Oil - again

Information relating to the Matchless G9 or AJS Model 20 500cc twin
Member
Posts: 135
Joined: Mon Jan 14, 2019 5:37 pm
Location: Aberdeenshire

Oil - again

Postby Oggers » Sun May 31, 2020 4:33 pm

Dynamo seal still drips. Not much, but still drips - annoying. A few weeps from a banjo bolt at the oil feed/return - don't know which at the base of the crankcase, and another weep now at the interface between block and crankcase. Whoever put this thing together needs a good thrashing!

A few Qs please

Perrty sure manual says use SAE 50 engine oil - so that is what I use. However, to alleviate oil pressure - especially on start - how about using Castrol 20/50? I have some knoching about.

Think I need the "special tool" to tighten the head bolts to try and cure the block leak. I have no suitable thin-walled socket. I assume club parts or is there a sneaky other way?

I balnked off the dynamo recess to check the crankcase joints before messing about with the dyanamo seal. All seemed well, but I did note the pressure at that joint from the timing case side was remarkably high. Much higher than I had thought. It even spurted oil a little from my clamped blanking plate. To alleviate that, I had thought of drilling a breather in it at the top of the timing case and checking the oil filter at front - the felt thing at the front of the crankcase. Never liked it, far too restrictive for my liking. If I remove it, would it this decrease the oil pressure in the timing case? I'll clean and replace it, but thinking of riding it without the filter for a while to see the effect it has on the dynamo oil seal.

Member
Posts: 2376
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Oil - again

Postby Mick D » Sun May 31, 2020 4:51 pm

Hi

Buy yourself a 3/8" drive set of sockets - you'll never use the same sizes in 1/2" again:

https://www.amazon.co.uk/Sealey-AK2676- ... B005TFRUQ8

if the timing chest is becoming pressurised it would suggest to me there is a breathing issue.

Does your 20/50 have a detergent constituent - if so I wouldn't use it on anything but a freshly fully reconditioned engine, (it will dislodge sludge/carbon and potentially block oil galleries).

Regards Mick

Member
Posts: 135
Joined: Mon Jan 14, 2019 5:37 pm
Location: Aberdeenshire

Re: Oil - again

Postby Oggers » Sun May 31, 2020 6:50 pm

Hi mick

The numerous oil leaks are fast becoming a real pain in the rear. I seem to be chasing shadows. Done everything and more by the book and following the good advice of you gents, but the thing still leaks like a sieve. Pity really as when it goes it isn't half bad.

Member
Posts: 135
Joined: Mon Jan 14, 2019 5:37 pm
Location: Aberdeenshire

Re: Oil - again

Postby Oggers » Mon Jun 01, 2020 8:39 am

Mick

I think you may be right regarding the breathing. I have been thinking a little deeper, re-reading various posts, and I have come to a similar conclusion. The bike is fairly newly rebuilt - less than 1000 miles since rebuild. It also kicks back hard on start sometimes and does not "feel" particularly revvy for a twin. In a sense, good compression is fine, but what I think is happenning is that the crankcase pressure is far too great for the small breather valve - under the primary chaincase to cope with. Also, from here it vents into the chaincase which is probabaly pretty much air tight, and may also explain why I also get a few weeps from the inspection hole and the clutch cover.

As regards the dynamo seal, it is similar failure mode. Crankcase pressure builds - finds its way into the timing case, cannot relieve, and forces oil through the seal. The only other way pressure can build here is that the timing case is full of oil - not credible in my view - but perhaps I'll consider drilling the hole as per workshop manual into the crankcase? in the event that hole does not exist.

In summary, I think I will introduce a breather hole atop the timing case. 1/4" should do it. Thinking of 1/4" inch tapped hole, into which goes a small BSP pipe fitting for a hose to the rear of the bike.

Member
Posts: 135
Joined: Mon Jan 14, 2019 5:37 pm
Location: Aberdeenshire

Re: Oil - again

Postby Oggers » Mon Jun 01, 2020 9:56 am

1/2" breather hole shoud do it more like!

Member
Posts: 1391
Joined: Thu Jul 04, 2002 12:00 am
Location: NORMANDIE FRANCE

Re: Oil - again

Postby Groily » Mon Jun 01, 2020 10:48 am

Before drilling holes in the timing case I'd check the operation of the flapper valve on the crank - and drill that hole recommended by Neill in the literature if you don't have it, as that reduces the oil level in the outer case.
The breather is unlikely to be stuck, I know, but strange things happen. It should emit little puffs as the pistons come down which you can feel on your finger, likely quite oily puffs if the engine has wet-sumped appreciably. But to check that, the chaincase has to come off.

I got the 'let's try a pipe to atmosphere' T shirt with my 500 when I had ongoing probs at the dynamo seal like you've got - and it made no difference, so I blanked it off again. I do have a big one to atmosphere on my 650, but that was made up by a PO for a very different engine, running ludicrously high compression, massively overbored and with a lot of other mods.

Thing is, the standard engine should be OK with the original disc valve assembly (which can be had from Club spares I think if need be), plus the additional hole the timing side case if absent, and if it isn't OK, there's something else not quite right.

If it's excess pressure that has blown the cylinder base gaskets, then applying extra torque on the head/barrel studs isn't a great attempted remedy (unless the bits aren't torqued up properly), because you could end up waisting the studs, or even worse, ripping the threads up at one end or t'other. Those base gaskets do fail sometimes, I've had to replace a few over the 45 years I've had the 500. If you were to replace them, you'd be able to confirm at the same time that your pistons/rings/bores weren't responsible for any excessive pressure.

