Author Topic: Chain broke!  (Read 656 times)

Online Black Sheep

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Re: Chain broke!
« Reply #15 on: 13.06. 2020 22:27 »
Too tight. Not surprised the chain failed. Spin the wheel and find the tightest spot - there will be one. Then set the looseness (tension is quite the wrong expression) to about an inch. A spot more won't hurt but certainly no less.
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Online Minto

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Re: Chain broke!
« Reply #16 on: 14.06. 2020 01:12 »
Berger and Black Sheep
Cheers for the advice, I'll crack on tomorrow and get Mrs minto to sit on it, hopefully get some dry time for a ride Monday.
Jase
52 A10 plunger
Aprilia RSVR

Offline Swarfcut

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Re: Chain broke!
« Reply #17 on: 14.06. 2020 08:26 »
 Minto  As the motor has been out of the frame, make a check that the sprockets are in line, maybe a loosen of the mounting bolts and a little tweak just to get things straight.

  BSA Service Sheet 212C recommends that for Plunger Models, the bike should be on the stand, rear suspension at its lowest point. Half an inch total up and down movement at the centre of the span is the figure suggested.

 In an ideal world the chain tension stays the same as the wheels sprockets and chain rotate. Usually wear and other factors mean that there may be tight and loose spots.  Best to adjust the chain at a tight spot so no undue strain is put on the transmission.

 Its tricky to do, keeping the wheel central, sprockets in line, chain tension the best compromise, so don't get too frustrated if it takes that little bit longer to get right. Easier to move the hub and drum if brake rod is disconnected.

 Don't forget to tighten the big nut securing the drum and then adjust the rear brake once the wheel position has been set. Off the stand the chain will be at the accepted running tension, slightly looser than set on the stand.

  On the stand sets the chain tension at the suspension's greatest point of deflection, so appears to be relatively tight, but the geometric relationship between the sprockets changes  off the stand to give the running tension. This relationship change is more on a plunger frame than on a S/A. Plunger axle moves in a straight line, S/A moves in an arc, so here , suspension loaded is the better method of setting.

 By my reckoning the chain was a bit too loose with 1 1/2" on the stand, even looser when running, enough to throw it off if the sprockets were offset.

 Swarfy.

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Re: Chain broke!
« Reply #18 on: 14.06. 2020 10:36 »
Thanks Swarfy. That advice about adjusting the chain on a plunger is very useful.  *smile*

Online Minto

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Re: Chain broke!
« Reply #19 on: 14.06. 2020 10:55 »
Thanks Swarfy, that's brilliant information.  It looks like I had, as I suspected, got this very wrong.
I can't remember where I was looking for the info yesterday but could only find a brief mention of rear chain adjustment for the plunger models.
Just looked in the scans and found what you were referring to.
Thanks again
Jase
52 A10 plunger
Aprilia RSVR

Online Minto

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Re: Chain broke!
« Reply #20 on: 16.06. 2020 20:53 »
I can't believe how far out the adjusters on the rear wheel of my plunger are.
I started by removing the wheel and hub so I could count and start with an equal amount of threads showing on the inside of the spindle slots (or whatever they're called) 5 threads on either side. Put the wheel and hub back in and string lined it. The rear wheel was a mile out of line. I counted the + & -  turns of each adjuster, when the rear wheel was finally in line with the recommended chain deflection was 4 threads on the right and 81/2 on the left.
I know it's had a sidecar for some of its previous life but bloody 'ell.
Also very surprised by how much the chain tension changes when I dropped the bike off the stand 1/2" on the stand (very tight) to 1 1/4" off the stand, 1 1/2" with me sat on it.
Hopefully get chance to test ride it soon.
Thanks for everyone's input.
Jase
52 A10 plunger
Aprilia RSVR

Offline Swarfcut

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Re: Chain broke!
« Reply #21 on: 17.06. 2020 07:42 »
 Minto, You may find the rear spindle lugs are not exactly an identical match, and one side has more scope for adjustment.

 Swarfy.

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Re: Chain broke!
« Reply #22 on: 17.06. 2020 09:09 »
When I'm adjusting the chain, with the bike on the lift, I close one eye and line up the back wheel sides with the centre stand bosses, adjusting until both sides are equal.

Online Minto

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Re: Chain broke!
« Reply #23 on: 17.06. 2020 10:11 »
Ooh I'd love a bike lift, and enough room to put one.
Didn't think to measure the spindle lug thicknesses, next time the wheel has to come out I'll check them.
Jase
52 A10 plunger
Aprilia RSVR

Offline Swarfcut

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Re: Chain broke!
« Reply #24 on: 17.06. 2020 10:22 »
Minto. No need for that, just look at the relative lengths of the slotted spindle hole.

Swarfy

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Re: Chain broke!
« Reply #25 on: 17.06. 2020 10:28 »
Ooh I'd love a bike lift, and enough room to put one.
A friend lent me his lift when I started to restore my bike. He eventually said, he was not going to need it again so I could keep it.  *smile*

I don't have a lot of room, just a large shed. I've added castors to the lift so I can move it to get at both sides of the shed, and the bike.

Online cyclobutch

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Re: Chain broke!
« Reply #26 on: 17.06. 2020 11:22 »
Ooh I'd love a bike lift, and enough room to put one.

Felt like something of a luxury when I bought mine. There is no way I'd be without it now, all that grubbing around at ground level.
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Online Minto

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Re: Chain broke!
« Reply #27 on: 17.06. 2020 15:17 »
GB, that's a lovely looking bike. What's the badge on the rear mudguard?
I'm about to have an electric roller door fitted to replace the old up and over garage door, which will give me some scope for extra shelving to reorganise all my stuff, and replacing one of my sheds with a bigger one, so maybe a lift could be squeezed in.
The Old girl does have to share the space with another bike though, and I've been trying to convince Mrs Minto she needs another bike in her life.
I'll have a look at how much they are, it would help my back no end.
Jase
52 A10 plunger
Aprilia RSVR

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Re: Chain broke!
« Reply #28 on: 17.06. 2020 15:28 »
GB, that's a lovely looking bike. What's the badge on the rear mudguard?
Thank you. That is the sellers badge. I'll see if I have a close-up photo of it to show you.

Later:
I can't find one so when the current torrential rain stops, I'll take a photo.

Online Minto

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Re: Chain broke!
« Reply #29 on: 17.06. 2020 15:44 »
Cheers, look forward to that.
52 A10 plunger
Aprilia RSVR