Timing - replacing mag.

[Worty]

I was sitting here pondering about the ignition timing set up after reading a couple of posts, and wondered if there was a way of setting the timing in a slightly different way after removing and replacing the mag - it goes something like this.

Assuming the timing is all good from the beginning, and making sure the ATD is jammed fully advanced, turn the engine so the points are just about to open (using fag papers, clips or the clever, audible device I got from CB).  Once the points are in this position, the pistons should be at the correct BTDC (as set originally).

Again, without moving the engine, carefully remove the mag.  On replacement, jam the ATD open again, then turn the mag so points are just opening (as above), then carefully replace the ATD without moving the engine (or points, of course).

If all goes well with the above, it should obviate the PITA need of trying to find the correct BTDC when setting up the timing (again, providing the timing was good prior to dismantling).

Anyone see a flaw in this .........?  Am I having a 'Worty moment'?

For me, the trickiest part of ignition timing is getting the pistons located correctly, the rest is relatively straightforward if not bloody awkward.

[RDfella]

Setting BTDC is a breeze compared with what follows.
There's one major problem with setting these mags, and that is tightening the nut often disturbs the timing. Often more than not, a spot-on timing, once tightened, is a fair bit off. We can try 'tapping' the gear onto the mag before tightening, but that is not a total cure. Usual process (for me at least) is, after half a dozen attempts, to determine the amount of error caused by tightening and then offset by that amount before tightening hoping that the error is constant and end result will be correct. I have sometimes spent over an hour taking the gear on and off until getting it right. A real pain.

[Worty]

I've had exactly the same with trying to anticipate the degree of error on tightening and compensating hoping that the window of error will be constant.

In my mind, though, although a PITA with the tightening thing, I do find BTDC difficult to get right.  I know there are rods down the plug 'ole, and discs attached to the cush drive, but I'm rarely confident the piston position is correct.

When Bergs built my motor, he set BTDC with the heads off (with a Vernier, I believe), this resulted in spot on timing.  He also widened the mag mounting points for fine adjustment - something I've not used yet but think is an excellent idea (why didn't BSA think of this!).

On advice from the forum, my way of locking the mag as I tighten the ATD is by removing the earth screw and screwing a plastic bolt into the hole quite firmly.  I did once use the nozzle off a tube of silicone sealant which, being plastic, self tapped into the hole - this worked pretty well.

As you'll have guessed, I'm just looking at ways of making this job a little easier.  The degree of precison needed to get it right coupled with the fixed, bolted position of the mag (without the elongated fixing holes), and the hassle of not moving the mag when tightening the ATD makes for a frustrating time.  Given that removal of the mag may be required quite a few times during the time we own the bikes for, it would be great if it were less of a chore.

[Triton Thrasher]

Try all these things if you like, but check the timing afterwards.

[Colsbeeza]

Worty, not sure how you mean. You would have to ensure the engine is set for your ideal BTDC before you remove the mag. If your mag was wrong before you removed it I can't see how you would be confident in the piston position.

In the quest for perfection, I gave up using a rod in the plug hole to find TDC, but it is certainly faster to get it close enough.

 I now go through this procedure after buying a few worthwhile bits of gear:-
1. Remove the chaincase and screw an SRM disc on the SRM cush nut.
2. Screw a proprietary piston stop down the plug hole and rotate the crank between stops, mark both extremes on the disc and then centre the crank between marks and mark TDC on
    the disc.
3. Loosen the ATD taper by the extractor nut. (Mine doesn't work and I have to use a puller).Adjust the points to 12-14 thou and wedge the ATD to full advance with a clothes peg.
4. Refering to the Crank angle Excel speadsheet (attached), rotate the crank backwards and set the piston to 31 deg BTDC or your preference - ( my selected advance for the Golden
    Flash - fraction under 5/16").
5. I have a Magneto Guys device connected across the points. (Cig papers can give you half a degree more retard).
6. Rotate the contact breaker centre bolt until the MGuys light just comes on. I use a  small T-bar with correct socket. Timing is now set perfectly.
7. Go through the frustration well covered by RDfella's procedure above to tighten the magneto ATD extractor without shifting the timing. Tap the ATD extractor head onto the taper
    lightly. Tighten the bolt - it helps if you can wedge the drive gear to minimise its movement. I use another clothes peg here - anywhere it fits.
8. Rotate the crank to check the timing, then repeat for the other cylinder. My magneto is newly overhauled and the timing is 180-180 deg perfect on both sides with a new points cam.

This all takes a few hours, but hopefully I won't have to touch it for a few years.
The 1960-61 GF runs beautifully at 31 deg BTDC. Standard Iron Head, 356 cam, IMD 7.25/1 pistons, Monobloc 389/18.

Pedantic I know but I don't have to guess afterwards.
Col

[Worty]

Cheers Col.  My 'method' assumes that the timing is spot on before doing anything.  The logic that follows says that if your timing is spot on, and you wedge the ATD open, and the points are just about to separate, then the pistons surely have to be at the correct position BTDC.  If it works one way round surely it does the other??

With the pistons at their correct position as outlined above, then (so long as the engine is not disturbed) the mag can be removed.  When the mag is put back, all you're doing is returning the mag to the same condition as before with the engine in the same place as it was before.

