AJS & Matchless Owners Club

Good point, how much was sucked into the pump. I will definitely look at that.

Moved topic to Help section for g12

Thanks Clive. Cleaned out the pump, had some crud in there but no damage and wear/end float seems minor. Going wash out the oil tank, pipes and all the things.

A discussion at West London club last night thinking was that the gudgeon pin may have seized so bending the conrod. Given that the pistons had been changed that probably involved changing the gudgeon pin. Worth checking the fit and whether the bush has rotated in the conrod.

clive wrote:Worth checking the fit and whether the bush has rotated in the conrod.

Hi

It's worth a look but the small end doesn't look bad in the photo, (are twin small ends bushed?).

Why not ask your engine re-builder to check the crank oil ways for blockage before he strips it down? the steel doesn't need to get hot enough to blue in order to seize and an aluminium alloy con rod will not discolour other than accumulate blackened oil.
I can't imagine any event other than a big end seizure that could fracture the big end, (assuming that the piston didn't seize).

Regards Mick

The fit in the small end is very nice (no bushes) and piston is undamaged. So far I am leaning towards oil starvation as well, caused by debris removed by the un-chamfered oil way blocking it. Its that or an outright failure.

Will definitely ask for a check for blockages before cleaning

Hi Bob

Do you know much about the bike's recent history? At the risk of promoting another 'which oil' discussion - if the bike has recently been converted to detergent multigrade oil from mono grade without a full overhaul, (clean), dislodged carbon may be responsible for rapidly blocking the crank shaft sludge traps.

Regards Mick

Gidday Mick,

Done 1400 or so miles since last full strip down, used running oil then multigrade, has spin on oil filters on pressure and return sides.

I reckon as well as con rods I need a young priest and a old priest to turn this into a exorcism/rebuild.

The centre web bearing clearance appears to have no published figure. The web less the bearing is 1.771", with bearing fitted and journal ground to spec the clearance will be 0.0027". This would seem to be in the expected range?

I have gone with Thunder engineering's rods

McBob wrote:Gidday Mick,

Done 1400 or so miles since last full strip down, used running oil then multigrade, has spin on oil filters on pressure and return sides.

Could it be that the conrod's end cap failed, allowing the bearing shells to dislodge and rotate, finally locking the conrod by wedging to another?
With twin filters and few miles since the rebuild, oil starvation seems to be an unlikely cause.

It would be interesting to see a picture of the end cap remains.

- Knut