How fast is fast???

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
chaz_lithik
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Joined: Thu Jun 04, 2020 6:52 pm
Location: LANCASHIRE UK

How fast is fast???

Post by chaz_lithik »

Hi All

I've now got the bike up and running successfully and ridden her a few times.
As this is my first classic im just wondering if she is running well, all sounds well and feels well.
She feels most comfortable around 45mph pushing any more feels like its straining it (could be my mechanical sympathy!)
Is that about right for a 1952 g80?

Or should it feel like its got more to give/be comfortable at a higher speed?

Thanks all

Charlie
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Pharisee
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Re: How fast is fast???

Post by Pharisee »

My '55 M18S is slightly geared up, running a 17 tooth final drive sprocket instead of the standard 16 tooth and will happily run at 70 mph. I regularly run it along the A1 from my home in Lincolnshire to my old haunt in Hitchin and back. Keeping up with the traffic on the dual carriageway is not a problem.
My '56 G80CS had lower gearing as standard, only running an 18 tooth engine sprocket, not the 21 tooth of the touring model. As I don't use it 'off-road', I replaced the 16 tooth final drive sprocket with a 19 tooth version to bring the gearing up to something close to the touring model. I think the internal gear ratios are different to my M18S as the CS will happily pull well over 50 mph in second gear and 80 mph (in top) is not hard to achieve given a long enough road and the ability to hang on!!

John
I'm from the Fens.... Gimme six.
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clive
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Re: How fast is fast???

Post by clive »

I regularly run my 1951 model 18 (same as the G80) at 60 mph as cruising speed. I wonder if there is any indication that your bike has been geared down for sidecar work. Any sidecar lugs on the frame bolt under the seat or the front stud that joins the bottom rail and the front loop through the engine? The usual modification for pulling a chair is to replace the engine drive sprocket which should have 21 teeth on a 500 with the 18 tooth sprocket which is on the 350. This gives more torque for sidecar use but makes the engine much busier above 45, even so it ought to run to 60 happily enough. I would start by trying to run it a bit faster, they seem to all have a sweet spot somewhere in the range 55 to 60 and you may find it sounds better a little faster. Next time you have the primary chaincase off count the teeth on the engine sprocket under the primary chain. If you do change up from 18 teeth to 21 you will need to get the the correct length primary chain as it will have the shorter 350 one fitted.
clive
if it ain't broke don't fix
chaz_lithik
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Location: LANCASHIRE UK

Re: How fast is fast???

Post by chaz_lithik »

Thanks all I will have a look at the gearing and mayb push a bit further!

I cant see any indication of sidecar work It was my god fathers before me for a good 30 years and he never used a sidecar.

Could there be any other reasons its down on power? Or is there possibly to many to list!

Thank you

Charlie
Mick D
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Re: How fast is fast???

Post by Mick D »

Hi

Check the timing, (you are fully advancing the lever aren't you), lack of oomff can be indicative of the timing being a little retarded.

Regards Mick
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Pharisee
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Re: How fast is fast???

Post by Pharisee »

Further to my earlier post... I should perhaps add that my M18S engine has the inlet valve timing advanced by 18°. Easily achieved by using the 350cc engine timing 'dots' on the inlet cam gear. Rumour has it that the factory retarded the timing deliberately to make the engine more of a 'slogger' and better suited to hauling a sidecar.
I have also fitted a lightweight inlet pushrod rocker arm which is 1/8" shorter than the heavyweight equivalent arm. This changes the rocker assembly ratio, giving the inlet valve more lift. It's probably due to these mods, and the slightly raised gearing, that the bike runs happily at 70 mph.
John
I'm from the Fens.... Gimme six.
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Group Leader
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Re: How fast is fast???

Post by Group Leader »

Pharisee wrote:I regularly run it along the A1 from my home in Lincolnshire to my old haunt in Hitchin and back.
Does that mean we'll see you at the Old George in Ickleford Wednesday evenings then John? :lol:

You'll need a good dynamo because it'll be dark by the time you get home! :rofl:

Alan
1953 AJS 16MS, 1939 BSA 250 and a 1/3 scale Sopwith Triplane but that's another story ..... :lol:
SPRIDDLER
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Re: How fast is fast???

Post by SPRIDDLER »

On solo gearing it should cruise very happily at 60/65 mph.
As Mick D mentioned, (and since these old bikes are new to you) are you sure you have the ign timing lever in the fully advanced position when riding and also the choke off?
If you don't have the manuals (Owners, Workshop and Spares) you can find them here under 'Books':

http://archives.jampot.dk/
'There is a tide in the affairs of men
Which taken at the flood............'
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Taid
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Re: How fast is fast???

Post by Taid »

SPRIDDLER wrote:...

If you don't have the manuals (Owners, Workshop and Spares) you can find them here under 'Books':

http://archives.jampot.dk/

You can get them printed and bound on the net .. I'm happy with the service that 'doxdirect' do
___

Now sold ... 1956 AJS 16MS Bitsa .. HSU 414 .. rebuilt/re-registered 1987
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Samuel
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Re: How fast is fast???

Post by Samuel »

Pharisee wrote:Further to my earlier post... I should perhaps add that my M18S engine has the inlet valve timing advanced by 18°. Easily achieved by using the 350cc engine timing 'dots' on the inlet cam gear. Rumour has it that the factory retarded the timing deliberately to make the engine more of a 'slogger' and better suited to hauling a sidecar.
I have also fitted a lightweight inlet pushrod rocker arm which is 1/8" shorter than the heavyweight equivalent arm. This changes the rocker assembly ratio, giving the inlet valve more lift. It's probably due to these mods, and the slightly raised gearing, that the bike runs happily at 70 mph.
John
From which year can you perform the above change - does it depend on whether it has hairpin or coil valve springs (mine is an iron head 49 500)?
Sam
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