She's hot

[R]

Not only is it passing x cubic feet of air per minute, its vapourizing the fuel into the airstream.
Most cars have heated manifolds, to prevent carburettor icing from this.

I once had a split water hose which forced a rejig to the heating to go elsewhere,
and the result was carburettor icing HELL - the carb would ice up, block off the flow,
the engine would cut out, freewheel for a while, the blockage would melt,
and the whole process repeat. You wondered if it was going to get home.
(It was a damp day.)

I note the above mentions only half advancing the timing.
This means its running with retarded timing.
Most engines hate this, it can leading to overheating most promptly.
Riders really need to control this function quite diligently.

Not fully opening the air lever means its effectively running with the choke part/half on.
Most engines hate this, and will chuff black smoke and carry on.
Riders really need to control this function quite diligently.

[cardan]

Hi Billington,

I see - here and on the BSA forum - that your starting/running/gutlessness/overheating problems with this bike have been going on for some years. You don't deserve that!

A 1932 500 sv BSA should be completely reliable, pull like a train, and not overheat until it gets to 38C outside. It should cruise comfortably at 40 mph. However to make it like that - assuming all the mechanicals are good - it has to be properly tuned and maintained. No amount of random fiddling with the controls will make the bike run nicely if the valve timing/tappet clearances/ignition timing/points gap/carburettor settings are incorrect.

My number one suggestion would be to get a knowledgeable person to help you. If you bring it to my place (in Adelaide Australia!) I'll help you tune it, but is there anyone closer? This is really hard because the are lots of "experts" out there, but you need to find someone who understands old motorcycles and can do the work. Tricky these days.

Failing that, you CAN do it yourself. But you have to be systematic, and work through the issues one at a time.

Maybe start by being CERTAIN that the magneto points gap is set to about 0.012" fully open, and that the points open about 35 degrees before TDC (piston say 3/8" or 10 mm before TDC on a longstroke bike like the BSA) when the lever is fully advanced (tight wire). When you're certain of this, retard the lever fully and you will hopefully find that the points have just opened (maybe the promised 3 thou) at TDC.

Once completely confident that the ignition timing is right, you can run the bike at full advance - no fiddling - and move onto the next things... (in order - loosen the tappets to say 10 thou so there is no chance of them closing up while running, check that the valves are rocking - exhaust closing and inlet opening - at TDC on the non-firing stroke, clean the carb, check the main jet size, check the needle, set the idle mixture screw to a best guess - all the way in then 1 1/2 turns out from memory - fit a new Champion D16 plug, fresh fuel in the tank...)

Good luck,

Leon

[Oggers]

I think you are masking the root cause of the problem by fiddling with the air lever and throttle, and observing air temperature. You need to be far more methodical in your approach. A 500 SV BSA is a pretty numb thing, not too disimilar to my VB600, and there are not an awful lot of variables which would give you the problems seen. If it was running fine last time around, then my bet is still on muck in the carb - so clean it out. After that, think of things which have happened since which could possibly affect the running of the bike. Therefore - clean the points, consider introducing fresh petrol, and fix any air leaks which could have developed since - particularly at carb intake flange - as a lean mix will make the bike run hot. Failing that, then do as Leon suggests. Points gap, tappets, timing etc.     

[Billington]

Part of the problem is that the ignition advance/retard lever does not stop in position I have turned it to. It slowly returns to closed which equates to full retarded. The friction available on the lever does not seem able to overcome the spring in the magneto.

[Rex]

Is the Belleville washer missing then? It's a bit pointless if it doesn't stay where it's put.

[Billington]

Part of the problem is that the ignition advance/retard lever does not stop in position I have turned it to. It slowly returns to closed which equates to full retarded. The friction available on the lever does not seem able to overcome the spring in the magneto.

[cardan]

As Rex suggests, there should be a belleville washer (conical) or a wave washer (wavy!) between the top plate of the lever (which should be fixed to the boss so it can't rotate) and the lever itself. The nut/screw on top is meant to control the friction. If your washer is missing or tired, you'll have to find a new one. In the meantime, you can cut a washer or two from cardboard (cereal packet maybe).

Leon

[R]

And/or take it apart and degrease all the components then.
Sounds like what is missing is friction ?

[Rex]

That would be curing the symptoms rather than the fault. When assembled and working correctly they still need grease to give a smooth action.

[Billington]

I’m a little embarrassed to tell you this, however the reason why the ignition lever would always return to retarded was because the nut had worked lose, after tightening the nut I can run on constant full advance. I had previously identified that this nut would work lose so had put some lock wire around it to stop it turning, however over time the lock wire around the nut was insufficient. When I first realised this I thought that I had finally found the solution, but I’m afraid I’ve only found part of the puzzle, because after riding four miles on full advance at 17 C (air temperature) the bike was so hot that smoke was coming from the cylinder head. So it’s not the ignition timing.
Should I take the cylinder head off an look for heavy carbon deposits, could it be that I need to decarbonise my bike, would that make it run so hot? 

[cardan]

OK, but you need to understand that having the lever set to full advance doesn't mean that the timing is correct. Plenty of good advice laid out above.

Leon

[Billington]

My thinking has moved on to the point people have been making  about weak fuel mixture and leaks at the head gasket. I had checked and tighten the cylinder head bolt as part of my spring service notes after taking the bike off the road in the autumn, but I now realised that I had set my torque wrench to 30 newton meters, but my notes state 30 foot pounds, which would equate to 40 newton meters.

When I stopped the bike yesterday smoke was coming out of the head gasket, which would indicate that is not hermetically sealed, there was also a shiny oil mark on the cooling fins that come from the cylinder head. All this would point to the cylinder head not being completely airtight. If smoke can get out air can get in during the intake stroke.

I will set the cylinder head bolts to their correct torque setting and see if this makes a difference. If it does not I will remove the cylinder head anneal the copper gasket again and refit the cylinder head.

[R]

You will also need to check exactly where your ignition timing is at some point !

[cardan]

In the photo at the top of the page it's clear that the engine is cooked. Literally. You can't repeatedly ride an old bike until it stops from overheating and expect it won't expire permanently at some stage. Unfortunately, as we've said before, no amount of random fiddling with controls will make this bike work. Clean it, tune it, repair whatever needs repairing, then enjoy it.

If you're not prepared to to work your way systematically through the issues, or get someone to do it for you, it will never run correctly and you might be better selling it. Pity, as it's a nice old bike.

Leon

[Billington]

Yesterday, I tightened the cylinder head bolts to 30 foot pounds, then set the engine at TDC using a gauge I made from a wire coat hanger. After this  I set the contact breaker points gap to 0.003 with the ignition fully retarded, these are the instruction in the BSA book for my model.

Today I went for a half mile ride; I stopped early because it had started to rain hard; however I could see smoke coming from the cylinder head again. Hence the next thing I intend is remove the cylinder head anneal the copper gasket and use Wellseal to improve the seal.

I will take photos of the head and post them.

Thanks again for your advice.