A10 Plunger Ignition Timing

[cotterpinkid]

Once again I'm back to putting the A10 PL together (it has been a while, but time has been against me). So, I have a number of daft questions that I will post in the appropriate sections. So, daft ignition question:

My mag. has been rebuilt and I'm close to refitting it. I intend to time the ignition using a degree disc (I much prefer this rather than poking things in dark holes, but that's just a personal thing!). I see from previous threads and dyno tests that 30.5 degrees btdc seems to be good, can anyone confirm this please as the SRM tech info states 33 (although some questions have been raised about this figure). 1957 A10 Pl 7.25:1 compression, std cam

Thanks

Brian

[muskrat]

G'day Brian,
                depends on the fuel you use. I think Richard used 95 for his dyno run. High octane fuel burns slower than lower octane so if he ran 98 it would need to be about 32 degrees and if 91 was used it could go back to 28 degrees. My rule of thumb is to advance till it starts to ping then back off 2 degrees. Ethanol will slow it down as well so I'd start at 32 and see how she goes.
Cheers

[orabanda]

Hi Brian,
30 degrees BTDC is the best setting!

Also best to check with a strobe, so invest in the SRM timing kit (with primary drive nut)

Richard

[muskrat]

G'day Richard,
                   was it 95 or 98 used on that dyno run ? Have you tried it on different octanes and with E10 to compare ?
Cheers

[orabanda]

Hi Musky,
I hope you are healing well!!
I always use BP Premium, which is readily available but with a higher octane rating than regular - however, that's not hard!

Not sure of the rating.

Richard

[cotterpinkid]

Thanks for the current advice. I know the use of a strobe will probably be in the SRM instructions, but how do you fix the strobe up?

Brian

[orabanda]

Brian,
Replace the primary drive nut with the SRM nut; their timing disc can be mounted to their nut.

Follow the instructions in their kit regarding finding TDC; you will have to make an indicator (pointer) and mount it solidly to the engine. I screw mine into one of the 1/4" BSW screws for the chain case, and adjust the pointer to suit.

When using the timing light, make sure to check the timing on both pots; the K2F maggie will often have 2 - 3 degrees variance (therefore average the timing between the two). It is a huge advantage to slot the magneto mounting (stud) holes, so that the nuts can be loosened enough that you can twist the housing and adjust the timing whilst running the bike. Minor adjustment (up to 2 degrees) can be achieved by adjusting the points gap, within the range of .012" - .015" (0.001" change = 2 degrees timing change). However, the cam ring can be the reason for the timing variance, because of manufacturing tolerances (the points opening can be different for each cam ramp).

You will need to find a 12V battery to power the timing light. Clip the "pick-up" from the timing light over the HT lead of the cylinder you are checking.

Richard

[cotterpinkid]

Cheers Richard.

Having always static timed my Velocette I wasn't sure. The timing disc etc will be on order shortly and I have a friend to supply the strobe. I understand what you're saying about variance in timing due to machining / wear so when I get round to it I'll optimise both cylinders for 30 degrees. Before then, I need to sort the points out, check over the 276 carb (I'll post in appropriate section) and remove the petseal from the tank and re-line with something suitable.

Thanks

Brian

Don't worry - more questions are bound to follow

[cotterpinkid]

.....I know it has been a while, but an update, so far...

Purchased and fitted SRM timing disc.

Set timing cyclinder to 30 BTDC (I use one of those buzzer thingies for telling when the points are just opening which saves juggling with fag paper)

Borrowed three strobes before I found one that worked (I thought I was going mad)
Timing cylinder was firing at 30
Drive cylinder was firing at 25
(me and my son like using the strobe)

Permanantly borrowed and fitted spare original cam ring from my mate

Now firing at 30 and 29 btdc (may tweak points to 31 and 30)

Consigned the piece of junk of a cam ring that was supplied during my original Flash rebuild (10 years ago) to the scrap box. When we compared the profiles of the two cam rings you could actually see the difference, you didn't need to measure it.

Now feeling a bit happier about the timing as the drive side seemed to be running hotter than the timing side and can probably attribute this to the difference in the ignition timing.


Still a few bits and pieces to do, but getting there gradually. It's definitely a good starter though, no problems there.

Thanks for he advice regarding using the strobe.