BSA Owners' Club Forum

The BSA Workshop => Lightweights => Topic started by: Arthur on 02 February, 2017, 07:47:54

Title: BSA Beagle Rocker Feed
Post by: Arthur on 02 February, 2017, 07:47:54
Although the BSA Beagle 75cc engine looked like a small Triumph Tiger Cub engine, it was notorious in not being provided with a separate oil supply to the rocker boxes. This ultimately led to premature engine failures and the Beagle then being dropped from the BSA line up after just over a year of production.

One solution to the Beagle rocker box problem is to lubricate them by hand before each run out which is obviously less than ideal. I would be interested to know if anyone has implemented a better engineered solution to this problem which then makes the BSA Beagle a more practical bike to own.
Title: Re: BSA Beagle Rocker Feed
Post by: DEAN SOUTHALL on 02 February, 2017, 21:17:34
I never used mine enough for this to become an issue.

How about a drip feed tapped into the rocker covers fed by a small remote tank under the petrol tank.  They only need  a small amount of oil so it should hardly overfill the sump,
Is there a champhered oil hole on the top of the rocker arms or am I mis-remembering?
Title: Re: BSA Beagle Rocker Feed
Post by: Arthur on 02 February, 2017, 23:20:33
If I remember correctly, there are small oval cut outs in the top of the rockers through which an oil mist might have come close to lubricating the rocker spindles. I think your suggestion is definitely one up on taking off the rocker covers off before each ride out and pouring in a bit of oil. However, the positioning of the inlet to each rocker box would have to be carefully chosen as the oil would need to drip on to the holes in the middle of the rockers since that's the only way to get oil on to the spindles. This would seem to mean the inlets being in the rocker covers themselves although the inclination of the front rocker box would be a bit challenging.
Title: Re: BSA Beagle Rocker Feed
Post by: Arthur on 03 February, 2017, 07:30:31
Here's a picture of the Beagle exhaust rocker box in which you can see the small hole in the rocker exposing the spindle underneath. The only way of lubricating the spindle as it stands is by dripping oil into this oil which would be very difficult because the spindle is not far off being vertical. Also, you can't flood the inside of the rocker box with oil because there's a relatively large hole down to the crankcase caused by the pushrod tunnel which would drain it very quickly.

Edward Turner's scheme was that oil mist generated in the bottom of the engine by the rotating crankshaft would find its way up the pushrod tunnel and then find its way on to the rocker spindle to lubricate it. I don't think that was ever going to happen!!
Title: Re: BSA Beagle Rocker Feed
Post by: DEAN SOUTHALL on 03 February, 2017, 17:59:49
Oil mist rocker lubrication was pretty standard on pre war machines. Both my Sloper and Trike run quite happily with mist lubrication via the push rod tubes. However, both of these have open rocker boxes so do not develop positive pressure. Perhaps positive pressure in the rocker boxes can offer a resistance to the oil mist.  Indeed my pal suspected this was a problem with poor oiling opf the rockers on his New Imperial, which were sealed. He fitted a breather to the rocker box and this did improve matters.

Perhaps as an experiment you could run the engine without the rocker covers or with washers between the studs and the rockers to allow breathing and see if it appears the box is getting wetter.

Title: Re: BSA Beagle Rocker Feed
Post by: Arthur on 04 February, 2017, 11:48:11
My knowledge of pre-war motorcycle engines is practically nil but I'm very surprised that they relied on 'oil mist' lubrication for the rockers. However, the Beagle engine was effectively derived from that of the Tiger Cub/Terrier and they used a proper oil supply to the rockers. Had 'oil mist' lubrication been effective for this type of small engine, the Tiger Cub/Terrier would have used it I would have thought!
Title: Re: BSA Beagle Rocker Feed
Post by: ANDY HIGHAM on 04 February, 2017, 13:13:44
For oil mist lubrication to work the oil mist has to reach the part requiring lubrication. If the beagle engine breather was on the rocker covers, then oil would be carried to the rockers. As it is the oil mist is required to be forced into a dead end, it just won't happen
Title: Re: BSA Beagle Rocker Feed
Post by: DEAN SOUTHALL on 04 February, 2017, 13:40:36
I find it stimulating to have topics like this to debate. Garage work is as integral to the pleasure we get form our bikes as is the riding and its fun to explore ways of modifying and improving them. The great joy of our machnes is that BSA left us with loads scope for this!

Sometimes, if asked why we do it we set aboit some of our projects we c an only reply that we just fancy the challenge : look at the work they guy did to get an A65 head to fit an A10 - phenomenal.

But I  feel that sometimes people can hear of possible upgrades and assume these indacte a flaw with the original design more serious than it really is.

Last summer I was at a country show where a chap had trailered his just beautifully restored Beagle. Having rstored one myself some  time ago I went over to have a chat with him to learn that he hadn't felt confident to start the engine yet. So, as it was all set ready to be started, I offered to give him a hand. No amount of persuasion would get him to start it because , as he explained, he was worried the rockers would get damaged due to oil supply problems he had heard about!

I bet you'd have a problem using it daily but I'd put money them surviving the type of use we put them to.