Hitchcocks Forum

Never done this job before and was hoping for advice. I wish to take the magnito off as intact as I can.

The bike is a 1957 350 Redditch Bullet with a Lucaas SR1 mag fitted. I understand I have to take of the auto advance unit inside the timing chest by unscrewing so far and then apply a spanner to hold the auto advance unit while continuing to unscrew as the auto advance pushes itself off the magnito shaft. Is this unscrew anticlockwise?

I then undo the three magnito screws from inside the magnito cover to remove it intact. I don't wish to damage the auto advance unit for obvious reasons.

Does the magnito spin clockwise or anticlockwise as the repairer (will do a pretest before dismantling) has asked could I check. I realise there is normally an arrow indicating direction of spin but can't as yet spot it. Maybe will be obvious when removed from the bike.

Any comments appreciated as although had the bike 14 years never done this job. Also I presume will need to retime the bike even if I don't disturb anything else, This will be another challenge!!
Regards

Hugh
.

The mag should rotate anticlockwise. The nut that holds the ATD on, is turned anticlock to undoo it. ( at least on mine )
It should produce a big healthy spark when turned by hand.
Yes just 3 1/4 Whit screws behind the ATD.
If it helps I had mine rebuilt by an ex Lucas engineer called Martin Dry in Bristol. 0117 9675225

The consumables in an SR1 magneto are easily replaced, with just two screws to undo to release the coil for replacement if it is suspect, and the condenser, which is also easy to change. The trickiest bit is timing the points cam if it gets disturbed - the points need to be breaking open at the point of the strongest magnetic flux, when you turn the shaft. Also, rotation can be set for either direction by positioning the cam correctly, as the cam ramps are a mirror image of each other.

Surely, a mag will normally turn in such a direction that the cam and points look as if they are a side view of a wheelbarrow being pulled, rather than pushed. In other words, the cam surface contacting the heel of the points will rotate away from the (points) fulcrum, rather than towards it.

My 350 Electra doesn’t have an external mag or points and I sold my mag equipped BSA A7SS in 1977, but I reckon with all the gearing on a Bullet, the end result is that the magneto rotates in the same direction as the crank.

The magneto on a Bullet spins in the opposite direction to the engine, so do the distributors on later ones.

Wheaters,

the SR1 magneto is (was?) made in both clock-wise and anti-clockwise (from the drive end) versions, I have examples of both, the points are on the right-hand side under the end cover in all cases.

Older types of magneto such as the BTH have the contact breaker assemblies facing in different directions according to their rotation.

Your 350 Electra is a bit different from the usual bullet in that it has no ignition and idler pinions. Looking at a "normal" Bullet from the timing side with the cover off, you can see if the crank rotates clockwise how all the intermediate cam, idler and mag/distributor pinions should rotate.

A.

BW and Adrian, thanks both - I've got it now, as soon as I saw the photo of the gear-train I realised where I'd gone wrong!

In my mind's eye I had forgotten that the initial drive from the crank actually goes via the exhaust cam and it then "crosses over" the crankshaft to the inlet cam, putting one more gear in the drive train, reversing everything. I'd imagined that the inlet cam was driven directly off the crank and the exhaust off that.

I even doodled a little diagram with direction arrows on the gear wheels to while away some time whilst waiting for my passenger for three hours in London this afternoon (it was supposed to be a day off until I received a frantic phone call from work whilst my car was undergoing its MOT test at 0915 this morning). Just got home.