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Re: 1929 Sloper oil feed to big end question
tzrewinds #649091 04/18/16 1:23 pm
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jemsk Offline OP
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Thanks very much tzrewinds, this is very useful info. I haven't visited here for quite some time as several of the earlier replies seem to be from people who have no first hand knowledge of early BSA engines but just want to pass critical comment

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Re: 1929 Sloper oil feed to big end question
jemsk #649119 04/18/16 5:50 pm
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Hi,
Quote
These bikes original pistons have no Oil ring of course, and there is no engine breathing,


Theres a drilling through the drive side mainshaft and out through the cush drive assembly to vent and lube the cush drive
I'm not very familiar with the sloper engines but have a couple of earlier L vertical engines, theres a breather on the drive side of the crankcase on these
I have rebuilt Blue star and Empire Star engines , but cannot remember the breathing arrangements
When the crankcase contains the oil reservoir theres more volume to accomodate crankcase pressure, but there has to be an outlet somewhere, theres no "seal" on the drive side bearing just a felt washer on some models which will also vent
The mid thirties BSA's have a spring loaded bronze plunger up against the mainshafts female taper end

The slopers were as far as I know the first BSA's to have an oil feed to the bigend, before that oil was just drippled into the crankcase and left to find its own way to the bearings and bushes
This was a common feature on most of the vintage era bike engines

Ariel engines have a small diamater quill sticking into the mainshaft end, no seal involved, centrifugal force sucks the oil to the bigend

Regards
John


Re: 1929 Sloper oil feed to big end question
jemsk #749202 09/14/18 10:07 pm
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Hello, I have a BSA Sloper 500 OHV 1931. I was wondering how many a turn should I go for with the oil pressure screw? Can it be that too much pressure can cause a bit of oil getting into the cylinder head area?

Re: 1929 Sloper oil feed to big end question
jemsk #749219 09/15/18 1:07 am
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From your pics, that shaft looks rough in all respects, not only does it have a partial thread on it, but the flats on the threads and the centre bore at the end look very rough. I really don't think those are original.
I have no doubt that the original shaft would have been a smooth and close fit to the bush. In which case it would work perfectly well for the B/E supply, as it does successfully in many designs.
I am more familiar with the similar setup in pre-unit Triumphs, which have a relatively high capacity pump. In your case, with a fairly small delivery pump to a roller B/E, I find it meaningless to speak "oil pressure on my tank-mounted gauge drops from 3 to 1 PSI as the seal eases off". I really cannot see the pump generating any significant pressure, with a "seal" between nut and bush or not.
What is that seal between nut and bush? It is not evident in the diagram kindly posted. All I can see is a concavity of the bush face. That is curious though, anyone know the reason for it?
"(At least the spiral tends to push the oil back in to the bush eh!)"
As best I can see, it's a left hand thread on that shaft. I don't know if the engine runs "backwards", but if not, then not so, so the thread had a tendency to divert the oil flow from the supply to the timing case.
With a small delivery pump, this is not good.
Kom's mechanism is fine with full flow, but in this system there are air gaps. The air will so easily escape via the clearances and threads.

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