Excess crankcase pressure won't be due to the presence of an oil filter, I don't think. The pressure in the chamber won't be any different whether the element is there or not - although oil would obviously be sent a fraction more easily on its merry way to crank and top end via the galleries and the oil distributor if it were removed as it wouldn't be passing through the felt/gauze. I would leave it and the pressure relief valve well alone as long as they're the correct bits for year and model, because - just my view - there's a risk of doing too many things at once and not being able to tell what has or hasn't made a difference.

FWIW I've run all my old bikes with shell bearings, without exception, on 20/50 since the stuff became generally available on every forecourt at the start of the 1970s. I can't ascribe any of the occasional unwelcome things that have befallen a multitude of machines over that period to the oil! Impoverishment, idleness, cack-handedness, all of those - but not the oil!

Member
Posts: 135
Joined: Mon Jan 14, 2019 5:37 pm
Location: Aberdeenshire

Re: Oil - again

Postby Oggers » Mon Jun 01, 2020 11:10 am

Groily - Firstly, many thanks for the reply. Flapper valve was working fine when I last looked. It has a very weak spring holding it closed if I recall correctly, so I cannot see an issue in its operation. There is also crud on the opposite face of the chaincase suggesting it relieves. However, it does vent to the chaincase - which is now very well sealed. Therefore, pressure may well build up in here, in turn causing backpressure, and also the oil weeps still seen at the chaincase - despite my careful attention, use of gaskets, use of club improved chaincase seal etc. Frankly, I don't think it is man enough for the job of venting properly - i.e. it's not big enough. It also fails to create a satisfactory pressure drop as it fails to vent to atmosphere. Both of these factors I don't think allow the bike to breathe properly and cause crankcase pressure to build up and the oil leaks witnessed.

Like you, I also don't think it is the oil per se or the filters. The pressure decreases after the oil pump and just volumetrically expands - into the timing case for starters! so I don't think it is a build up of oil pressure anywhere. I take your point about the drilled hole and that would certainly lower any oil level in the timing case, but not pressure I think. I'll think on that one.

I still think an additional breather is the way to go. All my other bikes have at least a 3/8 breather hole atop the crankcase, 1/2 or so on the larger ones. I cannot see any harm in it, so as 3/8 BSP taps are readily available, that's what I'll go for into the timing case. 1/2 taps seem stupidly expensive. 3/8 male BSPs adapter/hosetail for the hose are also readily available.

I agree on the 20/50 - again cannot see much harm in so doing until the bike is bedded in properly and these blasted oil leaks have disappeared!

Member
Posts: 2376
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Oil - again

Postby Mick D » Mon Jun 01, 2020 11:29 am

Hi Oggers

In my opinion, during normal running, the crank case breather is there to relieve blow by from the combustion chamber, not the difference generated from the swept volume of the pistons - if you think your pressure differential is greater than can be dissipated via the primary inner case mainshaft 'seal' you should be looking at your bore and rings.

Isn't there also a breather hole under the oil shield in the center of the inner case? The alternator singles have one.

Regards Mick

Member
Posts: 135
Joined: Mon Jan 14, 2019 5:37 pm
Location: Aberdeenshire

Re: Oil - again

Postby Oggers » Mon Jun 01, 2020 12:04 pm

Its surely there to relieve crankcase pressure - regardless of where it comes from. I appreciate that blow by is probably the main factor, but even on a tight engine, gases still get through. I am not going to start stripping it to find out - not yet anyways! Guess a compression check may help here.....

Breather hole - is this the same drilled hole in the Neill literature? Honest answer is I don't know, but I don't see how that hole helps pressure relief - just oil levels in the timing case.

Member
Posts: 1391
Joined: Thu Jul 04, 2002 12:00 am
Location: NORMANDIE FRANCE

Re: Oil - again

Postby Groily » Mon Jun 01, 2020 12:40 pm

It's so darn hard to tell Oggers sometimes! (Btw, I read what I said earlier again and should have put the words 'oil' or 'air/crankcase' in front of the word 'pressure' in a few places, but you could see what I meant obviously!)
No reason NOT to try an extra breather, none at all, if you don't mind drilling the case, and the flapper wotsit definitely works. (It is a light spring, yes, and in effect is one of those 'what's to go wrong' things, I agree.)
The curvature of the timing cover makes it important where you choose to drill! On a Matchie there is a flattish area on the top surface, on Ajays it's rather more curvaceous.
I suspect your engine probably has the level-reducer hole already, as most do - and yes, won't affect anything to do with pressure of any sort.

Having another breather, or a more effective one, might make the engine feel more revvable, that is certainly true. If yours is a bit slow to pick up, then there could be a problem, but I'm still a bit surprised because with my own 500, even with the crankshaft oil scroll replaced with an oil seal (which reduces what can pass into the primary - which just happens, Praise Be, to be oil tight at the moment too), the motor is very willing to rev. Too willing sometimes! As Mick says, there is very often a small route to atmosphere, even in the best regulated households, from the " 'seal' " as he put it! - on the gearbox mainshaft entry hole.
I can't help but still wonder, like Mick too, whether there isn't something in the top end that is causing the crankcase pressure problem, if it is that - and also maybe the blow-out of the base gasket(s). In theory the latter could also be caused by excess OIL pressure from the main gallery at the crankcase throat to the top end, but now we're getting into how much do we believe in coincidence!!??
(There's no other breather Mick, I don't think - just a hollow drive side mainshaft with a disc valve on the end, which opens as the pistons descend, to let out whatever it lets out. It's usually quite effective.)

Next

Return to G9 / AJS Model 20

Who is online

Users browsing this forum: No registered users and 6 guests