Engine Crankshaft Inspection, circa 2005


Last month, we related the story of the person who wanted to inspect a crankshaft for cracks, but who didn’t want to disassemble the engine. The question that was posed was whether the penetrant could be applied to the outside of the engine to locate a flaw in the crankshaft. We did not think that there was any way that this could be done, and we said so. Not surprisingly, we had a suggestion as to how this might be done, which came from Tom Larkin, the Level III inspector at Mitchell Labs, in Los Angeles. Tom wrote as follows, which we have copied verbatim from his email to us:

“As far as the individual who wanted ro PT his crankshaft while still in the engine, he could drain the oil, waiting 30 minutes of drain time. Re screw drain plug in, put a quart of Met-L­Chek red dye penetrant in motor & run engine for 5 seconds. Turn off motor, drain red dye penetrant from oil pan leaving drain plug out, then wait 30 minutes for drain/dwell time. Now put a fiber optic borescope through drain plug and look at crankshaft, excluding main cap & piston rod bolted connections. If the crack was long and severe enough, you might see it. Of course, his motor oil would have a reddish tint to it for the next 3 oil changes”.

This is pretty clever, but we don’t think that it would work for two reasons, First, without developer, any red flaw indication would be seen against the metal of the crankshaft, which would provide poor contrast. Secondly, any crack would potentially be in the fillet on the bearing journal, and not be visible due to the interference of either the connecting rod or the main bearing cap, depending upon which portion of the crankshaft was under view. Tom recognized this. But we applaud the ingenuity which Tom shows in thinking about this problem. There are many practical problems which arise in penetrant testing, and it is often, if not mostly, up to the Level Three inspector to think these through and to solve them. The care and ingenuity shown by Tom may be one reason why Mitchell Labs has the high reputation that it does.

The PENETRANT PROFESSOR receives much of what is reported in this newsletter from its faithful readers. We especially like input from testing labs, and if you have an interesting story or experience that you would like to relate, we are always pleased to receive it. Doing so not only can benefit the NOT community, but it also can call attention to the service which you provide.


We recently had a question as to how much time is allowed between the time that a part leaves the dryer and the time at which dry powder developer is applied. ASTM E-1417 does not address this, and so we queried a major engine manufacturer as to their practice. We were told that their internal procedure does not specify a time,