Sump Gauze Mystery

[Blackthou]

Hi,

This afternoon I removed the little sump to check / clean etc. Firstly what a marathon task!! I loosened every engine mounting bolt ane even removed some but it was still quite a fight.

When I eventually got it off and cleaned it I was faced with a dilemma I've seen the subject on here before but believe this is yet another permutation. My gauze has 1 hole but I have 2 pipes. The first pokes through the hole in the gauze, fair enough. The second protrodues from the face and was embedded in the gauze distorting it.

I've read about non return valves, pressure relief valves  and guess it's a PRV and not an NRV. Neither pipe appeared to have a ball in it, again thinking the smaller one in NRV. 

The Haynes manual seems to totally disregard the C15's so no help there. Couldn't find any references on the Net. Should my bike have a gauze with 2 holes in it? I thought that was only on later bikes, mines a Dec 60 although the engine has no stamping on it at all. Is it an PRV?

Thanks
Rick

[AWJDThumper]

I'm sure there were posts some time back about someone having two pipes projecting down towards the sump filter but I can't remember the details and can't find the posts.

In principle, the only thing that should poke down is the tube from the oil pump which should pass through the hole in the sump filter and allows the pump to suck up (scavange) oil from the sump. It contains a ball bearing and acts as a non-return valve.

Is it possible to provide a picture looking into the bottom of the engine so we can see what the other pipe looks like?

[Blackthou]

Hi,
Sorry, I thought I had posted a picture. Here goes again and thanks for your reply.

[Phil C]

Back on 28 April 2018 I started a thread called "Oil return tube", which I think is probably the one AWJDThumper is thinking of? That thread is easily found - I did it by clicking on my name, then on Show Posts, then on Topics, and went back until I found it. Only took a minute. As you now know the date I think you should very easily be able to track back to it. I hope it helps.     Phil

[Phil C]

 Remember though, mine is a B40, not a C15. Not sure if that's relevant.   Phil

[Phil C]

An easier way - I've now resurrected that old discussion, so you don't need to track back to find it.  Phil

[Blackthou]

Hi Phil,
Thanks. I did find and read that last night and anything else on the subject. In theory it shouldn't have a second pipe until much later. I wonder if someone has fitted an upgraded or later model pump? I don't even know if that's possible physically or mechanically. Lots of things on the engine don't make sense. One thing though, I assume it's pre 65 as it has a distributor.

[AWJDThumper]

I have just checked my late model 1967 C15 and, although it is fitted with a pressure relief valve, it does not have this additional pipe into the sump. However, my 1965 B40 does appear to have the pipe and I'm not sure why especially as both bikes use the same oil pump. I think a bit more research is needed but if the engine has this pipe then it looks as though it is nothing to worry about!

[Blackthou]

Thank you for looking and the update. Much appreciated.

Indeed. Just a mystery I'd like to understand.

At the end of the day, the oil returns nicely. I need a 2 hole gauze then all's well but can't locate one anywhere. Maybe I'll have to modify mine?

[AWJDThumper]

I've now done a bit of research to try to clarify which C15's had the second oil pipe in the engine sump. The full understanding is hampered a little by the fact that the parts books do not show this level of detail and the second pipe is not shown as a separate part. However, my best understanding is as follows:

All the C15's had a pressure relief valve fitted whose hexagonal plug can be seen at the front right of the RH crankcase. On the earliest C15's (pre-1960), the pressure relief valve bypass was directed into the inner crankcase, I believe.

There may have been a problem with this arrangement, possibly with the excess oil finding its way on to the crankshaft flywheel and producing undesirable effects. Therefore, around 1960, the bypass arrangement was changed and a new passageway with a length of tube at the lower end was added beneath the pressure relief valve which vented just above the sump. On these models, the scavenge pipe from the oil pump projects down through the gauze filter but the pressure relief valve bypass tube terminates just above the filter.

However, with the introduction of the end-fed crankshaft in 1967, the pressure relief valve bypass was changed again and a new passageway was added directing the excess oil straight into the scavenge side outlet from the engine and thus eliminating the second sump pipe.

Therefore, my 1967 C15 does not have the second pipe (it has the end-fed crank) but my 1965 B40 does. 

[Blackthou]

Thank you AWJDThumper for your interesting reply and research. It is much appreciated and makes sense.

The only thing I may add is that my PRV tube terminates below the filter, hence the need for the second hole?

 

[AWJDThumper]

It's possible the PRV tube has slipped down over time (50 years) and it might be worth gently tapping the end of it with a soft mallet to see if it can be pushed back up (gently!). If not, I'm sure there is no problem with the way you currently find it.

[Blackthou]

Thanks, also makes sense and I will try as you suggest but if it doesn't move, surely the need for the second hole in the gauze as it rather distorts it? I can find its part number but not stocked anywhere.

[Blackthou]

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.

[DaveH]

Hi. The gauze for the later oil pump should have one hole for the scavenge pipe and an oval type hole (to ease fitment) for the pressure release tube.Over a period of 50 years or so it is not unusual in my experience for engines to become a mishmash of parts from various years.
Your adaption is impressive.

Cheers,  Dave.