MTFCA Forum

All Joking aside; hanging a crankshaft up and hitting it with a hammer is not a true test in relation of it being cracked or not .

If I had that skill to know what a cracked part sounded like, the crack detection suppliers would be out of business.

The reason for crack detection or "Magnalfux," being a trade name like Band-Aid or Kleenex represents a big part of the engine rebuilding process.

There is a dry version where user has a electrified tool/magnet with a north and south pole that when placed on flat one dimensional parts, the user dusts iron powder over area to be checked, if part is cracked the powder which is magnetic will get drawn into the void highlighting crack. as seen in picture of water outlet cracked to serial number.

There is also a wet mag machine used for 3 dimensional objects such as crankshafts and cylinder heads, axles, etc.

The part to be checked is placed in the machine between copper pads to recreate North and south of a magnet, thereby when the part is charged through the machine causing part to become magnetized. Then there is a hoop that is passed over each of the rod and main journals to charge around the circumference of the part in question. See second photo.

The part is doused with a non-flammable liquid solution that has luminescent magnetic powder in it.
When the part becomes doused with the solution, the magnetism of the part will attract the iron particles of the solution to the crack.
If there are cracks they will immediately be highlighted by using the black light .
If you'll notice, picture of the crankshaft being highlighted with a fine green line ,as this is the crack in the crankshaft.

What I have mentioned above is for magnetic parts .

For non ferrous,non metallic parts there is the dye test which is done by spraying the part with a green dye that will seep into the crack over time and then a developer spray is used to highlight the area in question.

This procedure is more time consuming and is quite messy.

Above is general description of three methods of crack detection.

A good machine shop will perform these steps so you don't have this result of broken parts as you may notice that this crankshaft is broken, in a newly rebuilt engine.

Try ringing one of the cracked cranks sometime they deffinetly sound different. I hang and ring and if it rings then I mag it. If it doesn't ring
correctly I toss it saves mag time.......

Hanging from a wire & tapping is a good indication, If it (crank, drum or other) rings test it, if it goes thud you save the time & effort of further
testing. Mag-N-Flux is falling out of favor these days for the dry & liquid penetrant methods. I picked up a Mag-N-Flux yoke @ a swap meet for
$20 It cost more to buy the powder & dispenser.
Craig.

Just my experience- I only use dry mag with powder for castings- heads, blocks, trans drums etc. Always wet mag for steel parts like spindles, axles, crankshafts and conn rods. Not sure what industry practice is, just what has always worked for me.

And for Jeffrey's question below, yes there are blocks out the that are 100% free of cracks.

Just curious, have you guys EVER checked a block for cracks, and found NONE.

Chances are that all cast iron has a micro-crack somewhere...it's the nature of the beast! As it is cooled it shrinks, and that makes internal stresses, that might decide to release tomorrow...might only want to go through just so many heat cycles and then say 'outta here'..might never let go.

Bending does not help the cause as the hairpin just accelerates the crack. Look at most failed T cranks on the crank pin break...got down by cycle cracking to about 1/3 of the pin diameter before twisting off... . It's not bad iron...it wanted to let go just there...as it was the weakest stress point resister, even a scratch on the surface can be a crack host. I'll get pilloried for it but some of the best cast iron today comes from China. They still have 1930's places but at least 20 new foundries have been built since GM Shanghai, all to a higher standard than GM Shanghai...some way over the top.

I was lucky enough to have witnessed an almost dark factory where the iron was made and poured by taking mild steel stamping flash and working backwards on the melted and added materials to achieve the cast iron physical properties needed. Then the poured parts are cleaned and gleaned, and on a conveyor belt enter what looks like a car wash system...first room is mag particle with vision system in a black lit room with auto ejection and 4 guys who sit at the end of the room for a last visual chance to press an eject button. No issue on waste factor, it goes back as part of the formula to start with steel and work backwards to create iron the next time the big mix is made...next room is again more tunnel, this time 100% x-ray with auto eject by the time it reaches the end of the line. AI does most of the visual work, a human notes and is the overseer. Not black magic, real, their customers are MB, Brembo, Honda, VW, and TRW....

I asked them a question...today we Americans usually 'age' iron as a 4 season open air bath tends to accelerate the early cracking period to obvious. Then if it makes it the normalize time, it gets machined. Chinese don't do that, nor did Ford to my knowledge. I asked the iron-monger in charge is there a way to temper fresh castings that has not survived to the 21st century without the need for an oven? He smiled a curious smile and grin then pointed for me to follow...once the casting line reaches its end, the loaded core boxes are sent back along the backside of the furnace pour rooms and then get so hot they need to cool overnight before removing the core box. No proof, but I wonder if Ford did the same thing or just did everything to a green state and said 'live with the results'.....

big2bird wrote: ↑

Fri Aug 08, 2025 2:18 pm

Just curious, have you guys EVER checked a block for cracks, and found NONE.

Yes it was a 1927 Model T Block.

J and M Machine wrote: ↑

Fri Aug 08, 2025 7:03 pm

big2bird wrote: ↑

Fri Aug 08, 2025 2:18 pm

Just curious, have you guys EVER checked a block for cracks, and found NONE.

Yes it was a 1927 Model T Block.

That's great. That's one out of...........?

To me they have always been a crapshoot.

Very slow cooling after pouring will normalize a casting like an engine block, but that is not compatible with mass production. The T block must have been a pretty good design, since they are not known for cracking except as a result of abuse. I have no idea how they cast so many blocks so rapidly, but whatever they did seemed to work well. They produced castings and forgings at an incredible rate. Maybe they used extra sand around the casting to retain heat longer. Maybe they had some method of pre-heating the prepared molds to reduce thermal shock.