Big End Shells

[Orcade-Ian]

A strange one!
I got a call from a friend here in Orkney who has got involved with his friend's classic car - it's quite a nice 1937 Standard Flying 10.  He bought it from a dealer South and had it shipped up to Aviemore and had a few drives in it around there before driving it home up to Orkney.  I think the long climb up Berriedale might have started the problem but as he got about 10 miles from home it really started knocking - he had it recovered and now it's on my friend's two post lift with the sump off.
The sump has stacks of 'shrapnel' pieces in the bottom and on removing the big end caps there are no traces of big end shell, except on rod 4 with this piece stuck to the rod - ALL others have disappeared!

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You can actually break chunks off this shell with your fingers!

There is very minor scoring on the big end journals which are already 30 thou undersize.  We removed the centre main bearing cap which has traditional bi-metal shells with steel backing and looks almost as new with no damage to it or the journal.

Has anyone come across this type of shell which appears to be just one material - possibly sintered?  Or perhaps there are some cheap shells made from Chinesium?

He has found a set of -30 NOS shells which just MIGHT get it running but a full rebuild will be on cards soon, I fear.  If these fragments of soft bearing material have found themselves elsewhere (highly likely) then they may be soft enough not to cause further damage.

Ian

[K2-K6]

They could be "Babbited" type bearings, effectively cast in place alloy, to give bespoke big ends perhaps if the crank was ground and no shells readily available.

https://en.wikipedia.org/wiki/Babbitt_(alloy) gives more oversight of the arrangement etc.

I've heard of, but never experienced first hand such arrangement 

[McCabe-Thiele (Ted)]

My late father told me they used to supply shells for old cars (well pre-war) that you used a bearing scraper tool until you removed enough metal to gain a clearance.

[Bryanj]

I thought at that age they actualy put bearing metal onto the rods and caps then machined to suit.
Early pre unit 500 triumps had white metalled rods and ran direct on the alloy cap i had a pair machined out to take later shells then hand cut notches for shell location(hours and hours) then had to put semicircular grooves in the shells for the bolts.

If there is that much metal in the sump strip it now and sort it as those bits will destroy anything new

[Orcade-Ian]

Hi folks,
I am only familiar with Babbitt bearings on stationary engines, where, as you say Bryan, the rods and caps themselves are white-metalled and scraped to fit - something we did as apprentices.  I didn't notice whether these rods/caps were tabbed - the mains certainly were.  I'll see what the new shells are like when they arrive.  I know he is not keen to pull the engine, even though I told him it was the only way to prevent future heartache and expense.  Fortunately he's a 'mate of a mate', so I can walk away!

Ian

[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]

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.

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