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Chain clearance

Submitted by george_phillips on Tue, 17/04/2018
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Nortons - General

Pre f/bed ES2. The pic shows the minimal clearance between the the chain and the s/arm pivot cover bolts.The bike is on its centre stand so suspension is at full stretch but is this almost non existent gap normal? The sprocket is a normal 19T. George

Attachments norton-chain-clearance-htm

Submitted by ian_macdougall on Tue, 17/04/2018

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Hi George, clearance there is minimal. When I first acquired my 19S those bolt heads were completely worn away by the chain. Two things to check out: 1) The bolts look as if they may be a "normal" head size. I am fairly sure they should be reduced head in that location. I think there will be a shallow recess around the bolt holes in the swingarm cross brace. Reduced head bolts should sit down into the recess and give a little more clearance to the chain. 2) Suspension unit length. I have measured a set of original Armstrong units at 12.75". This is for my '56 model, I don't know if '55 models are the same. A longer shock will reduce the chain to bolt head clearance.

Cheers, Ian McD

Submitted by george_phillips on Tue, 17/04/2018

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Thanks for that Ian. I'll try and check the bolts but they look reasonably "low profile" on the bike. I'll also check for a recess in the cross brace. Did you remove the suspension unit to measure it? But again, they look original ie as I remember them. Comforting to know that minimal clearance seems to be normal. George

Submitted by ian_macdougall on Wed, 18/04/2018

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See photo for comparison of normal head bolt v. an original reduced head bolt in this application. Normal head has 1/4W spanner size, reduced head is 3/16W. This is one place where it is probably best not to use a washer. You will gain a few mm of clearance with the reduced head version.

Yes, the suspension units were measured off the bike.

Cheers, Ian McD

Attachments swingarm-pivot-bolts-jpg

Submitted by john_shorter on Wed, 18/04/2018

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Rear chain adjustment should be made with the bike on it's wheels , plus normal weight of rider, at least, that?s what the owners manual. says

Submitted by george_phillips on Wed, 18/04/2018

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Hi guys - thanks for the input. @Ian - I measured the suspension units (on the bike) and made it around 12.5" so that seems OK. The bolt looks low profile but without comparing it I can't tell. I'll check the spanner size this afternoon. Thanks for that bit of info. I did notice that the bolts have washers and - as far as I can see - no recess. But it may of course be covered by the washers. @John - yes - I realise that John. I was not adjusting the chain, simply noting how close it ran to the bolts. Even after adjustment it seems to run very close. George

Submitted by ian_cordes on Wed, 18/04/2018

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I can see the recess in your photos, George. The washers are part way in, but still standing proud. Removing the washers will allow your bolt heads down into the recess, as Ian pointed out.

Cheers. Ian C

Submitted by ian_goodhall on Wed, 18/04/2018

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Mine rubbed on the top just as others have said. Doesn't do it when under power or if carrying a pillion. I noticed it most when wheeling the bike around. I made a little slipper to fit over the top of the bolts out of some thin stainless sheet. It can wear that away rather than the heads of the bolts.

Ian G

 


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