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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flap valve in crankshaft allowing oil into chain case

Postby rump » Tue Aug 18, 2015 7:01 am

to do 50miles a half a cup of engine oil will finish in the chain case. This on a G9 twin matchless. I use a tap in the oil line It is only switched on the day I ride, Iam about to fit a PCV IN EACH ROCKER BOX to reduce sump pressure. Has anyone tryed this. The motor is in good nick no blowby. Iam sick of pulling chain cases off and playing with main shaft flapper valve.

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Re: flap valve in crankshaft allowing oil into chain case

Postby robcurrie » Tue Aug 18, 2015 3:53 pm

Is the scavenge pump working properly? The flap valve should only be venting gasses with maybe minute amounts of oil mist.

Rob C

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Re: flap valve in crankshaft allowing oil into chain case

Postby rump » Wed Aug 19, 2015 1:21 am

The oil pump works great if I leave the oil tap open for days the sump fills then the pump shoots a full stream untill it catches up other chaps have simular troubles with the generator and magy filling with oil because of air pessure in sump

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Re: flap valve in crankshaft allowing oil into chain case

Postby bjork » Wed Aug 19, 2015 10:06 am

I tried to repair a flap valve on my old 600 twin numerous times with new springs or flaps. It only worked after I replaced the whole assembly (from club spares scheme) suggesting the seat in the valve is to blame. If you fit PCV's in the rocker boxes they could well do the trick, but you would need to seal the original valve off or pressure and oil would still go that route. I'd be interested to hear how you get on, as if this works it could be an easy solution to a couple of problems-don't forget to tell us!
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Re: flap valve in crankshaft allowing oil into chain case

Postby rump » Thu Aug 20, 2015 4:01 am

bjork you might be spot on as i broke my unit by over tighting i made a new one of high tessile steel and i was not sure of some depth measurments I tried to buy a new one nil instock now iam finding out mine has a fiber disk against the seat followed by the spring then the thin metal shim sitting back in the cap now iam being told the fiber disk should not be in there and the metal shim should go in first then the spring so i will try that.I still will go with the pcv valves in the rocker boxes as i have the valves. I will be away for 2 weeks before i can try every thing.

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Re: flap valve in crankshaft allowing oil into chain case

Postby Groily » Thu Aug 20, 2015 6:49 am

Probably is your problem, assuming your scrolled flinger is doing its job and isn't letting the oil through (per discussion in your previous thread on the same subject).
I made a flapper assembly one time, in an emergency when the whole assembly had sheared off and caused a 'failure to proceed'. Despite best efforts with measurements the result was very so-so. A new part cured it.
There should be no need to fit the extra breathers on the rockers as the symptoms you're getting aren't typical if other things are in order, but 'tis true that extra breathing can help revvability.
If you have a lathe, the oil seal mod is well worth the effort in my view.

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Re: flap valve in crankshaft allowing oil into chain case

Postby bjork » Thu Aug 20, 2015 9:08 am

That's right, the steel disc and spring is all that should be there. As Groily says too the seal mod on the oil flinger is well worth the effort. It also helps the breather be more efficient in its job. Also that there shouldn't be a need for rocker breathers, but if you find it easier to fit these than get a new standard valve assembly the experiment should be of interest.
If you have a number of valves I'm guessing that probably only one of them will operate (the one with the lowest spring pressure) unless they are all very accurately made and set up?
Genuinely interested to hear what the result is!
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Re: flap valve in crankshaft allowing oil into chain case

Postby rump » Fri Aug 21, 2015 9:59 am

G'day fellas, Rump's son here just trying to clarify a few things that Dad doesn't follow from the posts and I'll clarify a few things from his post. He has tried through the Jampot club and Andrew's Engineering to buy a new flapper valve for the end of the crankshaft but there are none available. Any suggestions as where else he can try to buy one?? (because the one in the bike is letting through a LOT more than a mist of oil)

Bjork, you mention the seal mod on the oil flinger and Groily, you mention the scrolled flinger. Where is this oil/scrolled flinger? What is it and what is the seal mod for it?

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Re: flap valve in crankshaft allowing oil into chain case

Postby bjork » Fri Aug 21, 2015 11:23 pm

Evening (well it is here) chaps, We are both talking about the same thing. The oil scroll is on the spacer that sits between the crank sprocket and the main bearing. If you remove the sprocket you can see it as the next thing to come off the crank. It sits almost flush with the outer edge of the crankcase and will need to be teased out with a magnet or tooth-pick type sharp pointy tool. It is a very close sliding fit on the crank and should be only just clear of the casing on its outer diameter-that is where the scroll is and encourages oil back into the engine, It is close enough that hardly any gas can escape outwards.

The mod is to reduce that outer diameter to the size of the oil seal that you fit straight into the crankcase hole. (I think 47mm seal O/D rings a bell) The first spacer scroll I did was ground down to the same diameter over its length. I recently had one for my 650 ground down only on the outer edges where the seal will run, leaving a flange to but up against the main bearing. It isn't absolutely necessary but made me feel better and I know a really good accurate grinding engineer. ;)
You could make a new spacer from scratch but most people either turn it down or grind the original part.
Not sure where, but there are pictures and measurements on the forum somewhere, may take a bit of searching to find it.
Well worth the effort though!
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Re: flap valve in crankshaft allowing oil into chain case

Postby ajscomboman » Sat Aug 22, 2015 7:02 am

We have had a small batch of breather bolts made but they're not yet listed on the system. I'll check today and get them sorted. In the meantime, Rump if you send a mail directly to spares@jampot.com requesting the part along with it's Pt No. we'll get it sorted. Just to clarify, we are talking about the 2 piece breather bolt for shock absorber crankshafts aren't we?

Rob

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