Performance upgrade info needed

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Re: Performance upgrade info needed

Postby Rob Harknett » Tue Sep 24, 2019 11:29 pm

The bike and all its bits are 65 years old. Probably still capable of braking speed limits on most roads. You could quite easy wreck it without making it go faster. If riding the old bike beyond the limits it was built for, is intended, maybe you should replace the lot for a 650 twin. Perhaps even a modern bike.

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Re: Performance upgrade info needed

Postby SPRIDDLER » Wed Sep 25, 2019 6:37 am

Welcome to the Forums, Steve.
I agree with Rob's comments and enjoy these old bikes precisely for their thumping character and have no need nor interest in tuning them for more power than as designed.
However, in order to partly answer your question you could contact Ken de Groome (01945 870060) who specialises in H/W machines and can, or used to, supply hot cams. It all depends upon how far you want to go. There are several publications, one of which is Phil Irving's 'Tuning for Speed'.
If you search the link below you will find some articles on tuning but bear in mind that as well as more power/speed you'll need to stop the bike.
http://archives.jampot.dk/
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I poke badgers with spoons.

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Re: Performance upgrade info needed

Postby Pharisee » Wed Sep 25, 2019 7:29 am

A small increase in performance can be gained by using the 350cc timing mark on the inlet cam gear when setting up the valve timing. This will advance the inlet cam timing by 18°. Another small gain can be had by using a lightweight 250/350 rocker arm on the pushrod end of the inlet rocker shaft. This is 1/8" shorter than the heavyweight rocker arm, changing the ratio between the pushrod and valve rocker arms and giving the inlet valve proportionally more lift. I've used both these modifications on my own 500cc AJS and while the performance gain isn't enormous, it is noticable.

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Re: Performance upgrade info needed

Postby Janet » Wed Sep 25, 2019 10:57 am

Don't forget, if you upgrade the engine performance, you'll need to upgrade the brakes, otherwise you won't stop before you fly off the end of your island.
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Re: Performance upgrade info needed

Postby Rob Harknett » Wed Sep 25, 2019 11:12 am

What model 18 you have may make a little difference. You should have noticed BHP of these old machines being something like 18 BHP to about 24 BHP They are hardly the model built for racing. When I was a teen I wanted speed, but the bikes were new then. I fitted a hi comp piston. It was not long before I blew the bottom end. Very expensive engine rebuild. The shop said we've replaced your hi comp piston with a standard piston. Here's your hi comp piston. Put it back in the bike if you want another bill like this. That was in 1957, the bike was 1955. Lesson learned.

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Re: Performance upgrade info needed

Postby SPRIDDLER » Wed Sep 25, 2019 11:49 am

To get you started here are a couple of articles in the archives to which I linked earlier. The second one is by Ken de Groome on cam types/cam setting and his hot cams :

http://archives.jampot.dk/technical/Gen ... _types.pdf

http://archives.jampot.dk/technical/Gen ... e_Dots.pdf

Clip-ons and rearsets, plus a few strips of chequered tape, an empty silencer, thick white socks turned over my boot tops, white silk scarf and a Zippo lighter used to make me very fast indeed. ;)
I poke badgers with spoons.

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