1957 CS front frame

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John Jarrett
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1957 CS front frame

Post by John Jarrett »

Does anyone have a picture of the swinging arm area of the front frame including the cotter pins of a 1957 G80CS?

I am looking to fit an AMC gearbox to a 1956 CS but it doesn't clear the cotter pin nuts.

The reason I am asking for details of the 57 CS front frame is that it is the same part number as the 56 CS but had an AMC gearbox so I assumed it would be any easy fit... wrong! The cotter pin part number is different and I understand they are shorter by 5/16" for the 1957 CS so something is different.

The other thing that may be different is the engine plates as the part number is different. I have already corresponded with another member who had the same issue and ended up modifying the engine plates to overcome the problem.

Any help or advice much appreciated.
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dave16mct
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Re: 1957 CS front frame

Post by dave16mct »

Mine's '58 but may be the same dimension. Cotter pin nuts are well clear. Image
Dave.
John Jarrett
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Re: 1957 CS front frame

Post by John Jarrett »

Many thanks for the quick response and the picture... it definitely shows the difference. The swing arm mount on your frame is set much further back in the seat tube than on the 56 frame and means you have the clearance needed to clear the cotter pin nuts.
I have attached a picture of the 56 swing arm mount which is further forward... it may not be that obvious but hopefully can be seen.
IMG_20210411_191421.jpg
If anyone has any information on the 57 frame it would be good to hear/see.
John
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GOLDSTAR
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Re: 1957 CS front frame

Post by GOLDSTAR »

I have a '54 spring twin frame which houses a '56/'57 G80cs engine and now an AMC gearbox, it fitted without difficulty, I accept there are no cotter pins in this frame, although I have fitted one.
kind regards
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Pharisee
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Re: 1957 CS front frame

Post by Pharisee »

I put a 1960 AMC gearbox (and clutch) into my '54 G3/LS that was originally fitted with a Burman unit. OK, my G3 frame didn't have the cotter pins on the swinging arm pivot, so that wasn't a problem The only modification I had to make was to remove a small amount of metal from the right-hand engine plate to allow the gearbox to move over the full range of primary chain adjustment.

Image
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Rob Harknett
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Re: 1957 CS front frame

Post by Rob Harknett »

http://www.jampot.com/article_read.asp?id=227
John, Have you seen the above tech tip.
From what I see/read the special AMC cotter pin is unlike a tappered bicycle crank type pin
The AMC pin is trapped and cannot be removed until the spindle is removed.
So it would not come out if the threaded part with nut was removed ?
You no need remove the pins, just cut the end off ?
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Samuel
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Re: 1957 CS front frame

Post by Samuel »

A great video on how to remove the pins on AMC swinging arm bearings
Sam
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dave16mct
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Re: 1957 CS front frame

Post by dave16mct »

I know it's a lot of work but could you remove the swinging arm pin and cotter pins. Turn them around and put them from the front? They would be out of the way. Or the bottom gearbox mounting hole could be welded up and drill a new hole say 3/8" further forward. The top slot could be extended forwards if necessary too. Or you could just get a Burman B52 box (easiest option?) :D
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John Jarrett
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Re: 1957 CS front frame

Post by John Jarrett »

Thanks Dave,

Before I do anything I would be really interested to see whether the frame for a 57CS is the same/different in the area of the swinging arm boss/mounting. It may be an error in the spares list and the frames may indeed be different.

If they are different then I will need to consider changing paths but I prefer the AMC gearbox and have one with the clutch whereas I don't currently have a Burman setup. As you say in the end it may be easier to find a Burman gearbox/clutch.

If it is the same then I need to establish whether the engine plates were different and as others have fitted AMC gearboxes to a 56 CS it must be possible to modify to suit and still have the clearance the other way for the dynamo and chaincase. It may be as simple as modifying the engine plates. So if anyone has fitted an AMC gearbox to a 56 CS I would be interested in how you managed to avoid the problem I have encountered.

Machining clearance on the gearbox may be a part of the solution is there is enough material.

I don't think it is possible to reverse the cotter pins as there is no room at the rear of the mounting boss to fit nuts to tighten them as the swing arm is in the way. Depending on the clearances needed it may be possible to machine a recess the boss at the front to get the nuts further out of the way.... but that's getting complicated.

Cheers,
John
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Pharisee
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Re: 1957 CS front frame

Post by Pharisee »

Just out of curiosity... Are the cotter pins really necessary? My '54 G3/LS and '55 M18S don't have them. Could they just be, ummm... left out?
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