My 1961 G5 Rebuild - MASSIVE Update 1/7/2018

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
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My 1961 G5 Rebuild - MASSIVE Update 1/7/2018

Postby Cosmic-Wizard » Mon Jun 25, 2018 10:29 pm

Hello everyone :D

As promised, here is a thread dedicated to the rebuild of my 1961 G5. Firstly, I would like to say a big 'Thank You' to all those who have answered my questions on this board, you've been a big help :beer:

A little background to my Matchless. I bought it on the 1st of June after seeing it advertised on eBay. The engine had been stripped after piston ring failure, but the bike was in nice clean condition - it was just what I was after. A couple of days pass and I was off down to Kent to pick him up and bring him back home.

After unloading everything, I started to work out what bits went where and what bits I was likely to need. Fortunately, the previous owner had already had some of the work done. The piston had a new set of rings, the barrel had been honed and included with the sale, was a spare crankshaft, which had a nice big-end (ooh-er) lol.

With a shopping list made and the internal diameters of the camshaft bush and crankshaft bush checked, it was time to put it all in the shed.

The following pics were taken just after unloading the van. I will post some more pics and updates during the week.

Enjoy.
James :mrgreen:

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Last edited by Cosmic-Wizard on Sun Jul 01, 2018 4:49 pm, edited 1 time in total.

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Re: My 1961 G5 Rebuild

Postby Cosmic-Wizard » Sun Jul 01, 2018 4:45 pm

Hi all, Update Time! :D

This post will pretty-much bring you all up to date and there are lots of pics for your perusal.
The engine has now been rebuilt, but I had a couple of problems along the way, which meant it had to come apart again :roll: But it's back together again lol.

I will caption the pics to save a massive essay.
Enjoy!

+0.040 piston with new rings fitted:
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This pic shows a sheared woodruff key on the spare crank. Note, the ball bearing fitted next to the flywheel. This was the cause of one of my cock-ups :|
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Doing as the bible says - checking the diameter of all the big-end rollers:
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Con-rod ready for rebuilding:
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New top-end bush (right) ready for fitting:
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Removal of the old bush:
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Out it cometh:
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Drilling the oil holes into the new bush:
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All done:
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Both halves of the original crank:
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Time to fit the con-rod:
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Truing-up the crankshaft on old faithful:
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Re: My 1961 G5 Rebuild

Postby Cosmic-Wizard » Sun Jul 01, 2018 4:47 pm

Now, at this point, I noticed the con-rod wasn't sitting centre of the weights and it would grab while turning. This was cock-up number one. I hadn't realised that I fitted the slightly worn crank-pin which had some peculiar wear. Obviously this wasn't noticed until I stripped the crank back down. Oh well, these things happen. I didn't get any pics of the wonky con-rod, so the next pic was after strip-down.

Inspecting everything lol
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A-ha! That's the problem:
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The correct crank-pin now fitted:
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Going back together again:
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Back to the lathe:
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That's much better:
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New timing-side bush prior to fitting:
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Old bush removed:
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Heating the crankcase to expand the alloy. The bush had also been in the freezer all night :) :
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Lovely Jubbly:
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New crank outer bearing to be fitted:
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Some more heat:
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And in it pops:
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Crank breather spigot fitted:
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Re: My 1961 G5 Rebuild

Postby Cosmic-Wizard » Sun Jul 01, 2018 4:48 pm

Now, there are two things wrong in this picture, both will come back to haunt me. Firstly, this is not the correct bearing to use on the inner part of the crank and secondly, you may notice the thread of the crank-pin is sitting proud of the crank weight. This will see me having to strip the engine back down.
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Don't do this:
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Crank vent thingy fitted:
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This was in a bit of a sorry state, so I decided to have a play:
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That's a bit better:
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Reassembly of the crankcases:
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Cam timing pinion and oil pump fitted:
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Camshaft and followers fitted:
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New camshaft oil seal prior to fitting:
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Now this annoyed me. The drawing on the white paper shows the size the gasket SHOULD be. Out with the gasket paper:
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Timing cover fitted:
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Oil tank and weights fitted:
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Piston and barrel fitted:
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And head and rocker cover fitted:
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Starting to look like a G5:
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AND... back out with the engine :(
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When I went to tighten the rotor nut, the engine became very grabby. Doing a bit of research and asking a question on here, I found out I had fitted the wrong type of bearing on the inner part of the crank and I also needed a 0.020" shim behind the front drive sprocket. I ordered a pack of DIN988 shim washers which were 0.5mm thick. This works out to just a tad under the 0.020". Thanks to Clanger9 for this idea :)
So, apart came the engine to find the real reason of the grabbing, which was to be the crank pin sitting proud of the flywheel and being forced into the crankcase when everything was being done up.

'Ello 'ello:
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And after some work with a grinding stone:
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Time now to fit the correct two-piece bearing. Note, the marks on the crankcase where the pin was rubbing:
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Bearing track fitted:
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And the other part fitted to the crank:
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Reassembly... again:
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Another gasket made:
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And back in the frame :D
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Now, will it run? ........

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Re: My 1961 G5 Rebuild - MASSIVE Update 1/7/2018

Postby clanger9 » Mon Jul 02, 2018 7:11 am

Great write-up, James!
All my cam housing gaskets are also a mile off from the correct pattern. I guess they're all like that.
Very strange that the crank pin was protruding like that. The rest of the rebuild looks spot-on. :beer:
1966 AJS Model 14 250 CSR cafe racer
1989 Moto Morini Dart 350
1993 Ducati 750SS

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Re: My 1961 G5 Rebuild - MASSIVE Update 1/7/2018

Postby Mick D » Mon Jul 02, 2018 8:31 am

Hi

A couple of thoughts regarding the crank pin interference:

Is it handed?

Does the new one now have an identical length to the old one?

Regards Mick

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