Engine Shock Absorber Cap

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
56G80S
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Location: N YORKS UK

Re: Engine Shock Absorber Cap

Post by 56G80S »

George sent you 6 PMs with a pic attached to each. Unfortunately I thought you'd measured in mm so the vernier in the pics is showing mm. Should give a good enough idea though.

Johnny B
George Kaplan
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Re: Engine Shock Absorber Cap

Post by George Kaplan »

Thanks Johnny B (I have PM'd you back and please excuse the fact that i seem to have referred to you as the wrong name as I got mixed up with another message from someone else and mixed the screen names up)

The pictures are brilliant and I am happy with measurements in metric or imperial as I am pretty bi-lingual when it comes to measurements.

John
George Kaplan
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Location: York

Re: Engine Shock Absorber Cap

Post by George Kaplan »

Many thanks to Johnny B for the dimensions.

I had some distractions this morning but this afternoon I had some time to do some lathe work. Amongst other things I was able to make a cap. I thought I had some 2 inch BMS but it was a bit smaller than 2 inches so I looked for something else and found a lump of stainless.. It had a large bird-nesting factor but the finish was OK.

Image

Image

John
56G80S
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Re: Engine Shock Absorber Cap

Post by 56G80S »

I mixed up across this and your other post so back on the right one. On the depth of engagement of the nut and the cap reaching the end of the grooves in the shaft, take a look at this current post from JagLite which hopefully should be page 8: http://www.jampot.com/forum/viewtopic.p ... 7&start=70 It shows a shock absorber assembled that looks like how I would expect (scroll down the various pictures, quite a way past Rob's very large pictures, it's one on the engine on a stand).

Do I recall that you made the nut? Any chance it's too long? The spring is under compression, see JagLite's photo. Personally I wouldn't reduce the thickness of the base unless you've left it a lot thicker. I think one of the photos I sent shows the thickness at the lip and that is consistent throughout the part; I wouldn't advise going thinner than that.

Johnny B
Dixter
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Re: Engine Shock Absorber Cap

Post by Dixter »

Hi George, the dimensions of the engine shock absorber components are sized to permit the primary drive to still function with a broken spring. Limp-home mode, if you will. This means the length of the portion ‘inside' the spring must exceed the height of the spring when coilbound, ie. > 0.883”. (If I read your measurements correctly).

Some years back, The Club's Spares Scheme was experiencing failures of replacement caps. The flanges were being sheared from the cap. The cap was too shallow.

The easiest way to determine the minimum dimension for your cap is to remove the spring, reassemble with all other components, fully tighten the nut, twist the sprocket to force the sliding member to lock-up, and measure the area to be occupied by the spring. It must exceed the coilbound dimension.

Once you know this and because your cap is not heat treated steel, the flange can be made thicker, as long as the thickness ‘grows' towards the end of the shaft.

I'm enjoying your article, keep up your good work,
DC
Dick Casey
The RideNut
George Kaplan
Posts: 160
Joined: Tue Apr 25, 2017 1:24 pm
Location: York

Re: Engine Shock Absorber Cap

Post by George Kaplan »

56G80S wrote:I mixed up across this and your other post so back on the right one. On the depth of engagement of the nut and the cap reaching the end of the grooves in the shaft, take a look at this current post from JagLite which hopefully should be page 8: http://www.jampot.com/forum/viewtopic.p ... 7&start=70 It shows a shock absorber assembled that looks like how I would expect (scroll down the various pictures, quite a way past Rob's very large pictures, it's one on the engine on a stand).

Do I recall that you made the nut? Any chance it's too long? The spring is under compression, see JagLite's photo. Personally I wouldn't reduce the thickness of the base unless you've left it a lot thicker. I think one of the photos I sent shows the thickness at the lip and that is consistent throughout the part; I wouldn't advise going thinner than that.

Johnny B
Johnny B, thanks for the link, I have seen Jaglite's post but must have missed or forgotten that picture which is a great help.

The hole size in the cap as per your dimensions (17.79mm or 0.700") of your existing one is big enough to go on the threaded portion of my crank but too small to go over the splined section so it buts up to a shoulder created by the end of the splines. This limits how far on the cap will go onto the crank axle. Should the cap fit over the splines? It looks like it should from Jaglite's picture?

I didn't make the nut, it came from club spares. If I hadn't thought I already had one I would have ordered a cap too but it was only when I had everything together that I realised that I had a stray erroneous part from something else.
Dixter wrote:Hi George, the dimensions of the engine shock absorber components are sized to permit the primary drive to still function with a broken spring. Limp-home mode, if you will. This means the length of the portion ‘inside' the spring must exceed the height of the spring when coilbound, ie. > 0.883”. (If I read your measurements correctly).

Some years back, The Club's Spares Scheme was experiencing failures of replacement caps. The flanges were being sheared from the cap. The cap was too shallow.

The easiest way to determine the minimum dimension for your cap is to remove the spring, reassemble with all other components, fully tighten the nut, twist the sprocket to force the sliding member to lock-up, and measure the area to be occupied by the spring. It must exceed the coilbound dimension.

Once you know this and because your cap is not heat treated steel, the flange can be made thicker, as long as the thickness ‘grows' towards the end of the shaft.

I'm enjoying your article, keep up your good work,DC
Dixter, thanks for the explanation, that makes a lot of sense and provides the insight needed to determine the dimensions. Also its interesting about the previous failures due to parts being too weak.

Thanks everyone, I will have another look at this and report back.

John
56G80S
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Re: Engine Shock Absorber Cap

Post by 56G80S »

I'm pretty sure it's meant to sit on the end of the splines.

Others will come along to verify or disprove that. On the broken spring, I thought the trick was to remove it and reverse the broken halves (if lucky) so the "flat" parts faced each other and refit.

Then limp home.

Johnny B
Locked