Engine shock absorber nut

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

Postby Trefor » Thu Apr 08, 2021 8:30 am

I'm fitting a new engine shock absorber spring to my G80 (the previous had broken in half). According to the spares lists the fixing nut is a special job incorporating a spacer- I don't have such a nut. I have a plain nut with a thick washer. As it stands I can not, because of the strength of the new spring pickup the threads with the nut and washer in place. Two questions-
- The combined height of the nut and the washer is 19mm (5mm washer 14mm nut) is that about right in comparison to the standard nut 000610 ?
- Is there a way of compressing the spring to start the thread if the nut height is correct?

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Re: Engine shock absorber nut

Postby Mick D » Thu Apr 08, 2021 8:42 am

Hi

Nut 000610 is shouldered to allow, I think, the cylindrical section to pass through the spring cup 000831 and locate on the thread, (this also serves to centralise the spring and cup on the axle) - shame you didn't get the correct nut when you bought the spring.

Regards Mick

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Re: Engine shock absorber nut

Postby SPRIDDLER » Thu Apr 08, 2021 9:41 am

If it's for your '52 G80 (and assuming your other bits are correct for year) it's the shouldered nut 000610 which looks like this:

Shock absorber assy.JPG
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Last edited by SPRIDDLER on Thu Apr 08, 2021 10:17 am, edited 4 times in total.
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Re: Engine shock absorber nut

Postby Rob Harknett » Thu Apr 08, 2021 2:29 pm

SPRIDDLER wrote:If it's for your '52 G80 (and assuming your other bits are correct for year) it's the shouldered nut 000610 which looks like this:

Shock absorber assy.JPG


These parts were introduced in the prewar era the old part no. up to about 1950 would have had STD prefix instead of the 3 zero's

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Re: Engine shock absorber nut

Postby clive » Thu Apr 08, 2021 5:26 pm

Mick D wrote:Hi

Nut 000610 is shouldered to allow, I think, the cylindrical section to pass through the spring cup 000831 and locate on the thread, (this also serves to centralise the spring and cup on the axle) - shame you didn't get the correct nut when you bought the spring.

Regards Mick


That sounds like a bit of a bodge Mick. :o :rofl:
The nut does not pass through the spring cup which is a tightish fit on the shaft but butts up against it. With the 500 spring is hard to compress and even with the correct nut it is hard to get the thread started. My method is to use a sprocket and push hard against it whilst turning with fingers to makes sure its not cross threaded. With a nut and washer you are going to struggle more. To avoid disaster i would either have the handlebar against a wall whilst on the centre stand or have it strapped down on a bike lift.

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Re: Engine shock absorber nut

Postby Trefor » Fri Apr 09, 2021 7:19 am

Thanks for the suggestions. Trying to squeeze the shock absorber spring convinced me I was too puny to use the socket compression technique, and I had a horror of wrecking the thread on the end of the crank. I couldn't see any reason why the washer under the nut had to be so thick (5mm) so I substituted a 2.5mm washer which allows the thread to easily be engaged. I figured I could tighten the nut a bit to compensate. The two manuals which mentioned the shock absorber said the nut must be 'fully tightened' and 'firmly tightened against the flywheel driving side main shaft'.
Question-
Does that mean tighten to the end of the threads, or is there another measure of the correct torque?
(I know its a bit dodgy, but when parcels start moving around freely at a reasonable price I can get some proper bits)

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Re: Engine shock absorber nut

Postby clive » Fri Apr 09, 2021 8:28 pm

Trefor wrote:Thanks for the suggestions. Trying to squeeze the shock absorber spring convinced me I was too puny to use the socket compression technique, and I had a horror of wrecking the thread on the end of the crank.

The two manuals which mentioned the shock absorber said the nut must be 'fully tightened' and 'firmly tightened against the flywheel driving side main shaft'.
Question-
Does that mean tighten to the end of the threads, or is there another measure of the correct torque?
(I know its a bit dodgy, but when parcels start moving around freely at a reasonable price I can get some proper bits)


The correct nut is not threaded for the first part of it (where your washer is) this is only just wider than the thread so that once you get it compressed its hard for it to cross thread.

The only problem I can see with making the washer smaller is if not enough of the nut is showing to allow you to "fully tighten" the nut. for me "fully tighten" means engine in gear foot on foot brake wind round the nut with a socket and t-bar until the spring is fully compressed and then whack the t-bar with a hammer. Not exactly a torque setting but it does not come undone.

I have broken a couple of the springs and experience suggests that the risk is allowing the engine to labour which is a temptation as the 500 single plonks so easily.
clive
if it ain't broke don't fix

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