BSA L29 350 SV parts - and advice!

[robbsa]

Hi,

new to the forum and new to vintage bikes. I have started restoring a l29 350SV. The cylinder head is one of the worst parts for rust. Its fine on the inside, the bore seems okay, but there is corrosion to the fins and the valve caps are seized on (or are as much as i have liked to try to get them off). If anyone out there knows of a set of valve caps, or has a complete cylinder head i would be very grateful. Also if anyone can offer advice on removing these seized caps, or has a set of caps that they don't wish to sell but would be willing to measure so i can make a new set, it would be great to hear from you.

Cheers,

Rob

[cardan]

Hi Rob,

I don't know where the BSA fans are hiding! Removing the bungs over the valves is tricky. WHatever you do, don't holt the barrel in the vice when you do it - the bore will disort if you grip it by the bottom flange. Is the motor still in the bike? If so, do it there. You need a very close-fitting ring spanner or socket (hexagon preferred), and perhaps a bit of filing to get the hexagons on the caps back into shape. If possible put some gentle heat into the barrel (soft flame like gas, not oxy, spread gently and evenly over the whole top of the cylinder - if you can's be gently and even, don't use heat). If the spanner/socket fits well, either give it a good yank (with appropriate extension) or a "gentle" whack with a mallet/copper hammer. They might come undone. If not, I recommend drilling or machining them out. A neat line of overlapping holes from close to the thread on one side to close the thread on the other will allow some collapse of the cap, and you should be able to unscrew it easily.
Of course this doesn't help if you're not going to re-use the barrel. Perhaps if you let us know your location, someone might be able to suggest a source.

Leon

[robbsa]

Hi Leon,

thanks, this is very helpful. I had considered drilling them out, but I want to try and get them off first. The cylinder is not in the bike as the bike and engine are completely dismantled at the moment. Do you think if i made a plate for the cylinder to bolt into, acting like the crank case and then held that in a vice it would be safe? Hopefully this would stop the compression of the vice without distorting the cylinder, unless you think it would be the torque applied by the spanner that would twist the bore. I have tried heating the cylinder and then holding it by hand whilst trying to undo it, but I do not seem to be able to get enough purchase.

Thanks,

Rob

[cardan]

Hi Rob,

Last time I did it I bolted the cylinder (JAP) firmly to a steel girder (C section), and held that in the vice. I managed to undo a couple of the bungs, but two were so tight that I thought I would break something if I pesisted. These I drilled out as above. At least the cylinders survived. Good luck!

Leon

[Rex]

On my old stood-in-a-garden-for-years Roundtank, I soaked the barrel in a bucket of diesel for months, then attacked them with a gas torch. They always give way in the end...
{Barrel still stinks of diesel though.. }

If I needed a quicker resolution, I'd have given it the old heat-cool-tap tap treatment. The price and availability of new brass caps meant I wasn't going near them a drill or Stillsons.

[robbsa]

thanks guys, this is really helpful. Think i'm going to try the girder section first as this is what i had in mind. Failing that, it will be drilling  - then milling up some new ones. The only thing i'm not competent will be the tread cutting, so may have to get someone to do this for me as i suspect it will have to be done on a lathe with the correct tpi. unless anyone would think i could get a die that size?!

[robbsa]

Hi leon, or others,

do you know of anyone who may have  a cylinder for sale for my bike, there is currently a siezed one on ebay, but the exterior looks in better condition than mine. as i said before, my bore is fine, but the outside is bad, broken fins and quite heavily coroaded. any advice on which is easier to fix - re boring, or repairing the exterior?

cheers,

Rob

[cardan]

Usually in assessing the value of a cylinder I start from the outside and work inwards! Good fins a very important; fins rusted to a sharp edge are quite hard to recover.
A siezed cylinder can almost always be unstuck, and if the bore is standard (or close to it) it can probably be reocoved reasonably well. Beware of the other important bits: you need some metal left in the vincinity of the valve seats.
So far as where you might find another cylinder, we need to know which country you are in!

Leon

[robbsa]

Hi Leon, thanks again for your help, I'm based in bristol in the Uk.

[Rex]

cardan link=topic=3633.msg12479#msg12479 date=1303363878]
Usually in assessing the value of a cylinder I start from the outside and work inwards! Good fins a very important; fins rusted to a sharp edge are quite hard to recover.

True enough. Cylinders can always be rebored or fitted with a liner as a last resort, but paper-thin fins are a work of art to repair correctly. It's one of those rare situations where external looks really are more important than what's inside.

[robbsa]

Hmmm.... kciking myself that i just missed a complete engine that was seized but the cylinder and valve caps looked in good nick on ebay. went quite cheap too.

will have to take the risk next time i think, they don't seem to come round too often!

[robbsa]

thanks everyone for the help. As you can see below i have now removed the caps, without having to drill them. I made a base plate to clamp it in the vice as suggested. The first came away with a few taps, but the second was more stubborn. I had to heat it gently with a blow torch, and cooled the cap with ice (don;t know if this really created a temperature difference, think the ice jut melted,  but i suppose it took energy to do this), but the valve cap came off.

Thanks again, Rob

[rogerwilko]

I don't know what they were thinking in those days, having the head and barrel cast as one. All that extra machining and elaborate casting!! I wonder who first invented the separate head style? I hope he was acknowledged!

[R]

I don't know what they were thinking in those days, having the head and barrel cast as one. All that extra machining and elaborate casting!! I wonder who first invented the separate head style? I hope he was acknowledged!

Well actually,  de Dion Bouton engines (pre 1900 even) had separate cylinder heads - and Indian had separate bolt-on heads circa 1911.  AJS were in there somewhere too.

But many engines had a devil of a job making the head gasket seal.
So the one piece head-cylinder neatly solved that problem.

A case of engine design going backwards to solve a problem.
Not for everyone though, it should be noted...

Cheers.

[rogerwilko]

Well if i could go back in time, i would've suggested a piece of flat copper might do the job!!