55 G9 Primary chaincase

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Re: 55 G9 Primary chaincase

Postby matg80s » Sun Apr 07, 2019 1:13 am

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Last edited by matg80s on Sun Apr 07, 2019 9:16 am, edited 1 time in total.

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Re: 55 G9 Primary chaincase

Postby Mick D » Sun Apr 07, 2019 7:22 am

Oggers wrote:Oil pump seems to work fine enough, good splurge of oil though the return - but admittedly not checked it to see if it passing.


Hi Oggers

Your engine has two pumps one for delivery the other return, the above quote is relevant to the return one and not the one that can be responsible for wet sumping.

The engine utilises a dry sump oil system, the return pump capacity being significantly higher than that of the delivery one, so if the return pump is indication a good flow you can be reasonably assured the sump is dry in operation.

If the weather's stopping you using the bike at the moment make a dipstick from a piece of bent wire and monitor the level in the oil tank over a week or two, this will allow you to quantify the rate of wet sumping.

Regards Mick

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Re: 55 G9 Primary chaincase

Postby Oggers » Sun Apr 07, 2019 4:56 pm

Mick

Yes all understood. What I have at the moment is a container under the open sump. The level in the container has not risen over a day or so - but I'll leave it a while longer. You are right as regards the flow in operation of the return being a good sign, but I have known what looks to be a good return flow not being greater than that delivered - and thus wet sumping occurs when the bike is running. The test for that is run for 5 mins or so from a known dry sump condition, stop engine, drain sump. If I get more than about 100 cc, then I'm in trouble - or so the Triumph manual says.... What I was getting at previously - and perhaps explaining badly - is that wet sumping may be occurring when running rather than when not.

PS are you going to Crathes?

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Re: 55 G9 Primary chaincase

Postby Mick D » Sun Apr 07, 2019 5:20 pm

Hi Oggers

I see where you're coming from but think it would be highly unlikely for the delivery to exceed the scavenge and if it did you'd be blowing the contents of your oil tank all over the road in short order. Give monitoring the container more of a chance, or if you want a more visual indication, put the drain plug back in and remove 24 hours later, anything that comes out will have leaked past the delivery pump during that period.

Will definitely be trying to attend Crathes - not convinced I'll take a bike though as the prospect of a whole day there doesn't appeal. More likely to drop in on the Meldrum or Fyvie rallies and the Turra run.

Regards Mick

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Re: 55 G9 Primary chaincase

Postby Oggers » Sun Apr 07, 2019 5:27 pm

Mick

Well - I'll wait and see as you say. I'll be at Crathes - displaying with white 71 MG Midget with hardtop and flip front. Much better if it rains! Do say hello! Never been to the other rallies - any good?

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Re: 55 G9 Primary chaincase

Postby Groily » Wed Apr 10, 2019 6:08 am

Oggers wrote:Mick

If I get more than about 100 cc, then I'm in trouble - or so the Triumph manual says.... What I was getting at previously - and perhaps explaining badly - is that wet sumping may be occurring when running rather than when not.


A typical reasonable amount of oil to be in the crankcase on one of these is 8 fl oz approx, which is 200ml odd. That's after the motor has been running - no 'extras' due to trickle-down while standing. The Triumph info isn't really relevant, and in any case with their piston pumps, as mentioned, they don't suffer from the same things.
There isn't any route for the oil to get into the chaincase apart from seeping via the bearing or being forced through the disc valve breather on the end of the drive side mainshaft. An oil seal on the drive side case instead of the scrolled flinger can help on the former issue but would be addressing the symptom not the cause - there'd just be more oil in the crankcase!

Unless the oil pumps have been fitted the wrong way round - ie with the larger pump on the feed and the smaller one on the scavenge side - it's unlikely that it's wetsumping when running.

However, it can happen if the scavenge side isn't picking up properly . . . there's a drilling between the pumps inside the pump plate to prime the scavenge, and it has been known for scavenging not to happen until the timing case is pretty well flooded with oil if the return pump isn't priming properly. This would be evident by a lack of return flow, rapidly diminishing level of oil in tank, clouds of smoke and / or massive oil leaks and then a steady gush of returning oil, reducing smoke etc . . . as the level reduces in the timing chest and most of the oil is put back where it lives. Then the return flow stops again and the cycle repeats. But this is rare.

If when running the flow is always there on the return and the oil level in the tank stays constant, there is probably nothing wrong. I'd do what Mick says and see what happens.

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Re: 55 G9 Primary chaincase

Postby Oggers » Wed Apr 10, 2019 8:16 am

Groily

Thanks for that, useful info - especially as regards the amount of oil left in an allegedly dry sump system!....I will monitor any oil leeching past the pump when the bike is unusued. I replaced the sump plug two days ago, so I'll take it from there.

As regards wet sumping when running, I did think of the breather being blocked, causing crankcase pressure build up, and thus forcing oil into the chaincase from somewhere. However, as I now know what to monitor, I'll drain the sump after a run and note the levels before and after in the chaincase.

No smoke or horrible noises when running.....return flow looks good.

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Re: 55 G9 Primary chaincase

Postby clive » Thu Apr 11, 2019 7:39 pm

Oggers wrote:Groily

Thanks for that, useful info - especially as regards the amount of oil left in an allegedly dry sump system!....I will monitor any oil leeching past the pump when the bike is unusued. I replaced the sump plug two days ago, so I'll take it from there.

As regards wet sumping when running, I did think of the breather being blocked, causing crankcase pressure build up, and thus forcing oil into the chaincase from somewhere. However, as I now know what to monitor, I'll drain the sump after a run and note the levels before and after in the chaincase.

No smoke or horrible noises when running.....return flow looks good.


When I first built my twin I did not split the crankcases. First try starting it I appeared to get a good return into the oil tank. Rode it about 4 miles to the Ace Cafe and it started smoking badly. Rode it home and opened the inspection cover to the primary chaincase and oil poured out. Opened the sump drain when the engine was still hot and oil gushed out but so did a broken piece of piston ring. After that it was no problem. So it's possible even with a return flow at tickover to the oil tank that there is something blocking the scavenge pipeline from the sump.
clive
if it ain't broke don't fix

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Re: 55 G9 Primary chaincase

Postby Oggers » Fri Apr 12, 2019 8:18 am

Clive

More or less what happened to me - except for the smoking and broken ring. The question is - did the build up of oil in the chaincase arise beforehand due to leeching past the oil pump when the bike was not in use, or did it do it whilst running, because scavenge was blocked, breather u/s or something filling up the sump and consequently leeching into the chaincase. If my sump is dry-ish after first draining then leaving for a week or so, then draining again, then I guess the latter if it does it again.

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