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Big End Shells

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K2-K6:
A simple magnet test of the shrapnel will tell if there's any steel component that's dropped out from the missing locations of big end.

If its generally white metal and no steel, then unlikely (dependent on pickup gauze and filter arrangement) to have been distributed to any particular harm.

The material used though, must have picked up on the big end journal to effectively start its erosion and depletion as I see it.

The journal sites would at minimum need a polish to avoid the shells picking up when installed.

If it's sat for a long time, then possibly the bearings have been affected by corrosion to "attach" them partially to the journal and start that process. I've seen plain bearings with corrosion sites from storage which I've tentatively considered acid within the oil to be the cause. Manifested as little corrosion patches eaten into the soft shell material to then be removed by rotation.
To me, long extensive storage should involve changing the oil prior to that status, then rotated to distribute and not run with risk of combustion byproducts,  specifically partly and burnt fuel wetting past piston rings. My understanding is that contains, ultimately, sulphuric acid from combustion process containing sulphur. Ultimately the oil should be chemically buffered to accept that during use, but long term storage may see unwanted effects in tbat sphere.

Orcade-Ian:

--- Quote from: K2-K6 on September 06, 2025, 10:44:57 AM ---A simple magnet test of the shrapnel will tell if there's any steel component that's dropped out from the missing locations of big end.

If its generally white metal and no steel, then unlikely (dependent on pickup gauze and filter arrangement) to have been distributed to any particular harm.

The material used though, must have picked up on the big end journal to effectively start its erosion and depletion as I see it.

The journal sites would at minimum need a polish to avoid the shells picking up when installed.

If it's sat for a long time, then possibly the bearings have been affected by corrosion to "attach" them partially to the journal and start that process. I've seen plain bearings with corrosion sites from storage which I've tentatively considered acid within the oil to be the cause. Manifested as little corrosion patches eaten into the soft shell material to then be removed by rotation.
To me, long extensive storage should involve changing the oil prior to that status, then rotated to distribute and not run with risk of combustion byproducts,  specifically partly and burnt fuel wetting past piston rings. My understanding is that contains, ultimately, sulphuric acid from combustion process containing sulphur. Ultimately the oil should be chemically buffered to accept that during use, but long term storage may see unwanted effects in tbat sphere.

--- End quote ---

Many thanks for that, very comprehensive.  Yes, I tested the debris with a magnet and no evidence of ferrous swarf but the centre main shell was definitely steel backed.  Initially we intend polishing the journals and reassembling with the new shells when they arrive.  A few regular low interval oil changes and then see what happens.  The only wasted expense would be oil, the new shells and a sump gasket plus a few split pins if it all goes pear shaped.

I would still prefer to pull the motor now and do a proper job but hey ho!  I hope I'm proven wrong for his sake.

Ian

Bryanj:
Even for a mate of a mate i would make sure you have somebody else there when you tell them in your opinion it aught to be stripped and fully inspected and if it goes wrong its all on him, i have been there, done that and glad i had proof so i didnt get crucified

Orcade-Ian:
I agree Bryan,
Orkney is a small place, so I can get my considered opinion across to most of the people that matter to me and he has been told in front of the chap who asked if I could go and accurately measure the journals, just what the situation is.  I think he would go for a rebuild eventually but not just now - I think 'er in doors' wants a trip out in it after him spending the Kids inheritance on it - hope she gets her wish!  My gut feeling is that it will run fine enough for a few Sunday outings around Orkney - I doubt they will ever venture down to Mainland Scotland.

Ian

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