G5 Oil Consumption

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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starfield181
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Joined: Wed Aug 18, 2010 11:56 am
Location: WILTSHIRE UK

G5 Oil Consumption

Post by starfield181 »

I took the G5 for its first longish ride today about 40 miles each way. I checked all the oil levels before leaving and again when I got home. No visible drop in gearbox or chaincase levels but the engine needed just over 1/2 pint to top up. So the good news is that I have cured the leaky gearbox and it would seem that I don't need to touch the output shaft oil seal after all. The oil leaks when standing were principally on the near side mainly to the rear and this remains the case but it would seem that the oil doesn't come from the gearbox and since the chaincase is still right up to the mark not from there either.

The engine never smokes and seems to have stacks of power, making light of the hills on today's route even with the strong winds. Since its engine oil I am losing it looks like its mostly coming out of the breather. One possible clue is that I checked the engine oil level immediately upon arrival and it had dropped but no more than 1/2" which is just a few ccs because of the shape of the tank. So the bulk of the oil was lost on the return journey. Outbound I kept the speed around 40-45, on the way back it was more like 45-50. Harder riding seems to increase consumption though 45-50 does not seem too extreme even with its current low gearing.

One other thing I noticed for the first time was a slight oil leak from the rear (inlet side) of the rocker box joint. That is the only visible leak on the engine but I don't think it alone could explain the amount lost.

The strong gusty wind made it an unpleasant trip but that and the oil consumption issue aside the G5 performed well and was enjoyable to ride.

Any thoughts on what I can do about the oil consumption (other than the obvious of taking plenty with me when going more than 30-40 miles)

Thanks

PeterF
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Ozmadman
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Re: G5 Oil Consumption

Post by Ozmadman »

I did 156 miles on the last rally day (to the rally and back and the ride out) with some extended riding at 60 mph getting to and from the rally and my engine oil level hardly dropped at all. There are not too many places it can leak if you discount the chain case, either sump plugs (easily visible), crankcase joint (not so easily visible if underneath) oil tank to crankcase (seen if you take the RH engine casing off), cam/points housing gasket (as previous)or oil seal (oil in the points housing), oil pump retaining screw o ring (leak between the back of the engine and the gearbox casing) rocker gasket and oil filter dome cap washer (both easily visible) engine breather (oil splashed over the rear of the bike (wheel and tyre) or lots of oil dripping from the drain hole if you have a complete chain guard fitted
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
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clive
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Re: G5 Oil Consumption

Post by clive »

If there are no visible leaks the obvious conclusion is that you are burning the oil, despite it not looking smoky, mind you I am not sure how you know it's not smoky at 50 mph because it's all going to be behind you! A friends 350 shortstroke burned vast amounts of oil but you could only see a puff of smoke if he gave it a real handful.
clive
if it ain't broke don't fix
starfield181
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Location: WILTSHIRE UK

Re: G5 Oil Consumption

Post by starfield181 »

Paul,

I am relieved to hear that they can retain oil when set up correctly. I had heard elsewhere that they were prone to substantial oil tank loss and that it was something i would have to live with. you mentioned cruising at 60mph, would Ibe correct in thinking that you have fitted a larger gearbox sprocket? Mine would be running uncomfortably high revs on its present gearing - 50 or so is about all I would want to cruise at especially given the rate at which the oil level is dropping. I was (indeed am) planning to fit the 20t sprocket when the need to remove the primary drive side arises. The imperative was to change the gearbox oil seal but that has receded for the moment.

Your list of potential leak points was very useful and I will work through them in order. What leaks I can see don't on the face of it seem to amount to enough to account for the size of the drop in the tank, but then neither did the leak from the k/s spindle at first. A lot of the places you mention have been examined informally when I had the outer cover off to do the gearbox and I would say that they are not involved, but I will re-check.

Clive, you may we right as clearly at 50 mph I cannot see what is happening behind but if it is leaving smoke, its nothing on the scale that my MZs can do if given some whelly after a prolonged slow running session. I took the plug out this morning and it is darker than I would have wanted but hard to tell if its oil or too rich a mixture. Its not a damp black so I am inclined to suspect the carb settings; these are still under the microscope anyway but I do not want to muddy the waters with too many queries in one post.

Thanks guys

PeterF
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Ozmadman
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Re: G5 Oil Consumption

Post by Ozmadman »

Hi Peter

Yes I have a 20 tooth gearbox sprocket fitted which also makes first gear useful again as before it was a waste of time using it. It's funny how we get concerned about the apparent high revs on these bikes with the standard gearing. I can't imagine a teenage owner back in the 60's being too concerned and I imagine most of these engines got a good thrashing trying to keep up with the Jap bikes. According to one road test they said that they need to be revved and thrive on it!! Maybe we are just not used to the noise and vibration which was standard back in the day? I think the maximum revs on one of these is 7200rpm at about 80mph (with standard gearing) so 60 mph shouldn't be stressing it too much I wouldn't think. Know what you mean about the smoke, the only time I see smoke at speed is when I ride my Yamaha 1974 RD250!!!! and that buzzes along as smooth as can be at 70 mph @6000rpm in 6th gear with no feeling of overworking the engine in fact, they are one bike that actually thrives on revs
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
starfield181
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Re: G5 Oil Consumption

Post by starfield181 »

Did another 60 mile ride with much the same result in terms of loss of engine oil. This time a friend followed me and no smoke was evident from the exhaust. No oil was lost from the chaincase or the gearbox either - hurrah for small mercies.

Finally figured out how to get the tank off to investigate (and hopefully cure) the top end leak. This is probably an own goal as the rubber gasket was not located properly in the groove in the alloy cover, about 2" was tucked inside the engine. All the oil leakage from the top end anyway seems to be traceable back to that point. This time I will make sure its glued to the cover before refitting it.

Sorting the top end leak may or may not cure the loss of engine oil completely, but it does at least remove one complicating factor. Dealing with these bikes is like peeling an onion.

PeterF
Steve S
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Re: G5 Oil Consumption

Post by Steve S »

Just read this post 7 years on and I've had the same issue with the inspection cover gasket which was properly seated but pretty ineffective. Replaced it with the spares scheme item which is a lenghth of fully round rubber rather than the half round one I removed. Perfect sealing now, clean engine!

Steve S.
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Ozmadman
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Re: G5 Oil Consumption

Post by Ozmadman »

It will end up half round soon anyway once it gets hot and cools down a few times. I put some Wellseal on mine and have had no leaks since
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
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