New From Australia

[SimonJ]

Thanks to info from here and the Yahoo prewar group It seems the bike is made up of the following:
Gearbox 1927
Frame possibly 1930 M12
Engine 1928 or 1929 348cc
I have joined the club and will hopefully get this confirmed when I send this info to the dating officer.

I've posted earlier about my timing issue in this thread.
Basically with the timing dots lined up on the inlet, exhaust, and small engine cogs, I set the engine to 7/16 BTDC. At this set up the arrow on the engine mag sprocket should point towards the sprocket on the mag ie 3 o'clock. It instead actually points at the 7 o'clock position.


If I ignore all else and place the exhaust cam so the mag sprocket is pointing at 3 o'clock, the exhaust valve is open. With the mag sprocket at the 3 oclock position the exhaust (and inlet) valves should be closed (ie compression stroke.)


I'm thinking the exhaust cam and cog have spun on the shaft or been incorrectly assembled at some stage. I can see the groove on the inlet cam shaft with what looks like a woodruff key, but there seems to be no key in the groove on the exhaust cam shaft.
Can the cam and cog be pressed off the shaft and if so in what direction should I press it?
Hope this all makes sense.
Regards Simon

[Tommy RE]

Hi Simon, welcome to the club. Sounds like you have a bit of a Heinz 57 there. On the later obviously engines like the G3, the drive sprocket for the mag is on a taper shaft and once the valve timing is set to the crankshaft marks, with the piston set at 7/16 B.T.C.The sprocket is rotated with the mag mounted and chain attached until the points just open. Usually gauged with a cigarette paper inserted between the points. When the cigarette paper just starts to move as the points open then she's right. Not to sure about early S.V. engines, but the principle may be the same.

Neil

[SPRIDDLER]

I know little about pre-war bikes but I think you may find that the zorst cam gearwheel and the mag drive sprocket are two separate items.
The dots on the cam gears are for valve timing only; once they have been aligned (compression stroke) you rotate th'engine (backwards) to 7/16" BTDC then turn the mag drive sprocket (without th'engine rotating) until the mag points are just opening. As Neil said, the mag drive sprocket is most likely on a taper.
If the mag drive sprocket isn't separate from the zorst gear wheel you can set up the valve timing dots to spec'n and adjust the ignition timing by moving the mag driven sprocket on its (tapered) shaft.
I can't see any reason for having an arrow on the mag drive sprocket since it is only a sprocket and its orientation/function is the same in any position. Furthermore, if the zorst cam gear wheel and the mag sprocket are one piece (unlikely since they have different manufacturing criteria) once you have set the valve timing by aligning the dots you have no choice as to where the mag drive arrow points.
HTH

[SimonJ]

Thanks guys. The mag drive sprocket on the exhaust cam is a separate part but only fits on the cam shaft in one position, ie you can't spin it around and leave the cam in the same position. And that's my problem.... at 7/16 BTC the arrow on the mag drive sprocket on exhaust cam is pointing at 7 instead of 3 o'clock.
As already mentioned if you spin the mag drive sprocket on the exhaust cam (and hence you are also turning the cog and actual exhaust cam) so that the arrow is pointing to 3 oclock the exhaust cam is now opening the exhaust valve ie the engine is no longer on compression stroke.
Hopefully my pictures and explanation makes some sense of it!!!
Regards Simon

[SPRIDDLER]

Thanks guys. The mag drive sprocket on the exhaust cam is a separate part but only fits on the cam shaft in one position,

Well then I'd set up the valve timing dots and ignore the position of the arrow on the mag drive sprocket (the position of the arrow is irrelevant since its just a symmetrical sprocket ), and set the ignition timing by rotating the mag driven sprocket on its shaft.

[SimonJ]

if the zorst cam gear wheel and the mag sprocket are one piece (unlikely since they have different manufacturing criteria) once you have set the valve timing by aligning the dots you have no choice as to where the mag drive arrow points.
HTH

Yes that's right but I think the cam and cog (not sprocket) are a press fit on the shaft and held in correct position by a woodruff key. I think my key is missing and the cam etc may have spun on the shaft. I'm waiting to hear if that is the case

[SimonJ]

Thanks guys. The mag drive sprocket on the exhaust cam is a separate part but only fits on the cam shaft in one position,

Well then I'd set up the valve timing dots and ignore the position of the arrow on the mag drive sprocket (the position of the arrow is irrelevant since its just a symmetrical sprocket ), and set the ignition timing by rotating the mag driven sprocket on its shaft.

Yes...that is exactly the conclusion I'm coming to as well.

Regards Simon

[SPRIDDLER]

That's sorted then, so off you go, sweet dreams

[saltbox alf]

If you can see that there is/was a woodruff key way. I would first try and extract the mag chain wheel , it looks as there might be room for a two leg puller. A bit of heat on the mag wheel would help to free it off, especially if it has spun round
You may find that the mag chain wheel has friction welded itself to the cam wheel ,or as you say perhaps it's in one piece anyway. A look at a parts list might help ( if availiable) or for a similar model. I the type of puller you need is readily availiable and think club spares sells one.

The cam on later engines has the mag chain wheel taper fitted with a key way to the cam shaft and I would expect this to be the same for older models, as once found to work very little changes in design afterwards.

The timing would be set by position of the wheel on the mag, no doubt on a taper shaft.

You have to take the chain wheel off the cam shaft to check if it has spun or not.

[SimonJ]

The cam on later engines has the mag chain wheel taper fitted with a key way to the cam shaft and I would expect this to be the same for older models, as once found to work very little changes in design afterwards.

.

The mag chain wheel is on a spline with one spline bigger than the others so it can fit only one way. I can remove it no problems.
It's the actual cam and/or timing cog that I'm worried might have spun.

I appreciate everyone's help and patience.
Goodnight Spriddler

Regards Simon