56 G80 CS

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
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Re: 56 G80 CS

Postby clanger9 » Mon Aug 06, 2018 7:50 pm

Before you pull it to bits, I'd run it with the rocker inspection cover off (as suggested by Mick D). AT least that way you can see if oil is not draining from the head, or being blown up the pushrod tubes for some reason...
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: 56 G80 CS

Postby bjorn » Mon Aug 06, 2018 8:47 pm

Rob,
A highly unlikely occurrence, but one that could explain a large oil flow from the valve lifter:

The oil in the cambox drains into the crankcase via a single hole (about 3/16"). If this hole was clogged, the cambox and push rod tunnels would fill up with oil draining from the rocker box. The cam followers would exert a pumping action against the oil in the pushrod tunnels, pressurise the rocker box and push oil out wherever it could go.

I agree with others that you should run it with rocker box cover off to see what's happening, but run it sufficiently long that oil again starts oozing out before you remove cover.

Hope you sort it out.

Bjørn
(also owner of a 56 G80CS)

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Re: 56 G80 CS

Postby ajscomboman » Fri Aug 10, 2018 7:53 am

Not pulled it to bits yet. Having degreased it of all the excess oil I started it up and the oil flow return is spot on, so not the scavenge side. No smoke from the exhaust, so would indicate top end is ok. I then put a clear tube on the breather and formed a small u bend and filled it with oil. Nothing, the oil wasn't blown from the tube or sucked in, in fact it didn't move at all so the indications are that either the valve has stuck shut (unusual as there's bugger all in there other than the disc) or the drilling to the valve has become blocked. Ether way it's a strip down to access it and so I'll overhaul the G/box at the same time.

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Re: 56 G80 CS

Postby Mick D » Fri Aug 10, 2018 8:13 am

Hi

That breather bemuses me, it has such a small orifice that it cant pass anywhere near the displaced volume when the engine is running and there is nothing that I can see stopping the crankcase breathing via the drive side bearing and primary chain case, where the flow is much less restricted. (Rob's thoughts re a PO fitting a sealed bearing hadn't occurred to me - do people do this?).

Another consideration is as to how crankcase air is blown up the push rod tubes - to have a flow through the tubes the air needs to vent out of the rocker box, how does it do this?

My money's still on a blocked oil return.

Regards Mick

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Re: 56 G80 CS

Postby G15 Roy » Fri Aug 10, 2018 3:55 pm

IMG_1112.jpg
Could you be suffering from Bottom dirt left by the PO :o
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Re: 56 G80 CS

Postby ajscomboman » Sat Aug 11, 2018 3:55 pm

G15 Roy wrote:
IMG_1112.jpg
Could you be suffering from Bottom dirt left by the PO :o


Nope for once I can't blame you. Any way today it ran for best part of the afternoon with no leaks but a slight clack from the inlet rocker. Pulling the inspection cover revealed a slight end float. Off with the rocker box to find the top end awash with oil and tubes totally full! The pump returns nicely and the breather is definitely not blocked. I guess the return drain hole back into the crankcase must be blocked so its off with the timing case and out with the cams to check the hole.

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Re: 56 G80 CS

Postby bjorn » Sat Aug 11, 2018 9:52 pm

Rob,
From your post on Friday it appeared that the crankcase breather was not working, but now it is?

As I see it, the oil filling up the pushrod tunnels can only be caused by either the crankcase breather not working, or the drain hole in the cambox is clogged. Of these the first "suspect" is the most likely.

If it is the breather you can possibly clear it from outside by compressed air into the breather tube. If this doesnt work you can clear it after removing the primary chaincase.

Bjørn

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Re: 56 G80 CS

Postby g80csp11 » Sun Aug 12, 2018 8:48 am

perhaps a seized valve guide or loose in head , you did say 'slight clack from the inlet rocker' or possibly the bike is too clean and shinny , ive always found that over cleaning a bike can cause many similar problems
Neither Roy or myself suffer from this issue

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Re: 56 G80 CS

Postby ajscomboman » Sun Aug 12, 2018 9:11 am

Leaving the bike all night the tubes are still full so it's now pointing to the cam box drain into the crankcase. The breather is definitely working, it pulses air out at a fair rate and has shot out some oil. Valve guide is tight Peter and I've now moved out the bush to take up the end float. Off with the covers today and hopefully I'll find the issue. Strange why it's happened after 1500 miles with no issues.

You may have a point about clean bikes, my rusty's never have these problems. Once I've fixed it maybe I'll never polish it again. :D

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Re: 56 G80 CS

Postby G15 Roy » Sun Aug 12, 2018 9:15 am

Lets see a photo of what you find.
Roy

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