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This is the snout of a crank from a diesel engine.

The pulleys were running out of round so I removed the pulleys and on the crank was a flange that the pulleys bolted to. When I removed the flange to check face run out I saw this distortion on the snout. It looks like electrolysis to me but that doesn't explain the small fissure cracks that look like a heat related crack like what a manual gear box flywheel would have from disc slippage.

Some of the metal is eroded away but looks like enough to support flange and run true.

It will need to be polished in place.

Key for flange is in tack so the flange was not spinning on the snout and it is only about 1/3 of the snout.

Any ideas of cause?

Looks like the flange was moving around on that area hammering the shaft. Material only moves around so much before it fatigues and cracks. Kinda like over knurling. What does the mating piece look like? Repaired before? Hard to tell from the picture.

Mating piece looks the same.

As far as the repair, not sure. owner busted an alt bracket over in the bahamas in august and wrapped the belts around the pulleys and flange. Repair guy didn't say he took that apart but if he did it only has enough time to run from the Bahamas to Palm Beach.

Supposed to be a machined fit between snout and flange. Can't see how it was hammering on that side but flange face is 10 thousands out. Go out to 11 inch pulleys and damper and thats quite a wobble.

Always possible but in a 6 hour time period? I did notice that the steel on the flange is very soft.

It is really tough to tell by the pic. Possible that it is plated (nickle/elctroless nickle?) and that the plating is failing due to the wobble.

Looks like a m&m candy. Hard on the outside soft on the inside. When I worked with Dana we saw some hardness issues on pinion gears. This looks one the Same thing

Bruce how did the flange come off, too easy? And what fastens flange to crank,interference fit or was it a large bolt in center loose? I'm not a metalurgist but man that crank looks to have had heat cycles. Sure the crank is savable, looks toast from pic.

Flange I believe is supposed to be an interference fit, but not tight enough apparently that an oring groove is cut into the flange to ride against the snout to prevent oil seepage between the flang and snout.
It came off fairly snug like most crank snout dampers or flanges with a puller. I did think that the nut holding it on the snout was not as tight as it should have been, but we are not sure if the guy over in the Bahamas didn't have it apart.

Since the flange steel to me is extremely soft, when the belts came off the alt when the bracket broke and wrapped around the damper and flange, they twisted the flange and after the alt brackets were fixed, the mechanic didn't notice the pulley run out because it wasn't there before owner left for the Bahamas. It was bouncing the alt around and the repairs came apart from the run out. After I fixed the brackets firm, I noticed the alt bouncing and whne I glanced at the pulleys they were running out quite bad.

Thats what I'm trying to determine is if the crank is salvageable or has to be removed and try and grind down and a sleeve done or re weld and grind to specs or find another crank. The issue is removing the engine would involve a tremendous amount of work to do as the main salon structure and bulkhead sits right over the stb engine which this is.

JP, I thought the same thing, but these are over 25 year old engines with thousands of running hours with relatively no issues. One would think something would have broke by now.

To be sure I could pull the port engine apart and check it to see if its got the same damage.

Only need the slightest gap between shaft and flange to allow the flange to shift slightly on each rotation. Add a belt with tension and your deforming the material slightly each go around (hammering). Deform it so many times the material fatigues and begins to fritter.
That kinda explains why the O-ring area looks good...comparatively. If it was heat related that area should look similar, but it seems fairly good.
Similar to what Needle Bearings can do to a soft shaft or if used with excessive load.

Bruce- what did you figure out? Are you replacing or repairing in place? And what the heck was that condition?