The BSA A7-A10 Forum

Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Frenchy on 01.02. 2010 21:25

Title: Set timing?
Post by: Frenchy on 01.02. 2010 21:25

Thanks, everyone, for all your help so far with my A7 project...  After finding an advance/retard unit and a Joe Hunt magneto I think it's complete.  My question now is how do I time it?  I've found some old service sheets online, but nothing that outlines how to time an A7.

Title: Re: Set timing?
Post by: groily on 01.02. 2010 22:57

If the relevant service sheet tells you the required degrees of maximum advance, or inches/millimetres before top dead centre in terms of piston position,then it's not hard . . .About 32-34 degrees (5/16ths?) is probably close, but don't take that as gospel.
Put pistons in said position turning the engine in the normal direction of rotation to get them there, using timing disc on the crank, stick down plug hole or whatever. If the Hunt thing is a 'dead spark' magneto (ie fires both plugs at once - I think it is from what little I have read) then no need to worry which cylinder is on compression.
Set (correctly adjusted) points on mag to be just starting to open (turning them in the correct direction!). Mount the drive pinion and ATD, with it in the advanced position - ie held fully open against the springs with a bit of wedge-shaped wood or whatever. Carefully do up the nut - without letting the mag or engine setting move anywhere. (A good idea to check before-hand that the nut runs up its thread easily all the way.) The taper should grab the pinion quite quickly and easily. Tighten nut, and then check complete setting again before putting timing cover etc back.
If the gods are with you, the pinion should stick on the taper, the mag won't move, the pistons won't either, and you'll be ready to roll. Don't forget to take any wedges out of the ATD . . .
If it's not a dead spark magneto, then it's possible the plug leads will end up the wrong way round.  If you have sparks but it won't go, or makes embarrassing noises, swap 'em round. I don't know how the points' positon relates to the HT leads on a Hunt.
Good luck and hope you roar into life asap.

Title: Re: Set timing?
Post by: MG on 02.02. 2010 13:03

I use two clothes pegs to keep the auto advance unit in opened position. Simply use them the other way round, then they will act as a spring-loaded wedge.
For mounting the drive pinion (and advance unit) on the shaft I give it a slight tap with a large nut and a rubber mallet. This locks it on the shaft and the nut can be tightened easily without moving anything.

Cheers, MG

Title: Re: Set timing?
Post by: Frenchy on 02.02. 2010 14:19

Thanks groily and MG.  The clothes pins are a great idea...  I'll be working on the A7 Sunday afternoon.  If we get it running you'll probably be able to hear us hollering and high 5'ing all the way in Austria.

Title: Re: Set timing?
Post by: MG on 02.02. 2010 19:58

Thank you, I'm a little proud of myself for having that idea  *smile*
I will listen closely on Sunday to know whether you were successful.