Rebuilding a G12 engine - which parts?

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Rebuilding a G12 engine - which parts?

Postby mdt-son » Sat Feb 02, 2019 4:47 pm

Hi all,

I would like to review the spares needed for rebuilding my G12 engine (post 1960). Apart from the obvious, there may be some less obvious parts to consider.
Is there an individual out there who has compiled a list in electronic format and is willing to share with me and/or a broader audience?
Excel, Word, simple ASCII text format ..... all fits.

Please send a pm or contact me via the club*s messaging board.

Thanks!

Cheers,
Knut

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Re: Rebuilding a G12 engine - which parts?

Postby Yves.Astein » Sat Feb 02, 2019 5:50 pm

Hi Knut,

Here is my shoppinglist. I have almost completed the rebuild of my 59 G12...
It‘s not complete. I did not get new velve rodes and I already had a sealing Kit.

Oh in case you might not know dont forget to mount the seal around the oil filter compartment between the two engine halfs when refitting. And make shure you read the threads about how to refit the crankshaft. Have fun!!!

- [x] 025037 primary Chain Case Gasket
- [x] 014903 5/16 NUT CON ROD TWIN
- [x] 016845 NUT CENTRE WEB CAP
- [x] 018644/2 CONN. ROD BEARING; PLAIN; +020 2x29,62p
- [ ] 800030/S PISTON.650cc TWIN.1959 ONLY. STD 183,41 pair
- [x] 011543 ROLLER BEARING;CRANKSHAFT 55,90
- [x] 011654 FLANGED BUSH FOR CAMSHAFT; 4x
- [x] 014235 FELT FILTER. (TWINS) 8,00
- [x] 014411 GASKET FOR ROCKER COVERS
- [x] 016649/2 CENTRE WEB PLAIN BEARING; +020 81,00
- [x] 016648 THRUST WASHERs
- [x] 011617 WASHER; OIL RETURN PUMP
- [ ] 014283 CIRCLIP,TWIN GUDGEON PIN
- [ ] 026153 CRANKCASE STUD FOR CYL & HEAD
- [x] 022385 OIL DISTRIBUTOR; 1956-64
- [x] 014281 STUD FOR CONNECTING ROD
- [x] 022233 THIN TWIN CYLINDER BASE GASKET
- [ ] 023403 INLET VALVE 600/650 1957/59
- [ ] 025086 STUD IN CRANKCASE FOR CYL/HEAD
- [ ] 025320A EXHAUST VALVE GUIDE.1959 650cc.


Andrew
- [ ] 025320 exhaust valve guide 1959
- [ ] 014170 inlet valve guide
- [ ] 011111 valve guide circlip ( suplyed with valve guides)

Amcclassic


023403 Valve, inlet: 1957-58 600cc & 1959 650cc Twins £ 16.75 £ 13.96

014165 Valve, exhaust: 1949-59 500cc, 1955-58 600cc & 1959 650cc Twins
£ 20.00 £ 16.67

014170 Valve guide, inlet: 1949-59 500cc, 1955-58 600cc & 1959 650cc
£ 10.60 £ 8.83

025320 Valve guide, exhaust: 1959-only 500cc & 650cc Twins
£ 6.50 £ 5.42

011111 Circlip for valve guide

- [ ] 010474 PLAIN BUSH; CAMSHAFT; 2x


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Re: Rebuilding a G12 engine - which parts?

Postby Rob Harknett » Sat Feb 02, 2019 5:53 pm

Surely the parts list for the year and model of your bike will serve this purpose. It may not be electronic, but all engine parts are listed together. The only advantage with electronic file would be, I guess, the parts could be sorted in numerical order. But there would be a disadvantage, if they did not sort as in the printed parts list. That being, bottom end, top end etc. as found in the printed parts list. Here are some excel files some one has made available. http://archives.jampot.dk/book/Spares_l ... res_Lists/

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Re: Rebuilding a G12 engine - which parts?

