Most lightweight engines

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
Red Gauntlet
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Most lightweight engines

Post by Red Gauntlet »

It seems to me that most lightweight engines I dismantle suffer from the same rod migration such as this, anyone know why, not a bent rod or worn bearings.
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Joker_Bones
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Re: Most lightweight engines

Post by Joker_Bones »

I cannot help... But I am curious... What is rod migration? Can you explain further what the picture shows?
ChrisTheChippy
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Re: Most lightweight engines

Post by ChrisTheChippy »

I too am very curious ?? I have never heard of Rod migration. I would be interested to know what that means. I can't see anything amiss in that picture.
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Duncan
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Re: Most lightweight engines

Post by Duncan »

Looks like the flywheel is rubbing on the conrod.
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clive
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Re: Most lightweight engines

Post by clive »

Well there seems to be wear on the side of the rod suggesting it has migrated across where it should not.
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g80csp11
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Re: Most lightweight engines

Post by g80csp11 »

Big End wear most likely would allow the rod to move more in the flywheels , especially if you have seen it on multiple engines it unlikely to be mis-assembly , plus perhaps small end wear. i Assume you don't just reassembly the engine when you see it
SPRIDDLER
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Re: Most lightweight engines

Post by SPRIDDLER »

It looks to be around 5 (10?) thou worn off the side which could be due to rock in a worn big end. That would produce a lot of steel dust going round the engine.
Is the conrod worn on both sides?
Does it extend right down to the big end eye or is it only as far as the perimeter of the flywheel at TDC?
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Red Gauntlet
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Re: Most lightweight engines

Post by Red Gauntlet »

The big end has done about 4k miles and has no discernible wear and yes, it is worn right down to the B/E eye just on the drive side, I am going to fit a new assembly as this is obviously compromised. It is odd as I have seen this same phenomenon on several engines, always to the drive side. Bush is fine and so are the bearings on the drive side, the rod when centralised in the crank is bang in the middle of the barrel aperture. The magnetic plug has done a good job here along with the felt oil filter thankfully.
Greybeard
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Re: Most lightweight engines

Post by Greybeard »

A conrod can tend to 'walk' to one side if the big end outer bearing race has been poorly lapped after fitting so that it has a very slight taper. Perhaps if it has happened to several bikes it was down to poor workmanship or a worn out lapping tool.

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Joker_Bones
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Re: Most lightweight engines

Post by Joker_Bones »

Ohhhh... The two shiny strips on the side of the con rod are wear from rubbing on the flywheel. When I saw the picture I imagined the rod had been machined on the sides.
I didn't realise the little end got that close to the flywheel... Eeeek.
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