3brg crankcase reinforcement

[Ritchie Wilson]

Jamie was enquiring about Jack Cottons modification of the three-bearing engines crankcase to stiffen it so that the centre main bearing stays in alignment with the other two main bearings.
The three-bearing engine was chosen so that high revs could be achieved without running the big-ends which Jack found was a problem with the (pre-Phoenix) 1 5/16" two-bearing, jet-lubricated, crankshaft.
The diagram comes from the 750MC's 1966 publication "Design for Competition" which is the precursor of the "Companion".
Did many people try this modification in the Formula days?
Is Jack Cotton the famous UK politician?

   

The aluminium casting also reinforced the centre main bearing housing which, as Bob Culver pointed out, is not well supported.
Jack Cotton listed the machining needed on the crankcase and the casting - lots of tricky milling needed.

[Rogerfrench]

I remember looking at this 60-ish years ago, and wondering where the oil went.
Maybe you drill some holes?

[Tony Betts]

Must admit, I dont get it.

It looks like another stupid idea from the idiots companion.

I can  see the suggestion of supporting the centre main? But does it really.

It looks to be friction fit against the centre main. And if it is. Surly you dont need to be putting any upward force on the centre main. It would just push the inline bearings, out of line.

Tony.

[Tony Press]

Jamie was enquiring about Jack Cottons modification of the three-bearing engines crankcase to stiffen it so that the centre main bearing stays in alignment with the other two main bearings.
The three-bearing engine was chosen so that high revs could be achieved without running the big-ends which Jack found was a problem with the (pre-Phoenix) 1 5/16" two-bearing, jet-lubricated, crankshaft.
The diagram comes from the 750MC's 1966 publication "Design for Competition" which is the precursor of the "Companion".
Did many people try this modification in the Formula days?
Is Jack Cotton the famous UK politician?
The aluminium casting also reinforced the centre main bearing housing which, as Bob Culver pointed out, is not well supported.
Jack Cotton listed the machining needed on the crankcase and the casting - lots of tricky milling needed.

"The diagram comes from the 750MC's 1966 publication "Design for Competition" which is the precursor of the "Companion".The diagram comes from the 750MC's 1966 publication "Design for Competition" which is the precursor of the "Companion"."

I thought 'The Special Builders Guide' was the precursor to the Companion. 

I do not think this was in the SBG or the Companion so possibly not a success.

[Ian Williams]

No Tony, it was the SBG then Design for competition and then The Companion, I have all three publications, Design for competition is by far the more comprehensive from a special builders perspective. I think it fair to say that The Companion is not strictly aimed at special builders which the other's were, and as with all 750 MC publications the articles were very much the opinion of the writer, much like here, so you take more notice of those who have proven track records and make up your own mind rather than blindly take things as gospel.

[Jamie]

Thank you, Ritchie, for posting this.

I can see the logic, assuming that the centre bearing is restrained from flexing downwards by the support on the plate. Somehow, though, I can imagine it causing other problems by trying to push the centre bearing upwards too much if the whole set up is not machined and fitted extremely accurately.

I think that I will stick to the advice from the old Speedex site for setting up the centre bearing when I finally get to that stage.

Regards,

Jamie.

[Austin in the Shed]

I've only worked on one 3 brg engine,and checking the centre bearing alignment it was within around .001". The general consensus of these engines was that the centre bearing was often out of line,this and insufficient oil to the centre main meant a short life.
One chap I knew made a new centre bearing undersize and line bored it when all clamped up with the block.
A couple of tricks I was told were ,To use 2 of the offside bolts, ( The ones that bolt the block down ) and drill the block to suit (now a  9 bolt block )
Blank the oil feed past the centre main where it feeds the camshaft bushes and drill a couple of small holes into the bushes from above .
Check the crank centre webs for cracks ,the copper pipe to the centre bearing and use an oversized oil pump.
They do make a nice smooth engine.

[Ruairidh Dunford]

A properly rebuilt three bearing engine in standard form is sublime and, in my experience, no more or less reliable than a two bearing engine.

A poorly built three bearing engine is another matter entirely.

My rule of thumb is that I will only rebuild a three bearing engine if it comes in complete - so that I can see what has gone wrong as I break it down. I won't touch a dismantled one.

[Ritchie Wilson]

I had a look through the Austin Seven Companion (the green book) and Tony Press is quite right, the Jack Cotton article didn't make the cut from the Design for Competition book (also green). I agree that this doesn't inspire confidence. Mr Cotton did say that the modification cured the big-end failures, although he changed the centre-main bearing every 2 or 3 races and fitted a higher capacity oil pump.

Jack French has an article in the Companion from Nov 1959 where he discusses the 3 bearing engine. Like Austin in the Shed and Jack Cotton he recommends line-boring an under-size centre-main bearing. Jack French advocates machining several and replacing them at 5000 mile intervals citing Colin Chapman's experience with Lotus 3 in 1951

[Chris KC]

1985D P7 figs 2 - 3 + a decent crank : sorted.