Cause and effect on 58' G11

Information relating to the Matchless G11 or AJS Model 30 600cc twin
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g80csp11
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Cause and effect on 58' G11

Post by g80csp11 »

What causes the oil filter felt / gauze to collapse. I know the effect as I’ve just knocked out the drive side big end in a big way

Good old footman James recovery - excellent service
Just time for a couple of pints while witing for the recovery van

Time for another rebuild , but I need to identify the cause so it doesn’t happen again
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TommoT
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Cause and effect on 58' G11

Post by TommoT »

Interesting though a bit depressing as well. I would have thought that the by-pass valve incorporated in the filter set-up would have allowed oil to flow even though the filter has collapsed? If this is not the case, checking the filter regularly becomes vital! Could it be that your by-pass valve was not working? Apart from that the filter must have collapsed because it was blocked, i.e. it should have been cleaned or changed? I have heard others report oil filter collapse on the twins. When the oil is cold and thick it excerts a very high pressure on the filter, I understand there are several versions of these, so maybe its a matter of choosing the right one. Maybe the filter was not the cause of your bigend failure? Could also be lost pressure through a worn centre bearing? I'm rambling now, over'n out!

Looking forward to other comments on this one!
TommoT

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Biscuit
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Cause and effect on 58' G11

Post by Biscuit »

Peter. a little more information would be helpful. Have you yourself changed the filter in the past? has the oil been changed from a non-detergent to a detergent. When was the oil last changed (mileage wise)?

Not that I'm going to be of any help, just for my own interest!

Loved the pun, Tom, depressing, indeed!.



g80csp11
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Cause and effect on 58' G11

Post by g80csp11 »

The engine was checks only 2000 miles ago , bearing shells allmost new . only checked as bike was purchased off ebay for a song
The felt filter was washed clean approx 600 miles ago including the mesh filter in the oil tank
bearings were all in very good , if not new condition approx 1500 milles ago

Morris straight 50 oil

I've also heard that some filters on twins collape , but upto yesterday it's never happened to me

If only we all had hindsight , I would have stripped the engine down and checked everything Saturday morning rather than go out for a ride

Engine is now out and in bits . damage report:

Drive side big end totally shot , damage to big end journal and over heated con-rod
all other bearing shells in very good condition

shopping list :
1 off con rod ( any offers )
Drive side regrind and new shells
Oil filter gauze / felt
usual rebuild gaskets / nuts etc.. after washing all components and checking for damage


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Tolly
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Cause and effect on 58' G11

Post by Tolly »

If it's only the drive side big end that's shot and the other and main is unmarked I would suggest there is an oil blockage that feeds that side of the crank, bearing in mind oil starts its journey on the timing side of the crank.

Bad luck anyway, hope you sort it soon.

Regards, Mike T.

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Eric
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Cause and effect on 58' G11

Post by Eric »

The filter will collapse if it becomes so clogged that it cannot pass oil because the pressure in the filter tunnel can easily exceed 200 psi when the oil is cold. But this is one reason for the oil pressure relief valve or perhaps the 58 G11 was one of the years where it was omitted. This would allow the oil to escape into the timing chamber and down into the bottom of the crankcase but it will not let any oil into the high pressure system that looks after the big ends. The felt filter was dropped because it could block so easily but why it should have done so in 600 miles I dont know unless the oil tank is really full of rubbish.

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TommoT
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Cause and effect on 58' G11

Post by TommoT »

Hi Peter,
I do have a spare conrod, but it shouldn't be a problem finding one in the UK. If your usual sources fail, Tony and Stephen Surbey almost certainly can help out.
TommoT

Ride Your Motorcycle As If Your Life Depended On It - Cos' It Does!
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