10:45 pm
Location: N YORKS UK

Re: Rear chain fouling on the disc thrower behind gearbox sprocket

Post by 56G80S »

I realise that my description was incorrect, although it should make no actual difference! The "dish/thrower" is of course fitted under the lock washer and nut that holds the gearbox sprocket on. It wouldn't work at all the way I described it at first.

Johnny B
56G80S
Member
Posts: 3353
Joined: Wed Oct 12, 2005 10:45 pm
Location: N YORKS UK

Re: Rear chain fouling on the disc thrower behind gearbox sprocket

Post by 56G80S »

Hi,

I've investigated this further. Head underneath the Matchless and torch. It's clear that the chain is catching on the "thrower". I think it may be the split pin that is just before the cranked link.

The only way I can see of dealing with this is to take the dome off the chaincase, remove the clutch and see if I can get the clutch centre off, although I expect I'll have to remove the outer half of the chaincase to release the primary chain. remove the nut holding the gearbox sprocket and put a spacing washer behind the thrower to move it away from the sprocket. I have a spare lock washer! Ironically, the chaincase was filled with 50:50 SAE50 and ATF my preferred approach) several days ago and not leaking at all. Just goes to show, what we often think are leaks are really coming from the dynamo or clutch holes.

Before doing ththe above I will measure, as best I can, the available gap between the thrower and the chaincase. At a guess I think it's about 1/8". I expect that I only need about half of that or less but certainly don't want anything messing about with the split link. A little contact between the thrower and the back of the rear half of the chaincase not the end of the world as it would settle itself down.

On the positive side there is no discernible tight spot on the rear chain, so something must be working well.

Johnny B
User avatar
Ralph
Member
Posts: 87
Joined: Tue Jan 07, 2020 7:00 pm
Location: UK

Re: Rear chain fouling on the disc thrower behind gearbox sprocket

Post by Ralph »

I know Others will not agree but I would avoid a cranked link like the plague, if at all possible.
Ralph

Image

Image
56G80S
Member
Posts: 3353
Joined: Wed Oct 12, 2005 10:45 pm
Location: N YORKS UK

Re: Rear chain fouling on the disc thrower behind gearbox sprocket

Post by 56G80S »

Ralph,

It's difficult to get to an odd number of links otherwise. It's as supplied by Renold as 101 links, just took two off the other end to arrive at the 99 I required.

Johnny B
56G80S
Member
Posts: 3353
Joined: Wed Oct 12, 2005 10:45 pm
Location: N YORKS UK

Re: SOLVED! - Rear chain fouling on the disc thrower behind gearbox sprocket

Post by 56G80S »

It looks like the spring link that is wider, by maybe 1/16" to-3/32".

Renolds 107 rivet link ordered (x2) and need to buy a splitter/riveter tool. No need to do anything except the chain!

Husssahhh, as chris (Spookefoote) would say.

Johnny B
Post Reply