Knackered con rod

Information relating to the Matchless G12 or AJS Model 31 650cc twin
Member
Posts: 110
Joined: Sun Sep 19, 2010 9:17 am
Location: NEW ZEALAND

Re: Knackered con rod

Postby McBob » Wed Aug 28, 2019 12:06 pm

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

Member
User avatar
Posts: 3530
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: Knackered con rod

Postby clive » Wed Aug 28, 2019 7:55 pm

Moved topic to Help section for g12
clive
if it ain't broke don't fix

Member
Posts: 110
Joined: Sun Sep 19, 2010 9:17 am
Location: NEW ZEALAND

Re: Knackered con rod

Postby McBob » Thu Aug 29, 2019 10:08 am

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.

Member
User avatar
Posts: 3530
Joined: Mon Jan 01, 1990 12:00 am
Location: LONDON UK

Re: Knackered con rod

Postby clive » Thu Aug 29, 2019 3:18 pm

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
if it ain't broke don't fix

Member
Posts: 1473
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Knackered con rod

Postby Mick D » Thu Aug 29, 2019 4:44 pm

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

Member
Posts: 110
Joined: Sun Sep 19, 2010 9:17 am
Location: NEW ZEALAND

Re: Knackered con rod

Postby McBob » Fri Aug 30, 2019 11:31 am

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

Member
Posts: 1473
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Knackered con rod

Postby Mick D » Fri Aug 30, 2019 1:01 pm

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

Member
Posts: 110
Joined: Sun Sep 19, 2010 9:17 am
Location: NEW ZEALAND

Re: Knackered con rod

Postby McBob » Sat Aug 31, 2019 11:47 am

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.

Previous

Return to G12 / AJS Model 31

Who is online

Users browsing this forum: No registered users and 8 guests