Oil - again

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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1608
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Re: Oil - again

Post by 1608 »

Adding additional breathers seems to be too readily adopted when there seems to be oil leaks. I know AMC didn't get everything right
( especially lubrication on the twins ) but if it was as simple as just adding or enlarging the existing breather system then they would have done so. I remember reading somewhere that there is an optimum balance required on a normally aspirated engine and it is possible to overdo crankcase breathing. I have never felt the need to alter the standard breathing on any bikes I have owned. Excess crankcase pressure is caused by wear .
Oggers
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Re: Oil - again

Post by Oggers »

It is indeed very difficut to tell anything! I have since whipped off the oil pumps and plate. I cannot see the additional hole as per Neill, but then again, the idler pinion is in the way - and I am not removing that just to see. Pig of a job it seems.

I am still leaning to fitting an additional breather at the top of the timing case to the rear - where it is higher. It cannot do any harm so why not. May reduce it to 1/4 inch as originally suggested to get a better fit on the slighly curved case.

I am also thinking of removing the felt filter in the oil tank to get the scavenge pump working as best as I can get it in an attempt to lower the oil level in the timing case. Any other ideas as to how to lower this oil level are welcome......

I agree that usually blow by is caused by wear of the rings and bores. The only (somewhat tenuous) response is that mine is newly built (less than 1000 miles) and the rings have not quite bedded in yet.
Mick D
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Re: Oil - again

Post by Mick D »

Hi

The primary chain case on my alternator single breathes through the annular gap between the sleeve bearing and the 'seal':
Chaincase Seal.png
And the hole drilled below the oil shield:
Breather.png
And if that's not enough, up the alternator loom grommet.

I know the singles have a different arrangement to the twins but if twins breathing was an inherent issue I think it would have been dealt with historically - I'd be looking why your's isn't working rather than modifying it to work.

Regards Mick
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Oggers
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Re: Oil - again

Post by Oggers »

Cannot say I've noticed any of these breathing holes on my twin - but then again I wasn't looking. I realize an addtional breather may be considered something of a bodge, but in the light of exhausting everything practical I can think of without tearing the bike down, I think it is worth a try.

Any clues as to how to reduce the oil level in the timing case appreciated - drilling holes in crankcases excepted! Felt filter in the oil tank will be removed - as a trial to see if that increases efficiency of the scavenge and thus reduces the level that way,
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Re: Oil - again

Post by 1608 »

I take it you have researched the Tech articles re twin problems re over oiling. It explains the drilling of the hole in the timing side cover I believe you refered to. I think that if you went down this road it would mean dismantling the c/cases as you wouldn't want any swarf in the engine. I believe the G9 set up is the same as my G12 so removing the idle pinnion shouldn't be a problem as it simply lifts off its stub axle. If you do this make sure the engine is in neutral relax the tappets and mark the corresponding teeth with Tipex or similar.
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Duncan
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Re: Oil - again

Post by Duncan »

Oggers wrote:I am still leaning to fitting an additional breather at the top of the timing case to the rear - where it is higher.
If you are convinced that you want to fit an additional breather consider putting it in a relatively inexpensive replaceable item like a rocker box or remove the dynamo and plate the hole off and make a temporary breather there see what improvement is available before damaging a serviceable timing case. You should also fit a one way valve like a Bunn? valve.
Remember that the timing gear will also throw oil up to the top of the timing case when running,
With the number of leaks that you appear to have I would start to question how well the jointing surfaces were prepared prior to assembly and the methods used.
Oggers
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Re: Oil - again

Post by Oggers »

This is a very worthwhile discussion so thank you chaps.

In short - I am not convinced by anything! Additional breather is a possibility and no more, and I would not like to spoil a perfectly decent timing case so alternative locations are much appreciated. I also take the point that this is bit of bodge and not solving the root cause. I wasn't aware the idler gear just pulled off. This will make things easier if I wish to drill the hole, and yes, I am very aware of getting swarf into the engine.

Thinking a bit more and I realize I am somewhat indecisive here as I do value all comments, I am going to adopt a more cautious approach.

Stage 1

Remove felt filter in oil tank to possibly improve scavenger pump efficiency and possibly reduce timing case oil level.
Use 20/50 rather than straight 50 to encourage better oil flow through all passageways, reduce viscosity and possibly reduce any blow by/crankcase pressure. I'm not convinced at all by the latter, but you never know.....

Test by riding.

Stage 2

Drill the hole as per Neill - if there isn't one already....

Test by riding

Stage 3

Check out breather on drive side. If all is well then introduce another breather - somewhere....
shaunstaples
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Re: Oil - again

Post by shaunstaples »

Was there a conclusion to this please?
Andy G
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Re: Oil - again

Post by Andy G »

As Oggers hasn't been seen again since June 2020, we can only assume that while investigating the issue, he discovered alchemy, and is sunning himself somewhere comfortable. Or he gave up bikes entirely and moved to Neptune, or (and this is my guess), the endless oil leaks were actually because his garage is situated over a natural fissure from under the north sea and he is now routinely selling crude oil to the Scottish Government.
Either or any way, I wouldn't hold your breath.
Mebbe PM him?
Bombling contentedly around rural Aberdeenshire
shaunstaples
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Re: Oil - again

Post by shaunstaples »

:lol:
This one I bought, I get the impression its not breathing properly, but not sure at the moment.
Breathers can be funny things with condensation if your not careful, my old t140 had a breather on the chaincase that was a pipe that went over the rear mudguard and the chaincase used to get water in all the time (Grey oil within a week or so)- especially when its cold weather. I used to only do about 5 miles to work so that didn't help. I tried it with a short pipe down under exhaust and that stopped it, but the pipe was always oily on end so probably was losing a bit of oil? The pipe over the mudguard was always blocked with yellow snot, so long breather pipes condense quite bad in colder weather.
As was said earlier id maybe try one in rocker cover, not just to get pressure down (if any) but also to get some moisture out of its breath? ( Bit like me with Asthma )
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