Crankcase Breather

[shaunstaples]

Had a look at my breather to check its condition and that the crank axle is hollow.
My Bike is a 1952 model 20 and was expecting to find "016676 DIAPHRAGM C/CASE RELIEF VALVE TWINS 1952-56 ONLY"
The Crank is hollow but instead of the Diaphragm its a ball and spring, the seat in the bolt has a rough taper/ bevel but not sure if it's standard or not?
In the 1951 book the crank is shown as solid and 1952 shown as hollow.
Has there ever been a ball fitted or is is a modification by a previous owner?
(With his 2lb hammer and chisel)

[SPRIDDLER]

Has there ever been a ball fitted or is is a modification by a previous owner?
(With his 2lb hammer and chisel)

IKBA about twins but it seems there was a ball and spring up to engine no. 7000.
Do these details of changes for '51 and '52 from the 'Technical Articles' help?

https://www.jampot.com/article_read.asp?id=20

[clive]

I think the ball and spring referred to is the oil pressure relief valve in the timing side. However the crankcase pressure relief on the twins was originally mounted at the back of the crankcase behind the primary chaincase, similar to the one fitted to the singles I think. In 1952 this was converted to a hollow crank with the bolted in crankcase pressure relief valve. Its illustrated at the end of the 1952 section linked by Spriddler and did not have a ball but a flutter valve. Looks to me that the ball was an owner mod because they could not get the little valve bit. The club sells the whole unit but I am not sure they sell the bit you are missing on its own. https://www.amoc-parts.com//store/comer ... duct=21220

[Duncan]

If you are thinking of replacement parts, based on the experience of friends I would recommend replacing the whole unit rather than parts of it, their problem was oil getting into and filling the primary chaincase through the valve, initially they tried replacing parts of the assembly without great success and it was not until they replaced the entire unit as one that the problem was resolved. It may be that the ball bearing was the previous owners solution to this issue.

[Groily]

I rather agree with Duncan and his friends' experience, having had much the same issue as well.
For what it's worth though, the fluttery disc is 0.6" diameter, 15 thou thick, with 4 crescents 45° 'wide' and equally-spaced cut in to a max depth of 100 thou. In extremis, maybe a 'make'.

crank relief valve assy.jpg

[shaunstaples]

[/quote]
IKBA about twins but it seems there was a ball and spring up to engine no. 7000.
Do these details of changes for '51 and '52 from the 'Technical Articles' help?
https://www.jampot.com/article_read.asp?id=20
[/quote]
Thanks Neville I read that on an older version of the changes and thought the same at first, but couldn't get past the 1951 picture of the solid crank axle.

Thanks Clive think your right, when I looked at the tapered seat its a bit like its been done with a "chattering drill" its not an even cut. I suppose if the spring is the original it will be compressed more by the ball than it would be by the flat disc. Also if the seat was able to make a seal then that could be related to what I saw initially on the rocker cover, oil was leaking when I revved it up? just looked pressurised.

Thanks Duncan I would probably have tried replacing just the disc!, but with the oil tap now I'm hoping to avoid it filling up.
When I went to buy the bike the previous owner had drained the crankcase, but when we started it oil was running down from centre nut of the chaincase and when I opened the inspection hole at home it must have been near on 1/2 full!

Thanks Bill will probably have a go at making one if its the whole unit only, I am retired maybe buy one when I reach 67 with my state pension if they haven't raised it again!
I have all the measurements printed out thanks.
Just the seat in the bolt, I'm guessing it was a flat machined face (before OGRI got his Black & Decker on it) ?
I can get my friend to machine the face then add the extra depth to the disc to get the same spring tension.(or a hollow shim behind spring)
It'll be a job to add to the winter list, hoping to get a few more miles on it now the weather is getting better. (its not my birthday yet)
If I could get the spring dimensions also please, just to compare with my spring?

Thanks again

[shaunstaples]

Just found this, so got everything I need with your dimensions Bill thanks

Twin Spring Data.JPG

[Groily]

Yup, I think you'd need to get rid of the chamfer Shaun, and make sure the disc sat 'nicely' in the main component.

I think I'd perhaps use a spacer at the other end of the spring (in the outer element) rather than make the disc thicker, just in case weight could mess up the suck and blow using the correct spring - but I don't know if it'd make any real odds (not the sort of thing one experiments with in the normal run of events!)
You can test it works by sticking a finger over the hole with the engine running to see if it evacuates pressure, but who knows exactly what volume should exit?

I've got a separate big diameter breather off the timing case on one of mine - a PO's affectation which I have retained from when the bike had a ridiculously overbored (to 70.5mm!!!) and extremely quick standard G9 engine in it (NOT a G11 or G9B), with very lumpy pistons, ported heads and twin concentrics. I never knew why it didn't explode frankly . . . . luckily I was able to get it back to standard before it did, with much help from T&L Engineering . . . But the timing cover looks 'interesting' and was quite nicely done. And who knows, might even be helpful.
Many Beesa pre-unit twin owners add extra breathing via a pipe off a rocker box lid, for added relief (they just have a timed breather with holes that align every rev or two as standard). Don't know if that's something anyone does with our twins if the standard bits aren't doing the job.
Lots of ways to skin cats, as ever, some of them may even work!

[shaunstaples]

I was thinking last night about putting my time into making two sandwich plates with four holes that press the shim together, then would be easy to make one.
Mine probably has a bit of breathing but if its not using too much oil, I'll settle for that.
I would do an additional breather but at the top and only in the rocker covers so it can be reversed. At the top also helps get moisture out, and hidden would be good.
I think an engine can run worn pretty well, but not worn out. Just might have to work round a few more things.
Standard sounds better too, that's ok for racing and a big pot of money.

Well got my first short ride on it today, only gear lever to drop one spline tooth, really enjoyed it, just need a mirror.

Very Disappointed with oil, its supposed to be straight 40, getting 100psi cold and barely 10psi after 5 miles. Oil wasn't that hot, I could dip my finger in and it was warm, the problem was there was none on it when I pulled it out! Honestly should be badged up for a singer sewing machine.
I think there will be a lot of pressure drop due to expansion, but this would be minimised with some decent oil. Not sure if I can mention brand but I'll use it in the oil can, not even in the mower!

[Groily]

Dunno about the oil Shaun. But glad you enjoyed the quick run out.
Cold, three figs psi is normal and the prv helps stop joints failing by blowing off. Hot,I'd be very pleased to see 1 bar of pressure - at tickover - (if I had a gauge on anything), so not sure 10psi quite hot is necessarily all that bad. A typical car warning light will flick on between 5 and 10psi.

If the return is good and if there's no tell-tale light rattle at light loads to indicate the beginning of the end for the b/ends, could still be fine down below. Only one real way to find out though . . . if you were so inclined and have time on your hands.
Always worth having a quick look at the crankcase filter, to be sure it's not blocked or collapsed and that the prv is not stuck 'open'.
I agree a worn top end could last for ages, but might cost you in oil and cause heavy breathing and general piston slap type noises.

End of the day, any major worries can only really be dispelled by doing the hard thing and taking it to bits to have a good look.