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Re: 1958 Matchless G3 [Re: George Kaplan] #768727
03/20/19 8:50 pm
03/20/19 8:50 pm
Joined: Oct 2017
Posts: 222
England
G
George Kaplan Online content OP
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England
Petrol.

No actual progress on the bike today but there was a package waiting for me when I got home.


[Linked Image]

A Mikuni on its own is available much cheaper from other sources but Allens Performance sell a kit specifically for a G80 with the correct jetting, manifold adapter, screws and a throttle cable so I decided to go to them for the sake of convenience. Before I bought it I called them to check on availability, price etc. They asked me for details of the existing manifold so I sent them the image below.

I will call them back tomorrow because I have two queries that need to be addressed. First the screws that they have sent to me are 26tpi but the head is threaded 22tpi so I need new ones. I could make them myself if I needed to but it will be easier to get them to send them given that its not urgent. The second query is that there is no hose clamp to attach the carb to the rubber manifold. They told me that the kit contained everything that I would need so I am sure that they have just forgotten to enclose it.

The third picture (the montage) illustrates why a plain cap screw wouldn't be correct.


[Linked Image]


[Linked Image]


Obviously a carb will need fuel. I have not cleaned the tank out yet but once I do I will need to leak test it. Fingers crossed.

Looking at the tank mountings three of them would accept a 5/16" x 26tpi bolt which is the correct thread and the last one was stripped and the bolt just slid in. I cleaned up the three that still had some thread with a tap and although the tap went in quite easily, the bolt is now a loose fit in all three, in fact it might be a bit too loose but I will leave them for now.. The fourth will need an insert making which I have had to do before on tanks with similar issues.

John

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Re: 1958 Matchless G3 [Re: George Kaplan] #769015
03/23/19 10:25 pm
03/23/19 10:25 pm
Joined: Oct 2017
Posts: 222
England
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George Kaplan Online content OP
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England
After spending far too long messing about with a Chinese collet chuck before deciding it was garbage I did a bit more work on the Matchless. I made an insert for the bad tank mount.


[Linked Image]

The correct screws for the carb also turned up so I was able to offer the carb up and see how it fits.


[Linked Image]

I also had a look at controls. A few months ago I acquired a set of levers with integral air/advance controls. I have cleaned them up and fitted them, however with the SR1 and the Mikuni I don't need either. I will use them for Phase One but swap them for something more appropriate in Phase Two.

[Linked Image]

At the same time that I got the levers I got a twistgrip. I hadn't paid much attention to it until now. It turns out its a Patented Feridax Locking Twistgrip. I know nothing about these other than I found the advert below online. I fancy giving it a go but don't have a key so I was wondering if anyone on here knows anything about them? I assume that I will need to remove the lock barrel to either replace it or get a key cut. I can only find two pins on the side of the body which I assume are there to retain the lock so I assume that they would need drilling out? Before I do anything with it I will speak to a locksmith.


[Linked Image]


[Linked Image]


[Linked Image]


Stop Thief!

No need, I just remembered I've got a FERIDAX LOCKING TWIST GRIP smile



John

Re: 1958 Matchless G3 [Re: George Kaplan] #769031
03/24/19 12:52 am
03/24/19 12:52 am
Joined: Nov 2011
Posts: 5,202
U.S.
Magnetoman Online content

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Originally Posted by George Kaplan
It turns out its a Patented Feridax Locking Twistgrip.
I have one on the C15S I keep in Ireland. Not that the Irish are untrustworthy, mind you, it's all those American tourists...

Locking the twistgrip will make you feel a lot better. Just don't think about the fact any thief who knows how to start a magneto-equipped bike will realize they can easily operate the bike to go faster than you can run by pulling down on the outer cable. Erase the last sentence from your memory.

Re: 1958 Matchless G3 [Re: Magnetoman] #769051
03/24/19 8:19 am
03/24/19 8:19 am
Joined: Oct 2017
Posts: 222
England
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George Kaplan Online content OP
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England
Originally Posted by Magnetoman
Locking the twistgrip will make you feel a lot better.

