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Dye penetrant crack detection


Bhigdog
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Anyone have experiance using a dye penetrant on cast iron heads for crack detection. I,m familiar with magnaflux but want know if dye is an effective substitute......bob

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I usually think about dye penetrant for aluminum parts that can't be magnafluxed to test for cracks.  It ought to work well on cast iron, as long as the metal has been thoroughly cleaned.  Dye penetrant testing can be done at home while magnaflux testing requires more substantial equipment.  Even so, the dye penetrant materials are not cheap.

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I was in an aircraft shop just the other day asking about magnetic particle testing. This particular outfit has dye testing but no magnetic. Nor surprising considering so many aircraft parts are non-ferrous. He said magnetic particles can detect smaller cracks than dye, but of course only in ferrous metals. What sort of a shop keeps magnetic particle testing equipment these days? Where should one go and ask?

 

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I used to PPAP differential housings on test stands and used a spray dye and black light to highlight the crack.    It was magnaflux brand and it worked well.    I use magnatic in my shop.  It was a lot cheaper to purchase a used setup than the dye.   The dye is cleaner and doesn't leave grit all over like magnetic.  

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I had breakfast this AM with my friend and neighbor, Paul. His side business is old oil field hit and miss engine (big stuff) repair and metal stitching.  He has both mag and dye crack detection set ups so I think I'm covered..................Bob

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An old timer once checked a cylinder head for me using only an anacetylene torch.  He blackened the machined surfaces and wiped it down with a clean rag.  He then inspected it with a magnifying glass for cracks.  He didn't find any and said it was good to go.  I installed it and it is still running in the car.

Edited by Mark Shaw (see edit history)
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That's an interesting trick but your case  doesn't prove it works. The out come would have been same no matter what he did because it wasn't cracked. Can't prove a negative.

I got the head off and I "THINK" I see a sign of gasket failure. I sure hope so. Thanks...........Bob

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I worked in an automotive machine shop back in the early '70s. We took a simple approach to checking cylinder heads for cracks.

 

After running the heads through the hot tank and wire brushing the combustion chamber to get it clean, we attached a large horseshoe magnet called a "yoke" to the the flat surface of the head close to the combustion chamber to induce a magnetic field. (Nowadays I think they use an electromagnet to do the same thing.)

 

Then, using a rubber squeeze ball with magnaflux powder in it, we lightly dusted the combustion chamber with the powder and carefully blew away any excess. Because of the magnetic field, the powder would settle in a crack making it visible. Usually a crack would be between the valve seats or between a valve seat and a spark plug hole.

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Bhigdog, I do have a bit of experience using just about all methods of test equipment, as I did NDT/QA for the Nuclear and Aircraft industries from 1968 until 2009. I would think any decent sized machine shop would have a hand-held mag yoke at the very least, probably penetrant equipment too. BUT, if not, do you have any aircraft repair shops or even private hangars near you ? They should have the stuff too. One simple trick, and it's actually the way dye penetrant was 1st used, is to clean (ALWAYS) the part very well, put some dark, thin oil on the area, wait a while with an hour or so being best since this isn't the exact Penetrant material commercially available, gently WIPE it clean with a dry cloth or towel, wipe it again gently with a wipe dampened with alcohol, let it dry a couple of minutes, then sprinkle corn starch or flour on it, wait a few minutes and then blow off the excess gently, and you will get an indication if there is a crack, pinhole, lap, or other defect that held the oil.  Now, magnetic testing.... If you could round up a couple of strong magnets, some fine iron powder, hold the magnets a couple or 3 inches apart and sprinkle the powder between the magnets and blow off the excess, that may  work for you also. These are the basic methods of course, but commercial equipment does the same thing, only easier, better, and a bit more costly of course ! Good luck !

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Thanks all.

I'm kind of on the horns of a dilemma here. The head and gasket both show no egregious signs of failure. I've suffered a cracked head in other cars and the result was obvious in both how the car ran and the crack was visually obvious. No sign of a head crack and other than using water and exhaust bubbles in the expansion tank the car ran fine. So I'm leaning toward a Sneaky Pete type gasket failure. There is one small area only 1/4" from a water galley that shows slight rust discoloration under the gasket. It gives me hope.

I REALLY hate the thoughts of breaking down a perfectly good head to magna flux it. On the other hand the thoughts of putting it all

back together only to have it still leak is depressing.

The tentative plan is to wire brush the head area between the valves since that's the most common fail point and dye check it. If it looks OK I'll put it back together just enough for a test run. No ex manifolds, alternator, power steering etc etc.

Hopefully it will be good to go. All the ancillary crap I mentioned is what took all the time and aggravation to get the head off. That and making special wrenches to get to buried nuts/bolts.

If I have to tear it down again to chase the problem it will be easier second time around.

Corvettes are spawn of the Devil...........Bob

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I'll second that Corvettes are the spawn of the Devil.   Kryptonite cars right there.  I'd load them all onto a container ship and dump in the ocean.  Been saying that for years.  

 

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  • 2 weeks later...

Epilog:

I power wire brushed both the head and block. Minute inspection with magnification showed no signs of a crack. I finished putting it all back together yesterday. After two twenty minute test runs no sign of water loss. I'm calling it good to go.

As an aside I don't believe there is a bigger PITA car to work on. Everything is buried with lots of "You can't get there from here, you have to go someplace else first" parts and bolts. The distributor is surrounded with an anti  static interference housing and the ignition wires are also shielded. The tach  is cable driven from the bottom back of the distributor, the connection for which can hardly be seen much less reached.

If after you finally get the distributor back in at TDC, and replace the anti static housing, and attach all the coil wires and ignition wires and fire it up (thus losing TDC) you then realize you forgot all about the tach drive, it must all be done over including pulling the dist.

Do not ask me how I know this..............Bob

 

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