G2 oil transfer from sump to primary chaincase

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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G2 oil transfer from sump to primary chaincase

Postby Richard Hyatt » Sat Apr 27, 2019 3:36 pm

Hi all,
We've been rebuilding the g2 which had an oil supply problem to the head.
This has now been resolved by a new pump , guide pin etc. Good supply of oil up to the head and rocker jets now.
But we seem to have now the integral oil tank wet sumping into the sump and when starting and running the oil pump scavenges back to the tank ( clearly flowing in spurts from the little hole), but the surplus in the sump transfers into the primary chain case ? Obviously through the near side main bearing.
I assume that the surplus oil cannot be scavenged quickly enough.

Question 1, what is causing the wet sump ing overnight?

Question 2 is the oil just blown through the the main bearing ? I would have thought it should have come out the breather hole in front of the sprocket ?

Any suggestions gratefully received

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Re: G2 oil transfer from sump to primary chaincase

Postby clanger9 » Sat Apr 27, 2019 8:46 pm

Hi Richard,

If it's not scavenging properly then that suggests an air leak on the scavenge side. Is the big plug/oil pump end cover fully home and sealed?
If it's wet sumping overnight, that suggests the oil pump isn't a good fit in the bore. Which would be strange, given that you've just fitted a new pump...
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: G2 oil transfer from sump to primary chaincase

Postby Richard Hyatt » Sun Apr 28, 2019 6:08 am

It's a mystery for sure , the new pump is snug in the bore , all new O rings , sump plug dry and tight ,
I know there aren't any ball valves like triumphs etc with plunger pumps.
And of course you only have about 4 or 5" of gravity to create a head from the tank.
We get a good scavenge back through the hole in the tank as well , as good a flow as the old pump gave I'm sure, spits and spurts , bearing in mind the stroke of the pump is only about 1/8" or 3/16" , there won't be massive movement.
I'm going to run it briefly without the filter to see if that is bunged up, we did clean it well during the rebuild .
See if the flow is better without it.

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Re: G2 oil transfer from sump to primary chaincase

Postby clanger9 » Sun Apr 28, 2019 7:45 am

If you've had the filter out, make sure the cap at the bottom of the filter is seated correctly - if not, this will restrict the return circuit.
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Posts: 113
Joined: Sun Jan 27, 2019 8:52 pm
Location: Dorset

Re: G2 oil transfer from sump to primary chaincase

Postby Richard Hyatt » Sun Apr 28, 2019 6:29 pm

We have the original felt filter with a gauze round the outside 5 and 5/8" long , with a cup and spring under the chrome Allen key lid.
But I could see any cup down the bottom of the filter tube/housing. I'll try a magnet down there later.
Maybe it's not there at all in which case I need to find one !

We've run it without the filter and it scavenges well for sure, I have a feeling that we inadvertently overfilled it and there was no room 8 the tank (with the cap on) for the surplus scavenged oil.
We've run it for about 15 or 20 minutes now and keep sucking out the overfilled oil from the tank whilst it's running, so hopefully , we've now got a realistic "running"oil level 1/2" or so below the outlet hole.
As a matter of interest, why did our new pump have an extra drilling in it please? The original , worn pump had G2 on the end but no extra drilling .
Does this give extra output I wonder? Or just a generic replacement . Les at Russells said it was new old stock still in its greasy paper, just nice to know

I'll check the little cap and explore a new filter , are there different types to consider ? Please?

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