I would not rely on the locking twistgrip for security but seeing as I have the Feridax I would like to get it fully functional including the lock.

Originally Posted by Magnetoman
Erase the last sentence from your memory.

What sentence?


Going off on a tangent (not that any threads on here ever do that), that last remark (although I cant remember exactly what it was) reminds me of when I was twenty something and my daily transport was a MkII Transit van. On the way to work one day on the A52 from Derby to Nottingham the throttle cable broke leaving me stranded. Being both poor and overly confident in my own abilities to fix things I didn't have breakdown cover. I did though have in the back of the van a roll of that orange nylon line that they sell in British seaside towns to tourists as fishing line. So I ran some orange line from the throttle on the carb, through the bulkhead and to the area near the steering wheel. I tied on a piece of wood to make a tee handle and carried on my way using this makeshift hand throttle.

At the time I was working long hours and mobile phones were the stuff of Science Fiction films plus the internet wasn't even imagined. So the hand throttle lasted several weeks and I got quite used to it, It only got fixed as soon as it did because I remember my girlfriend at the time (who didn't have a car so used my van quite often) got really annoyed with me about it.

I hate to think what a cop would do to me these days if they stopped me with such a thing. Probably jail.

John

Re: 1958 Matchless G3 [Re: George Kaplan] #769412
03/27/19 7:58 pm
03/27/19 7:58 pm
Joined: Oct 2017
Posts: 222
England
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George Kaplan Online content OP
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England
I realised a few days ago that the NEB clutch is a fraction too deep for the steel chaincase. Never mind I paid much less for it than it is worth so i will put it to use on something else. So I am reverting to using an AMC clutch. I acquired one a couple of days ago and as expected and in keeping with all of the other ones I have seen it is not in great condition.

I have cleaned it up but it needs, as a minimum, a new centre, cush rubbers and bearings.

[Linked Image]

[Linked Image]

I will order a new centre and cush tomorrow but I was wondering if there are any differences in centres? I have checked the part numbers from 1957 to 1960 and they are the same but I am not certain of the year of this clutch.

Also, I have seen reference online to needing a special tool to fit the rubbers but do I need it?

John

Last edited by George Kaplan; 03/27/19 8:17 pm.
Re: 1958 Matchless G3 [Re: George Kaplan] #769579
03/29/19 9:31 pm
03/29/19 9:31 pm
Joined: Oct 2017
Posts: 222
England
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George Kaplan Online content OP
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The centre turned up today along with the new cush rubbers. I didn't have the special tool but used the spare mainshaft and a strap wrench and the rubbers went in quite easily

[Linked Image]


[Linked Image]

With the AMC clutch together I was able to offer it up and whilst the sprockets line up perfectly the back of the clutch rubs on the chaincase. The problem seems to be a raised part of the chaincase aligns with a ridge on the back of the clutch. The later alloy chaincase that would have been used with this clutch has a raised bit but it is a larger diameter.

I have read online about others using an AMC clutch and gearbox with the tin chaincase but haven't seen any comment about them rubbing.

I can see three possible solutions:

1. Make spacers to move the clutch out from the case and a corresponding one for the engine sprocket. The issue with this is that I am pretty sure it will make the clutch rub on the front of the chaincase. (I had just finished making spacers this evening when I had to finish up to attend to something else.). I will confirm that in the morning.

2. Remove the raised part from the rear of the tin chaincase. I am not sure what problems this will cause. One thing that I am not clear about is how the chaincase keeps oil inside, i.e. how it seals around the gearbox mainshaft? Or does it just rely on the raised bit to act as a deflector?

3. Use a later alloy chaincase. I have a complete chaincase plus a spare inside half. The later inner case would need the hole at the engine end boring larger to fit the boss on the crankcase. The screw holes are at the same positions.


[Linked Image]


[Linked Image]


[Linked Image]


All comments welcome.


