Rear wheel sprockets

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alan.moore
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Rear wheel sprockets

Postby alan.moore » Thu Jun 28, 2018 11:13 pm

Gents,
I have another question regarding the 4345-32 rear 47T wheel sprockets. I have a new one from John Budgen (same source as those sold by Peter Kemp at single spares). I have also got 10 new sprocket bolts from Acme Stainless.

My problem / question is that the 0.250" (1/4") bolts from Acme are a nice fit in the holes of the old original sprocket (holes are 0.255") but are a loose fit in the new sprocket where the holes are 0.280" (9/32"). The actual clearance is about 30 thou compared with 5 thou on the old sprocket.

My understanding is that the bolts locate the sprocket as well as secure it and should be a snug fit. Can anyone comment on whether this is the case.

I have checked with Peter Kemp and the club ones are the same. However, Peter says that he has checked an original sprocket and the holes in that were also 0.282", which is at odds with my original sprockets 0.255".

I am going to see if Clay at Acme can make me up some 9/32" bolts but before I go ahead I thought I would ask the forum to see if anyone could help and confirm the hole size in an original sprocket if they have one.

Cheers
Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t

robert.clark
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Re: Rear wheel sprockets

Postby robert.clark » Wed Jul 04, 2018 9:54 pm

How about loose fitting the bolts and tapping the sprocket anticlockwise (in the direction of drive) and when you are satisfied you've taken up any slack - tighten up.
Just about to fit one so I will check to see how mine goes. My sprocket was ebay used so Ill check the hole dia's
Cheers Rob
54 Square Four, 1934 RH500 twin port, 1936 RH500 single port, 1945 RH500 (1936 ) twin port, 1947 VB Buttermilk.

nevhunter
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Re: Rear wheel sprockets

Postby nevhunter » Wed Jul 04, 2018 11:30 pm

If you oversize the threads you can never again fit the original sprocket without modification.. The sprocket is aligned by the fit of the sprocket on the brake drum as to running concentric, but it's very desirable to have the bolts a good fit. I've fitted up 4 rear wheels lately and the bolts ARE a close fit in the holes of the original sprockets. I found one hub where the bolts had obviously been loose at some stage and the threads in the hub had worn oval enough to weaken them and that hub has been discarded in favour of one in better condition. The original bolts are a good fit on the plain (unthreaded) section. I don't recall them being a significant over size there but hey are at lest a full 1/4 ". I always have them quite tight to absolutely prevent movement. Those threads in the cast iron are not that long and need to be in good condition to tighten right up. Nev

john.whiting
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Re: Rear wheel sprockets

Postby john.whiting » Wed Jul 04, 2018 11:42 pm

Why not just redrill the sprocket with 1/4 " holes to suit your new stainless bolts.......When you are in the engineering business,you often have customers provide a sample which has actually been modified,then they start complaining its not right.........solution,make them provide drawings of what they want.....and what they get.

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Re: Rear wheel sprockets

Postby robert.clark » Thu Jul 05, 2018 3:13 pm

Mine are 0.258 inch dia. Using a piece of round bar which was a tight fit in the hole and measured with a vernier.

Sprocket fitting - Q recess on the inside or outside?

Rob
54 Square Four, 1934 RH500 twin port, 1936 RH500 single port, 1945 RH500 (1936 ) twin port, 1947 VB Buttermilk.

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paul.jameson
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Re: Rear wheel sprockets

Postby paul.jameson » Thu Jul 05, 2018 8:23 pm

Recess goes on the inside.
Paul Jameson
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
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Now Archivist once more - but not Machine Registrar.

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alan.moore
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Re: Rear wheel sprockets

Postby alan.moore » Thu Jul 05, 2018 9:33 pm

just to update.....as Nev and Robert have conformed the holes in the original sprockets are 1/4" give or take a few thou. The original bolts are 1/4" and are supposed to be a good fit in the sprocket. The replacement sprockets that have 0.280 (9/32) holes will, in my opinion, eventually cause looseness of the 1/4" mounting bolts and this can (as Nev says) eventually damage the threads in the hub.

Moving the sprocket anticlockwise, to take up the slack before tightening, will not work as under deceleration the forces are in the opposite direction so there is still the chance of them working loose.

I have solved my issue as Clay at Acme Stainless is making me up some 9/32" shouldered, 1/4" thread bolts to fit the oversize holes. The length also needs altering as the flange on the new sprockets is about 1mm wider then the original. I have sent him my new sprocket so that the supplied bolts will be spot on.

I have also sent him the spring for the rigid front brake rod, as at present he does not supply the spring with his stainless brake rod assembly. Hopefully he is going to get some stainless springs made up.

He is also looking at making some of the locking tabs for the rear sprocket bolts ( viewtopic.php?f=4&t=8063). I don't have one to send him but it would be great if someone who has an original could stick it in an envelope and post it to him.

Cheers
Alan
1939 VH Redhunter;1942 RN WNG;1951 Triumph 6T Thunderbird;1970 BSA B175 Bantam;1986 Yamaha SRX600 single
http://cloggymoore.wix.com/triumph-pre-unit-6t

nevhunter
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Re: Rear wheel sprockets

Postby nevhunter » Fri Jul 06, 2018 12:41 am

To align your sprocket with the holes insert a 1/4 x 26 tpi stud (or two) to guide the sprocket onto the flange. It's sometimes quite tight and hard to adjust once in place. Fit all bolts before tightening any. They should be quite a neat fit so need to b3e close to the correct position. Nev


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