Primary shock absorber spring

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Primary shock absorber spring

Postby adz25 » Mon Aug 27, 2018 4:50 pm

I'm looking for some clarification on the primary shock absorber spring for my 53/54 m18. I have a 19 tooth sprocket assembly that came with the bike but it had no spring or cup washer. I have found an AMC spring in my boxes, a flat style spring as per the parts catalogue pictures but the coil bore is too sloppy by approximately 1/8th inch( measures 1.622 bore x 1.76 high 4 coils) I also purchased another spring which fits perfectly but it is not flat style but traditional wire coils (measures 1.5 inch bore x 1.55 high .24 thick wire, 4 coils)

Could anyone tell me if they have seen a wire type spring fitted at all, or is flat coil the only type?

I'm worried the wire type one will not be man enough for the job as it looks significantly weaker than the beefy flat coil type.

Would anyone have one to hand that they wouldn't mind measuring please so I can compare my 2 different springs.

Many thanks

Adam

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Re: Primary shock absorber spring

Postby clive » Mon Aug 27, 2018 5:51 pm

For a 500 the standard sprocket would be 21 teeth and 18 for a 350. Yours is between and was probably for use of a 500 with a sidecar. I have used the round type spring as well as the flat type. Once you get the cup and nut (the first section of it has no thread) if you have the correct spring for the 500 it should be a real b**ger getting the nut onto the shaft far enough for the thread to start engaging. If it is easy then the spring is probably a 350 one.
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Re: Primary shock absorber spring

Postby adz25 » Mon Aug 27, 2018 6:33 pm

Thank you for the reply Clive.

Looks like I'm back on the hunt for a 21 tooth sprocket then! I have the cup and nut and they would fit very easily with the wire spring unfortunately. The flat spring would be perfect if it wasn't such a sloppy fit. I guess it's also possible the keyed cam is not a match for the sprocket I have.

Soon close to being able to try and start her now!

Best regards

Adam

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Re: Primary shock absorber spring

Postby clive » Tue Aug 28, 2018 8:10 am

The spring should be a sliding fit on the keyed cam and the end cap should sit neatly on it. If yours does not it is probably the wrong spring even if it is flat profile. The club sell a round profile spring for the 500....when it's in stock
Part no 000703.
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Re: Primary shock absorber spring

Postby Rob Harknett » Tue Aug 28, 2018 9:52 am

clive wrote:The spring should be a sliding fit on the keyed cam and the end cap should sit neatly on it. If yours does not it is probably the wrong spring even if it is flat profile. The club sell a round profile spring for the 500....when it's in stock
Part no 000703.

A lot of the drive shaft parts have been in use since as far back as 1937. Like the spring in question 000703. Which is a new pt. no. used from approx. 1952. So for some 15 years the part went under its old number STD 703. Suppliers like Russells may still find this number on NOS parts. They do have the 350 and 500 springs in stock under the new pt. no. but for some reason state it as 00.0703 for the 500 spring.

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Re: Primary shock absorber spring

Postby adz25 » Wed Aug 29, 2018 12:09 pm

Thank you for the replies gents.

It's a very sloppy fit with the flat spring, and a sliding fit with the coil spring. It will be a whole sprocket and cam I think as it looks like possibly the 350 model sprocket that I have.

Will have to keep an eye out for a used one although they may have stock in the spares scheme, I don't have the cash at the minute!

Many thanks

Adam

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Re: Primary shock absorber spring

Postby adz25 » Sun Sep 16, 2018 9:37 am

Still working on this, a helpful chap from the owners club has been able to supply a 21 tooth sprocket, which has arrived but the dynamo sprocket has only 19 teeth instead of the 21 the other one had. Apart from having to get a smaller dynamo chain, are there any other issues I may have?

I have a lucas low output dynamo, so will having 3 less teeth on the front sprocket significantly reduce the output?

Many thanks

Adam

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Re: Primary shock absorber spring

Postby cfaber » Sun Sep 16, 2018 4:37 pm

adz25 wrote:Still working on this, a helpful chap from the owners club has been able to supply a 21 tooth sprocket, which has arrived but the dynamo sprocket has only 19 teeth instead of the 21 the other one had. Apart from having to get a smaller dynamo chain, are there any other issues I may have?

I have a lucas low output dynamo, so will having 3 less teeth on the front sprocket significantly reduce the output?

Many thanks

Adam


What size on the dynamo vs engine sprocket ?

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Re: Primary shock absorber spring

Postby SPRIDDLER » Sun Sep 16, 2018 5:23 pm

It will reduce the output from what it was with the 21T sprocket but since your '53/'54 bike will have a mag the ignition is independent from the battery.
You'll only need 'battery' power for the lights/hooter so if you do a lot of night time riding and the battery doesn't stay charged a change to LED lights would considerably lessen the demand.
The standard filament headlight bulb plus tail light draw about 42 watts which is about the max you can expect from a 'short' dynamo in tip top condition in fourth gear at around 40mph (on factory standard sprockets).
Last edited by SPRIDDLER on Sun Sep 16, 2018 5:26 pm, edited 2 times in total.
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Re: Primary shock absorber spring

Postby adz25 » Sun Sep 16, 2018 5:24 pm

Having just double checked they are both 17 teeth.

Many thanks

Adam

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