Cracked Crank

[Dave Wortley]

A very gently used crank and still it's cracked! Attempting to reassemble the original engine from the family heirloom RN saloon which my dad bought in 1936. The engine has been stood on the floor in my garage since 1983. He " nursed" (his terminology) that engine for decades and when I took it over I was careful with it. It must have been abused in its first 4 years before he purchased it.

[Bob Culver]

That would have to be the longest intact crack ever discovered! There is a huge statistical scatter in metal fatigue. Items never overloaded often have shorter lives (The Comet test aircraft was overstressed and led to very wrong life fatigue predictions). It may not be the original crank. Parts could have been substituted t a low mileage for various reasons (My car had an exchange engine by 1940 and 40,000 miles). Steels and the heat treatment etc were not as controlled as now. may have ben cracked by some factory straightening correction (as seems to have occurred with many Javelin cars)

[Dave Wortley]

Bob, it's the original crank  because it has the number stamped on it, the same one as on the block and crankcase. I think. Will check tomorrow.
Cheers,Dave.

[Dave Wortley]

Bob, yes crank, case and block all same numbers.

[Chris KC]

Dave, are you quite sure that's a crack? Not saying it isn't but it can be hard to read these things on a part never mind from a photo. Also not sure what kit you're using.

Fatigue is cumulative, doesn't necessarily have to be thrashed, just run for a long time. Many originals have a fillet radius no more than 1/16" (and that's the good 'uns) - it's a big stress raiser on an already smallish crank.

[Dave Wortley]

Ok Chris, going to give it another test. (Already done it twice) It' s a  Neocol kit ie white spray with black magnetic particles in suspension. Purchased from Tony B. Just found out it is made in Sheffield where I live.

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I have a really good magnifying glass made from the lens of an old cine projector. Nevertheless I will give it another go.

[Chris KC]

I know of those but have never used one. Certainly with dye pen once you've flagged up where to look it's not hard to see a crack with a decent looking-glass.

[Tony Betts]

Hi Dave,

Must say I've got to echo Bob.

That's by far the largest crack I've seen before breaking.

Be cearful it's not a machining mark.

Hopefully below is a picture of one I crack tested two weeks ago.

Usually the cracks start to get little steps in them.

And although there is a fillet to deture cracks. More often than not, the crack is right in the middle of the fillet.

And yes the supply company is just down the road from you. I've only supplied it for people in the past. Because you have to buy a minimum of 10 tins at a time. 10 white and 10 black ink that is. Not many people want to buy such quantity. So i split it down in kits for you boys.

Thanks tony.

   

[Dave Wortley]

Chris and Tony, just retested the crank rear main journal and no doubt now that it is a crack and not a machining mark. I filed the rad with a tiny round needle file and still the mark appeared. It has steps in it as you say Tony so it's a scrapper. Just tested my last spare Austin crank which is sound so it's going in the engine. 
Cheers,
Dave.

[Bob Culver]

It should go in a museum! Persons used to say cranks broke at 30 mph etc but the situation when finally let go has little to do with anything.