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+--- Thread: Three Bearing Crank Engine - Centre Bearing Question (/showthread.php?tid=4299)
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RE: Three Bearing Crank Engine - Centre Bearing Question - dickie65 - 04-05-2020
I seem to recall that Stuart Rolt built a three bearing engine for father.
If I recall correctly he used an undersize centre shell set. bolted the block onto the engine did up the centre bearing housing then bored the centre shells in line and to size.
I also have a recollection of a second set of shells being done at the same time and being marked top and bottom.
RE: Three Bearing Crank Engine - Centre Bearing Question - Chris KC - 04-05-2020
I wouldn't rule that out Dickie and it's the way the Ozzies still do it I believe; it depends of course on being able to find undersize shells suitable for boring.
Stuart's Reliant crank engines though were built as I describe above. I spent a good few hours with Stuart transcribing his notes on this topic for posterity!
RE: Three Bearing Crank Engine - Centre Bearing Question - Bob Culver - 06-05-2020
The racers here and others have mentioned how they use extreme hugh tensile b.e bolts tightened to exotic torques. It is interesting to reflect that these bolts only handle the upward force of one conrod and piston. Whereas, whilst not pulling on the bolts, the centre bearing handles a goodly proportion of the the same from two pistons together plus the very considerable off centre unbalance of the circular webs and part of the crankpins. Hence the great emphasis placed on rigid crankcases, saviour of the Model T despite bent wire crank. Many cars had alloy crankcases often separate but apparently managed to acheive reasonable rigidity. (Did not succeed with Javelin cars!)
RE: Three Bearing Crank Engine - Centre Bearing Question - Peter Hamstead - 28-06-2020
The Wheaton/Hastings centre bearing modification as Chris KC explained, followed by line boring is definitely the way to go. I also think that an improvement to longevity could be had by feeding oil to the centre bearing from the top via a drilling from the crankshaft jet oil way. The bearing is then being fed oil into the low pressure area rather than the high pressure point at the bottom.
I have been giving this a lot of thought over the last few years which is how long my engine has been sitting on the bench! Determined to start work on it soon as I want the car back on the road early next year.
Any thoughts anyone?
RE: Three Bearing Crank Engine - Centre Bearing Question - Robert Leigh - 28-06-2020
Rather as an aside to the sound advice given, I am aware that when a 3 bearing crank breaks it is usually across one of the circular webs. If there is misalignment these webs have to flex, and after this has happened enough times the result is inevitable.
RE: Three Bearing Crank Engine - Centre Bearing Question - Chris KC - 28-06-2020
Robert, yes pretty much every one I have seen cracks across the circular web at the fillet radius.
Either running misaligned, or running unsupported, as the centre bearing has failed and gone unnoticed; result is the same.
Peter, yes, better fed from above - I have just been doing this mod on a 3-brg case over the weekend, p.m. me if you would like details/ pictures.