Author Topic: B31 question  (Read 284 times)

Online flashblack

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B31 question
« on: 11.04. 2021 13:27 »
Hi,. 
I'm trying to get to the bottom of a problem regarding the amount of oil exiting the B31 crank breather. 
I've checked all the usual stuff like the clack valve, cam seals, wet sumping,  non return valves, and  the oil pump has a good return flow. I did notice though, that the big end feed quill is way smaller than the hole in the end of the crank! To check it I removed the two rubber cam seals and offered the casing up till it was all the way home and was able to move the casing sideways and up and down quite a considerable amount. My question is, how can the oil not squirt everywhere when there is no seal on the end of the crank and with such a loose fitting quill?

I'd be most grateful for any suggestions as it's ruining an otherwise nice oil tight bike! I'd even consider a Bunn breather if they were still available.

Regards Richard
1959 golden flash
1949 B31 plunger

Online Bsareg

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Re: B31 question
« Reply #1 on: 11.04. 2021 13:55 »
The later cranks didn't use the quill but had a rubber seal similar to the cam wheels. Could it be that you have a later crank?
C11,B40,B44 Victor,A10,RGS,M21,Rocket3,REBSA

Offline Klaus

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Re: B31 question
« Reply #2 on: 11.04. 2021 15:22 »
The later or Goldstar Cranks are longer at this end to fit the rubberseal.

You can push over an O ring to the quill befor you fit the cover.

But most of the Oilsquirt to the breather is caused to blow by from worn out Pistonrings.

cheers Klaus


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Online flashblack

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Re: B31 question
« Reply #3 on: 11.04. 2021 15:32 »
That's interesting, I will try an o ring over the quill. I also previously found aluminium inserts instead of cam seals, and o rings fitted to the cam pinion nuts. I have since replaced with standard seals and nuts. Are they a later BSA part or homemade like they look? I have found no reference to them anywhere?
As regards blowby, it was rebored 900 miles ago so I may check it for a glazed bore

Regards Richard
1959 golden flash
1949 B31 plunger

Online RDfella

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Re: B31 question
« Reply #4 on: 11.04. 2021 16:07 »
An ill-fitting quill may reduce oil to big end but will have no effect on breathing. Never seen a B31 emitting oil from the breather yet.

Add: maybe a pic or two of the parts involved would help. I've had a B31 for over 50yrs. Beeen inside it many times as it was raced for over a decade but struggling to figure this problem out.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Offline scotty

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Re: B31 question
« Reply #5 on: 11.04. 2021 16:14 »
Ive got oil leaks galore on my B33 😃........
but strangely I don’t get oil coming out out of the stock breather/quill

Scotty

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Online flashblack

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Re: B31 question
« Reply #6 on: 11.04. 2021 17:54 »
Rdfella, here's a couple of pics.

You can see the cam pinion nuts with the o rings, they are a good snug fit in the rubber seals,so i've left them on.I don't know if the breather stand pipe is too short? It was just an open ended pipe that i crimped shut then drilled a hole in the side to try and cure this problem.
The quill measures 7/32" OD and the hole in the crank measures 1/4"

Regards Richard
1959 golden flash
1949 B31 plunger

Online RDfella

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Re: B31 question
« Reply #7 on: 11.04. 2021 19:48 »
Looks OK to me.
Pics below of my old race engine (reminds me, must dig it out and clean it up) pinched a few parts when I built a 500cc version following amalgamation of historic classes but I recall your breather looks original. My feeds for cam spindles didn't have O rings (no point going into rubber sockets) and were more acorn shaped.
If it's breathing a lot, how's the compression?
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Online KiwiGF

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Re: B31 question
« Reply #8 on: 11.04. 2021 22:08 »
That's interesting, I will try an o ring over the quill. I also previously found aluminium inserts instead of cam seals, and o rings fitted to the cam pinion nuts. I have since replaced with standard seals and nuts. Are they a later BSA part or homemade like they look? I have found no reference to them anywhere?
As regards blowby, it was rebored 900 miles ago so I may check it for a glazed bore

Regards Richard

Do you get much in the way of gases coming out of the breather pipe? Particularly at start up? I have run a rubber pipe to the rear of the bike from the breather, only the odd drop of oil comes out of it, and very little detectable gas, I don’t know if the length of pipe or it’s routing makes a difference, but it might.

From memory the breather pipe inside the case has a an entry hole that should point down? Is that right?

I don’t think there is a connection between the quill oil feed to the crank and this problem. Either you are getting blowby or the breather itself is at fault. The breather valve I found does not do much, I have run my bike with and without one (by accident) and not noticed any difference.

Coincidentally here is a pic of a breather for sale
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Online flashblack

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Re: B31 question
« Reply #9 on: 12.04. 2021 06:32 »
I don't seem to get gases out of the breather, just a steady drip of oil. The plug is oily, so I will be investigating any blow by/ compression issues with a look at the topend. Although compression is very good?
That breather for sale doesn't have a crimped end like others I've seen which have a hole in the side of the pipe which is supposed to point towards the outer casing and a bit to the rear. The one for sale looks like mine did ? I thought someone had chopped the end off?
1959 golden flash
1949 B31 plunger

Online chaterlea25

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Re: B31 question
« Reply #10 on: 12.04. 2021 21:29 »
Hi flashback,
In the photo advertisement of the breather unit it is apparent that there is a disc valve fitted in the union as used on almost all B31/33 M20's and so on
I wonder if the disc valve is stuck or blocked on your engine  *????*

The centrifugal action of the crank will suck in the oil from the quill , an O ring could get damaged and sucked into the crank oilways  *eek*

You could try removing the tappet inspection plate and run the engine to see if it has been pressurising the crankcase??
What make piston and rings were fitted at the rebore?
JP rings have a bad reputation for  not bedding in and causing blow by problems... so had the earlier plain boxed Wassel pistons/ rings where the rings were just crap

John


1961 Super Rocket
1963 RGS (ongoing)

Online flashblack

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Re: B31 question
« Reply #11 on: 13.04. 2021 06:26 »
Hi John,
The disc in the breather valve is free after a good clean with brake cleaner, it was gummed up when I first looked at it, as regards the o ring, I think I will leave that out now, I hadn't thought of the centrifugal force to help the oil on it's way!
I have got a jp piston fitted, but I didn't use the rings after reading the threads on here about them!
I originally bought a set of nos wellworthy milemaster rings, but the radial depth didn't match that of the pistons which had a deeper ring groove than standard. I bought a set from a ring specialist I have used before (turner and Cox) which consists of a chrome top ring and a tapered second ring.
I just wonder wether they haven't bedded in properly yet? It's still on less than 1000 miles since the rebore. Otherwise the compression is good and there is no  hint of smoke from the exhaust!
I'm undecided wether to check the bore and rings or to just continue riding it and get some more miles on it and hope it improves? It is a shame, because the bike is running lovely otherwise.

Regards Richard
1959 golden flash
1949 B31 plunger

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Re: B31 question
« Reply #12 on: 13.04. 2021 23:33 »
Hi Richard
Fixing the breather valve should sort things out hopefully, once the "modification" to its
standpipe does not affect things  *????*

John
 
1961 Super Rocket
1963 RGS (ongoing)