Ignition timing ? -18CS short stroke

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
Posts: 6
Joined: Thu Jul 12, 2018 7:26 pm
Location: Denmark

Ignition timing ? -18CS short stroke

Postby pergarbos » Fri Jul 13, 2018 12:42 pm

I am a relative new owner of an AJS 18CS from 57 (shortstroke) and just want to check the ingition timing , valve clearance ect..

The book covering all models (1957 -1954) shows that fully advanced should be 8,9 mm before TDC
In another book covering Competition models shows that fully advanced should be 12,7 mm before TDC for all models - both the 500 and the smaller 350 as well all trial models.

Another thing is that the fuel of today is different than back in the fifties and that could also have an impact

Any advice for best setting ?

Per

Posts: 6
Joined: Thu Jul 12, 2018 7:26 pm
Location: Denmark

Re: Ignition timing ? -18CS short stroke

Postby pergarbos » Sun Jul 15, 2018 1:32 pm

Hi - After some reading here and there it seems that 7/16 (11 mm) before TDC / fully advanced would be a fair choice.

BR Per

Member
Posts: 290
Joined: Wed Sep 30, 2009 5:54 pm
Location: BUCKS UK

Re: Ignition timing ? -18CS short stroke

Postby uktom77 » Sun Jul 15, 2018 3:56 pm

7/16 BTDC (fully adv) works for me (not competition) and saves your leg a little when starting.


Sent from my iPhone using Tapatalk

Member
User avatar
Posts: 2573
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: Ignition timing ? -18CS short stroke

Postby ajscomboman » Sun Jul 15, 2018 4:27 pm

7/16 doesn't work on my 56 G80CS, pinks like buggery!!!! I've set it to 8.5mm BTDC and still it pinks even on superunleaded fuel. I play with the advance retard to keep it under control. On the 350 56 CS 7/16 BTDC is spot on.

Member
Posts: 6121
Joined: Wed Sep 01, 2004 12:00 am
Location: WEST SUSSEX UK

Re: Ignition timing ? -18CS short stroke

Postby SPRIDDLER » Sun Jul 15, 2018 5:50 pm

ajscomboman wrote: I've set it to 8.5mm BTDC and still it pinks even on superunleaded fuel.

Most tech data timing settings are just a starting point. Allowance must also be made for the weight of the rider.
I poke badgers with spoons.

Member
User avatar
Posts: 2573
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: Ignition timing ? -18CS short stroke

Postby ajscomboman » Sun Jul 15, 2018 6:17 pm

SPRIDDLER wrote:
ajscomboman wrote: I've set it to 8.5mm BTDC and still it pinks even on superunleaded fuel.

Most tech data timing settings are just a starting point. Allowance must also be made for the weight of the rider.


And your point is????? :rofl: :rofl:

Member
User avatar
Posts: 3530
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: Ignition timing ? -18CS short stroke

Postby clive » Sun Jul 15, 2018 7:23 pm

And your point is????? :rofl: :rofl:

Perhaps the point of balance has changed over the years!
clive
if it ain't broke don't fix

Member
Posts: 6121
Joined: Wed Sep 01, 2004 12:00 am
Location: WEST SUSSEX UK

Re: Ignition timing ? -18CS short stroke

Postby SPRIDDLER » Sun Jul 15, 2018 7:33 pm

ajscomboman wrote:
SPRIDDLER wrote:
ajscomboman wrote: I've set it to 8.5mm BTDC and still it pinks even on superunleaded fuel.

Most tech data timing settings are just a starting point. Allowance must also be made for the weight of the rider.


And your point is????? :rofl: :rofl:


To clarify..........

With automatic advance/retard the ignition timing won't advance until the engine revs increase, therefore the amount of advance is always matched to engine speed.

However, with manual advance/retard it is customary to fully advance the timing as soon as the engine has started. Hence when the throttle is opened from a low engine speed the engine will tend to labour over-advanced (pinking) until the engine accelerates the inertia of the total bike weight to an engine speed more suited to full advance.

It has been my long-held opinion that Owner's Manuals should have two columns for ignition timing in the same way that they are given for tyre pressures: One column giving recommended settings for riders up to 20 stone and a second one for the rather less lithe Fray Bentos and Ginsters Peppered Steak pie eaters.
Last edited by SPRIDDLER on Sun Jul 15, 2018 8:11 pm, edited 1 time in total.
I poke badgers with spoons.

Member
Posts: 2953
Joined: Sun Jan 01, 1995 12:00 am
Location: ESSEX UK

Re: Ignition timing ? -18CS short stroke

Postby G15 Roy » Sun Jul 15, 2018 7:39 pm

clive wrote:And your point is????? :rofl: :rofl:

Perhaps the point of balance has changed over the years!


May be the conrods have got shorter and the piston has got larger :lol:
Roy

Member
User avatar
Posts: 1165
Joined: Sat Oct 09, 2010 8:17 pm
Location: SWANSEA UK

Re: Ignition timing ? -18CS short stroke

Postby cbranni » Mon Jul 16, 2018 4:09 pm

My G80cs runs great on 7/16" BTDC scares the life out of me :lol:

Colin
only dead fish go with the flow

Next

Return to Competition / Racers

Who is online

Users browsing this forum: No registered users and 2 guests