Slack-Tight Drive Chain Syndrome

[Swarfcut]

 Although the relationship between the two sprockets remains the same, I think the chain moves along the teeth in the same way as the timing gear teeth do, only ending up where they started after several turns. A dab o' paint would prove this, must admit something I have never bothered about.

 Even new chains and sprockets are adjusted at their tightest point, and the old adage of all new or nothing applies, worn sprockets will wear a new chain, and an old worn chain will wear the new sprockets.

 Make sure the new master link is an imperial size, not some parts man idea of a metric equivalent.

 Sadly comparing the image of the rear sprocket teeth with those of new parts on the web, those are definitely past their best, showing a sharp point and more wear to the load side of the teeth. This will go a long way to explaining the slack-tight you have. Having said that, there is still some life left, provided the chain is adjusted at the tightest point. We've all seen worse....An estimate of how bad  chain and sprocket wear is can be to simply to lift the chain away from the sprocket, while pulling on the chain run. A good chain and sprocket will be nigh impossible to move, a badly worn example will lift almost to the top of the teeth.

 Swarfy.

[limeyrob]

That rear sprocket is worn beyond the point I would use it.  It will trash a chain quite quickly.

[Rex]

Absolutely. That sprocket was fecked quite a while back, let alone now.

[RichardL]

You guys are absolutely correct about the rear sprocket. Thanks for the well-deserved push.  I have been reluctant to change it for years, mostly for the sentimental attachment to the original 1955 parts that were chromed in the '70s and carried forward with the 2003 restoration that followed the 1979 crash. So, yes, I will limp forward with the existing sprocket for this season of sparse riding while I acquire the new parts.

Richard L.

[limeyrob]

It is possible (if not necessarily easy..) to machine off the worn teeth and modify to take a new sprocket ring.  I have seen it done by electron beam welding the sprocket to the drum but of course the person who did that was doing it on the sly at work. More doable is to machine the new ring as a slip fit and cross bolt.

[RichardL]

It is possible (if not necessarily easy..) to machine off the worn teeth and modify to take a new sprocket ring.  I have seen it done by electron beam welding the sprocket to the drum but of course the person who did that was doing it on the sly at work. More doable is to machine the new ring as a slip fit and cross bolt.

Rob,

Yes, that occured to me, as well. I went looking for a ring without having great success. I found one that cost as much as a new drum and required macining beyond the capability of my own equipment (really, it was more of a disc that would need to have most of its diameter removed.

Richard L..

[muskrat]

It is possible (if not necessarily easy..) to machine off the worn teeth and modify to take a new sprocket ring.  I have seen it done by electron beam welding the sprocket to the drum but of course the person who did that was doing it on the sly at work. More doable is to machine the new ring as a slip fit and cross bolt.

G'day Rob/Richard.
That's what I did to the rear sprocket of my racer to have different tooth counts for different circuits. Turned the teeth off the original and bored out blank alloy sprockets to fit (with a spigot) and scotch keyed them with 6 bolts.
Cheers

[limeyrob]

I'm thinking of something similar for my Matchless.  Do you have different length chains or a section you take out?

Would the OIF conical hub sprocket be a base for the A10? I think there's quite a few about.

[muskrat]

G'day Rob.
Back then I had 3 different chains to suit the three sprockets (36, 38, 40). I used Talon alloy sprockets from John Titman Racing.

Would the OIF conical hub sprocket be a base for the A10? I would imagine so.
Cheers

[RichardL]

Returning to this topic, I've discovered some things I'm embarrased not to have discovered before now.

My rear sprocket (for QD hub) is 46 tooth for 5/8" x 3/8" chain. The part number I see for this 67-6123, which is listed for a plunger, though, my bike is a '55 swingarm. Since this is the sprocket that was on the bike when I bought it in '73, I have assumed it came from the factory like this. To me, this could make sense, since I have an "SC" (scrambler) gearbox.

Question 1: Are plunger and swingarm spline-drive sprockets interchangeable?
Question 2: I'm not doing any hill climbing, so, would I be well-served to go with 67-6149, the 42 tooth sprocket listed for a swingarm? (Engine sprocket is 22T; Drive spocket is 19T)

Added questions: Does fewer teath change the brake shoe radius or brake plate diameter?

Thanks, in advance for insights and advice.

Richard L.

[limeyrob]

First I would check you have the correct rear wheel just in case.  Then I would go for a 42T, it should be a straight swap.  Perhaps it has had a chair in the past?
No effect on brakes but you will have a shorter chain and a noticeable difference in indicated speed, but this may correct it since its unlikely it read correctly with the 46T

[Rex]

Speaking of plunger frames and chain tension, the chain is adjusted on the centre stand so does it get slacker or tighter when the bike is being ridden?

[berger]

tight as me mate

[RichardL]

Speaking of plunger frames and chain tension, the chain is adjusted on the centre stand so does it get slacker or tighter when the bike is being ridden?

The condition (as I can test) is going from slack to tight when hand rotating the wheel whith the bike on the center stand. If I adjust for normal chain up and down during the slack, the tight will get very tight, so, until I work this out, I run slack enough that the tight portion is tolerable. I suppose that's worked for a couple thousand miles. However, when trying to figure this all out, I did notice that the gearbox drive-side bushing is worn a bit oval, I presume, from going between slack and really too tight.

Richard L. 

[RichardL]

First I would check you have the correct rear wheel just in case.  Then I would go for a 42T, it should be a straight swap.  Perhaps it has had a chair in the past?
No effect on brakes but you will have a shorter chain and a noticeable difference in indicated speed, but this may correct it since its unlikely it read correctly with the 46T

Thanks for the advice, sounds good. Look out Ton-Up, here I come    Regarding the speedo, it seemed OK against the bicycle speedo gauged from the front wheel.

Richard L.