1961 G80CS Spark Plug and Silencer

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
Locked
Peter Baker
Posts: 8
Joined: Mon May 09, 2016 11:00 am
Location: Devon UK

1961 G80CS Spark Plug and Silencer

Post by Peter Baker »

Thanks to you guys for all the help, I have now got my bike running well (re-bore, new piston and valves, change inlet cam from CI to SH, war of attrition on oil leaks, correct jets in monobloc etc.). I have yet to helicoil the thread for one of the studs in the cylinder head for the engine steady which is a bit dodgy but can wait till the winter I think.

Two questions left:-

From your experience, which is the best Spark Plug to use?

My "silencer" is really pretty anti-social: it frightens the horses and gets the children scurrying for the hedges round here! It appears to have no baffles at all. Is there an "off the shelf" fix for this. It's really very noisy when pulling and especially on the overrun with the banging and popping. I quite like the noise but I'm not convinced that the sentiment is shared by others. I have looked at previous posts but most solutions tend to involve drastic surgery for which I am definitely not qualified.

Any suggestions?

Cheers

Peter
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: 1961 G80CS Spark Plug and Silencer

Post by Rob Harknett »

You may have a miss match exhaust system. I sure original exhaust systems most models of the era had straight through silencer, but the pipe had pepper pot holes and the end blocked off. So you may have an old type silencer , with a pipe like many repros, much shorter, and no pepper pot or end blocked off. I recall back in the 1980's I got an Amours repro system. When the parcel arrived, I thought, that's wrong, no where near long enough to have the correct pipe inside. You could try a standard recommended plug, not having 1050's/60's fuel, another type may prove better. Others will make recommendations, that suit their own bike and its set up. If you are not happy with your plug, perhaps you have cleaned it. If so dump it. Since the 70's plugs have not had the central electrode glazed. Without glazing, cleaning will damage the plug more. It will then quickly contaminate. Note if you have a clean engine and exhaust, it will quieten a bit once it gets dirty.
Don Madden
Member
Posts: 2882
Joined: Mon Jan 01, 1990 12:00 am
Location: USA USA

Re: 1961 G80CS Spark Plug and Silencer

Post by Don Madden »

The CI inlet cam is more radical than the SH, more power at upper range & less a low end but the increased overlap makes for less effort to kick start the engine. With either cam the low end response can be improved by using the 1963-up inlet rockers. They use the lightweight pushrod arm, which is slightly shorter than the heavyweight, giving more lift at the valve. My 1963 G80CS, otherwise the same as 60-61 pulls from low down, as a touring but revs very high, pulling with no flat spots.

The Short stroke CS header pipe is not capped, nor perforated as the touring type. The silencer had a baffle plate with a large opening at the center. Modern regulations in the UK prohibit unbaffled silencers so the makers build one in. The CS cams will not breath properly with any back pressure in the exhaust, going very flat in the mid range & not revving up. I use a fork station tube with one end cut at an angle to drive out the baffle, which is only tack welded in. The Armour's exhaust has fitted all my scramblers from 1956-63 except for the mounting brackets so I make my own mountings. The NGK B8ES works well for me on all CS but the 1956 only had a strange pre-ignition chamber above the valves requiring special plugs that are no longer available.

Cheers! Don.
User avatar
GOLDSTAR
Member
Posts: 2521
Joined: Thu Sep 11, 2003 1:00 am
Location: KENT UK

Re: 1961 G80CS Spark Plug and Silencer

Post by GOLDSTAR »

my '57 has a strange head and if I use an ordinary l/r plug the electode will foul and close the gap, I have to use two washers under the plug to give me clearance, 'twas Don who informed me way back that there was an unusual length plug for these models. kind regards
silverfoxracing
Posts: 13
Joined: Wed Jun 29, 2022 1:37 pm
Location: australia

Re: 1961 G80CS Spark Plug and Silencer

Post by silverfoxracing »

GOLDSTAR wrote: Sun Aug 07, 2016 9:10 am my '57 has a strange head and if I use an ordinary l/r plug the electode will foul and close the gap, I have to use two washers under the plug to give me clearance, 'twas Don who informed me way back that there was an unusual length plug for these models. kind regards
Dragging up an old post, but I to have a 57 CS and I have the plug issue as well, Normal lenght plug bends electrode over, It has a rectangle shape hole going into the piston? Maybe to index the plug? what plug is supposed to fit? Is the head something special??
g80csp11
Member
Posts: 1567
Joined: Mon Jan 01, 1990 12:00 am
Location: WEST SUSSEX UK

Re: 1961 G80CS Spark Plug and Silencer

Post by g80csp11 »

I have a 61CS as well , and what you need to do is fit 2 spark plug washers to the spark plug , that will fix the issue
apparently that is normal according to Ken De Groome when I asked him the same question
mdt-son
Member
Posts: 373
Joined: Wed Feb 01, 2012 1:22 pm
Location: Vestland NORWAY

Re: 1961 G80CS Spark Plug and Silencer

Post by mdt-son »

I believe the problem with bent electrode in '57-'59 cylinder heads is due to the slot firing design, which requires a special type of spark plug. The '61 head should not be affected in the same way. Howeveerm if the plug sticks too far out in the combustion chamber, for whatever reason, using multiple spark plug washers will cure the problem. Trial fitting a spark plug while head is off is required.

- Knut
Locked