G80 Salt Flat Racer

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
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Farmsci
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Joined: Fri Oct 26, 2018 4:09 am
Location: Australian Capital Territory AUSTRALIA

G80 Salt Flat Racer

Post by Farmsci »

Hi everyone,

Long time member, but first time poster here. I'm an Aussie with an inherited interest in Matchless bikes. My first bike was my Grandfathers 55 G9 which I learned to ride on, and still have, and I have a lightly modified 54 G80 which is an ongoing project.

For a long time I have wanted to go landspeed racing on the salt flats in South Australia, and I recently decided a Matchless made sense to me to do it on. So I've kicked off the process by tracking down a 49 G80 engine, alloy head and a rigid frame to form the basis of the racer.

At this point purists should probably turn around and leave the room.

Plans are:

Engine:
Retain 500cc for class
Hi comp piston
Carillo rod
Machine head to take triumph valves and modern valve springs
Run on E85 fuel with a Mikuni or modified Amal
Ignitech programmable CDI ignition computer

Frame:
Slight increase to rake angle
Modern sport bike forks
Weld into a single piece frame
Motocross wheels and axles for serviceability and selection of sprockets
Single rear disc brake only

Lots of other bits and pieces, but that's the rough plan.

Would love to hear from anyone here with experience building these engines for salt flat, or speedway racing and any tips on helping them hang together and perform at sustained high rpm.

If I decide after the first outing that I want to keep doing it, methanol and nitrous would be fun!

Steve
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century
Posts: 90
Joined: Sat Jan 09, 2021 10:02 am
Location: Queensland AUSTRALIA

Re: G80 Salt Flat Racer

Post by century »

go for it mate,with my brothers bike we both grabbed a record there ,the last was mine in 13 on a modified sr 500 yam,a amazingly quick thing for a single,got some big old world machines but that yam would smash them,a world out on the salt,tears and joy,do it for sure,meet some folk,cheers ,dave
bodgie dave
SPRIDDLER
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Location: WEST SUSSEX UK

Re: G80 Salt Flat Racer

Post by SPRIDDLER »

Welcome, Steve.

That sort of tuning and riding is way above my aspirations. However a couple of general thoughts:

The alloy cyl head wasn't introduced til '51.

It would benefit from having the robust AMC designed gearbox (not the earlier Burman CP and B52 'boxes) and which was widely used by other manufacturers for their road and competition machines.

Have a browse under 'Editorial' in Christians Archive (link under) where there are some articles with techy info on tuning and mods on the G80 and G80RR for flat tracking and salt flat racers. Look under the 'Road racers' as well as under the 'Scramblers' headings:
The G50 articles may also have something of interest even though it was an OHC 500 racing single.

http://archives.jampot.dk/

Under the 'Technical' - 'Specific models' you'll find this article by the highly regarded Ken de Groome (a club member) on tuning the G80.

http://archives.jampot.dk/technical/Spe ... cing_c.pdf

Ken can also produce/supply 'hot' cams for the G80. See his advert in the Jampot magazine.

and his article in this link which refers to 'hot' cams:

http://archives.jampot.dk/technical/Gen ... e_Dots.pdf
'There is a tide in the affairs of men
Which taken at the flood............'
Farmsci
Posts: 4
Joined: Fri Oct 26, 2018 4:09 am
Location: Australian Capital Territory AUSTRALIA

Re: G80 Salt Flat Racer

Post by Farmsci »

Oh wow, thank you! There's some brilliant reading in there, and a lot of great insights. Especially reading about oil circulation, one of my big concerns is how well it'll keep oil circulating and I had actually thought about a dry sump pump running in place of the magneto drive.

Much appreciated!
g80csp11
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Location: WEST SUSSEX UK

Re: G80 Salt Flat Racer

Post by g80csp11 »

Id say do it , and write up you build , test stories for a series of articles in the Jampot magazine
Good old fashioned engineering stories make such great reading
Plenty of spares about , so it doesn't really matter if there are a few teething problems along the way
SPRIDDLER
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Re: G80 Salt Flat Racer

Post by SPRIDDLER »

Farmsci wrote: Fri Jul 29, 2022 4:43 am Especially reading about oil circulation, one of my big concerns is how well it'll keep oil circulating and I had actually thought about a dry sump pump running in place of the magneto drive.
This is the oil circulation on your engine:
Oil circ system.JPG


Maybe it's of little help to you with the '49 crankcase but later 'competition' singles used a gear type of oil pump.

See the manual here:

http://archives.jampot.dk/book/Owners_m ... CS_P11.pdf

On page 10 there's this info..........
Oil pump Gear 1.JPG
Oil pump Gear 2.JPG
EDIT
The gear pump is generally referred to as the 'Norton pump' from the days when Norton were part of the AMC group.
The company, 'Andover Norton', has gear type pumps and parts which may be of passing interest although I doubt very much that one could be used with your '49 crankcase, even with a great deal of skilled machining.
Search 'Oil pump' here:

https://andover-norton.co.uk/en/shop/

Another supplier of the ' Norton' oil pumps and parts is here:
(Unfortunately their excessively 'busy' multi-coloured website design may give you a migraine).

https://www.norvilmotorcycle.co.uk/
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Farmsci
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Location: Australian Capital Territory AUSTRALIA

Re: G80 Salt Flat Racer

Post by Farmsci »

Again, thank you very much, that's hugely helpful.
SPRIDDLER
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Re: G80 Salt Flat Racer

Post by SPRIDDLER »

I've just stumbled upon a cutaway engine drawing showing the 'Norton' pump installed in an updated crankcase.
Oil pump Norton.JPG
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Which taken at the flood............'
Farmsci
Posts: 4
Joined: Fri Oct 26, 2018 4:09 am
Location: Australian Capital Territory AUSTRALIA

Re: G80 Salt Flat Racer

Post by Farmsci »

SPRIDDLER wrote: Mon Aug 01, 2022 10:15 am I've just stumbled upon a cutaway engine drawing showing the 'Norton' pump installed in an updated crankcase.

Oil pump Norton.JPG
Interesting, thanks for that! I've been thinking a bit about ways to adapt a gear drive oil pump. In the most basic form an oil pump could be chain driven in place of the magneto I won't have, but that's a lot of plumbing. Plus I still need a crank angle sensor for the CDI box. I've been getting a bit handy with Fusion 360 (CAD Software) and might start playing around with a replacement housing that can gear drive off the crank and mount a CAS with a pick up disk inside as well.

Waiting to chat to my engineer about it though and think about the existing pump aperture as well.
biggles
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Re: G80 Salt Flat Racer

Post by biggles »

In 1949 there were 3 of the factory special Shelsley engines that were sent to Australia. These engines had 12.1 compression ratios. They were fitted with special radiused cam followers and In O 44" In.CL 64" EX.O 63" EX.CL 46" The ignition lead was 40" All of the 3 engines developed over 40 bhp at 5,600 rpm. Externally they looked like standard engines.

I cannot see why you would use a later CS or G85CS engine as you might as well by a complete bike if you wanted to do that.
Cheers John Tinley (Dating Officer)
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