G80 inlet rocker mod?

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Locked
jim griff
Member
Posts: 56
Joined: Fri Jul 16, 2010 5:10 pm
Location: WREXHAM UK

G80 inlet rocker mod?

Post by jim griff »

Hi, Ive just heard of a mod to increase the power on a G80 by changing the inlet rocker arm to a lightweight version, anyone carried this out successfully? I'd love a little bit more output from my G80 to aid overtaking etc. Any thoughts on this? If its genuine, does it improves all models? Intrigued by this, can anyone add any enlightenment on this subject please?
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: G80 inlet rocker mod?

Post by Rob Harknett »

Most traffic is probably doing what the speed limit of the road allows. So you would break the law if you did overtake anything .
DickV
Posts: 16
Joined: Tue Jul 28, 2020 4:41 am
Location: B.C. Canada

Re: G80 inlet rocker mod?

Post by DickV »

I have a G80 as well, 1966, short stroke. I believe it has only 7.3 compression also. The piston does not appear to come anywhere near the cylinder. So this winter I would like to mill the bottom of the cylinder to gain some more compression and change the inlet rocker arm to a lightweight version. Are these rockers still available? From where? Where we live there are big semi trucks going up long hills and its nice to have a little extra passing power then. thanks, Dick V.
User avatar
Pharisee
Member
Posts: 1126
Joined: Tue Mar 15, 2016 8:51 pm
Location: Lincolnshire UK
Contact:

Re: G80 inlet rocker mod?

Post by Pharisee »

I've carried out this mod to my '55 AJS M18S. At the same time, I advanced the inlet cam timing by 18° (one tooth on the cam-gear) by using the 350cc timing mark. Taken together, there is a small but noticeable improvement to the bike's performance. The exhaust note was also noticeably "sharper". I've also upped the overall gearing a little by fitting a 17 tooth final drive sprocket.
I recently took the bike on a 380 mile round trip to visit my brother in Kent. The bike ran happily at the legal limit and had enough left in hand for a bit of overtaking, given that there was enough time, as acceleration at that speed wasn't rapid. The bike also returned around 65 m.p.g. for the trip.
John
I'm from the Fens.... Gimme six.
Locked