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18-11-2018, 04:07 PM
(This post was last modified: 18-11-2018, 04:08 PM by cardiffrob.)
Would any kind soul be able to post a brief video that demonstrates the sort of sound one might find trying to make a crankshaft ring after being hit? Not exactly NDT Science but I have several old cranks here and I noticed they all sound the same with neither a Crystal Wineglass ring nor a dull thud. All cracked or all good? Dinggggg, Dangg or Donk? I have an excess of old blocks and crankcases that I need to sort through and am not sure if anything is really worth hanging onto.
Thanks.
Rob
Joined: Aug 2017 Posts: 725 Threads: 38
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Location: Herefordshire
Hmmm.....I'd go for "Denggggg". Definitely not "Donk".
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Rob, you are looking for a clear ring, which you are only likely to get if the shaft is suspended e.g. from a bit of string.
But...it's not a reliable test, and consider what's at stake (at best, you throw away a perfectly good crankshaft; at worst, you blow your engine to bits).
Buy a dye penetrant crack test kit, which will set you back 25 quid or so, follow the instructions.
If it flags up any clear cracks then you know what to do.
If you are unsure of the result, try it again.
Any that pass, or that you're still not sure about, take them to a specialist and get them crack tested by magnetic particle inspection (MPI).
DP is most effective at finding surface cracks. MPI can pick up cracks just below the surface where DP won't see them.
If a shaft passes both tests you can proceed with reasonable confidence.
Joined: Aug 2017 Posts: 3,425 Threads: 107
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Location: Darkest Bedfordshire
It may also be worth saying that while crack test kits are good for drawing your attention to areas of interest, they sometimes highlight tool marks etc. which are not cracks, so the test must be followed up by careful inspection with a magnifying glass. If you don't have a crack test kit it is perfectly possible to find surface cracks - the larger ones at least - by optical means. None of these methods is infallible so they are best used in concert with each other.
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
The ringing test works on crockery but based on a pile of cracked Seven cranks, useless. If reduced to a donk very seriously cracked. Have to be free of any other dampening factor; grease etc.
I have timed the ring on apparently good Jowett cranks and varies greatly (although these do come with various heat treatments)
I purchased a gallon of black not ultra violet fluid 45 years ago ago " for use with a Benault portable detector". A bit of a fiddle for an amateur to use, but only use a few drops at a time. .I supect it is just fine iron dust in kero.If such a basic product still available a Club may be able to purchase and dispense in small (shielded) bottles. Might be able to make with fine emery paper!
Joined: May 2018 Posts: 2,124 Threads: 111
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Location: Llandrindod Wells
Car type: 29 Special, 30 RK, 28 C Cab
Hi Rob
I found a local machine shop that tested a crank and a steering arm for 10 quid. Worth it!!!
Howard
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Car type: Race Ulster, 1926 Special, 1927 Chummy, 1930 Box
18-11-2018, 08:52 PM
(This post was last modified: 18-11-2018, 08:53 PM by Alan.)
The ring of an uncracked crank is unmistakable and it goes on for ages. Equally unmistakable is the donk of a badly cracked crank. It’s the bit between that’s difficult. Having said that I wouldn’t waste time deciding. If I’m building an engine it gets a new crank. End of.
Alan Fairless
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Location: South yorkshire
Hi Howard
Useful,
Is “Local” anywhere near South Yorkshire ( tho I travel to Brum a lot ) ?
Ian
