oil feed to head

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Chris Berry
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oil feed to head

Post by Chris Berry »

I overhauled my Matchless 1948 G80 3000 miles ago and replaced the oil pump in the process. I also put a length of clear plastic hose on the oil feed pipe to the head to check oil flow. I have noticed that when the bike is cold I get a reasonable flow to the head (slow drip) which provides sufficient lubrication. I also notice that when the bike warms up and after running for around half an hour the oil flow ceases. I have checked the return to the oil tank and am still getting oil return suggesting that the pump is functioning OK. When I remove the rocker cover and inspect the pushrods there is the presence of oil. I am running 50 grade penrite mineral oil and have just changed it so the oil is new. Is it normal for the oil flow to cease to the head when the bike warms up.
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Rob Harknett
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Re: oil feed to head

Post by Rob Harknett »

When you get the answer you may consider changing the plastic back to rubber. The pipe is split and joined with rubber to prevent vibration splitting joints. Plastic will harden which may result in splitting joints.
SPRIDDLER
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Re: oil feed to head

Post by SPRIDDLER »

To state the obvious, the oil pump is not designed for that to happen.
I've never fitted a transparent section so don't know whether or not it's normal for the flow/drips to cease.
The cam gears, cams and 'tappets' are lubricated by the oil returning from the rocker box down the pushrod tubes so I would assume the flow should continue at all times.
Oil in the rocker feed pipe is under a little pressure (therefore it's unlikely to be an air leak in the rocker feed pipe) so if there was a leak you would have oil appearing where it shouldn't.
I'd just ensure that there isn't any debris in the pipe and fittings that becomes softened and blocks the pipe when warmed with oil and replace transparent pipe section with rubber pipe and keep an eye on the rocker assembly for signs of lack of oil. A squeaking inlet valve stem may be an indication of oil shortage.
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Chris Berry
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Re: oil feed to head

Post by Chris Berry »

Thanks Spriddler,
As it happens I just had to remove the cover off the cams today and they all seemed sufficiently lubricated. There was a pool of oil in the base of the cam housing so all seems OK. It all seems a bit strange. I did consider that with the warmer temperatures here In Australia that a different grade of oil would be better but that hasn't gone any further than thought only. I checked the pump output at the pump outlet (undid the base of the oil pipe) and there is a flow there. I also restarted the bike after around thirty minutes cooling and the flow restarted. There are no obvious leaks in the circuit anywhere so who knows
SPRIDDLER
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Re: oil feed to head

Post by SPRIDDLER »

Contrary to my earlier comment I suppose that, in theory, when the oil pump plunger is on its return stroke there may be a slight and brief vacuum in the rocker feed pipe since there is no one-way valve in the system apart from the timed 'shut-off' effect of the plunger returning. If there's leak anywhere (copper pipe joints, oil pump front plate) air could be drawn into the system and an air bubble would appear and pulse to and fro in your transparent section. But if there was an air leak I'd expect an oil weep to occur when the plunger returns on its 'delivery' strokes.
I doubt that thicker oil would make any difference. I'd leave it, as maybe when you're riding and the engine is running at a higher speed for longer than when testing it stationary the flow restarts without you being able to see it.
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Chris Berry
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Re: oil feed to head

Post by Chris Berry »

Is there a pressure relief valve in the system anywhere that may leak? Certainly a long shot. The fact that the engine has now done 3000 Miles without drama and I am getting return flow back to the tank would suggest that things are OK. I first noticed the problem around 1500 miles ago and would think if anything was going to happen it would have by now
SPRIDDLER
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Re: oil feed to head

Post by SPRIDDLER »

Chris Berry wrote:Is there a pressure relief valve in the system anywhere that may leak?
No inline or any other valve at all if the bike is as standard.
The plunger pumps in pulses not a constant flow because it reciprocates and rotates, opening (uncovering) and closing (covering) inlets and outlets as it moves, therefore there could be some degree of ebb and flow (a greater flow than ebb) of the oil in the pipe to the rocker box which most (all?) of us never see as we don't have a transparent pipe.
I have a transparent petrol pipe tank to carb and there's always a longish bubble in it which never seems to move even when fuel is flowing. I would have expected the bubble to move along the pipe and disappear into the carb but it never does. To the eye it appears that no fuel is flowing, maybe it's the same with your oil pipe?
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Mick D
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Re: oil feed to head

Post by Mick D »

Hi

There's no reason not to remove the rocker box cover and observe the flow - it's so minimal it probably won't even escape the confines of the box.

My guess is that as the oil warms up it's viscosity reduces to the point where it's flow becomes difficult to observe inside the plastic tube.

Regards Mick
Chris Berry
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Re: oil feed to head

Post by Chris Berry »

Mick D wrote:Hi

There's no reason not to remove the rocker box cover and observe the flow - it's so minimal it probably won't even escape the confines of the box.

My guess is that as the oil warms up it's viscosity reduces to the point where it's flow becomes difficult to observe inside the plastic tube.

Regards Mick
Thanks Mick,
that's what if figured also. My main concern is that the oil level 'recedes' down the clear pipe until there is no oil in the pipe at all. so its not just a car of holding the level it loses it. I guess if I hadn't have put that clear pipe on I would never have know (silly me). I'm thinking, other than trying heavier oil, if it hasn't failed in 3000 miles it should be OK
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Re: oil feed to head

Post by 56G80S »

This is going to sound daft but I cut the side off a transparent washing machine tablet box and put it in place of the rocker cover because I was concerned about flow. I have a transparent pipe on the pipe but still couldn't see flow over a very short gap between ends of the copper pipe; I've always had this type of pipe and it's never split yet (damn, bound to happen now).

Anyhow. it was reassuring to see oil spurting out of the little jets by the rocker arms. And trickling past my makeshift arrangement quite quickly.

Johnny B
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