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AWJD

Here is my attempt to explain the difference in operation of the Zener diode with and without the battery being connected: In normal operation, the alternator output via the rectifier will charge up the battery until it reaches about 14.5V. At this point, the reverse bias of the Zener diode will app...

AWJD

In BSA motorbikes, the Zener diode effectively stops the voltage reaching the battery from the rectifier from exceeding 14.5V - it's basically acting as a regulator. It's unlikely that a defective rectifier could result in harm to the Zener diode. However, if the battery is not connected to the Zene...

AWJD

I wouldn't have thought you need heat treatment to enable you to remove dents from an aluminium tank - I'm pretty sure the professional don't do it that way. Aluminium is such a tricky material depending on the particular alloy, I would steer well clear of applying heat. In any case, 200 deg C sound...

AWJD

Timing spec is actually ok - the photo shows it's a B25

AWJD

You are quite right. The B50 owners manual gives the static timing as 30 degs BTDC as does Rupert Ratio. It is the OIF B25 that has a static timing of 37 degs BTDC. If the timing has been set at 37 rather than 30 degs then that would definitely induce pinking

AWJD

That does make sense in that if I dial it back a notch it seems to go fine. What does rather bug me is that it only pinks once its warm though wereas if it were a purely timing issue I would expect it to pink all the time. Still perhaps Im over thinking it thanks for your thoughts all. Pinking or d...

AWJD

Just looking at the figures: my B50 was specified as requiring fuel with an octane rating of no less than 98. Modern unleaded is about 91 and premium unleaded is about 95. So, even with the best unleaded, the timing needs to be retarded a few degrees to prevent possible pinking. I normally start wit...

AWJD

I'm actually about to put this bike up for sale and so this last minute problem almost threw a spanner in the works. In the end, I was glad I was able to get to the bottom of the problem and no real damage was caused. However, I'll be particularly careful next time I dismantle another steering head ...

AWJD

I suspect that it came from the steering head bearings when I overhauled them a few days ago. Inevitably, the old dry balls fell out as I removed the bottom yoke. I think it was just bad luck that I must have had the spark plug out and one found its way in. However, it was good practice for me to ha...

AWJD

Bugger!! The foreign object was a 1/4" ball bearing which must have been ping ponging around in the combustion chamber periodically hitting the spark plug and bending its outer electrode. Unfortunately, I had to take off the head to find it but, fortunately, it didn't do any real damage. I should ha...

AWJD

I think you're probably right - the head's got to come off!! I don't think it's possible for the piston to hit the plug and the only thing that makes sense is for a foreign object to be present above the piston which is too big to get blown out of the exhaust port but is big enough to bend the plug ...

AWJD

The B40 uses an N5 plug with a 3/4" reach. For some reason, the previous owner had used a plug with a shorter reach of 1/2" so that the threaded end wasn't long enough for the plug to reach properly into the combustion chamber. Since the outer electrode, even on the shorter plug, is being bent towar...

AWJD

I'm trying to get a B40 engine bike to run having stood idle since I bought it about a year ago. At that time, it ran fairly reliably without any obvious problems. I've done nothing to the engine since although I've serviced it and checked all the settings. It's fitted with a concentric carb althoug...

AWJD

I think they had to use up the non-unified nuts and bolts they had first before making the complete change over to unified. Found some BSA bikes from 1969 - 1970 a real challenge because of this sometimes

AWJD

The shouldered nut is part 29-2053 which is mainly listed as 5/8 x 20 BSC although some suppliers list it as UNF. Must be one of the few threads on a 1970 BSA which wasn't changed to UNF! That said, I had to time a 1967 B40 the other day and found the rotor strobe mark on it was completely wrong. I ...

AWJD

Victor500T wrote:Also, does anyone know the answer to my question about which way the oil rings go?

In answer to your piston ring question, look at this previous thread and see if it helps.

viewtopic.php?t=225

AWJD

When the marks on the crankshaft and camshaft pinions are aligned, the piston will be at TDC if I remember correctly. This means that when the crankshaft mark is at 12 o'clock, the piston is at TDC.

AWJD

It's a remarkably tricky bearing to remove. The one thing I didn't try was to use an expanding bolt to expand behind the outer lip of the bearing case so that you could apply force against this lip rather against the sides of the case (which would expand against the gearbox casing making it even har...

AWJD

Dave T.

