Oil Serculation,

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Oil Serculation,

Postby freddie 136 » Mon Sep 04, 2017 6:31 pm

Hello, i have a 1953 G80s, 500 single. about a year ago i had the big end changed in my bike, ever since the volume of Oil serculating has appeared to me to be very low. Looking in the oil tank at the serculatin with the bike on the stand and engin running it seems low. I have not used this bike in the last year much only a couple of short runs 20 odd miles or so due to being involved in an accident i was knocked off another of my bikes just a year ago by a chap who pulled out of a junction just as i was passing, anyway i have only just got round to trying with this bike and yesterday i uncoupled the pipe that comes from the oil pump section to the rocker cover. With the engine warm the flow out of the oil pump was approx ( One drop of oil per second ) and with the pipe disconected at the rocker cover it was approx ( one drop of oil every 3 seconds ) this to me is totaly inadquet. I have checked round and can not find any air leeks in the system. I had the Big end changed just after i bought the bike, so not sure if this has any thing to do with problem. Any help would be appreciated, thanks.

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Re: Oil Serculation,

Postby raffles » Mon Sep 04, 2017 7:02 pm

Your oil feed to the rockers sounds about right. You will never get continuous flow on your oil return
Tony

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Re: Oil Serculation,

Postby Rob Harknett » Mon Sep 04, 2017 7:20 pm

It takes quite some time for oil to start circulating. This could be minutes. You should then see oil return by looking in the oil tank. AMC bikes never even had oil going to the Tappet box until 1937, then to the rockers when fully enclosed valve springs were introduced in 1939. Up until then, the top end only got a shot of grease about every 500 miles, or when the owner felt like doing it.

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Re: Oil Serculation,

Postby Stephen G80 » Mon Sep 04, 2017 7:42 pm

when I check the oil on start up before pulling away on my '54 G80, it takes about 1 /2 minutes, and longer if on the side stand, for the oil to return. The rate of return, once it starts, as seen through the oil tank filler, is about a desert spoon every second at tick over.

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Re: Oil Serculation,

Postby Pharisee » Mon Sep 04, 2017 9:16 pm

Stephen G80 wrote:when I check the oil on start up before pulling away on my '54 G80, it takes about 1 /2 minutes, and longer if on the side stand, for the oil to return. The rate of return, once it starts, as seen through the oil tank filler, is about a desert spoon every second at tick over.


I reckon your 'dessert spoonful every second at tick-over' might be just a touch optimistic, Stephen.
I'm bored this evening so I've just been down the shed to get an old oil pump plunger....
As near as I can measure, the stroke of the pump is 1/8"... Call it 3.2mm. The delivery end of the plunger is 14.3mm diameter. That gives a swept volume for the delivery pump of 0.51ml. (I won't bore you with the simple maths) Bearing in mind the way the pump porting works, I'll be generous and say that the pump will deliver 75% of that... Lets call it 0.4ml per stroke. With 16 teeth on the pump plunger and a two start worm on the crankshaft, that's 0.4ml every 8 revolutions of the crankshaft. What's your tick-over speed...? 1000 r.p.m. would be reasonable, I guess. That's an oil delivery of 1000/8 x 0.4 or 50ml per minute. The return pump can't return more than the delivery pump delivers. According to Google, a dessert spoon has a volume of 11.8ml so you'd get 4.1/4 spoonfuls per minute or one every 14 seconds.

Sorry... I told you I was bored!

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Re: Oil Serculation,

Postby Stephen G80 » Mon Sep 04, 2017 9:46 pm

Well John, I think you do need to get out more, however an interesting read. Did you take in to account that the scavenger side will have more than what is has been delivered initially due to the residual oil having settled in the sump from the previous run in your calculation? and also google will have all most certainly giving the volume of an America desert spoon - maybe a little re-calculation is need ;-)

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Re: Oil Serculation,

Postby clive » Mon Sep 04, 2017 9:48 pm

:headbang:
clive
if it ain't broke don't fix

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Re: Oil Serculation,

Postby freddie 136 » Tue Sep 05, 2017 12:00 pm

Thank you to all who answered my question, it looks like the oil flow on my bike is not that bad after all, just don't know how the valve stems and guides keep going. Thanks again appreciate the help.

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Re: Oil Serculation,

Postby 1608 » Tue Sep 05, 2017 12:01 pm

The rockers need very little oil. Too much and it would build up in the head and cause a very smokey exhaust and burn on the exh valve etc. etc.

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Re: Oil Serculation,

Postby Rob Harknett » Tue Sep 05, 2017 12:21 pm

freddie 136 wrote:Thank you to all who answered my question, it looks like the oil flow on my bike is not that bad after all, just don't know how the valve stems and guides keep going. Thanks again appreciate the help.

Inlet valve gets petrol, exhaust gasses, but does not do much good. Running hotter oil just gets burnt on stems. There is also oil feed to inlet valve only, which should be adjusted as stated in the manual.

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