Postby Mick D » Sat Feb 02, 2019 6:04 pm

Hi

That's a really strange request, apart from gaskets, seals and locking devices all other engine components need to be inspected for condition and assessed whether refurbishment / replacement is required / desirable.
I'd print off the spares list and tick off items as you inspect them.

Regards Mick

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Re: Rebuilding a G12 engine - which parts?

Postby bob121 » Sat Feb 02, 2019 7:15 pm

Surely the list is based on what is required after a thorough inspection. For my m31, it was almost everything. Crank regrind, new pistons, rebore, cams and followers, valves and guides, bearings and bushes and oil filter assembly. Plus gaskets and seals and washers and also some fasteners. (bone of contention with so called stainless fasteners. Corroding faster than the original steel ones).someone elses list is not really relevant.

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Re: Rebuilding a G12 engine - which parts?

Postby SPRIDDLER » Sat Feb 02, 2019 7:38 pm

Mick D wrote:That's a really strange request, apart from gaskets, seals and locking devices all other engine components need to be inspected for condition and assessed whether refurbishment / replacement is required / desirable.
I'd print off the spares list and tick off items as you inspect them.


bob121 wrote:Surely the list is based on what is required after a thorough inspection. ...........(bone of contention with so called stainless fasteners. Corroding faster than the original steel ones).

Couldn't agree more. As much respected ITMA, late of this club (ex AMC employee then authorised dealer) used to say very frequently in respect of owners enthusiastically or unnecessarily replacing parts that may have served for 50, 100 or 150,000 miles: "Half worn original parts are likely to be of better quality and last far longer than many new pattern parts".
How many miles will you be doing on the bike?

EDIT- What I omitted to clarify, but assumed in my simplistic reply was that the decision to replace or not depends upon whether one has the experience to assess whether a worn part is still serviceable or needs to be replaced.
Last edited by SPRIDDLER on Sat Feb 02, 2019 9:20 pm, edited 1 time in total.
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Re: Rebuilding a G12 engine - which parts?

Postby Rob Harknett » Sat Feb 02, 2019 7:49 pm

SPRIDDLER wrote:
bob121 wrote:Surely the list is based on what is required after a thorough inspection. ...........(bone of contention with so called stainless fasteners. Corroding faster than the original steel ones).

Couldn't agree more. As much respected ITMA, late of this club (ex AMC employee then authorised dealer) used to say very frequently in respect of owners enthusiastically or unnecessarily replacing parts that may have served for 50, 100 or 150,000 miles: "Half worn original parts are likely to be of better quality and last far longer than many new pattern parts".
How many miles will you be doing on the bike?

Some new parts fitted to a bike that is seldom used may son need replacing as they will have gone rusty.
If anyone got hold of my found in a field 1936 before I did. They would have pulled the engine apart and spent ages finding or making new parts. I have never even had the head off. Still untouched after 32 years. I don't care about oil leaks I don't care about rattles, I don't care about a bit of smoke. With that attitude I've had 32 years of riding. I have had puncture's, chain came off once, gear box sprocket nut come off once. All happened with an easy push for home or rally site. Punture's even pumped up to get me home.

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Re: Rebuilding a G12 engine - which parts?

Postby mdt-son » Sun Feb 03, 2019 2:55 pm

Bob, my starting point is similar to yours. Apart from timing gear, cam followers, rockers and castings, I expect having to replace or recondition everything else.

Having a list of wearing parts that will need to be ordered anyway allows me to concentrate on the major singular parts which will be closely inspected for sure.
To me, this simplifies the rebuild considerably. Yes, I may spend 10 hours constructing a shopping list by dissecting the spares book for wearing parts.
In my naivity I expected someone had made this exercise already. Alas, I will do it myself. Please note I do not live in the UK, thus spare part bulk orders need to be placed.

Thanks for your views, chaps. Thanks for the referral, Rob. Special thanks goes to Yves for sharing his experience!

- Knut

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