John


Re: 1958 Matchless G3 [Re: George Kaplan] #769652
03/30/19 9:36 pm
03/30/19 9:36 pm
Joined: Oct 2017
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England
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George Kaplan Online content OP
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I have found out via the owners club forum that the tin chaincase was used with the AMC box and clutch for 1957. Before then it was the tin case with Burman transmission and after then it was AMC transmission with alloy chaincase. The 1957 tin inner case was different to the previous years. I have made 1/8" spacers which gives enough clearance for now but will look for a 1957 inner case.

I seemed to be busy today although only made a bit of progress on the Matchless. I managed to get an ATD from Tony Cooper which arrived today. I had already got a rubber seal but realised that I must have had a brain fart when I ordered the new sprockets and forgot to get the one to drive the mag so I need to get one of those before I can position the magneto correctly to get the chain aligned correctly.

[Linked Image]

[Linked Image]

I also made a bracket to enable me to tumble the tank to clean the inside. I had assumed that the tap connections would be BSP but they are Cycle thread so I will use 2 screws with fibre washers to plug them up.

[Linked Image]

I also started making control cables but realised that whilst I have enough cable outer, inner and nipples, I don't have any ferrules so that was curtailed. When looking on the web for ferrules I also decided to order a bird caging tool. I was going to order one from here https://cable-shop.nl/contents/en-uk/d111.htmlre https://cable-shop.nl/contents/en-uk/d111.html because the one from Venhill is £99 and the one from the Dutch site is about £56. Unfortunately the Dutch one is out of stock. Maybe there has been a rush to get them before we crash out of the EU?

On the subject of cables what do people use to crimp the ferrules on the end of the cables? I want to be able to make professional looking crimps on them but cant seem to find a decent tool.

John

Re: 1958 Matchless G3 [Re: George Kaplan] #769658
03/30/19 10:57 pm
03/30/19 10:57 pm
Joined: Aug 2001
Posts: 4,502
argyll. scotland, uk
gavin eisler Online content
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I looked at the Venhill tool and was inspired by the price.
Bird nest tool recipe, 2 off 2" lengths of 1 inch angle iron. Length not critical.
Drills to match cable size and birds nest size.
Put the two bits of angle iron face to face in a vice, if you put a piece of thin card between them it will leave a bit more nip for the cable , drill the join interface with the cable size drill right through.
Do one hole for throttle cables, one slightly larger one for brake and clutch.
At the top flat face of the pair using the cable holes as pilots, drill slightly larger birds nest holes about 3/16" deep.

Find a punch the same OD as the birds nest holes, with a small rotary burr in a dremel type tool make a concave on the face of the punch.
Thats it , about 1 hrs work. if you want to fancy it up you could add indexing pins to keep the irons in alignment.
Works great.
I used to secure ferrules with a small pin punch two dabs 180 apart, now I use a small drop of superglue.


71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: 1958 Matchless G3 [Re: gavin eisler] #769738
03/31/19 7:18 pm
03/31/19 7:18 pm
Joined: Oct 2017
Posts: 222
England
G
George Kaplan Online content OP
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England
Originally Posted by gavin eisler
I looked at the Venhill tool and was inspired by the price.

"inspired" was not the first word I thought of but I did feel motivated not to hand over £99 to Venhill

Originally Posted by gavin eisler
Bird nest tool recipe,.................


......Thats it , about 1 hrs work. if you want to fancy it up you could add indexing pins to keep the irons in alignment.
Works great.

I had pondered making one myself and its good to hear feedback from someone who has already done so. I have all of the ingredients for the recipe so maybe I will follow your example.


Originally Posted by gavin eisler
I used to secure ferrules with a small pin punch two dabs 180 apart, now I use a small drop of superglue.

I have used with a pin punch previously but hadn't considered superglue. Thanks for the tip, I will gladly use it.

Thanks gavin.

John







Re: 1958 Matchless G3 [Re: George Kaplan] #769739
03/31/19 7:28 pm
03/31/19 7:28 pm
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England
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George Kaplan Online content OP
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England
Brain fart number 2, I picked up a screw from a tub of fasteners yesterday to try it in the tank and I assumed it was cycle judging by the fine pitch but it turns out it was BSP. After getting back from visiting family today I used a thread gauge to determine the pitch is 28tpi.

