piston

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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piston

Postby red_dog49 » Wed Apr 11, 2018 4:28 pm

:beer: hi all, well after a lot of doing absolutely everything to get the bike to run it turns
out the wrong piston has been fitted, clever of the previous owner to find a piston of the correct stroke and to get it to run,,,lol.
but that is my problem now, low compression, not any of the other reasons from my previous post.
i'm told they are rarer than gearbox's even, non in club spares,etc,etc, so the search is on.
if any of you know of someone who has one or somewhere to look i would be in your debt and the wife would be happier as well.
can a 250 barrel and piston fit does anyone know.
regards
Rob.

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Re: piston

Postby clanger9 » Wed Apr 11, 2018 4:44 pm

Hi Rob,

Apparently a 1959 650 twin piston will fit (and should be easier to find):
viewtopic.php?t=15584&p=136007#p135761

You can't fit a 250 barrel and piston - the 350 stroke is much longer.

Good luck with your search!
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: piston

Postby clanger9 » Wed Apr 11, 2018 5:19 pm

Wow, there's a NOS 350 piston on fleabay right now:
https://www.ebay.co.uk/itm/AJS-MATCHLES ... SwkyxazJW~

Not cheap, rubbish photos, but maybe what you're looking for?
1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: piston

Postby red_dog49 » Wed Apr 11, 2018 5:49 pm

hi, yes have seen ,do not think it's the correct one, some confusion over the part number, and should be domed head , I have messaged seller for more info.

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Re: piston

Postby ajscomboman » Wed Apr 11, 2018 6:28 pm

red_dog49 wrote:hi, yes have seen ,do not think it's the correct one, some confusion over the part number, and should be domed head , I have messaged seller for more info.


Nope 350's are flat top piston and that is a JP piston not an original and it looks to be very heavy if the metal around the pin is anything to go by. I have an AE +60 piston (no rings or gudgeon pin) and also a barrel that can be bored to suit for the same money if you're interested. PM me quick though as the forum adverts police will be onto us pronto. :rofl: :rofl:

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Re: piston

Postby clanger9 » Wed Apr 11, 2018 6:30 pm

You may be right about the eBay one, but 350 Lightweight pistons are definitely flat-topped.
It's the 250 ones that are domed.

Here's Paul's 350 piston:
S1760012.jpg


Here's are my 250 ones (CSR 9.5:1 on the right):
IMG_2241.jpg
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1966 AJS Model 14 250 CSR "cafe racer"
1993 Ducati 750SS

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Re: piston

Postby Ozmadman » Wed Apr 11, 2018 10:09 pm

Here's a few better pictures of my piston which is as mentioned a JP piston (JP0894) bike runs fine with this fitted
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Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: piston

Postby red_dog49 » Thu Apr 12, 2018 3:13 pm

all, well more questions than answers as usual,
the parts list only shows up to +40(2nd) for rebore , so will the barrel take a +60 , where did pauls +60 piston come from.
I have yet to find a drawing of a 350 piston, but in the manuals the exploded view of 250 and 350 shows a domed piston.
anyway I am looking for a solution my barrel is good and standard size and the useless piston from bike made pre 1950 flat topped and undersize of the barrel, not ajs.
regards
Rob

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Re: piston

Postby Ozmadman » Thu Apr 12, 2018 10:18 pm

The original piston was a wire wound type but they are long gone Mine is +.040" not 60 thou, but I seem to remember them doing a plus 60 here's a link to a page on their site. if the bore is fine why not just get a standard one from them?

https://www.norndaautomotive.com.au/jp- ... %20CR7.4:1

or this one

https://www.norndaautomotive.com.au/jp-pistons.html

Interestingly, they list a JP01070 for a matchless G5 which is the same engine?? A JP0895 fits

JPO895 Royal Enfield Motorcycle 500 Bullet, 499cc, OHV,
CR6.5:1; 500 Bullet, OHV, CR 7.25:1 (1960-) 1953-59

Here is their catalogue

https://www.norndaautomotive.com.au/ima ... 2016v2.pdf
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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