1953 G80S ignition timing.

[Bantam62]

Hello all. I have a G80 with the N1 magneto. It was a poor starter as the mag was tired. Had it overhauled, nice big spark now.
Reassembled with a new timing chain with correct slack.
I have had several attempts at timing it up to run, but have got nowhere satisfactory.
Super unleaded fuel. Had it running on tick over and as soon as I advance on the lever it dies.
Now it just kicks me back either on full advance or full retard.
Can someone please give me the correct timing procedure to sort it?
I am in East Lancashire.
Regards, Graham Lowthion.

[clive]

two things to think about. Firstly is it slack wire or tight wire for advance? does not matter if it is in front or behind the barrel (by 53 its in front I think) but its where the cable enters the mag that is important. If it is entering at the rear of the mag it is tight wire for advance, if it enters at the front of the mag its slack wire advance. Take the points cover off and make sure the cable is free enough to allow the face cam to move when you tighten and slacken the lever.
Check the points gap, I would go for about 12 thou when fully open. At the same time as you have the feeler gauges out check the gap on the plug. All new ones come with 25 thou gap and for a magneto they need to be 20 thou in my experience (or even 18 if the mag is poor). leave the plug out.
Find top dead centre by jacking the rear wheel off the ground and having the bike in gear, both valves should be fully closed with free movement of the pushrods at TDC. if they are not you have got the other TDC!
Put your marker in the plug hole and mark TDC against some recognisable point (usually the top of the plug hole). remove marker and mark 7/16 higher on the rod. Assuming you are not just checking the timing but actually setting it go round to the timing side and remove the cover. undo the nut about two turns on the sprocket at the BOTTOM of the timing chain and put a tyre lever either side behind the sprocket and with a sharp push on both pull the sprocket off its seal to the shaft. Avoid damaging the face of the casing whilst doing this which is why I use tyre levers but of course a puller would probably be safer. I have never managed to get the timing set correctly when undoing the sprocket at the magneto end, it always seems to move as you do it up.
back to the other side, make sure you have the lever set at fully advanced whichever it needs to be slack or tight wire and rotate the wheel backwards beyond the higher mark on your rod. This allows the slack in the system to be taken up as you rotate the wheel forward until your higher mark just coincides with your recognisable point. this is now set and you want the points to be just opening. Normally that is with a cigarette paper between the points which should just be coming free and you may need to move the mag to find this point. I now use a special gismo electronically shows when the points open as it means you can do it all from the other side.
Once you have set the opening go to the other side and take a socket or box spanner that will clear the nut which you left in place and slide it onto the face of the sprocket. Give it a sharp tap and this should seal it to the shaft allowing you to do up the nut without changing the relative settings.
Always go back to the beginning and check the opening of the points against your timing rod.

Some manuals say 1/2 inch before TDC and for years I was using this measurement thinking it would give me a more lively machine until I realised I was using one of those screw in devises that go in the plughole which is at an angle and consequently it was actually 7/16ths in reality! I have used an old spoke as my marker rod since as you can get it to sit vertically and never tried 1/2 before TDC since!

retard by about 1/4 to start and fully advance once its running then leave it alone. Good luck.

[Groily]

See page 34 here which sets it out as clearly as anywhere: http://archives.jampot.dk/book/Owners_m ... Manual.pdf;

Note piston position BTDC is the same (7/16" or 35-odd°) on 350s and 500s, as the stroke's the same at 93mm, so nothing to have to think about there.
Note too that it's dead easy to set things the wrong way about - with the piston AFTER TDC - which you don't want. The sense of the engine's rotation must be respected while finding the right spot for the piston, as it must also be at the magneto when setting that at full advance on the lever.
The crankshaft goes clockwise from the right hand /timing side of the engine, your magneto goes ANTI-clockwise from the sprocket end and the points therefore go CLOCKwise from their end. Essential to turn the thing the right way to set the timing.
You probably have to pull your ignition cable taut for full advance, but you need to check. If the ignition cable enters the magneto on the right hand side of the contact breaker unit, then it's Tight for Advanced; if it should enter on the left on yours by any chance, it would be slack cable for advance.

Some would argue in favour of a puller rather than a tyre lever for getting the sprocket off - others that it's easier to slacken the lower sprocket on the camshaft rather than the one on the mag. But it all comes to the same whichever way you go.

And see what Clive has just said!

[Joker_Bones]

If you would like a few pictures in addition to words:
Dick Casey has a video 'Timing a G80'.

A lot of the video is shot using a N1 comp mag with a ring cam, but it also shows the N1 with a face cam and explains the slack wire/tight wire types.