Recommendations for ignition timing please

[orabanda]

Hi All,
What is the recommended ignition timing (in degrees), for the following:

'51 Gold Flash (pre-unit)
'54 GF (swinging arm)
Road Rocket
'60 Super Rocket

Thanks in anticipation,
Richard

[beezalex]

According to BSA service sheet 216

'51 Gold Flash (pre-unit) : 11/32"
'54 GF (swinging arm) : 11/32"
Road Rocket :3/8"
'60 Super Rocket: 13/32"

I wrote a conversion calculator which gives the following degree numbers:
'51 Gold Flash (pre-unit) : 33
'54 GF (swinging arm) : 33
Road Rocket :35
'60 Super Rocket: 36

[trevinoz]

Don't even think about 13/32 for your Rocket, even 3/8 seems too much. Eddie Dow recommended 5/16 or 32 degrees for engines with 8.75:1 pistons.
From my experience and others, A10 engines tend to ping badly, especially with the dish water that passes for fuel these days.
I am running 11/32 on my Flash with 7.25:1 pistons and it runs very well.
   Trev.

[Brian]

Totally agree with Trev. I run my plunger A10 at 11/32" (7.25-1) but mt 61' I run at 5/16", (9.5-1) Any more advance and it pings like crazy. Like Trev says, the stuff they sell us that they reckon is fuel is absolute rubbish.

I have a friend who has access to aviation fuel which is full leaded 100 octane and he uses this in his bikes and its amazing the difference it makes.

Unleaded fuel obviously doesnt have lead in it but it is carsonogenic which may yet turn out to be more harmfull to us all than the leaded was.

[BSA_54A10]

Not trying to hyjack the thread but tetra ethyl lead used in fuels was never a problem to human health.
Lead oxides, lead chlorides, lead vapour, free lead ions or very fine lead dust can be assimilated by the human body.
All the rest goes in one end & comes out the other.
Your digestive system is a hydrachloric acid based system.
Hydrachloric acid was transported in lead lined tanks for years till synthetic rubber became cheaper.
The combustion products formed at engine temperature & pressures can not be broken down by the human body and never ever posed any risk to health.
Unburned hydrocarbon emmissions do represent a health risk.
They could be avoided by tighter controls on the quality of fuels ( expensive) or by adding after burners ( cheaper).
The powers to be know all voters are totally stupid, ceriably really lazy & easily emotionally manipulated so rather than tell you the truth, they piggy backed the unleaded petrol bull on the back of the lead paint campaign.
Lead in paint is a health risk.

[groily]

I wonder sometimes whether we all get the same sort of fuel these days, across the world?
When I lived in the US, I had engines that pinked on pump petrol regularly - but which, back in Europe, never did, on allegedly the same stuff. My 7.25:1 A10 runs fine at 11/32 advance on European 95/85RON and a very long-term owned AMC twin, with relatively short stroke and similar compression ratio, runs likewise at the 'book' 3/8th (close to 39 degrees I think) without ever pinking. Other engines I have (or have had), some with much higher compression ratios (in the 9:1 to 10:1 range) have also proved fine, although I treat them to the 98/88RON more expensive brew.
I've no idea - but could there be subtle differences in the juice supplied to different markets?

[trevinoz]

I have never understood why BSA specified 13/32 advance for the high compression engines, it seems to me that the timing should be retarded with increased compression.
Even in the leaded petrol days my RGS would ping under load and looking at several alloy heads over the years it seems to have always been a problem.
A friend bought a Big Valve new in 1962 and he said it pinged from day one.
  Trev.