Hello, I hope you can help me I don’t have a war time motorcycle but I do have a 1932 BSA 500cc side valve, W32-6. Which was the predecessor to the M20 which I know you have lots of experience with.
My bike will start on the first or second kick and then pull beautifully on full advance and the air lever full open. However after 2 or 3 miles (depending on air temperature) the engine is so hot that it heats up the carburettor resulting in vapour lock. If I wait until it cools down it will run again. The carburettor is fitted with a 5mm Tufnol spacer, but this is insufficient at stopping the excess heat transferring.
What could be causing it to overheat? It was fine last autumn when I drained all the fuel from the petrol tank and carburettor for winter storage.
Thank you for any useful advice, I will near Halesown in the West Midlands.
The two potential causes of overheating are incorrect ignition setting and a weak fuel/air mixture.....Start by checking the points gap to determine that it is correctly set...If it has moved it alters the timing...Next check the ignition timing setting. Once done and determined to be accurately set that will eliminate one thing from the equation.
If the problem persists go down the route of looking for causes of weakness...Carb settings, a blockage causing reduction in the fuel supply, air leaks at the head gasket, spark plug or the carburettor flange joint for example...Also check the valve lifter is correctly set with sufficient clearance when the engine is hot...Finally check that both tappet clearances are set accurately and not too tight...
A 5mm insulation spacer should be sufficient under normal operating conditions....Ian
email (option): ian@wright52.plus.com
Thank you Ian, I’m grateful for your advice. I believe the contact breaker points gap should be open 0.003 inches when the piston is at TDC and the ignition fully retarded. However it currently is 0.08 inches, so I’ve ordered two Ex - Military Magneto spanner sets so that I can correct this.
The timing on the magneto was set by following the instructions in the BSA book for my model in 2017 after having the magneto/dyno rewound. The timing was fine then and it has not been changed since, so I’m hoping that after I’ve changed the contact breaker points gap the timing should be okay.
I think your most pertinent point is 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 fines 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.
Does your model have a 'composite' head gasket or a solid copper one?....If it's the former I'd remove it, throw it over the nearest hedge and replace it with a solid copper one... (just my opinion)...If it's a solid copper gasket you may get away with just tightening it down...If not remove it, normalise it and refit...If you still have problems after that consider some sealant such as Wellseal..Saying that I never use sealant on my M20 with a solid gasket....A solid gasket of .040" (1mm) thickness should work well..Ian
email (option): ian@wright52.plus.com
I currently use a copper gasket, which I purchased from “Copper Gaskets Unlimited” ( www.coppergaskets.us ). Previously I used a composite gasket which blew a hole, this was the source of much head scratching until I noticed I could feel the compression stroke if I put my hand to the cylinder head.
Without forums like this and people willing to give friendly advice I would be hopelessly lost, so I’ve just made a site donation.
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.
I think you are miss reading your manual? The points gap should be set to 0.012" with the points fully open (the easiest point to check them is at or just past the 12 o'clock position).
The ignition timing should be set at the fully advanced position with the piston at 7/16" BTDC on the compression stroke. At which point the points should be just breaking.
Traditionally a fag paper was used to detect the parting of the points. But I use a 0.0015" feeler gauge.
This is all best done with the head off to accurately measure the position of the piston. Ron
email (option): ronpier@talk21.com
The ignition timing should be set at the fully advanced position with the piston at 7/16" BTDC on the compression stroke. At which point the points should be just breaking.
Traditionally a fag paper was used to detect the parting of the points. But I use a 0.0015" feeler gauge.
This is all best done with the head off to accurately measure the position of the piston. Ron
It is a W series engine not an M series and the instructions are to set the timing at TDC on full retard to 0.003"
The W is 85mm bore x 88mm stroke so 32 deg before TDC should not be 7/16" of piston drop as on a M20
For 1928 through to 1932 the instruction book specifies setting the timing fully retarderd but the 1934 to 1936 instruction books specify the fully advanced timing method
Also woth noting that the 1932 magneto has a ring cam as per A 7's and A 10's and not the face cam used on the M20's
Not sure if that makes any difference .
There is also no maximum points measurement printed because the points are gapped to the size of the magneto spannar
I will have to check to see if the W used the same one as the M but rolling around in the back of the head is the gap was bigger .
However also rolling around in the back of the head was BSA changed the method of timing due to oveheating .
I stand corrected Trevor. The way I read it, he had set the points gap at 3 thou. Not the 12 thou I was thinking of, and also had forgotten that we are not talking about an M20. Oops. Ron
email (option): ronpier@talk21.com
1931 to 35 useful data
Darren sounds like he is more up to speed with these models than I am so he will probably know for sure.
But I do remember reading somewhere that the method of setting the timing was changed due to overheating caused by it being easy to get wrong .
The paert books do not seem to list a magneto spannar so I can't verify if the gap is in fact .012"
That is what I set mine to but that does not mean it is correct .
I really should start taking notes on these things.
What was BSA thinking? Measuring .003" is not going to be easy and you could be off by a few thou and you don't ride the bike at full retard but at full advance. Lucas and BTH magneto cam rings are not always ground perfectly so setting the timing at TDC full retard is a bad idea. If you have a Triumph, BSA, Norton.....etc twin you know the cam rings are never perfect and have to split the difference between the cylinders.
I would have like to have met the person who decided this was the best way to set the ignition timing!
A valid point but try not to overthink it
These are very basic low compression SV engines that would rarely be run at anything over 4000 rpm with fixed ignition timimg .
They are not 11:1 OHV engines running at near valve bounce with a proper advance curve proportional to the engine speed .
The timimg is not that critical but you do know when it is spot on .
Interesting that here BSA thought "just opening" was 0.003" where as a few years latter it became 0.002" and a lot of us ( me included ) use 0.0015"
Add to that no two people on the planet measure the same with a set of feelers .
Way way back there was a display at a vintage car day spruking an electronic ignition conversion
The had what was sort of a set of points on the end of some long levers
They invited the public to set the points then unveiled the other end which was 10 times bigger and had a scale as to what the gap at the feeler end actually was
Almost no one got to within 0.001" of being correct ( me included )and most were too tight .
I completed my top end overhaul, which included torqueing the head bolts several times, when cold and after running the bike to get it warm. The bike now seems to be air tight at the cylinder head. On my 3 mile ride today it is now pulling strongly up the hills where I live, however this was not long enough for me to satisfy myself that I’ve completely resolved this issue, hence I plan some longer rides over the next few weeks.
Thank you for any ideas and advice you may have given.