Pre ignition pre detonation

[berger]

golden flash 11/30tooths

[Black Sheep]

Just wondering if the average rider (as opposed to owner) could actually get the ignition timing accurate to 11/32". Pretty close to 5/16" with a stick down the plug hole is I suspect what most highly skilled bodgers manage. Just pointing out for a friend.

[groily]

The A10 engines pinged badly from new. I should say the high compression engines.

Couldn't agree more.
Alloy head SRs or any other HC motors friends have brought round over the years have always seemed to need retarding a bit, despite owners' occasional reluctance to depart from some magic number they've got in their head, read in a book or were told by some bloke 'who knows'.

To BoN's point about manual + ATD  . . .  can be done, has been done. Just set timing with ATD wedged open and camring at full advance, then you obviously have the best of both worlds in terms of adjustability to cope with heavy loads or 'big throttle low revs' situation.
But a few things to bear in mind: first, running with a manual cam retarded from its advance setting weakens the spark; and secondly, the chances of wear gradually interfering with the firing interval on manual cams is greater than on fixed ones. Not to mention AR cable arrangements that sometimes jam or self-detach at the cam and / or are impeded by fuel lines, carb fitments etc on some bikes. Also requires a cranked  HT pick-up at 45° on the cable side usually on As, and the quality of the available part is a bit so-so.

I have a mix of manual AR & ATDs myself (but no bike with both)and I prefer  fixed cams, once having got the firing interval to 180:180° across the rev range.

[JulianS]

Worth checking the ATD function if an engine pings, if the springs are tired it will go to full advance too soon and it will probably ping. On the other hand if the unit is sticky, maybe because of corrosion inside the unit it will advance too slowly.

If an engine gets hot and bothered and down on power it can be an indication of ignition being too retarded.

BSA altered the recommended ignition timing for all the A10s to 13/32 btdc in 1959 (previous 3/8 for Rocket and 11/32 for GF). That is in the service literature and the handbook, as RogerSB says.

It will remain a subject of debate, personal opinion and experience as to what the best figure is.

My own experience, bike currently iron head 7.25:1 pistons is that it runs fine on my approximation of 13/32 btdc and also on 11/32 btdc. So not too fussy.

[RogerSB]

Thanks Julian.

Trevinoz no apology needed. I’m grateful for your input.

I’m fairly meticulous and I’ve been searching the info I have because I was sure I would have got 13/32" in my head from somewhere legit.  First check was the BSA Instruction Manual printed Aug 1971 and there it says 13/32”. Next checked the Haynes book published 1990 and there it says 11/32” but I’d pencilled 13/32” beside it at sometime.

I suppose an exact figure is a bit redundant these days with the different petrol and, as Julian pointed out, wear and tear. That’s why I wondered if there was a ball park figure members used based on todays petrol. So for a 1960 GF 11/32" - 13/32" Julian's info is good enough for me.

Rog.

[Yeti]

I would say that you should be able to get timing pretty exact by using a razor/ a calibrated rod and a points buzzer

[Jules]

I presume the new plugs are one step cooler, I think thats a good step based on your "overheating" you mentioned, particularly when it was confirmed by another forum member when using the chair. For that same reason though I think you would be better off setting the timing back too, from all reports it will not affect performance/driveability but would give you a greater margin should those conditions arise again.....

[BSA_54A10]

All the more reason to use a timing disc.

[Colsbeeza]

From my experience, setting ignition by each method ( Stick & Fag Paper vs timing disc and electronic points opening ) are chalk and cheese. I am sure that the difference is close to 2 degrees of crank rotation. The fag paper pulls out some 2 deg after the points light would indicate. So my 32 Deg ( 5/16" BTDC) by disc is closer to 11 or 12 /32 by stick & fag paper.
Col

[BSA_54A10]

If you really want to frighten yourself, or convince your self just how agricultural these bikes are then dos quick search on the wed for Piston drop Vs crank rotation calculator
There are a lot of them
Slip in your dimensions then plot the two out on graph paper and see the masive difference a 64 of an inch makes .

[RDfella]

 Every engine is individual with its own likes / dislikes. Add a change of points gap, bit of wear on the camring, strange fuel for petrol and those 70yr old figures start to mean a lot less. Set an engine to where it's happiest. Easily done with manual advance, rather less so with auto.