55 Primary chaincase - again!

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

55 Primary chaincase - again!

Post by Oggers »

Gents

Right, I think I have bottomed out the root cause of this problem! Chaincase still leaks - only drips - but annoying nevertherless. What seems to be happening is that the chaincase is filling up with oil, reaching too high a level, and leeching through either the clutch cover gasket or the filler hole gasket.

So where is the oil coming from? I can think of only two places.

1 - Wet sumping leeching from engine/crankcase when laid up. However, as a precaution against this, I remove the sump plug after a run, let it drain, then replace the oil before a run. Thus I presume it is not possible for the oil to build up in the sump and overflow into the chaincase.

2 - Breather valve u/s. I have pulled the outer chaincase cover and it seems fine. The Maltese cross plate thing looks fine, but I guess it may have been in a permanently open position allowing oil/condensate into the primary chaincase and thus filling it up. Is this feasible? Spring holding the plate looks fine.

Once again, your thoughts are very welcome.
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dave16mct
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Re: 55 Primary chaincase - again!

Post by dave16mct »

If you are draining the crankcase then it must be filling the chaincase when you're riding. The scavenge oilpump (rear one) may have a slight air leak between it and the pump plate. Is the return oil line restricted anywhere? Have you got one of the pattern oil filters that are turned over too far at the top, restricting the return? Have you got good compression (good bores and pistons/rings) not causing blow-by? Any blue smoke?
Dave.
Mick D
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Re: 55 Primary chaincase - again!

Post by Mick D »

Hi

Yep, you have a scavenge problem, start with the easy stuff as Dave says - do you see a good return in the oil tank, does temporary removal of the filter improve things?
Thinking outside of the box - is it possible to transpose the feed and scavenge pumps?

Regards Mick
Oggers
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Re: 55 Primary chaincase - again!

Post by Oggers »

Gents

It certainly appears to fill the chaincase whilst riding - problem is where from. To answer various points, return is good and strong, and return line does not appear to be restricted. Pump air leak - no idea, but screws on the pump plate were very tight. No idea about the filter, but I will check it out. I like the idea of removing it temporarily. I assume we are talking about the foam filter forward of the crankcase with the non return ball valve?

Engine is very recently rebuilt - no smoke at all after or during a run.

Many thanks again - all good stuff.
Oggers
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Location: Aberdeenshire

Re: 55 Primary chaincase - again!

Post by Oggers »

Another thought. To rule out - or not - the scavenge pump, any idea of just how much should be in the cases after a run?
Mick D
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Re: 55 Primary chaincase - again!

Post by Mick D »

Hi Oggers

The scavenge pump has a higher capacity than that of the feed pump, hence when you observe the return flow to the oil tank you should see an interrupted foamy flow, (after the pump has cleared any wet sumping that has occurred since last start).
If you see a steady liquid flow that would be indicative of poor scavenging.
If you see a steady foamy flow that could indicate an internal air leak.

Regards Mick
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dave16mct
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Re: 55 Primary chaincase - again!

Post by dave16mct »

Not sure how much should be in the crankcases, perhaps a cupfull. The filter I (and Mike) was referring to is the felt one in the oiltank. There are a lot of pattern ones which have the top folded over too far and it can obstruct the return pipe where you see it returning into the oiltank. There are only 2 places engine oil can get into the primary chaincase: through the main roller bearings or via the crankcase releif valve which holds the sprocket on the mainshaft. the spacer agimst the main bearing should be scrolled to fling the oil back into the crankcase. You can fit a seal to stop oil coming out here. Do a search to see how. The releif valve can only be tested by removing it a see if you can only blow through it from the engine side. You should only be able to suck air in from the engine side. The bleed valve in the pump plate might be blocked. This primes the scavenge pump to start it. If it's blocked the oil builds up too high before it starts pumping back to the tank.
Dave.
Oggers
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Location: Aberdeenshire

Re: 55 Primary chaincase - again!

Post by Oggers »

Gents

Many thanks. This is all very useful. I have the felt filter apart and indeed the ends are folded over the tube - inside the tube. Can I just cut them off flush to the tube ends? I'll wash it out with petrol anyways.

Incidentally, forgive my ignorance, but if this filter was restricting oil flow, then how does it fill up the crankcase with oil? Does it just relieve into there if the filter is obstructed enough?

Definitely more than a cupful after a run - more like 3/4 pint...
Mick D
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Re: 55 Primary chaincase - again!

Post by Mick D »

Hi

If the felt is turned over too far and blocking the return flow from the filter chamber to the oil tank the pressure increases downstream of the pump and reduces it's efficiency, this is compounded by the fact that now the filter will not go into bypass.

Try running for a couple of miles with the filter removed.

Regards Mick
rudelan_LAPSED
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Re: 55 Primary chaincase - again!

Post by rudelan_LAPSED »

No oil in chaincaise... only
Geloil 5095 on chains and. Clutch

-->>For grease lubricated gearboxes, characteristic for the years 20/40, it is not recommended to use a 'thick' grease because the rotation of the axles will fling the grease off and the gears will run 'dry'.
The use of oil, even viscous, is hardly possible, due to the only rudimentary sealing of these gearboxes.

The semi-liquid Restom Geloil 5095 is a thixotropic grease :

- Jelled at rest -gt; no leaks
- Liquid in motion -gt; lubrication possible without centrifugal action.

Does not affect the seals.

Features: Has an anti-corrosion action and high wear resistant properties.
Packaging: Can of 1 litre.
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