I tumbled the tank for about half an hour (that's all I could stand of the noise) and rinsed it out. It is very good inside and has no leaks. It will need a bit more work but it is good enough for now.

The cap is dented and needs a new seal. I was wondering how to remove the spring loaded part so I can un-dent it. Any ideas anyone?

[Linked Image]

[Linked Image]


Other than that I just tidied up and made a list of stuff to get next week.

John


When putting some stuff away I was reminded I have a bucket sitting in the corner so here is a Rust Update.

Apologies to everyone who has done this already but it has worked better than I had expected given the temperatures that we have over here.

After one week (a week ago) I took the crank out of the molasses solution and pressure washed it. Here it is in the next 3 pictures. In picture 2 you can see where the end of the drive side axle was not in solution. You can also see where someone (not me) has hammered the end of the axle and mushroomed it. In picture 3 you can still see a bit of rust so it went back in the bucket for another week.

[Linked Image]

[Linked Image]

[Linked Image]

Here it is after the second week in the next 3 pictures. All of the rust is gone although in picture 3 you can see some dark grey deposits on the surface in a few places that looks just like mill scale. I am not sure if more time will improve things so I am calling it done until (or if) it gets stripped down.

[Linked Image]

[Linked Image]

[Linked Image]

Tidying up earlier today I remembered I have a spare set of 5T cylinders intended for my spare pre-war engine (if I ever get around to it). They are now in the molasses.

[Linked Image]

John


Re: 1958 Matchless G3 [Re: George Kaplan] #769749
03/31/19 9:08 pm
03/31/19 9:08 pm
Joined: Sep 2004
Posts: 1,027
Farnham, Surrey, UK
gunner Offline
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Seems like the molasses has worked well, must give it a try next time I need to desrust something.

Regarding the fuel cap, I'm not sure disassembly is possible but maybe one approach is to micro weld on a slide hammer and pull out the dent? You can even get glue on slide hammers as used by car body shops. Alternately you could probably buy a new cap which would be alot less hassle.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: 1958 Matchless G3 [Re: gunner] #769751
03/31/19 9:21 pm
03/31/19 9:21 pm
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Posts: 222
England
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George Kaplan Online content OP
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England
Originally Posted by gunner
Regarding the fuel cap, I'm not sure disassembly is possible but maybe one approach is to micro weld on a slide hammer and pull out the dent?


You might be right on it not being serviceable. I pondered it for a while when I was trying to get it to seal the tank so I could tumble it without it leaking. The seal in the cap is dried out and has shrunk so it leaks.

The cap is brass so I would need to solder or silver solder the slide hammer or use the glue on one. However, long term I don't intend to use this tank so I will give a new cap a miss for now and leave this one dented.

John

Last edited by George Kaplan; 03/31/19 9:23 pm.
Re: 1958 Matchless G3 [Re: George Kaplan] #769758
03/31/19 10:04 pm
03/31/19 10:04 pm
Joined: Sep 2004
Posts: 1,027
Farnham, Surrey, UK
gunner Offline
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Farnham, Surrey, UK
Regarding sealing the cap I would try making a gasket from cork rubber sheet, see This Example. You would have to carefully cut out a nice "washer" size but I does work, I did a similar fix on my 1968 A65 fuel cap which leaks no more.


1968 A65 Firebird
1967 B44 Shooting Star
1972 Norton Commando
Re: 1958 Matchless G3 [Re: George Kaplan] #769771
04/01/19 1:40 am
04/01/19 1:40 am
Joined: Nov 2011
Posts: 5,202
U.S.
Magnetoman Online content

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Originally Posted by George Kaplan
I took the crank out of the molasses solution ... Here it is after the second week in the next 3 pictures. All of the rust is gone
That's why I love the stuff. It's "set and forget," as opposed to requiring hard manual labor. And it works even better in places where the sun actually shines, and a refrigerator is the only place where you can see ice...

