Rocker oil feed

[BruceB]

Going over my new Spitfire I have noticed there is a blocked pipe coming from the return pipe into the oil tank that would normally feed the rockers. A pipe from the rockers dives under the engine (haven't got under to find out where yet but assume an alternative oil feed from somewhere else)
When the SRM conversion is done is the rocker feed diverted from somewhere else and the original return feed made redundant? ie can I safely block off the spigot from the oil tank that originally went to the rockers rather than have a bit of pipe hanging down doing nothing and is the oil feed coming from the bottom of the engine part of the SRM works?

[Bess]

Hi,
    In Sept 1966 BSA issued a service sheet to improve camshaft lubrication. It had a list of parts to carry this out, a new crankcase oil pipe union where the oil to the head comes from under the engine. The original feed from the top of the oil tank was plugged.

It seems from your description this has happened. Later models were dispatched with the new oil union under the engine and an oil tank without the oil feed.

Best wishes... 

[BruceB]

I had assumed because SRM had rebuilt the engine that maybe they had made the mod but if it is an inservice mod that is great. I can permanently block off the spigot and remove the bike of old manky plastic hose that hangs down the back of the carbs without worrying I am doing anything bad.

[Bess]

Hi,
    BSA suggested cutting approx 2" of hose, fit onto pipe at the top of the oil tank, blank the other end with a rivet securing with 2 hose clips either end.

Whilst building my bike I brazed the oil tank pipe end and finished with a plastic cap end.

Best wishes...

[Taffyboy]

Could you just splice a T piece into the oil  pipe? Seems a bit cheaper then a new pipe union. (don't seem to be available anyway). Than blank the spigot left in the tank...?

[DAVE BRADY]

Hi,

Thinking about this I was wondering if the difference in the angle the feed leaves the main union is what gives a better feed.
Oil being pumped along a tube is more likely to bleed in to a smaller side pipe if the angle is less than 90º.  If at 90º then the oil will follow the line of least resistance which is the main pipe.

Dave.

[Bess]

Hi,
    Dave is hitting on the problem which can be quite complex, worth reading this:

https://neutrium.net/fluid-flow/pressure-loss-from-fittings-equivalent-length-method/#:~:text=The%20equivalent%20length%20method%20(L,at%20that%20corresponding%20flow%20rate.

Best wishes...

[DAVE BRADY]

Hi Bess,

I had look at the article and to be honest I did not quite get it as it is complicated as you said.
A simple analogy could be a fast and busy one way street with a small side road. To get in to the side road if is at 90º to the main road requires slowing down so that the momentum and the drag of the main traffic does not carry you past the junction.  If the road leaves at an angle of 45º then less slowing is needed and this makes the turn a lot easier.  30º would make it even easier.  The smaller size of the road (rocker feed) presents a limited resistance that has to be overcome.
In our bikes I would think that this serves to keep the main pipe as the line of least resistance so almost all the oil goes back to the tank and just enough gets bled off to feed the rockers.

Dave.

[Bess]

Hi Dave,
             Good analogy.

The equivalent pipe length system is mainly used by humble plumbers as it gives a speedy way to calculate pipe diameters to keep pressure losses within requirements. Using a swept tee or better still a 'Y' piece would be preferable.

There are still some BSA unions still about:

https://www.ebay.co.uk/itm/BSA-A65-A50-L-T-F-R-ENGINE-OIL-PIPE-UNION-LATE-68-0942/353286646679?hash=item5241866b97:g:08gAAOSwS4dfuMEc

https://www.ebay.co.uk/itm/BSA-A50-A65-NEW-OLD-STOCK-OIL-FEED-PIPE-68-0920/164532845160?hash=item264eebfa68:g:whsAAOSwMJZfvDFY

Best wishes...

[DAVE BRADY]

Hi,

Both of my A65s have the later union and I have a spare.  There might even be an early one somewhere in the shed.
Interesting that the A10s have a banjo off the return which in theory is less than ideal but the A10 has the oil trough for the cam to run in.  This however did not make up what appears to be a less than perfect cam follower design as A65 ones seem to last a lot longer than A10 ones.

Dave.