Re: Matchless 350 G5 piston and rings.

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
SPRIDDLER
Member
Posts: 8541
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Re: Matchless 350 G5 piston and rings.

Post by SPRIDDLER »

I don't think you been given this link which may help you to identify your '650' piston.

http://archives.jampot.dk/technical/Pis ... istons.pdf
'There is a tide in the affairs of men
Which taken at the flood............'
Red Gauntlet
Member
Posts: 173
Joined: Wed Aug 19, 2020 11:22 am
Location: Dorset UK

Re: Re: Matchless 350 G5 piston and rings.

Post by Red Gauntlet »

Thanks for that, I just found another set of drawings on the web as well, really useful info, it would appear that the ones I require have a top of piston to pin centre of 1.66". Perfect, looks like I have the wrong set. Have a great Easter.
Max
Red Gauntlet
Member
Posts: 173
Joined: Wed Aug 19, 2020 11:22 am
Location: Dorset UK

Re: Re: Matchless 350 G5 piston and rings.

Post by Red Gauntlet »

Today I machined the replacement piston and for reference it weighs in at 395g against the original of 360g, inc. pin and clips, I doubt that it will make any significant difference to the balance of the engine, although I have not done a dynamic test as the crank is now in the cases so too late. Anyway pictures of the finished item here for those that are interested.
You do not have the required permissions to view the files attached to this post.
Red Gauntlet
Member
Posts: 173
Joined: Wed Aug 19, 2020 11:22 am
Location: Dorset UK

Re: Matchless 350 G5 piston and rings.

Post by Red Gauntlet »

ajscomboman wrote: Fri Feb 26, 2021 8:07 pm
Mighty Max wrote:The '59 650 piston that fits the G5, do the over bores match i.e is a +20 G5 the same as the +20 650 piston? I gather that the skirt has to be shortened by about 1/4" presumably the balance will be about the same once modded? I would imagine the carb might require a small re-jet as well.
Max
Yep they size up the same, the rear skirt of the piston needs to be shortened to clear the flywheels as the crank and head are off centre. Gives higher compression but the jetting should remain standard, I don't recall having to change mine.
I notice the normal G5 flat top piston has valve cutaways, without measuring, is this going to be a problem as the new pistons don't have them? Don't need any valve / piston collisions.
User avatar
ajscomboman
Member
Posts: 3963
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: Matchless 350 G5 piston and rings.

Post by ajscomboman »

You should be fine, the shoulder of the piston is slightly lower than the standard piston but the dome helps to compensate and up the comp.
Red Gauntlet
Member
Posts: 173
Joined: Wed Aug 19, 2020 11:22 am
Location: Dorset UK

Re: Re: Matchless 350 G5 piston and rings.

Post by Red Gauntlet »

Been running this new higher comp piston for a while now, certainly goes well however there is a certain amount of piston slap when I back off the throttle slightly at about 40/50mph, does anyone else experience this, maybe all lightweights do it, 40 years since I had one on the road before. I thought it was the rotor nut loose but that has remained tight, that I do remember as being a pita..
User avatar
ajscomboman
Member
Posts: 3963
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: Matchless 350 G5 piston and rings.

Post by ajscomboman »

They are prone to slap and to compensate I have seen Wellworthy piston with a longer front thrust face and deep scallop to clear the flywheels. I only removed the rear portion of the 59 piston to clear them. Still had a very small amount of slap when cold but nothing of concern when warmed up.
User avatar
Martin.S
Posts: 443
Joined: Sun Mar 18, 2018 12:02 pm
Location: Bristol UK

Re: Matchless 350 G5 piston and rings.

Post by Martin.S »

G5 and G12csr pistons.jpg
This is what I've used - A G12 piston - was a little while ago and it still hasn't run. Needed a little fettling on the valve pockets I think but it fits!

P.S - Just found the post I did :- viewtopic.php?f=16&t=24107&p=206527&hil ... on#p206527
You do not have the required permissions to view the files attached to this post.
Red Gauntlet
Member
Posts: 173
Joined: Wed Aug 19, 2020 11:22 am
Location: Dorset UK

Re: Matchless 350 G5 piston and rings.

Post by Red Gauntlet »

If you want a standard piston these guys still supply them.
https://www.fwthornton.co.uk/15151-std- ... l-8-295352
£145.00
Yes the Hi comp pistons do slap a bit plus I managed to nip one up the other day, not sure why but needs investigation, was not going quickly but maybe the timing needs a bit of compensation, I was running std timing and super unleaded non E.
Locked