flap valve in crankshaft allowing oil into chain case

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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Re: flap valve in crankshaft allowing oil into chain case

Postby ajscomboman » Sat Aug 22, 2015 4:09 pm

Carrying out some further research it appears that there is and never was a specific part number for the complete breather bolt assembly on shock absorber models up to 56. In there wisdom AMC listed the 4 components separately I suppose thinking that it could be overhauled using replacement components. 60 years on and having tried I know it doesn't work. Anyway we do have some breathers made up as complete units but have yet to list them with an appropriate Pt No. I'll discuss it with Gary on Monday morning and report back.

If we're talking about models from 57- which don't have shock absorber crankshafts then Pt No. 025526 is in stock and is a replacement for the 57 models which also had a breather that could be overhauled.

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Re: flap valve in crankshaft allowing oil into chain case

Postby stuart132 » Wed Aug 26, 2015 3:44 am

RE Flap valve Asm,
I purchased one recently from Steven at AMC classic spares, the complete asm. I also made the 'Oil Seal' conversion as per the technical article found on this website.
With my rebuild I discovered that the crankshaft had been replaced by the previous owner and used a 1950 crankshaft which did not have the breather hole all the way into the crankcase, (it did have the flapper valve asm screwed into the end of the crankshaft but of course, was inaffective) I had to drill through the shaft with a 1/4" drill. I would suspect this is not part of your problem but worth a mention and check.
Regards
Stuart

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Re: flap valve in crankshaft allowing oil into chain case

Postby rump » Wed Sep 02, 2015 1:59 am

Groil to fit the oil seal and grind down the oil slinger would be done when doing a rebuild as I take it the sump would need boring Iam doing catch up work now. I put a breather in each rocker box and one through the sump just beside the magneto. I have played around with flapper valve and re-machined the depth the cap screwes in allowing the flapper disk to stay in the cap. Iam running all breather hoses back into the air fillter I will report the results in about 2 weeks as there so many other things to be done before the wheels go back in. Thanks for your help.

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Re: flap valve in crankshaft allowing oil into chain case

Postby Groily » Wed Sep 02, 2015 5:31 am

Actually, no - the seal goes into the drive side without machining the crankcase - or mine did on my Mod 20.
With all that extra breathing you could probably disable the flapper by sealing it shut I would think - which would stop anything getting into the primary case that way.
It will be interesting to hear how things have gone when you get a chance to try!

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Re: flap valve in crankshaft allowing oil into chain case

Postby bjork » Wed Sep 02, 2015 10:04 pm

As Groily said, the seal fits in the original hole in the casing. It's only the spacer/flinger that needs machining to size. No need to strip the engine for this as it's all accessible via the primary drive casing.

Not sure I understand your mod to the flapper valve but I do think having that still in place along with extra breathers is pointless. The gas pressure out will take the easiest route (that's good) but the negative pressure as the pistons rise will draw fresh air back in. If they are into the air filter you could get too much oil mist in there (I think) You might be better off joining all the extra breathers together in one chamber then run a pipe to atmosphere from that, but via a single non-return valve. You won't need much volume but it will be better with a good positive shut-off action in the non-return valve.

Back to the pipes routed into the air intake/filter-lots of more modern engines did this but you also risk the motor regurgitating combustion by-products that can be harmful to it. As our old clunkers have a lot of that stuff floating around I would personally avoid it.
Using yesterdays technology to create tomorrows problems today

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Re: flap valve in crankshaft allowing oil into chain case

Postby rump » Mon Sep 07, 2015 9:41 am

the seal that will fit straight into the drive side sump would it be 2 and one thirty second O/D. would you know the brand name. I will be trying the breathers from the rocker boxes with out one way valves for a start if it dont work I will try with valves in as I have four ready to go.

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Re: flap valve in crankshaft allowing oil into chain case

Postby Groily » Mon Sep 07, 2015 3:14 pm

On my 500 I used 40-52-7mm.
Just checked a spare one, and offered it up to a '53 crankcase to see if it looks right. It does. If I recall correctly, I needed to get the case warm to get it in nice and squarely, then turned the scrolled flinger to 40mm and re-quenched in oil to get some hardness back into it. 7mm is wide enough (almost too wide on the early engines, but the lip is where it needs to be).
On another engine, which was having major crankcase surgery, I went 40-55-7 - that won't fit.
40-52-7 is a standard size seal, or was when I did it, and cost very little. Should be available from many a bearing stockist I think. No maker's name on the loose one I have here.
Hope that helps.

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Re: flap valve in crankshaft allowing oil into chain case

Postby rump » Tue Sep 15, 2015 2:34 am

No luck with all the breather pipes or the modified flapper valve in the crankshaft. By bringing up the oil seal size on the computer for the drive side sump there are none listed in Australia but some in USA so that is the next job. Thanks for the help from everyone. RUMP.

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Re: flap valve in crankshaft allowing oil into chain case

Postby Groily » Tue Sep 15, 2015 6:15 am

Here are a few links, inc one in NZ, for the oil seal, taken from a google search on my machine of 'oil seal 40-52-7'
40-52-7 R21 Metric Oil Seal Rubber Covered Case Single Lip
www.bearings-direct.com/...Oil-Seals/40 ... e.tpl.ht...
A 40-52-7 R21 Metric Oil Seal Rubber Covered Case Single Lip - Inside Diameter: 40mm, Outside Diameter: 52mm, Width: 7 mm.
40 X 52 X 7 R23 Trailer Oil Seals Metric & Imperial - Bearing ...
www.bearing-king.co.uk › Bearings
40 X 52 X 7 R23 - Double lip nitrile rubber metric rotary shaft oil seal with garter spring 40mm inside x 52mm outside x 7mm wide.
40 52 7: 40X52X7MM Oil Seal Metric - Farrell Bearings
www.farrellbearings.co.nz/shop/.../Oil+ ... -52-7.html
NZ$7.24
40 52 7: 40X52X7MM Oil Seal Metric. ... 32 62 8: 32X62X8MM Oil Seal Metric. NZ $5.19 excl GST. Qty. 43 55 8: 43X55X8MM Oil Seal Metric. NZ $8.71 excl GST.

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Re: flap valve in crankshaft allowing oil into chain case

Postby rump » Sat Sep 19, 2015 7:35 am

Groil, you must be magic with computers any how I now have the seal thanks to your directions.Now if or when I machine the oil flinger the flinger will only be about 3 m.m. thick is that strong enough considering the compression effect coming back from the cam, engine shock absorber. rump.

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