Re: 1958 Matchless G3 [Re: Magnetoman] #769848
04/01/19 6:35 pm
04/01/19 6:35 pm
Joined: Oct 2017
Posts: 222
England
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George Kaplan Online content OP
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England
Originally Posted by gunner
Regarding sealing the cap I would try making a gasket from cork rubber sheet, see This Example. You would have to carefully cut out a nice "washer" size but I does work, I did a similar fix on my 1968 A65 fuel cap which leaks no more.

Thanks for the tip gunner, I will bear it in mind when I come back to the cap. For cutting washers out of stuff like this I find one of these is great. Disclaimer, I got the idea from Kevin Naser.


Originally Posted by Magnetoman
......as opposed to requiring hard manual labor. And it works even better in places where the sun actually shines, and a refrigerator is the only place where you can see ice...

I am in favour of minimising manual effort although the hard labour does help keep us Anglo Saxons warm!

John

Re: 1958 Matchless G3 [Re: gunner] #769854
04/01/19 7:45 pm
04/01/19 7:45 pm
Joined: Aug 2001
Posts: 7,726
scotland
triton thrasher Online content
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scotland
Originally Posted by gunner
Regarding sealing the cap I would try making a gasket from cork rubber sheet, see This Example. You would have to carefully cut out a nice "washer" size but I does work, I did a similar fix on my 1968 A65 fuel cap which leaks no more.


Yes, cork mat or leather.


Amateur Loctite enthusiast.
Re: 1958 Matchless G3 [Re: triton thrasher] #770421
04/07/19 8:39 pm
04/07/19 8:39 pm
Joined: Oct 2017
Posts: 222
England
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George Kaplan Online content OP
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England
I have been busy this week with lots of other stuff but managed to do a few Matchless related things. Nothing of particular note but here are a few pictures anyway.

I got the magneto in the right place and cut the seal between the mag and the case to fit. To cut the seal down I made an arbor and held the seal to it with double sided tape. Then I ground a HSS tool to a sharp edge and cut the seal down. It worked very well as long as I kept the cuts down to about 0.020" at a time it cut perfect discs off the seal.

[Linked Image]

[Linked Image]

I looked at lots of little details and made various spacers for the mag, footrest bar and chaincase.

I found an oil pipe that I assume connects as per the next two pictures.

[Linked Image]

[Linked Image]

However, this engine had a rear mounted mag previously but I am using a front mounted mag and the pipe needs to be routed differently which means making a new, longer, one.

I note that the end connected to the rocker box is flared whereas the other end has a nipple. I tried removing the nipple using heat on the assumption that it was soft soldered but to no avail. I then assumed it must be silver soldered and heated it up as hot as I dared but it wasn't budging to the extent that the now softened brass tore when I tapped it with an adjustable spanner acting as a slide hammer. So I made a new nipple. I haven't made a new pipe yet, I have plenty of 1/4" copper pipe and a flaring tool but I need some tight bends and cant find my brake pipe bender, I think I might have lent it to someone but I cant remember who has it. I will get another one for my use only.

[Linked Image]

[Linked Image]

I noticed that this stud has a full nut and a half nut on it. Any ideas why?


[Linked Image]


I need to fix the primary case where it looks like a loose cush drive has damaged it. I note that the area on the side with the hole is paper thin so I will need to cut the hole larger to get to back to thicker metal. I will get rid of the bit on the end too and make a neater job.

[Linked Image]


John

Re: 1958 Matchless G3 [Re: George Kaplan] #771043
04/14/19 8:51 pm
04/14/19 8:51 pm
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Posts: 222
England
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George Kaplan Online content OP
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England
I have been discussing the issue of using an SR1 magneto on a G80/AJS Model 18 over on the owners Club forum. I have learnt that a slightly different cylinder was used on 500's that used an SR1. These had reduced size fins on the front to make room for the SR1 which is much taller than the N1 Magneto. Obviously my cylinder is the non-SR1 version and so the SR1 doesn't fit. I have two options. Option 1 is to swap my cylinder for an SR1 one. Option two is to mill some of my fins to make the SR1 fit.

My initial plan was to sculpt my existing cylinder but someone on the OC forum has said that they might have the correct one available to swap so I am pausing this course of action for a day or two until I know if the correct SR1 cylinder is available.

