BSA A10 ignition

[BSA59]

Hello,I'm sorry I live in France and i don't speak english very well
I want to know the ignition advance for my BSA A 10 Road rocket of 56
I need this information but not in inch but in degrees
I hope you understand me
Thank You!
good afternoon
Fred

[a10 gf]

Bonjour, et soyez le bienvenu ici. N'ayez pas de doute, votre anglais est très bon, et ne posera aucun problême. Maintenant la France est representée sur le forum, excellent!
Moi, j'ai passé beaucoup d'années en France, banlieue de Paris et les Alpes Maritimes. Dans quel département habitez vous?
e.

ps, we will keep the forum in english, this is just a welcome note to our new french member.

[dpaddock]

Fred: Try 32 degrees BTC, equivalant to 5/16-inch.

[BSA59]

Hello
to a10gf: thank you for your welcome note,I'm living near Valenciennes- I have a recent bike(TRIUMPH TBIRD BIRD) and old bikes (SAROLEA 30R, NSu 200lux,MOTOBECANE R 44 C,BSA M20...)
to dpaddock: thank you for your information
Fred

[a10 gf]

Some GF timing I picked up somewhere, think it was recommended by SRM using their timing disc:

35 deg btdc for super98
33 deg btdc for 95

Fred, post a few pictures of your bikes? (other than a10 pics welcome as well, especially BSA's, as long as you own an A10 too, BTW, I have a Triumph 900 Legend, good stuff ! )

e.

[Beezageezauk]

Hi Fred,  

Welcome to our BSA A7/A10 forum and congratulations on your English.  We can understand you very well.

I have just done some calculations using the Ignition Timing Converter and these are the results.

Using the A10 stroke of 84mm....3.307 inches and the conrod centre distance of 6.469 inches the ignition timing conversions are as follows.

5/16in. before top dead centre is 0.3125inches or 32.5deg.
11/32in. btdc is 0.344inches or 34deg.
3/8in. btdc is 0.375inches or 35.5deg.
13/32in. btdc is 0.406inches or 35.5deg.

You decide what your ignition timing should be   in inches before top dead centre and the answer you are looking for is here.

Beezageezauk.

[Alan @Ncl]

I just came across the post quoted below and realised I was probably using the wrong data in my calculation (posted yesterday and now corrected).  Can I just seek confirmation of consensus that A10 con-rod length between centres is in fact 6.469inches (I was using 6 inches which obviously gives a slightly different answer).

Also, can anyone say how many degrees the autoadvance mechanism normally provides?  I did some measurements (gap to be taken up by the centrifugal action, about 6mm, and the diameter across yoke about 60mm).  This indicated an equivalent of about 23 crankshaft degrees.  On this basis, fully retarded would be about 12 degrees BTDC.  Does that sound sensible? I seem to recall seeing somewhere that it was nearer TDC.

I have just done some calculations using the Ignition Timing Converter and these are the results.

Using the A10 stroke of 84mm....3.307 inches and the conrod centre distance of 6.469 inches the ignition timing conversions are as follows.

5/16in. before top dead centre is 0.3125inches or 32.5deg.
11/32in. btdc is 0.344inches or 34deg.
3/8in. btdc is 0.375inches or 35.5deg.
13/32in. btdc is 0.406inches or 35.5deg.

Beezageezauk.

[KeithJ]

Hi, I have just checked my A/R unit on my A10RR and it has 12 deg of movementwhich agrees with the above post.  However, I think it should be more than this. Is there a difinitive figure for this taking in to account the modern fuels?  Also, what degree of retard should there be with, say 8:1 pistons to ensure easy starting and correct advance?  Hope this is clear?  ATB

[KenF]

Keith, the spec for the ATD range on 1955-57 A10RRs was 11 to 13 degrees, and I doubt if they would have changed it by 1959. See page G22 of
http://brightsparkmagnetos.com/library/Parts%20lists/Lucas%20motor%20cycle%20parts%201936-57/G09-23%20Magnetos%20and%20ATDs.pdf
So, your 12 degrees sounds good to me. Bear in mind that that equates to 24 degrees of advance/retard at the crankshaft.

I can't say anything definitive about modern fuels and 8:1 pistons, other than I wouldn't worry about it.

Cheers,
Ken
brightsparkmagnetos.com

[KeithJ]

Thanks for the posts.  Why would SRM give 35 & 33 Deg?
"Some GF timing I picked up somewhere, think it was recommended by SRM using their timing disc: 35 deg btdc for super98
33 deg btdc for 95"

Sounds quite different to 24 Deg with a std A/R unit?

So if the ignition is set at 33 deg BTDC and there is 24 degrees of advance, does that mean static timing at tickover will be 9 deg BTDC?  Surely, it will need to be set up to start with much less than 9 deg BTDC?

If the standard A/R unit is used with 12 deg (24 crankshaft), then with say 2 deg BTDC at "rest", there is only about 22 deg of advance.  What have i missed?

Keith

[muskrat]

10 degrees BTDC at idle sounds about right Keith
Cheers

[Retired Fireman]

Comfirm what Muski said, I had to modify my A10's mag as it had a Triumph advance unit (15-18deg) unit that someone put a BSA pinion on and the advance range was too much. Idled at TDC then advanced to 33 deg, now it idles at 6deg and advances to 33, this transformed the performance and idle of the bike as the advance curve now seems correct for the given RPM of the engine. The note of the engine at idle always sounded flat before I discovered this and it was unstable when hot at idle, when experimenting I set the timing at 10 BTDC and the idle was perfect but after checking with a strobe light after modifying the ears on the auto unit it worked out to 6deg idle and 33 fully advanced and it runs stronger than it ever did. Of course don't forget the mag degrees are half of what the crank degrees will be.

[muskrat]

G'day Arthur, long time no see here.
At zero BTDC it will start easy and idle when cold but as Retired Fireman found not good when hot (or even warm).
Cheers

[KeithJ]

Some GF timing I picked up somewhere, think it was recommended by SRM using their timing disc:

35 deg btdc for super98
33 deg btdc for 95

Fred, post a few pictures of your bikes? (other than a10 pics welcome as well, especially BSA's, as long as you own an A10 too, BTW, I have a Triumph 900 Legend, good stuff ! )

e.

Just took this from the SRM web site
http://www.srmclassicbikes.com/technical/timing-figures
BSA A7/A10
A7.  Alloy Head: 35 degrees (5/16th) (btdc)
A10, Iron Head: 33 degrees (9/32) (btdc)
A10, Alloy Head: 35 degrees (5/16th) (btdc)
 
ATB

KeithJ

[orabanda]

I find the best results are when the timing is retarded 3 degrees on the commonly published figures: ie 32 degrees BTDC for alloy heads, and 30 degrees for iron heads. More HP, torque, and less pinging.

Richard