1955 matchless g9

Information relating to the Matchless G9 or AJS Model 20 500cc twin
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1955 matchless g9

Postby ducati2242 » Wed Jul 11, 2018 3:51 pm

Ive bought a basket case 1955 G9 I built it and registered it but I am now about to restore it properly . When I rebuilt the engine I did the bottom end properly i.e. reground crank , bearings and shells so im not going back in there I also had the frame etc powder coated . One problem I did have was the barrels didnt fit the cases as the stud spacing was too wide . I milled them to fit and rebuilt it like that . Although it runs ok it dosent seem to be as powerful as it should be. It has 6 fin barrels but as I said the stud spacing on the barrels was too far apart . Any advice on which barrels and pistons I should be looking for .

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Re: 1955 matchless g9

Postby raffles » Wed Jul 11, 2018 7:00 pm

You would appear to have the wrong barrels pre 1956 should have two large groves in the spiggot the later barrels have straight
spiggots both use the same pistons.
Tony

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Re: 1955 matchless g9

Postby ducati2242 » Wed Jul 11, 2018 7:08 pm

raffles wrote:You would appear to have the wrong barrels pre 1956 should have two large groves in the spiggot the later barrels have straight spiggots both use the same pistons.
Tony


Now you mention the spiggot that was too big near the flange and I had to turn that down to fit in the casing aperture . As I said I only did this to get it running and registered , now done , i'l look out for a set of barrels with the large grooves . Thanks

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Re: 1955 matchless g9

Postby SPRIDDLER » Thu Jul 12, 2018 2:21 pm

ducati2242 wrote:Although it runs ok it dosent seem to be as powerful as it should be.

I know little about twins but would the cuckoo barrels and pistons make much difference unless they have also lowered the compression ratio?
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Re: 1955 matchless g9

Postby ajsph » Thu Jul 12, 2018 2:42 pm

the grooves in the barrel are an important part of the oil system.
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Re: 1955 matchless g9

Postby ducati2242 » Thu Jul 12, 2018 3:44 pm

SPRIDDLER wrote:
ducati2242 wrote:Although it runs ok it dosent seem to be as powerful as it should be.

I know little about twins but would the cuckoo barrels and pistons make much difference unless they have also lowered the compression ratio?


I always intended getting the correct barrels and with them i will renew the pistons . I'm not sure on the dome of the pistons at all and that could well lower the compression . Oiling is probably quite an important issue as I see the grooved liner also has small holes in them presumably for oil . Just have to locate a set now . feelers are out and i'm sure they will turn up .

Come to think about it I timed it off the top of the piston and if it does have a different height , be it higher or lower , it wont be timed correct which would account for the loss of expected power .

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Re: 1955 matchless g9

Postby Mick D » Thu Jul 12, 2018 4:42 pm

ducati2242 wrote:Come to think about it I timed it off the top of the piston and if it does have a different height , be it higher or lower , it wont be timed correct which would account for the loss of expected power .


Hi

How does the height of the piston crown affect timing? Don't you set at TDC and work from there?

Regards Mick

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Re: 1955 matchless g9

Postby raffles » Thu Jul 12, 2018 6:33 pm

There are several early twin (with the oil groves) for sale at club HQ at kettering, I dont know bore sizes.
Tony

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Re: 1955 matchless g9

Postby ducati2242 » Thu Jul 12, 2018 6:57 pm

Mick D wrote:
ducati2242 wrote:Come to think about it I timed it off the top of the piston and if it does have a different height , be it higher or lower , it wont be timed correct which would account for the loss of expected power .


Hi

How does the height of the piston crown affect timing? Don't you set at TDC and work from there?

Regards Mick


Oh yeah wasnt thinking properly .

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Re: 1955 matchless g9

Postby Expat » Thu Jul 12, 2018 7:40 pm

Wouldn’t the incorrect piston height change the crank angle and therefore the valve timing?

Or am I not thinking correctly. ;)
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