Sunday, April 22, 2018

BSA Bantam rebuild

It was slightly inevitable wasn't it, my Bantam that has not been used for thirteen years and that was thrashed around by seventeen year old me has turned out to need a rebuild. After reviving the little Beesa three months back it has proved to be a difficult starter and a most prodigious leaker of oil. Old two strokes have many qualities which some folks find endearing and others less so, but oil leaks are not normally one of them. This particular example dumps its full load of gearbox oil out within a couple of days. I can stand a small, or even medium sized oil leak, I don't mind a few spots left in the pub car park but this is next level and unacceptable.

One leaky Bantam.

Easy, a quick rebuild was in order. New gaskets to cure the leaks and new seals whilst it was apart: should be do-able in an evening or two. Of course life doesn't always work out as planned and the scope of the job expanded considerably.

It can't leak without an engine....

The motor came out of the frame wonderfully easily. I haven't worked on a small two stroke for a good while and it was a joy not to have to strain with lifting up a brutish lump of British cast iron four stroke. It did not however come apart quite so willingly. The points cam should slide off as it is just held on by a small nut and a keyway. Such was the confidence of BSA engineers that it would just slide free once the nut was undone that they made no provision for a puller to fit it at all. So I gave it a couple of light clouts with a hammer to shock it in to action. The clouts gradually increased in magnitude. Next step I gave up on salvaging the cam and resigned myself to buying a new one so out came the mole grips. Still nowt in the way of movement. OK, hammer combined with mole grips, next step, oh crap, the end of the crank has snapped off.

Whoops! Broken crankshaft.

In mitigation of my seemingly mechanically inept actions there is no easy way of getting a stuck points cam off a Bantam and after it had snapped off it did indeed prove itself to be rust welded to the crank. lesson from this to share with all is to never assemble keyed components dry, use oil and preferably, if the application allows (as a Bantam points cam does), copper grease /anti-seize.

Here's the points cam complete with snapped off end of the

The rest of the motor was happily a breeze to dismantle. Rather remarkably as the engine has not been apart for well over forty years and was ridden by teenage me the bearings were all in fairly decent condition. The seals however were completely shot to the point where they were in two pieces with one part turning with the crank and the other sitting in the cases and a healthy gap between the two. It is a minor miracle that it ran at all.

The options for the crank were a second hand crank that would more than likely then need rebuilding or to go for a cdi ignition system that wouldn't need the points cam so I could use the original crank. I decided on a new ignition as the sparks were rather weedy and it seemed that in the end it wouldn't cost much more than a refurbed crank. There are two different cdi options available for Wipac flywheel magneto equipped Bantams, the Rex Caunt designed one now sold by Rusty Rooster Motorcycles and the Electrex World one. I've heard good reports of both but I went for the Electrex World item as it is a plug and play job whereas the Rusty Rooster kit requires you to send in your old stator plate for light modification. I was in a hurry to get the job finished and off my workbench plus the Electrex World item is stocked by my local old bike suppliers Feked.

Spanky new Electrex World ignition fitted.

A Bantam motor is a nice and easy motor to put back together and I gained some respect for the design engineers behind it as it all falls to place nicely, each part has its obvious place and it really is fairly hard to get it wrong. The cdi ignition was equally doddle like to fit in place and time up. I hid the coil and regulator /rectifier away between the battery carrier and tool box. I was a bit sad to see the characteristic Wipac rectifier go as, to give credit where due, the lighting was always pretty good on the bike even if the sparks were slightly feeble.

The ignition part of the Electrex World system is simplicity itself to wire and get going. The charging circuit is claimed to be very easy to wire in, as indeed it would be if you were to wire from scratch a simple battery charging circuit. If you are looking to match it in to your existing wiring to go through the ammeter you need to get your thinking head on and a multimeter out...

And here's the Electrex World stator plate. Just strip down the
Wipac stator and this bolts straight on.

With the motor back in and wired up the bike fired up fairly readily. A few kicks to get it primed and going, after that it was pretty much a first kick job. So far so good then for the Electrex World ignition. I'm not convinced it will make a whole load of difference out on the road, I'm confident I'll still need to rev the nuts off the bike in second at thirty at the sign of an incline and not have the added flexibility to chug up in third. However if I have only gained easy starting and been saved having to throw away the original crank I shall be happy.

I'll post again after a few miles have been covered to give the Electrex World system a proper review.

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