83-2674 Chainguard extension

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83-2674 Chainguard extension

Postby minetymenace » Fri Dec 03, 2010 2:42 pm

Many moons ago I did a sketch of the 83-2674 Chainguard extension (you know the thing, normally most of it is invisible and all that remains is a square washer bolted just above the final drive sprocket!). The dimensions came off an original piece (not a pattern), so the measurements should be pretty close (not sure about the angle, but it will be somewhere close, say 150°?).

I think Burton Bike Bits have pattern parts, but if you want to make your own, this should help.
front chain guard.JPG

P.S. If some clever person has a drawing package (or pencil and time), maybe they could do a proper drawing, I think all the relevant dimensions are there, and if you can't read anything pm me :grin:
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Re: 83-2674 Chainguard extension

Postby Richard Hunt » Fri Dec 03, 2010 4:16 pm

The one I bought last year from Burton Bike Bits fits very well on my B50SS, you wouldn't know it was a pattern piece. They still have them on their price list for £13.50

http://www.burtonbikebits.net/TRIStock.pdf

Rich

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Re: 83-2674 Chainguard extension

Postby SteveS » Fri Dec 03, 2010 8:57 pm

Hi Gerry

Don't know if the attached will help confirm your dimensions

83-2674.JPG


Regards Steve
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Re: 83-2674 Chainguard extension

Postby minetymenace » Sat Dec 04, 2010 1:33 pm

Any info that guides the topic to total understanding of this bit of tin is good!! Thank you.
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Re: 83-2674 Chainguard extension

Postby AJ CCM » Sat Dec 04, 2010 11:13 pm

Gerry

Hopefully this as downloaded correctly if not send me your e-mail and I will pass on
Check out the details and dimensions and see if they are correct
PART No 83-2674.pdf
(101.83 KiB) Downloaded 107 times
Regards AJ CCM

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Re: 83-2674 Chainguard extension

Postby minetymenace » Sun Dec 05, 2010 12:26 am

AJ that is pretty much spot on, a couple of differences but these could be manufacturing variations: the small return (on the outside/left of the guard as fitted) on mine does not bend 90 deg, only about 60, and the tab that screws to the LH crank case was straight on mine (but as it was a long time ago, I don't know if I missed the 4 deg bend!). I do seem to recall that the spot welds were not evenly spaced, but done roughly as if by hand.

Anyway thank you AJ, I think there is enough here now for someone to reproduce a good replacement part....guess it was just made out of metal stuff, someone probably has a technical description of the steel.
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Re: 83-2674 Chainguard extension

Postby b50root » Sun Dec 05, 2010 10:53 am

AJ. Thanks for making this <200 <200 . And thanks for adding mm in the drawing :thumb . Can I add it to the downloading section?
Rickard
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Re: 83-2674 Chainguard extension

Postby AJ CCM » Sun Dec 05, 2010 12:55 pm

Gerry / Rickard

If you want me to change the drawing to suit your comments I will
The drawing was based on SteveS and Gerry's Sketch so it might not be 100% correct.
The drawing can be added to the downloading section.
If you have anything else you require to be drawn out please ask I can allways find time.
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Re: 83-2674 Chainguard extension

Postby beesaoldman » Mon Mar 04, 2013 11:15 pm

I have purchased a replica from Burton Bike Bits for my B25SS , but there is no way it will fit. I have compared the dimensions with those in the sketch and it is almost spot on for size. I thought the dimensions for the B25 maybe different but the part number is the same, so I think that they are identical across the range. The bolt that goes into the crank case will not line up , as the guard is hitting against the inside of the inner chaincase casting preventing it moving over far enough, and the slotted bracket won't go anywhere near the underneath of the engine plate mounting bolt head that it should fit under. To make it fit it looks as though I will need to cut away at least 1/16" along the length of the front face where it fits against the inner chaincase, to get it to fit under the bolt head and to get the bolt in the crank case to line up.. Has anyone else had difficulty in fitting these things?

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Re: 83-2674 Chainguard extension

Postby Richard Hunt » Mon Mar 04, 2013 11:48 pm

The ones on both my B50's fit very well and they are both pattern (I think both from BBB over the last few years). Perhaps there is a difference for the 250cc engines. Others will hopefully be along soon to confirm or deny.

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Re: 83-2674 Chainguard extension

Postby steve m » Tue Mar 05, 2013 3:37 am

i bought one from a local supplier and have the same problem as beesaoldman. seems to me (from memory ) they forgot to allow for the thickness of material when they bent the rear mount. it might fit if it situates between the engine mount plate and the mounting lug - but there is NO WAY i'm doing that.
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it's wrapped up and stored in a safe place somewhere or other :cry:

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Re: 83-2674 Chainguard extension

Postby midgie » Tue Mar 05, 2013 4:54 pm

the b25/t25/b50 chainguard extension is indeed the same part 83-2674. i have also tried to fit a pattern example no chance. the only thing that would suprise me with a pattern part is if it actually fitted!

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Re: 83-2674 Chainguard extension

Postby beesaoldman » Wed Mar 13, 2013 10:27 pm

Having bought the thing, I was not giving up and took the bull by the horns, or rather a sharp cold chisel and hammer , and with the aid of a junior hacksaw cut off the spot welded bracket, straightened it and re bent it to make it the correct size. Tomorrow I will weld it back on. I also applied some judicious hammer work to the mid section. It would appear that during manufacture after bending the sides over and then bending the angle on the top, the sides are not constrained allowing the whole guard to bend inwards from the ends, ( in effect creating a bump in the middle on the outer edge, which prevents it from fitting between the frame and the inside of the engine chain case) Moral is, make sure any pattern parts fit before painting them and making them look pretty. It was supplied black and I had painted it grey to match the rest of the frame etc. Just waiting for the new tank trim that goes round the centre fixing and Will post a photograph of the bike when it is finally all back together after its 30 year rebuild.

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Re: 83-2674 Chainguard extension

Postby minetymenace » Thu Mar 14, 2013 9:47 am

beesaoldman wrote:Just waiting for the new tank trim that goes round the centre fixing


Ah, hope that is not a pattern piece too...the only ones I've seen have the top at right angles to the shaft and don't fit snuggly on the tank, BSA ones are at a slight angle.


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