Knackered con rod

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Re: Knackered con rod

Postby McBob » Wed Oct 09, 2019 10:56 am

That is correct Duncan, modified to take BMC bearings, I believe at the time this was the only option (or maybe that was just here)

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Re: Knackered con rod

Postby mdt-son » Mon Nov 18, 2019 9:08 am

McBob wrote:Don't think the bearings have spun, picture below.


Going by the picture it seems clear to me the beanring shells have spun, probably wedging and have locked the conrod solid, which explains damage to the mains and the bent rod.

-Knut

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Re: Knackered con rod

Postby McBob » Mon Nov 18, 2019 11:27 am

Picked up the crank from the machinist, seems where the previous receipt states "oil galleries cleaned out" was bollocks.

They were packed with crud including lead from fuel. The rebuilt engine was only in use after the banning of leaded fuel here.

At the time I cleaned out the oil tank, but couldn't remove the build up of what turned out to be lead in the bottom of the tank, so had it professional cleaned,

surprising how much of it there was.

So yes, this is what happens when the big end is starved of oil.

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Re: Knackered con rod

Postby mdt-son » Mon Nov 18, 2019 12:01 pm

Sorry to hear you suffered by poor workmanship. Will you make a claim against the villains? I have been treated similarly by a garage lately, luckily no engine damage. They will be whipped!!

Good lesson for all twin owners. Do you know how to clean the oil galleries - will oilway blind plugs have to be drilled out and oversize plugs fitted?

-Knut

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Re: Knackered con rod

Postby McBob » Mon Nov 18, 2019 12:46 pm

The chap who carried out the work is long since deceased, so I am taking this one on the chin.

They had a sod of a time removing the screws, which is possibly why it wasn't done last time, there are blind plugs that need removing as well?

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Re: Knackered con rod

Postby McBob » Fri Nov 22, 2019 12:36 pm

When fitting the con rods and centre web, is it best to use assembly lube on the journals or just eng oil?

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Re: Knackered con rod

Postby Duncan » Fri Nov 22, 2019 5:01 pm

Personal choice really, I tend to use graphogen most of the time as the part is protected until the oil circulates and if there is a time lag from assembly to running the lube stays in place, but there is nothing wrong with using oil.

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Re: Knackered con rod

Postby JEAN-NOEL » Fri Nov 22, 2019 6:19 pm

I agree with DUNCAN,GRAPHOGEN is a good stuff that I use on bearings, camshafts, cam followers, but also on centre stand bushes, rear brake pedal...
Before starting the engine the first time, remember to oil the rockers, the pushrods, and pour half a cup of oil trough the valve gear to fill each camshaft tunnel. Because of oïl distributor and restrictors, oïl takes a rather long time to reach the top end and fill the tunnels. And also after a long rest.

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Re: Knackered con rod

Postby McBob » Sat Nov 23, 2019 10:15 am

Thanks, I will definitely use graphogen or equivalent.

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