Shakedown results - Engine shock!

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Jdraper
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Joined: Mon Mar 07, 2011 9:41 am
Location: BUCKS UK

Shakedown results - Engine shock!

Post by Jdraper »

When I split the engine shock absorber, I found this! The engine sprocket is original and doesn't show much wear. The driven half was new from club spares and has only done around 200 miles. I needed a new one to match the new primary drive shaft (old one was well worn). Is this normal?? I can't imagine so. Any ideas of the cause? Is the part case hardened after machining? Do I need to worry, or has it now worn to match the lands on the old drive sprocket. I guess I will run it for a a few more miles and see if it gets worse.

Jeremy
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Mick D
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Re: Shakedown results - Engine shock!

Post by Mick D »

Hi

That looks like impact damage - did you have the shock absorber assembled so as it couldn't ride over the peaks?

I wouldn't continue to use it as it looks like the damage will impinge on the bearing faces and will probably cause metal debris generation.

I would expect it to have been case hardened.

Regards Mick
Jdraper
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Re: Shakedown results - Engine shock!

Post by Jdraper »

A close up of the chip fracture. some further radiating cracks show up.. Nasty

Jeremy
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Mick D
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Re: Shakedown results - Engine shock!

Post by Mick D »

Hi

Looks to be case hardened.

Was the shock absorber able to ride over the cams? that's the only way I can imagine the damage happening.

Definitely scrap now.

Regards Mick
Jdraper
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Re: Shakedown results - Engine shock!

Post by Jdraper »

I would have thought I would tell if the cams had overridden each other by noise or a slipped clutch feeling - no recollection of that. The nut was done up tight. Could the spring be weak? It is the original one. Anyone know what the serviceable free length of the spring should be?

Jeremy
bob
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Re: Shakedown results - Engine shock!

Post by bob »

Just a guess but if the old shaft splines were buggered has it jammed on the splines and someone has hammered the cam to try to remove it . A hammer is the only way I can see this sort of damage being caused .
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ajscomboman
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Re: Shakedown results - Engine shock!

Post by ajscomboman »

I'm using a club drive cam on the G80 CS and it's been fine, however when I first got the bike on the road it had been fitted with a 350 spring and eventually it went over and broke the drive cam in half! Since I fitted the club replacement cam and correct spring it's been fine with no wear issues. Too me that looks like debris damage, from what or how it would happen, who knows! It doesn't look to be natural operational wear/damage. No signs of any excess material floating around in the oil or bit's missing from anywhere else?
Jdraper
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Re: Shakedown results - Engine shock!

Post by Jdraper »

No debris, as this was a clean build last year, with clean oil in the case. I am favouring the incorrect spring theory at the moment. Club is out of stock for the cams at the moment, but I guess I can go for a new spring.

These are the problems of a bike that was in a very sorry state when I got it in 1977, with parts from goodness knows what and where. I am going on a journey of discovery with the parts book in one hand and a steel rule/vernier gauge in the other. The engine was re-built by Ken DG a couple of years ago and he found allsorts in the old unit.. Runs sweet now.

Jeremy
Mick D
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Re: Shakedown results - Engine shock!

Post by Mick D »

Hi

There's no evidence of debris damage that I can see there, (no scores or scratches).

I am under the impression that the cams should not be physically able to ramp over each other, though I don't know if the spring becoming 'bound' is the limiting factor or the fully torqued nut and washer - if its the nut washer position you can do a trial run without the spring installed.

Fitting a stronger spring to an assembly that can over cam will just impart a larger impact if/when it does over cam and increase the potential for similar damage.

Regards Mick
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clive
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Re: Shakedown results - Engine shock!

Post by clive »

I would suggest a close inspection of the cap that holds the spring. I have had a pattern one of these gradually bend so that the spring was not held so firmly to the cam. If you can start the nut on the end of the spline without a struggle I would suggest either the spring is knackered, a 350 one, or the cap has bent. The cap should have a 90 degree bend on the part that retains the spring. The 500 springs require some compression before you can start the thread on the nut. I think that with it all set up correctly the spring should be coil bound before the cam will ride over, obviously if the cap has bent this may not be the case.
clive
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