Decompression Setup - All Sorted 05/03/19

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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Decompression Setup - All Sorted 05/03/19

Postby Cosmic-Wizard » Wed Feb 27, 2019 11:04 pm

Hello again, it's been a while since my last post due to an accident, but today I actually felt well enough to get outside and continue my G5 recommissioning.

My decompression system doesn't work due to too much slack in the cable. Do you fellow Matchless owners have any pics of their decompression bracket and cable setup (where it fits to the head).
I have a home-made bracket which is useless and I'm unsure if the actuating lever is in the correct position.

Any guidance will be appreciated.
Many thanks,
Jim
Last edited by Cosmic-Wizard on Wed Mar 06, 2019 9:37 am, edited 1 time in total.

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Re: Decompression Setup

Postby Ozmadman » Thu Feb 28, 2019 12:04 am

Cosmic-Wizard wrote:Hello again, it's been a while since my last post due to an accident, but today I actually felt well enough to get outside and continue my G5 recommissioning.

My decompression system doesn't work due to too much slack in the cable. Do you fellow Matchless owners have any pics of their decompression bracket and cable setup (where it fits to the head).
I have a home-made bracket which is useless and I'm unsure if the actuating lever is in the correct position.

Any guidance will be appreciated.
Many thanks,
Jim
Here is a picture of the lever and return spring, the cable outer goes into the hole in the lever and the inner screws into the head, There is no bracket just the lever and return spring. Once assembled adjust the cable (using the threaded section and lock nut at the head end) just until the lever on the handlebars when fully compressed allows you to turn it over without any compression making sure that once you let go of the lever compression returns. Don't over do it as you may not allow the exhaust valve to fully close.
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Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Decompression Setup

Postby Cosmic-Wizard » Thu Feb 28, 2019 9:26 am

Hi Ozmadman, thanks for the picture. That makes a lot more sense to me than what someone has tried to do to mine.

I forgot I could upload pics directly to here, so here's a pic I took yesterday.

By the way, I have just seen your reply to my other thread regarding your oil flow to your head. I'll reply to that in a bit ;)

Cheers mate :D
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Re: Decompression Setup

Postby Ozmadman » Thu Feb 28, 2019 10:40 am

Oh!! looking at that I am wondering if the P.O did that as they couldn't get the correct cable? The correct cable has a ferrule at the end of the outer which locates in the lever, the inner cable has a threaded sleeve with a lock nut attached at the end with a small nipple fixed to the inner which wont pass through threaded section. This parts screws into the head and you can adjust the tension there. Haven't got a picture of the cable though but maybe club spares or any of the other suppliers may do one. Just hope that the thread in the head hasn't been ruined when that bolt has been fixed in there. If all else fails and the thread has been damaged I think your arrangement may work it you got a cable (possibly a bicycle one) with a ferrule on the outer, pass the through the lever, cut off the nipple pass the cable through your bracket and then attach ( or solder another nipple ) on the cable other side of the bracket... You would need to get it the right length as you wont have much adjustment apart from bending the bracket, unless you can make some kind of threaded adjustment (maybe a small diameter bolt and two locknuts with the centre drilled out where the cable could go through before putting on the nipple etc) cheer Paul
Last edited by Ozmadman on Thu Feb 28, 2019 11:23 pm, edited 1 time in total.
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1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Decompression Setup

Postby Martin.S » Thu Feb 28, 2019 3:08 pm

That looks like two different types of lever - I'm on the lookout for one - so which is correct?

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Re: Decompression Setup

Postby ajscomboman » Thu Feb 28, 2019 5:40 pm

Both levers appear to be correct but I won't comment on the cable run. The top picture shows the original lever and the lower a 2 piece pattern part similar to the type the parts service sell (which also fits a lightweight).

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Re: Decompression Setup

Postby Cosmic-Wizard » Thu Feb 28, 2019 10:38 pm

Hi Paul,

I'll pop out tomorrow and remove that bracket to check the thread, but I'm not too worried. Now I know how it should be fitted, I'll make some parts to fit it properly. I find this is all part of the fun. I've just had to turn up and thread a lug which I need to weld to the bracket that the side panel screws onto, as this has been broken off at some point in its life.

I'll update this when I've got it all working ;)

Thanks for the help.
Jim :D

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Re: Decompression Setup

Postby Cosmic-Wizard » Wed Mar 06, 2019 9:36 am

Morning all :D

Just thought I'd update this thread. I went out yesterday to sort out the decompression setup and it turned out to be easier than I thought.

I undid everything and removed the home-made bracket. The threads in the adjuster were a bit rough, so I re-cut those with a 1/4 x 26tpi die. The bolt I removed from the rocker cover that held the bracket, was also the same size. I ran a tap through to clean the thread, then screwed the adjuster in.

Unfortunately, the thread in the rocker cover was a bit oversize, so fully tightening the adjuster would've stripped the thread. The only way to rectify this was to insert a Heli-Coil. Unfortunately, I have no imperial Heli-Coils and to be honest, I don't know if you'd even be able to get a 26tpi insert.
As it turns out, M6 x 1.0mm is a very close match to 1/4 x 26tpi, so I decided to re-tap the thread and insert the Heli-Coil.

I expect to get some stick here as I've now infected my Matchless with a bit of Metric LOL :lol: I make up for that later when I repair the bracket that the side panel screws onto (see my G5 rebuild thread).

Anyway, everything all went back together and works a charm. Unfortunately there is no more adjustment on the cable, but the cable itself is old and has probably done all the stretching it's going to do.

I shall leave you with a few pics and thanks for the help 8-)

Before Removal:
Image

First Re-Tapping with 1/4 x 26tpi Tap:
Image

Adjuster Thread Re-Cut:
Image

My Old Heli-Coil Kit:
Image

Re-Tapping The Oversize Thread For The Insert:
Image

Inserting the... Insert:
Image

Adjuster and Cable Refitted :) :
Image

Cheers
Jim :)

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Re: Decompression Setup - All Sorted 05/03/19

Postby Ozmadman » Wed Mar 06, 2019 8:28 pm

looks good!!! just make sure that its not over adjusted to prevent the exhaust valve from closing fully, it only needs to open that valve a tad.
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed

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Re: Decompression Setup - All Sorted 05/03/19

Postby Cosmic-Wizard » Wed Mar 06, 2019 9:45 pm

Cheers :beer:

No worries mate, it's got about 1/3 slack on the handlebar lever and no tight spots, but I'll keep an eye on it when he goes back on the road ;)

Cheers
Jim

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