I've only ever timed one side, probably wrongfully assuming the other will be there or thereabouts.  I think if you do both sides, isn't there an 'average' timing setting if they're slightly out?

Looking at the way your set-up is, I bet it runs really smoothly.

[a101960]

All of which begs the question: How I wonder, was this task carried out on the production line? Was every bike delivered with the timing absolutely spot on, or more likely "near enough"? The question arises because, back in the day it was common place for many tasks to be paid on piece work rates. IE the more work you did the more you earned. Not exactly conducive to encouraging care and accuracy I would suggest.

[Rex]

The method you describe was commonplace back when these bikes were daily hacks, and the timing needed to be set "good enough" for you to make it home.
Given the amount of times any of these engines has been dismantled, parts changed, manufacturing tolerances and wear of the various parts, difference in fuels then to now etc etc these settings are more of a guide than set in stone.
Velo books give timing in degrees, and when first building my Venom engine I did it by the book (valve and ignition timing) using a degree wheel etc, and the engine ran well.
Through a fault in the mag (repaired under warranty) the mag had to be removed and subsequently replaced, and this time to save all the fannying around it was stick down the plug 'ole time.
It ran just as good as before.
These engines are 75 years old rather than to Moto GP standards, and it's possible to overthink the standards of accuracy achievable.
(Posted the same time as above)

[berger]

worty i used a clock on it

[a101960]

According to the RGS owners instruction manual:

 "Insert a slim rod through the right hand sparking plug hole to feel the top of the piston. Rotate until the piston is at top dead centre on the compression stroke (i.e., both valves closed). Keep the rod as as vertical as possible and mark the top dead centre postion on it. The best way of rotating the engine is to engage top gear and turn the rear wheel. Turn the engine backwards through about 45 degrees then bring it forward again until the points are just opening. This is best determined by inserting a piece of paper (such as a cigarette paper) between the points. The points are just about to open when the paper is only lightly gripped and can be withdrawn with a gentle pull. The correct postion for the piston is 13/32 in as measured by the rod through the plug hole".

Rather vague and lacking in detail. No mention of of preparing the rod first by marking it ready for use. It does say to mark TDC but omits to mention to mark 13/32 before TDC also. How would you judge that then? and how would you know if the rod was in the exact same postion?  Niether does it mention that the mag must be fully advanced. All very misleading and open to misinterpretation. Far from precise accuracy, but that's the factory method according to the instruction manual. Therefore as far as BSA is concerned near enough is good enough it would seem

[Triton Thrasher]

They assumed a certain level of handiness and possibly even some common sense.

[Worty]

13/32" = 10.3mm.  I did the rod method by attaching a straight 'mending' plate to the cylinder head and passed the rod through one of the holes and into the cylinder.  Found TDC and marked it, then measured 10mm down (or up) from it.  Put the rod back in t'ole, and rotated backwards (then forwards to eliminate lash) until the 10mm mark was reached.  I actually used some tape to mark the two places as it has a 'sharper' edge.

One has to be careful to read the measurement from the same place on the mending plate.  If you measure at the top and read from the bottom, you've lost around 2mm immediately.  Also, if you use a marker, the thickness of the mark can also throw you out a bit.  Ideally, a dial gauge like Bergs is probably the best (or a degree disc).  I take it there's a dial gauge that'll screw into the spark plug 'ole, to accurately measure TDC and BTDC.  Is 31 degrees near to 10mm, by the way?

I got some good results - through trial and error.  What I didn't have then is the enlarged holes on the mag to make fine adjustments.

I can see why some people opt for electronic ignition, although I'll stick with the mag - more fun and games that way.

Er, I can't see the Small Heath workers measuring to 0.3mm, by the way.  Would probably be lucky to get within a couple of mm.

[Swarfcut]

  Rotating the crank backwards to the firing point introduces a certain amount of error, due to the backlash in the timing gears.

   So either push the cam gear backwards by hand with the crank positioned, or go backwards past the firing point and then move the crank forwards to final setting, as in the factory instructions, and followed to the letter by Worty.
   Either method ensures the gear train is loaded as if being driven by the crank. To be honest, with modern fuels the published figures are a starting point, and there is a good case for a manual mag fitted with an ATD. Slimmed down mounting studs and slots on the mounting flange also work for easier final setting. If anyone starts repro magneto bodies, please make the mounting flange with nice big slots!

 Never assume it is all fine to start with. Start from the basics, it's easier than trying to achieve an original setting. Remember the points gap has an important role in determining the firing point. The old trick of opening the points to advance the timing worked by moving the heel closer to the cam.

 Swarfy.

[Slymo]

My SR is very timing sensitive as its running 9:1 pistons. No ATD just a manual advance and retard. I had it timed to perfection but a simple cleaning of the points advanced it sufficiently that it started to pink under load at speed. Fortunately I can dial it back a notch on the lever when required but with old fashioned no squish combustion chambers it is something you want right. That said I've always used a stick down the plug hole and a fag paper in the points. The big issue, as mentioned, is the propensity of the mag drive to find its happy place on tightening. I've found some smart blows with a soft hammer before nipping up ensures the desired outcome.