1966 G15CSR Fork Measurements

Information relating to the Matchless G15 or AJS Model 33 750cc twin. This also includes the G15 Mk II and the G15/45
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DRW
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1966 G15CSR Fork Measurements

Post by DRW »

I am hoping to get definitive measurements for the correct forks parts for a 1966 G15CSR.
Some say the CS and CSR forks are the same for 1966 - others say no!
I've heard measurements for 1966 G15CSR fork stanchions ranging from 21 7/8" to 24 7/8".

Does anyone know what the proper lengths are for:
(1) fork stanchions (2) damper rod (3) damper tube (4) springs?

I am also curious, what the difference is between the crown-and-column assembly for CSR (030026) vs CS (030499)?
Any other info/specs that would help determine the proper fork arrangement would be GREATLY appreciated.
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Re: 1966 G15CSR Fork Measurements

Post by SPRIDDLER »

Welcome!
It probably won't give you dimensions but you could compare differences in part nos from this parts list taken from Christian's Archive:

http://archives.jampot.dk/Book/Spares_l ... 15MkII.pdf
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John Donne
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Re: 1966 G15CSR Fork Measurements

Post by John Donne »

The fork stauntions for the G15 models were 25 inches long and the damper lengths were one inch longer than the standard Dominator ones. The only changes post or from 1966 onwards were the stauntion changes and damper types. The later stauntions used a circlip to secure the lower bush. The 1963 to 1965 stauntions, used a larger nut and a special washer to secure the lower steel bush. All the models used a 25 inch stauntion length. The post 1966 G15 models used the springs, damper rods and all the other internal parts were the same as the later Atlas and 650ss Roadholder forks. The oil seal collers were also longer due to the longer forks stauntions used. The 1963 to 1965 forks had different stauntions, outside springs, and the internal damper arrangment came from the G80CS, but with a longer damper. The outside springs where different from 1963/4 to the ones in 1965.
The top and bottom yokes are different to the Dominator featherbed framed ones. The lower yoke was machined so that it could be used in the G12 duplex frame. The very first models of the so called G15CS, or the Norton Atlas Scrambler used a 7 inch top yoke or it did not have the steering lock. The later ones or the 7 3/8 top yoke had a steering lock added and also for the fitting of a larger front tyre. As to if all the earlier first batch of scramblers used the 7 inch yokes from standard it a very mute point. There was also the probablity that the steering angle was different for the off road scrmblers than the more road based models. 8-)
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Re: 1966 G15CSR Fork Measurements

Post by SPRIDDLER »

Yep, just as I thought, John. ;)
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John Donne
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Re: 1966 G15CSR Fork Measurements

Post by John Donne »

The front fork springs lengths for post or 1966 onwards were part number 18813. These were also the same for the later Norton Commandos, and the length was the same for these springs at 18.687nches. The fork stauntions for the Commando's were shorter than the G15CSR's as they were 23.161 inches long. The G15CSR and all the G15,N15,33 series being 25 inches long. The fork stauntions for the Long Roadholders were 23.312 and the Short Roadholders were 21.843 inches long. I have never seen a frame head angle published but i suspect it would be he same as the G12CSR, whose frame the G15 series used from the start of the production in 1963 till the end in 1968. 8-)
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Re: 1966 G15CSR Fork Measurements

Post by DRW »

Thank you very much for all the info. It confirms I have is a set of Commando stanchions (setup with disk-brake sliders).
I'm curious,

(1) Are the CSR/CS stanchions exactly 25" or are they the 24.875" length I have heard elsewhere?

(2) Currently, I have bottom yoke 030025 or 26 (it's hard to tell) and top yoke 030028. The Parts Book lists the bottom for '66 CSR should be 030026 and the top as 030027 not 28. What is the difference between these - can anyone shed some light? I'd like to know if I can use my yokes with the correct CSR stanchions.

(3) Also, I'm just curious, is there any benefit in keeping the shorter Commando fork arrangement (e.g. handling)? If so, could Atlas (drum-brake) sliders be fitted as a straight swap to get rid of the disk brake?

Thanks again,
Dustin
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John Donne
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Re: 1966 G15CSR Fork Measurements

Post by John Donne »

The fork stauntions for the G15 series are 25 inches long. The Commando ones are shorter, so the handling may or can be effected by the shorter stauntions. The factory made them this length for a reason. All the parts will interchange, as only the stauntions and the internal dampers were longer. So the alloy fork sliders will change over for the drum brake variaty from the disc brake version. The correct length of stauntions are can be obtained from Walridge Motors in Canada, as of course you must know of their exsistence.

The pictures that you have shown are correct for the G15 models, as the lower fork yoke has the correct machined away part for clearence to be used on the G12 duplex type frame, that is used on the G15 models. The featherbed version of that lower yoke is different, and has extra parts of the casting left on. Do not confuse the casting number for a part number, as the part number is different to the casting number. This being one of two numbers different. The factory produced part numbers for the bare casting, then the machined and finished part. Hence the parts book would read the part number then complete, or finished after the discription. The top yoke only changed to show SIDECAR stamped in them, for the reason that these were for sidecar use only. That top yoke was used through out the Norton range, in the later 1960's as it is of 7 3/8 type. This can clearly be seen as it has the steering lock hole machined into the top of the yoke. Get a copy of the Norton Workshop manual, as these forks, or the earlier scrambler type are explaned. There is also pictures of the forks. For far better diagrams try to find a copy of the Royal Enfield series 2 parts book and workshop manuals. These have far better pictures of the front forks, and the RE Series 2 forks used the G15 type forks. Plumstead was very bad at technical, pictures and drawings that it made avilable for the G15, N15,33, and the P11 series of machines. One very good reason could have been they were going broke at the time, but RE managed to do a far better job of the front fork as an expoloded diagram than AMC or Norton Matchless managed to do, and NM and AMC actually made that front fork. 8-)
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John Donne
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Re: 1966 G15CSR Fork Measurements

Post by John Donne »

As you have a G15CSR, then you must also have the correct length for the chromed oil seal screw in cover. This is longer than the featherbed version. The top painted black cover will also be shorter, as the stauntions are covered with an accordian boot, and these did not have a clip to hold them in place as the P11 series did. The 1966 onwards models of the G15, N15 series all uses an accordian boot between the top and bottom chrome and black covers on the front forks. 8-)
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John Donne
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Re: 1966 G15CSR Fork Measurements

Post by John Donne »

The G15, N15 fork main tube or stauntion length is 24 7/8 inches. 8-)
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