cam shaft bush removal/replacement

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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cam shaft bush removal/replacement

Postby Chris Berry » Sat Dec 02, 2017 9:41 am

HI all, Just a quick question, can the timing bushes on a G80 drive side be removed and replaced without completely stripping the engine (perhaps slide hammer, puller or something similar)

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Re: cam shaft bush removal/replacement

Postby SPRIDDLER » Sat Dec 02, 2017 10:43 am

Chris, I take it you mean on the timing side, not the drive side?
I have used a Rawlbolt 'sharpened' or roughed up a bit a bit to remove a blind bush (not those though) but it's a fine line between gripping the bush and expanding it to make it tighter in its housing. As you realise the best way is to remove the bushes from split and heated c/case halves because removing them cold with an expanding puller may mean that the new bushes will not be a sufficiently tight fit. There's only a tiny gap between the inner end of the bush and the flywheel.
Rawlbolt.JPG

There's a neat way (which you may already know) to determine the end float of the cam shaft which is closed with a core plug - i.e. the zorst or inlet (depending upon whether your mag is front or rear mounted) shaft which has the blanking plug. In short you position the bush or fit too many shims so that when you offer up the outer cover nice and square the cover will not close up, and measure the gap, removing shims or moving the bush accordingly.

(The bush on the mag sprocket shaft has an internal helix to 'screw' the oil back into the crankcase. I fitted one (from club spares) which had the helix cut clockwise and on first run out it drew the oil into the mag drive housing, up the mag chain into the mag, over my boots and my father-out-law's new red brick-paved drive).
This is the incorrect bush with the helix cut clockwise which causes the anti-clock mag sprocket drive axle to draw oil into the mag drive cover.....
2017-12-02 Zorst shaft incorrect bush helix 011 (640x480).jpg
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Last edited by SPRIDDLER on Sat Dec 02, 2017 12:18 pm, edited 3 times in total.
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Re: cam shaft bush removal/replacement

Postby zwarts » Sat Dec 02, 2017 11:42 am

A cam bush with an incorrect fast thread (helix) will not work on the inlet or exhaust cam as both rotate in the same direction!

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Re: cam shaft bush removal/replacement

Postby SPRIDDLER » Sat Dec 02, 2017 12:08 pm

zwarts wrote:A cam bush with an incorrect fast thread (helix) will not work on the inlet or exhaust cam as both rotate in the same direction!


Thanks, Bob. You're quite correct; both shafts turn in the same direction regardless of whether the mag is front or rear mounted. I had brain fade whilst writing but have edited my reply so it should make sense now. :oops: After I fitted the bush with the anti-clock helix all was fine.
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Re: cam shaft bush removal/replacement

Postby adz25 » Sun Dec 24, 2017 9:26 pm

Hi,

I just this week used a blind bush removal tool to pull the 2 crankcase bushes out .010" as there was a little too much slack in the cams. It can be done if you have the tooling. I guess it depends how much you dont want to split the cases.

It was a half inch blind bush remover from work, basically a split belled shaft with an expander peg screwed through the middle.

Hope this kind of helps

Adam

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