Felt oil filter cap

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Titch
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Felt oil filter cap

Post by Titch »

Hi, I recently purchased a 1963 AJS model 31 that was restored many years ago but never used. The felt oil filter relief valve cap was re chromed which damaged/corroded the ball unfortunately the club spares do not have a stock of this type of filter relief cap. I do have very good earlier model valve cap with a screw in the centre, can I use this in place of the later model cap ?
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dave16mct
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Re: Felt oil filter cap

Post by dave16mct »

No, you need the cap and filter in one piece. By felt filter I hope you mean gauze filter covered with felt which is in one piece with the cap? By the way it isn't a relief valve, it's a one way non-return valve to prvent oil draining down from the rockers.
Dave.
Titch
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Re: Felt oil filter cap

Post by Titch »

I have a real problem it would appear, the filter I have is a felt over metal gauze and as you say doesn't appear to be the correct one. I've checked the oil galleries and it appears the oil enters the filter housing from the pump through an angle drilled hole then passes into the filter through the valve in the cap and into the main bearing feed up to the cam oil regulator/distributor. It would appear I could use the felt filter? but I'm missing some parts. The AMC parts supplier describes the cap I have as a relief valve. Any help as to where to get the filter assembly describe would be really appreciated.
Cheers Lionel
Groily
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Re: Felt oil filter cap

Post by Groily »

Confusion often reigns in this area, as people describe things a bit loosely sometimes.
I think the following is a reasonably accurate description, but am always happy to be put right by them as knows better!

Pressure relief is handled either by a valve at the timing cover end of the filter chamber (more than one version, early ones 'not captive' and fall out when you take the timing cover off, later ones retained in place) or by a valve on the oil pump plate body. They have the same objective. (Some engines didn't have a valve at all, however, but not I think yours. The factory did without for a period in the late '50s I think, and then reverted to using one again.)

The shorter earlier filter, associated with the multi-part dismantle-able cap at the drive side, is free to slide across the filter chamber against a spring.This is with the 'non captive' plunger and spring on the timing cover. These filters are a felt tube with end pieces comprising a steel dished disc (timing side) and an ali piece with deep recess for the spring (drive side) both gently fitted into the hollow ends of the filter tube.

With the longer fixed filter (plain gauze, or gauze with felt sleeve), pressure is released by the similar valve which is retained in place mechanically. On later engines, relief is by a valve on the oil pump body. There be people here who could give chapter and verse as to years and models.

In the drive-side end cap there is a ball and spring. Detachable on early motors, sealed in on later. This is an anti-drain valve, which prevents the oil in the engine draining back into the filter chamber etc when it's stopped, so in theory there is oil in the upper half of the motor and all the galleries north of the ball and spring for the next start-up. From the ball and spring, the main oil feed goes straight to the centre main bearing where it splits equally for the big ends via the crank. That's the majority of the oil; the rest goes via the distributor bush (2 types, one with a hole, one with a flat - later engines - and they interchange) to feed a gallery at the rear of the cylinders and thence up drillings in the cylinders and heads to feed the rockers etc. Also, to lube the bores.

There are loads of minor differences over the years. The gallery for the top end feed may be created by annular grooves in the cylinder spigots (early motors), or by a machined groove in the crankcase casting (later motors, yours included). And as mentioned, some engines had no pressure relief valve at all.

It all tends to suggest that the factory was never quite 100% happy with the arrangements. But that said, I have one early-ish set-up (Mod 20, '54) and one intermediate set up ('61 Mod 31) and provided the right bits are used, I've never had a problem. A word with Steve Surbey at AMC Classic Spares might help you -it certainly has helped me over the years! I THINK my 650 engine had a plain gauze filter initially, but now has a felt-covered one on coarse gauze frame, which has been fine for over 10 years. I suppose in the worst case, one could leave the filter out by detaching it from the drive-side plug (soldered on as I recall), especially if using a typical add-on filter on the return line . . . ?
Titch
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Re: Felt oil filter cap

Post by Titch »

Hi, thanks very much for your help. I have now sorted the parts of my filter, I have cap with a hole in the centre, then the felt filter then with what the book calls a blow off valve pushed in the end. This has spring in the centre which contacts the non return valve chromed cap. Apparently if the filter gets blocked the blow off valve slides out of the filter slightly to allow oil to flow to the big ends etc. This is all good in theory but all assembled in the filter chamber everything is tight with zero clearance for any movement of the supposed blow off valve. I guess something is still not correct.
Groily
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Re: Felt oil filter cap

Post by Groily »

Sounds as if you have got the earlier assembly, whereas per previous comments you need the later non sliding type with the filter attached to the inner end of the one-piece drive-side plug.
In the pic, two versions (my 'alternates' at oil changes).
Top is the sliding sort with steel disc and (long-ago home-made) ali valve (no spring shown). For my Mod 20, 1954
Below is the one piece item, felt covered in this case. For my Mod 31, 1961
I am not certain as to the exact combination of bits on a 1963, as you could have fat oil pumps, prv on the body etc etc, but you'll need a one piece filter, that's pretty much certain. I think I'm right in saying 'Do Not Proceed' with the sliding sort, but don't know for certain whether it invites disaster or not
twin filters.jpg
I said earlier the sliding sort was shorter - I think that's a 'specsavers moment', as not true! Just seems smaller as not attached to the anti-drain bits.
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