I hadn't planned on touching the engine until Phase 2 but due to this issue, earlier today I pulled the top end off.

The piston is +0.040.

[Linked Image]

[Linked Image]

The cylinder has some light scoring which coincides with some bad areas on the piston.

[Linked Image]

[Linked Image]

If I use this cylinder I might have to bore it in Phase 2. Plus 0.060" pistons are available.

Also, over the last couple of days I have done a few small jobs like making oil pipe fittings and making a primary chain adjuster from two crappy ones and a few other small items. I will have to sort out the cylinder before I can make much more progress.


John

Re: 1958 Matchless G3 [Re: George Kaplan] #771116
04/15/19 12:23 pm
04/15/19 12:23 pm
Joined: Aug 2001
Posts: 444
Iowa
konon Online content

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Iowa
A lot of progress. Always liked Matchless, singles and twins.


1968 BSA Firebird
1200 HD
XS 1100
1972 Rickman 125
Re: 1958 Matchless G3 [Re: George Kaplan] #771131
04/15/19 3:33 pm
04/15/19 3:33 pm
Joined: Sep 2016
Posts: 196
County Durham
D
ducati2242 Offline
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County Durham
Just been to the national motor museum in uk . Had a look at that double nut area of your bike on an original G3 and there was only a single nut but the bolt looked the same length .

Re: 1958 Matchless G3 [Re: George Kaplan] #771134
04/15/19 3:43 pm
04/15/19 3:43 pm
Joined: Feb 2008
Posts: 4,356
New Jersey USA
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New Jersey USA
The surface on the bore looks pretty fresh.
However the cross hatching looks to be at more like 30 degrees rather than the 45 degrees recommended.
The vertical striations in the bore do not look good and the piston looks very unhealthy.
Perhaps the abrasives used in reboring were not properly washed out?
Perhaps a hand hone with emery paper and all the abrasive not removed?
Was there an air filter fitted to the bike?
Just trying to learn as much as possible from the previous life of the bike to ensure that past mistqakes are not repeated in the present and future.
HTH

Re: 1958 Matchless G3 [Re: George Kaplan] #771142
04/15/19 5:15 pm
04/15/19 5:15 pm
Joined: Aug 2001
Posts: 7,726
scotland
triton thrasher Online content
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scotland
[Linked Image]

That’s been seized. May have been bored to too-tight a clearance. If you get the bore measured, it may only need a hone to correct clearance on a new +40 piston. Or maybe that’s too much for a hone and they’ll have to bore it to +60.

Piston clearance quoted in a 1950s manual is likely to be wrong for a modern piston. When new, many AMC road bikes used unique wire-wound pistons.


Amateur Loctite enthusiast.
Re: 1958 Matchless G3 [Re: triton thrasher] #771165
04/15/19 8:49 pm
04/15/19 8:49 pm
Joined: Oct 2017
Posts: 222
England
G
George Kaplan Online content OP
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George Kaplan  Online Content OP
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Joined: Oct 2017
Posts: 222
England
Originally Posted by Tridentman
The surface on the bore looks pretty fresh.

I thought that too for about 500 milliseconds when I pulled the cylinder and then I saw the scoring and the piston. There is zero lip at the top so it certainly hasn't had too much wear since the re-bore.


Originally Posted by Tridentman
The vertical striations in the bore do not look good and the piston looks very unhealthy.
Perhaps the abrasives used in reboring were not properly washed out?
Perhaps a hand hone with emery paper and all the abrasive not removed?
Was there an air filter fitted to the bike?
Just trying to learn as much as possible from the previous life of the bike to ensure that past mistakes are not repeated in the present and future.

This engine came to me separate from the chassis with no known history.


Originally Posted by triton thrasher


That’s been seized. May have been bored to too-tight a clearance. If you get the bore measured, it may only need a hone to correct clearance on a new +40 piston. Or maybe that’s too much for a hone and they’ll have to bore it to +60.

