Sump Gauze Mystery

[courtney]

Hi,

Checked and tested the pipe was firm today and it was absolutely solid. Very carefully plotted the position of the hole, made and enlarged it until perfect then soldered around it to secure and clipped off any loose ends.

Either way, whether it should be there or not, it now has a filter to suit rather than being distorted to cope.

Thanks for all your replies on the subject.

Very neat job with that soldering. Looks good.

[AWJDThumper]

All the pictures I could find showed the PRV tube terminating above the gauze filter. However, the picture of gauze filter 41-0163 below seems to contradict this as pointed out by DaveH!

[Blackthou]

Thanks all for the compliments and AWJD for your continued research. The pipe does indeed stick through about 3mm.
I did contemplate soldering on a washer but having tinned it I decided not to in case it became loose plus the solder had secured the raw edges.

[Phil C]

Yes, very neat bit of of soldering. Must have been a bit tricky.  Phil

[Phil C]

One of the two holes on my (1965 B40) gauze is elongated, and I didn't know why. I guess as Dave says, for ease of fitment.  Phil

[Blackthou]

Now you tell me 

[Phil C]

Sorry, Rick, didn't occur to me to say anything about that or I would have.
But then come to think of it, I'm not sure the pipe on mine extends that far anyway, so maybe it's mishmash, as Dave says.

[Blackthou]

Only joking. You're always more than helpful.

[AWJDThumper]

I think one of the lessons to be learn from this in regard to identifying parts from the BSA parts books is that sometimes these can be a little inaccurate and may not show some of the important details.

The original sump filter for the C15 (40-0311) was 1-hole because the 1959 C15 PRV bypass was directed into the inner crankcase (I believe). However, when this was changed in 1960 (I believe) and the PRV bypass tube into the sump added, the sump filter/plate design was changed (41-0163) but the parts book drawings were not and still show a 1-hole filter (and no PRV tube).

Most of the examples I could find (see below) seemed to show the PRV tube terminating above the sump filter implying that a 1-hole filter was used in these cases. Although a little academic, it would be interesting from an engineering point of view to understand why BSA decided that there was a need for the extra PRV tube since it can be seen that the bypass passageway itself cast into the crankcase terminated only a cm or so above the filter. Maybe there was a problem with frothing without the tube but why did it have to extend into the sump below the filter?

[Blackthou]

Thanks for the additional info and continued fact finding.

It is a strange as pipes usually terminate below a fluid level to avoid aeration and it's not long enough to be in the sump itself. Also by being under the gauze anything it discharges is not filtered. A PRV should rarely operate either unless it was different back then.

Perhaps the oil level is deeper when running but I don't see how as if you're filling up faster than the scavenge pump can cope with, you'd end up with all the oil in the crankcase? The scavenge inlet only just pokes through but the sump is shallow there. I reckon there was 1/2 to 3/4 of a cup of oil in situ when I removed the sump plate.

Bit of a continued mystery but either way, better than it was.

[AWJDThumper]

I would expect the PRV to kick in at relatively low revs and the amount of oil from the bypass tube to increase with engine rpm. The problem with the bypass arrangement was probably foaming - that is, too much aeration of the oil jetting out of the end of the pipe. Although there's usually not a lot of oil in the sump below the filter, it was probably better to use what there was to try to cushion the impact of the jet of oil from the bypass tube than to let it splatter against the top of the gauze filter? As mentioned, they got rid of this problem in the end-fed 1967 C15 by routing the PRV bypass straight to the scavenge outlet port of the engine.