G5 wet sumping

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
vigo
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Location: Cheshire UK

G5 wet sumping

Post by vigo »

Now this lightweight is running well, shedding bolts and fasteners on the road, I move on to the next quirk....wet sumping. This bike will wet sump 200mls overnight and then stop. I assume because the head of oil and levels between sump and tank are in equilibrium.
1. A couple of Qs gents: can I start the engine with 200mls in the sump?
2. Can I run the engine with the oil tank 200mls down ie about 2 inches low from return hole in tank and hope to avoid wet sumping?
3. Does this indicate a very worn pump?

Any advice gratefully accepted gents.
Red Gauntlet
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Re: G5 wet sumping

Post by Red Gauntlet »

Sounds like a worn engine casing, but maybe the 'O' ring at the pump bung inside the oil tank is split allowing oil to seep back. It might be worth making sure that the piston is at TDC when you stop as I expect if there is a major wear issue it is syphoning via the big end bearing, placing that uppermost should stop that.
In answer to your questions, yes you can start it with oil in the casing, it maybe a bit smokey to start with but should not do any harm, if you are not doing any great long trips then a lower oil level should be ok there is quite a lot of oil south of the pump, probably not the pump but more likely the casing is worn or scored up causing a gap where the oil can get through. Maybe a combination of pump, main bearing bushing and casing.
You don't say what oil you are running but it's all pretty thin when hot.
You will have to remove the gearbox, pull out the pump and take a look at the pump machining, with an endoscope.
vigo
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Re: G5 wet sumping

Post by vigo »

Thanks Red G, great detail info. Yes I always park with piston at tdc, makes no difference. I'm using sae 50, no detergent but with 2 changes in 100mls turns the oil very quickly black. This is an earlier recon with +40 pistons and I think this bike has seen a lot of miles in it's life. Unfortunately I didn't get much history with it. Sounds like a winter 22 project.
Brocher
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Joined: Mon Sep 25, 2023 8:15 pm
Location: Yorkshire England

Re: G5 wet sumping

Post by Brocher »

Hi Folks

As you can see this is my first post and I'm sorry that it's a rather lengthy one. I recently purchased a 1962 Matchless G5 (first classic bike) which appeared to be in great condition. Even though I've looked at several other oil-related posts in the G5 section, I can't find a solution to the problem so I thought posting in this thread would be best as it covers G5 wetsumping.

Before I left the vendor I checked that the oil (SAE 20W50) was returning when the engine was ticking over and could see lots in the reservoir. After riding my bike over 50 miles to get home (average speed 45 mph) I put it in my garage on the centre stand and put a piece of cardboard infront of the centre stand and one behind.

Due to poor weather I've not riden my bike since then but on the fourth day when I checked the oil and there wasn't any in the reservoir! I checked that the sump plug was secure and there wasn't much oil on the outside of the engine and only a few spots on the piece of cardboard to the rear of the stand but none elsewhere.

Does this mean my bike has completely wetsumped? If so, what could have caused such a large transfer of oil in a few days - perhaps a faulty pump seal? From what I've read so far it doesn't seem as if G5s wetsump like this but would there be any point in running the engine whilst on the centre stand to see if the oil fully returns? Any advice will be most welcome.
SPRIDDLER
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Re: G5 wet sumping

Post by SPRIDDLER »

Brocher wrote: Sat Sep 30, 2023 1:23 pm

Due to poor weather I've not riden my bike since then but on the fourth day when I checked the oil and there wasn't any in the reservoir!
Does this mean my bike has completely wet sumped?
Welcome to the club and Forums, Kerrin.

If there's no oil on the outside it almost certainly has wet sumped (rarely is any diagnosis 'absolutely certain' on our old bikes ;) ) , but to confirm what seems the cause, drain the crankcase - you ought to do that anyway before trying to start the engine or you'll most likely get a fouled sparkling plug and clouds of of smoke.
The oil tank only requires 2.5 pints (less than the gearbox at 3 pints!).
As far as I know (I've never worked on a L/W) there isn't 'a seal' inside the pump. (There is an 'O' ring on each of the two plugs). See the engine drawing here:

http://archives.jampot.dk/technical/Cut ... _Parts.pdf

and page 6 of the Spares List here:

http://archives.jampot.dk/book/Spares_l ... s_List.pdf

I've never used multigrade so can't say for certain, but maybe using straight 50 (as per the Manual) would improve things.
If you don't have one, an Owners Manual is here:

http://archives.jampot.dk/book/Owners_m ... n_Book.pdf
'There is a tide in the affairs of men
Which taken at the flood............'
Brocher
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Joined: Mon Sep 25, 2023 8:15 pm
Location: Yorkshire England

Re: G5 wet sumping

Post by Brocher »

Thank you for your quick reply - I'll drain the crankcase tomorrow and see what I get😂.

I have recently purchased a large can of oil (in anticipation!) so I'll measure what comes out and refill with fresh.

Thanks also for the <links>
Brocher
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Joined: Mon Sep 25, 2023 8:15 pm
Location: Yorkshire England

Re: G5 wet sumping

Post by Brocher »

I couldn't shift the sump drain plug. However, the smaller nut that's in the centre of the sump drain plug was loose so I removed that and drained-off what was in the sump, about 50-60ml. I couldn't shift the reservoir/tank drain plug so I'll have to get a longer arm for my socket set and have another go - to be continued 😂.
SPRIDDLER
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Re: G5 wet sumping

Post by SPRIDDLER »

Brocher wrote: Mon Oct 02, 2023 5:11 pm I couldn't shift the sump drain plug. However, the smaller nut that's in the centre of the sump drain plug was loose so I removed that and drained-off what was in the sump, about 50-60ml
That's barely half a cupful, seems satisfactory to me.
If there wasn't any oil on the floor, the engine, or over your boots it seems to me that there was too little oil in the tank when you bought the bike.
I'd be inclined to put in say, just a pint of oil to start with and give the bike a run and look at how much is in the tank when you get back.
I couldn't shift the reservoir/tank drain plug so I'll have to get a longer arm for my socket set and have another go.. 😂.
I'm not sure that a longer bar is a good idea as there's a real risk of tearing the plug and thread out of the tank.
Sometimes there's 'stickshen' on tank and sump drain screws which need a sharp and quick application of force rather than an increased steady force to unstick them. If you don't have a rattle gun try striking the socket bar *reasonably* firmly with a hammer - it's not easy and needs care as it tends to twist the socket over (sideways) but worth a try. However, if you can drain the sump with the small screw I wouldn't bother trying to shift the large one.

Disclaimer - I've never worked on a L/W engine. :oops:
'There is a tide in the affairs of men
Which taken at the flood............'
Brocher
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Joined: Mon Sep 25, 2023 8:15 pm
Location: Yorkshire England

Re: G5 wet sumping

Post by Brocher »

Thanks again for your comments and suggestions. I topped up the oil tank to just below the small orifice where the oil re-enters the tank and went for a 25 mile ride. Back home I waited for the engine to cool and noticed the oil level was well below where I'd topped it up to so I'll do the same today and see how things turn out.

BTW, still very few drips on the cardboard and a clean exhaust.
Cheers
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jackstringer
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Re: G5 wet sumping

Post by jackstringer »

The drips are normal, it's a part of the total loss oil system that reduces the amount of times you need to replace the oil as you are constantly topping up.

It it stops dripping oil it's a good sign its ran out of oil.

When my bike has wet sumped I just find it's hard to kick over and doesn't want to start. So I just drop the oil from the bottom of the engine and then put it back in the oil tank. Takes just a few minutes. Though I think mine has done it like 3 or 4 times in the past 8 years.
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