G12 CSR engine noises

Information relating to the Matchless G12 or AJS Model 31 650cc twin
ajsm18
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G12 CSR engine noises

Post by ajsm18 »

Hello,

I've got a 1960 G12 CSR fake. At least, the frame is a de luxe model, although it does have a 1961 Model 31CSR engine.

Anyway, it has become very rattly and, as I don't want to strip it down as I'll never get it back together, I thought I'd ask my fellow AMC enthusiasts for some ideas of what to check.

I can't identify when the noise started as it has always made a lot of noise but it no longer ticks over and, when I shut the throttle off, the engine just wants to die. I've checked the tappets but they were adjusted correctly. It always starts with no trouble, it just makes a lot of rattly noises and worries me that I have a serious problem! I can't hear any grinding noises and, when I touch the crankcases with the engine running, I can't feel any knocking but I feely admit that I'm not good at identifying noises!

A friend has suggested checking the rocker feed but, unlike my Model 18, there isn't an external feed to detach. If I remove the rocker covers and run the engine, should I be able to see a dribble around the rockers?

Any thoughts or suggestions would be very gratefully received.

Many thanks

Mark
petert120r
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Re: G12 CSR engine noises

Post by petert120r »

If you run the engine with the rocker covers off you'll quickly cover your knees with a fine spray of oil if the feed is OK. Are you getting a decent return to the oil tank? A more specific definition of the "rattly noises" would be helpful in trying to diagnose the problem!
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dave16mct
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Re: G12 CSR engine noises

Post by dave16mct »

Is there any blue smoke from the exhausts? Are the plugs oily black? If so it might be severe piston slap, needing a rebore. Dave
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1608
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Re: G12 CSR engine noises

Post by 1608 »

You need to use the old screwdriver handle to the lughole test and see if you can narrow down the area of rattle at least. If it was me I would first check the easiest to get to parts. Start with checking the oil distributor, it could be worn and rattly, cost about a 'tenner' if memory serves. Then check the rockers, are they getting oil and is there any excessive play. If the engine is cutting out I would suggest that it is valve train related. Sticking valve, coil bound valve spring/s, pushrod tip loose. Whats the compression like hot and cold.
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Janet
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Re: G12 CSR engine noises

Post by Janet »

Could one of the valve guides be loose? This happened to Glyn's Beeza coming back from Poland and it made a rattly noise. Then it died. It only had one cylinder so I suppose that's to be expected.
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saltbox alf
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Re: G12 CSR engine noises

Post by saltbox alf »

If yon rattle is half engine speed it's valve train orientated, at engine speed it's crank,pistons, small ends. As said before screwdriver to lughole and see if you can locate the general area of noise. Rattles tend to be timing wheels upwards to valves, knocks on load is mains, knocks on over run is ends.
Knocks on yer front door is the neighbours complaining about all the revving up :lol:
Allons-y, amis de Matchless et AJS
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robcurrie
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Re: G12 CSR engine noises

Post by robcurrie »

And knock on wood it's none of the above!
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robcurrie
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Re: G12 CSR engine noises

Post by robcurrie »

Check the slide in the carb, too much clearance and it could lead to idling problems and engine stalling.
ajsm18
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Re: G12 CSR engine noises

Post by ajsm18 »

Thank you all for your kind and helpful replies and advice. I'll certainly try all of the suggestions. The reason my description is so non-specific is that I couldn't really work out how to narrow it down, other than the rockers. I checked those clearances and they were fine but I didn't check for sticking valves, loose rockers or any other problems and, I think, that is why my mate suggested checking the rocker oil feed.

I did think I would try easy things first, like taking the timing cover off, then primary chaincase etc. It does smoke a bit on initial start up and I think it is blue smoke rather than black but I'll check. It also has a good flow of oil back to the tank.

Anyway, all good suggestions and I'll wheel it out tomorrow and start trying to narrow the problem down.

Thanks again

Mark
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Janet
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Re: G12 CSR engine noises

Post by Janet »

ajsm18 wrote: It does smoke a bit on initial start up and I think it is blue smoke rather than black but I'll check.
Blue smoke on startup is often caused by worn valve seals or guides which allow oil to seep into the cylinder when standing. It normally goes away after the initial amount has burned off. Blue smoke when running can be a sign of oil passing by the piston rings.
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