Russell Kent wrote:

Bill Jepson asked:

Paul, If strength of the tension bolt threads is a problem why wouldn't a standard "j" rolled thread form, followed by shot peening the shank handle the problem?

Paul Lamar responded:

It might but I think it is the wrong approach. Better to change the resonant frequency
or stop it from vibrating somehow. The bolts are plenty strong for the purpose.

Remember that when dealing with resonance, you're dealing with essentially infinite force.  Making the bolt stronger won't help (except that it will probably change
the resonant frequency, and thus move the problem to a different RPM).  Better to damp the resonance.

Russell Kent

Finn recently broke a tension bolt after failing to remove them one at a time and coating
them with RTV and replacing them as suggested on here after Perry Mick broke a bolt.
He was able to get the broken stub out by welding
a drill bit to a long rod and using a centering collar to drill the broken stub. He then used
a Easy Out welded to a rod and removed the broken stub. Unfortunately the water seal
O-ring melted (he was not using teflon encapsulated water seal O-rings) and still leaked
coolant. Never the less he flew the airplane about 50 miles back and fourth to
Sun & Fun for several days by adding a gallon or so of antifreeze before each takeoff.

Paul Lamar

A few corrections:
I used common 12" #40 and #30 drill bits.
As usual Paul is exaggerating: less than a pint of coolant after .6 hours.
Last weekend it was even lower, maybe only 4 - 8 oz of coolant. I ran the engine hotter (up to 212 F water and oil) after taping shut my left cowl cheek (in preparation
to adding the cowl cheek extensions). Maybe the engine will pull itself back together (heal itself) if I run it hot enough ?!

Finn

I stand corrected Finn. Sorry. I was quoting from memory a comment Tracy made on the
situation. I should have interviewed you on the subject at Sun & Fun. I was too
busy this year being responsible for Dave Grabber's DG1.

"(heal itself)"? I would not count on it.

Paul Lamar
 
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