Joined: Jul 2018 Posts: 102 Threads: 33
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I may be buying a 1937 ruby with a three bearing engine, the question is how do I make sure the cars bottom end is reliable, what options other than converting to a 2 bearing crank is there.
I drive my cars daily so she'd be seeing around 5k miles a year, I'm not bothered about having the most power, valves, pistons etc can be left well alone I really don't want to have to and can't afford a full rebuild, just to give myself confidence in the bottom end as I really do use the cars as if they're new, keeping at low rpm up hills to protect it isn't practical and presume no new three bearing cranks are being produced?
Hope to hear back!!
Joined: Mar 2015 Posts: 5,452 Threads: 231
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Location: Scotchland
The honest answer, in my experience, is that if it is quiet on testing (before purchase) that is about as good as you'll get to answer your question.
If it fails, then work can be carried out to replace with original or change to two bearing.
A well sorted three bearing engine is an absolute delight to drive, I hope you have found a good-un.
Joined: Aug 2017 Posts: 3,407 Threads: 107
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Location: Darkest Bedfordshire
If it were mine, I would crack test the crank just to be sure, with special attention to the fillets at the centre webs.
But as Ruairidh says, if already running smoothly chances are it is OK. I for one wouldn't convert it to 2.
Don't go crazy with tuning / ignition advance and if the engine starts to sound noisy stop and investigate.
Joined: Aug 2017 Posts: 1,654 Threads: 23
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Location: The village of Evenley
Car type: 1934 Austin Seven RP Deluxe
I put loads of miles on a three bearing motor, which was on an original crank and as long as you treat it with "mechanical sympathy" it should be as reliable as any other original crank.
Joined: Aug 2017 Posts: 1,054 Threads: 108
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Location: Cheshire
Others may have more to say on this, but sensible revs are better rather than straining up a hill in too high a gear? If there is a chance to check the crank then it would seem worthwhile, but otherwise it is just a case of sensible driving and hope? After twenty years on an original crank, which must now be 84 yrs old, I still think about it failing, and wonder about swapping to a 2 bearing before it does - but this 3-bearing engine is so smooth...
Joined: Aug 2017 Posts: 1,654 Threads: 23
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Location: The village of Evenley
Car type: 1934 Austin Seven RP Deluxe
I forgot to mention, the three bearing I did so many miles on without a problem, I fitted with a low compression head so it would t be quite so harsh and tough on the crank. The engine was very smooth and I didn’t notice any significant decrease in power, to be honest!