Piston clearance quoted in a 1950s manual is likely to be wrong for a modern piston. When new, many AMC road bikes used unique wire-wound pistons.

I agree it looks like it has been seized.

I haven't measured the bore yet because I was waiting to hear about the SR1 cylinder before doing anything. However I have heard back now and decided to stick with this one as it needs less work. The scores can be felt when running a fingernail across them so it all depends on what it measures at.

Phase 1 for this bike is to just get something into one piece what would in theory be roadworthy so I can get a dating certificate and a V5. At this point I am not bothered about looks or long term functionality. Therefore I will be re-installing the cylinder with the bore as it is with this piston. It literally only needs to be able to start and run for a minute or two in case it gets inspected.

After that I plan on tearing it all apart and sorting it out. I would like more performance so at that point I will be investigating my piston options along with other various mods. I do know that fitting the rocker arms from the G2 seems to be an accepted upgrade and I will see if there is any head work that might be worthwhile. I note that the con rod is steel and wonder if there is a lighter and better alternative and I am sure there is lots of other stuff to consider. However, all of that is at some point in the future, for now I just need to get it functional and in one piece.

John










Re: 1958 Matchless G3 [Re: George Kaplan] #771238
04/16/19 8:10 pm
04/16/19 8:10 pm
Joined: Oct 2017
Posts: 222
England
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George Kaplan Online content OP
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George Kaplan  Online Content OP
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Joined: Oct 2017
Posts: 222
England
I have had a good search on the owners club forum, online and in the books that I have for information regarding the bore and piston specifications to evaluate my options.

I also had an offline discussion with someone in the owners club who informs me that the maximum recommended oversize re-bore is +0.040". However I note that pistons are available up to +0.060" oversize and others in the owners club have gone up as far as 0.100" oversize using both Volvo or later short stroke pistons.

If 0.060" oversize pistons are available from the owners club spares scheme then it makes sense that a re-bore to this size is OK.

The pistons available for these bikes are JP Pistons and I am told that they need a bit of extra clearance although I need to verify if this is correct. What I cant find is the actual size of JP pistons of various over-sizes so I have emailed JP to enquire. The reason for wanting to know this is so that I can ascertain if I need to do a re-bore or if I can just hone to the correct size. One possibility (mentioned above by Triton Thrasher) for the apparent previous seizure is that the previous re-bore didn't allow enough clearance.

The standard bore is stated to be 3.250" That would make a plus 0.040" re-bore to be 3.290". Now, if I have read the various posts on the owners club about JP piston clearance correctly then the JP piston needs something in the region of 0.0013" to 0.0015" per inch of bore for clearance depending on which thread to believe. Therefore the plus 0.040" piston needs to be about 3.285"

The piston I have seems to be about 3.276" although the size is effected by the fact that it is missing some aluminium on the skirt so it might have started off a bit bigger although its size is actually irrelevant for current purposes.

The bore, however, is relevant and measures as per the table below but in approximate terms it is 3.285"

So it all depends on the size of the JP piston. If my ramblings above are near the mark then I might have ~0.005" (or even more given the measurement further down the bore) to play with to remove the scoring which is not too deep.

Hopefully JP will reply overnight and I can confirm the piston sizes and I can determine what I will do with the bore.

[Linked Image]

John

Last edited by George Kaplan; 04/16/19 8:14 pm.
Re: 1958 Matchless G3 [Re: George Kaplan] #771255
04/16/19 10:58 pm
04/16/19 10:58 pm
Joined: Nov 2011
Posts: 5,202
U.S.
Magnetoman Online content

BritBike Forum member
Magnetoman  Online Content

BritBike Forum member

Joined: Nov 2011
Posts: 5,202
U.S.
I'm sure you know this but be prepared to re-balance the crankshaft after you sort out the piston. For what it's worth, the original complete piston assembly (including gudgeon pin) for my Ariel weighs 505 grams, an aftermarket Omega is 31 g lighter and an aftermarket Gardini is 17 g heavier. These differences would have a significant effect on the balance factor if left uncorrected. Whether or not it is correct, or an urban legend, JP pistons are said to be particularly heavy.

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