<VV> [fastvair] Crankshaft

[Michael Kovacs]

Decades ago I built a strong 140 hp engine. I magnafluxed the crank at the aerospace company I worked at. I found cracks. The consensus of opinion was to chase the cracks then etch to remove embedded (smeared) material and remagnafluxed. No evidence of the cracks. Only have 6,000 miles on the engine so I can't vouch for racing conditions, but the engine was pushed often when first built.

 MIKE KOVACS 




________________________________
From: Charlie Danner <cdanner at comcast.net>
To: fastvair at yahoogroups.com
Sent: Fri, March 12, 2010 6:19:46 PM
Subject: Re: [fastvair] Crankshaft

  
I may regret coming out of " lurking mode " 
here, but I got an education on cracked cranks when I ran the supercharged 
twin Corvair dragcar. After initial crank coupling problems that ruined two 
cranks and required a new coupling design; things seemed to go well. I 
checked the rod bearings from time to time with no bad bearings and nothing 
in the oil. The first time I had the engines out; I split the cases and 
checked the mains. No main bearing problem. Since we were running 30+ lbs of 
boost, I sent the cranks to be magnafluxed. Bad news! Both cranks showed 
fillet cracks. To make a shorter story....... I built new cranks three times 
until , in frustration; I decided to send them to Crankshaft Specialist in 
Tennesee to be hard chromed, thinking that would cure my problem. After 
inspection, they called me to ask what was wrong with my cranks! They said 
the small surface cracks that I was experiencing were harmless and rarely 
led to any problems. I talked to many knowledgeable people after that and 
they agreed. No guarantees, mind you , but most of that type of crack is 
harmless and will lead no where, especially when you know what to look for 
and checking the bearings is regular maintenance. Remember that this was a 
dragracing application of short duration, but the car ran 8's in the 
quarter mile at over 150 mph with no more cranks required for the next two 
years. Yes, the hard chromed cranks with larger radiused fillets showed 
cracks also.

-20 Flame suit on!

Charlie Danner


The other route, since you need a new crank anyway, would be to start with a 
standard crank and have it nitrided. Comments?

--Bryan

On Mar 12, 2010, at 1:28 PM, Jimbrandberg@ aol.com wrote:

> I took the crankshaft out of my spare race engine to get Magnafluxed.
> Just about every rod journal had a crack starting down in the fillet
> edge. I'm sure glad I had it checked. It's an otherwise beautiful
> .010/.010 crank but scrap to me now.
> I've shied away from using PG cranks as the gear seems to be quite
> difficult to get off to change the key. I suppose heating the gear with
> a torch is in order but reusing the gear after that seems questionable.
> I guess yet another $100 Failsafe cam gear with an offset key would
> work too. I figure about the time I invest in an adjustable cam gear
> the cam will lose a lobe or something.

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