1950 SQ4 - Big End Shells (Bearings)

[paul.ptak]

My crankshafts are at the machinist right now and I have to return a voice message asking what undersize big end bearings are available.

I see on the Draganfly site that -020, -030, and -040 are available for my SQ4.

If my machinist tells me he can get by with a cut of -010, other than Draganfly, are -010 shells available anywhere else? Does the club have any of these spares on hand?

Thanks!

Paul

[nevhunter]

Advisable to have them and install in rods to get final shaft size rather than just go by a book size. Remove crankshaft oil gallery plugs and clean oil passages carefully. Nev

[simon.holyfield]

Some stuff on my blog about cleaning those galleries...

[chaz.wheeler]

Ive been waiting for -0.010 shells for 3 months now, apparently there isn't a big enough order yet to get them made, certainly not having 3 ten thou throws and a twenty!! as suggested

[graham.wade]

Why not?

[paul.ptak]

The good news - the plain bearing ends on each crank is round and at stock dimensions.

The expected news - big end journals for #1, 2, & 3 could be ground to -010.

The bad news - big end journal on #4 has to go to -030.

Not wanting to wait for -010 shells; 2 & 3 will be cut to -020 unless I can turn up some -010 over the weekend. 1 & 4 will be cut to -030.

[nevhunter]

Get the (undersize) .030, shells and bore them to the size you need. Check crush first and once you have machined them this way you can't MIX the bearings around. They have to be assembled as they were arranged in each con rod when it was machined. Nev

[john.whiting]

Regrettably,very few bearings can be bored now,they have what is known as microlayer surface.This means the whitemetal is only 005 to 007 thick.Your machinist will know all about this,I would imagine.These days, resizable bearings will be generally be a leadbronze, golden brown in color and not a white bearing metal.If you re ever stuck for a slipper bearing,they are easily made from another shell with the same wall thickness,and preferably width(but can be wider),and somewhat larger tunnel.This is what we used to do for Matchless twin bearings when they were unavailable years ago.Cut off the end opposite the lock tab to provide the required crush.If your rods are cactus,you can get the bigends sized at the same time.When boring bearings,place a 002 shim between the parting surfaces of the cap and rod.Bore to the correct size plus the shim thickness,and when the shim is removed the bearing will be free at the sides,which is how it should be.Regards John.

[simon.holyfield]

Couldn't you get the shells reinstalled? I know my favourite machine shop, Ashpoles in Bishops Stortford, can reline white metal bearings. I know these are not normally thin walled, but it might be worth asking.

He had a cammy square in last time I saw him.

[nevhunter]

John has added a few points which I thought should have to be taken into account. If the original bearings are babbit on steel you can remetal them and bore them out to size. You have to check the crush, as always. This won't be cheap but white metal was what most of them had originally and is more suited to an engine running without a filter than copper lead or Alutin. Also needs less running clearance. I did this to a BSA ZA7 when I was young, as well as doing the timing side bush the same way .Nev