Glad it worked ok - I find the grind stone on the Dremel to be incredible useful at times

AWJD

Yes an orange one!! The conical shaped one is probably best for getting into the far end of the needle bearing. As said, you are trying to grind a uniform small groove along the length of the bearing case until you weaken it enough to fracture. You need to be careful and accurate.

AWJD

I used a ~6-9 mm wide cylindrical grinding stone or a conical shaped one. It was fairly effective but you have to carry out the grinding carefully.

AWJD

I've removed quite a few of these and have done it using a Dremel and grinding bit in order to grind away a groove on one side of the bearing case after removing the needles. It's fiddly work but, once you've ground almost all the way through the metal from one end of the bearing to the other, you c...

AWJD

Normally, the brake plate has a boss on the inside which is pulled against the bearing inner race when you do the brake plate nut up. However, if the bearing is seated too far into the hub (because of missing spacer or circlip), the brake plate will bind against the outside of the brake drum. You sh...

AWJD

You haven't said which brake it is - 6" or 8"? When you say you have nipped up the front axle, do you mean the nut on the brake plate or the bolts on the fork leg caps?

AWJD

It always struck me that this was a bit of fragile way of sealing the inlet and outlet. Obviously, the mating surface on the bottom of the engine must be flat and undamaged. I would also check that the O-rings are as thick as possible so that there's plenty of O-ring projecting from the union mating...

AWJD

Plain round O-rings.

AWJD

It would worry me to use cap heads or even hex bolts because the threads in the head are easily worn or damaged. I've converted at least one of my unit singles back to studs. I also can't see any real advantage in doing this and think the use of nyloc nuts on the ends of the studs is very pleasing t...

AWJD

It's listed in the 1972 Parts Book as a +1 mm piston. I thought we'd established that your bike is a 1972 season bike (Aug 1971 - Jul 1972)?

AWJD

You can download it for Windows from:

https://iresize.en.softonic.com/

AWJD

I always get a little confused over this issue but your Sep '71 bike makes it a 1972 model. In other words, you need to look at the 1972 Parts Book rather than the intuitive approach of looking at the 1971 Parts Book!

AWJD

Sorry, I quoted the inner and outer lengths the wrong way round!! In practice, I would have thought the difference in outer of 48" compared with 49" is not going to make a lot of difference but might depend more on what handlebars you have fitted and what rise they have.

AWJD

From what I can see, 60-2083 has inner length of 49" and outer length of 53 but has no adjuster included at the handlebar end. However, 40-8615 comes with an adjuster at the handlebar end and has an inner length of 48" and an outer length of 54". So, it probably depends on whether or not you need an...

AWJD

Thank you Beat. I'll look, online and see if I can find a Rupert Ratio. Wow, I saw some on Amazon ranging from $83 to $4010 (must be the gold plated slip cover edition) Perhaps a B50.org member has a copy of the page I need. Clive Clive. You can find a copy of the B50MX Owners Manual on the followi...

AWJD

Its difficult to judge with the clutch still mounted on the end of the gearbox mainshaft - I think it highly unlikely that the clutch rubbers have disintegrated enough to allow you to feel play in the clutch centre with it is still mounted in the engine.

AWJD

The earlier B50's used screws but the later ones used rivets. If it was me, I'd seriously consider whether it was necessary to take it apart to replace the rubber inserts as it would be quite a challenge to remove the rivets and then to replace them.

AWJD

The only other special tool I've ever needed is a clutch locking plate - basically a plain plate with dogs on both the inside and outside edges.

AWJD

the t25/b25 models originally came with no greasing points, and as such over time the spindles would seize, making them a pain to remove. all the b50's had grease nipples, and I have never had any problems removing a spindle. I will continue to use the seals, even though its obvious bsa didn't have...

AWJD

I'm not convinced by the design of the B50 swinging arm bearings and seals. In a sense, the environment for these bearings is less demanding than for a 2R sealed wheel hub bearing which will last a very long time without any maintenance. Why you would need grease nipples for the swinging arm bearing...

AWJD

That's an interesting issue - I note the 1971 B50 parts book doesn't show grease nipples but the 1972 & 1973 parts books do. With seals fitted, the grease should not need to be replaced until after a very long period (same as wheel bearings). I wonder whether BSA reversed the seals when the grease n...

AWJD

The metal side should face away from the needle rollers and the rubber lip should point towards them.

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