Miata Mailing List: May 1996, Message #135
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   From: "D. Scott MacKenzie" 
Subject: Re: More data:90 cranks.
   Date: Thu, 2 May 1996 22:41:19 -0400

At 07:13 PM 5/2/96 -0400, you wrote:

>Got some interesting news today from DelVal member Ed Avol. He owns a '90
>Miata with 116,000 miles, has had a Bell turbo for at least 50% or more of
>its life. Ed had been noticing a wobble to his front pulley since about
>100,000 miles. He actually went out and bought a new front pulley, but
>noticed no difference when it was installed.
>This past weekend Ed decided to start disassembling things before disaster
>claimed him.  When he put a ratchet on the front crank pulley bolt, it came
>out with no more than light pressure--did NOT have to lock the crankshaft in
>any way, just unscrewed the bolt.  When I have done timing belts with seals,
>I have always had to put a special tool to lock the crank tightly so that I
>could unscrew that bolt. It has never come out without some serious force.
>Once Ed got the bolt out he could see that about 3/4 of it looked rusty.
>Usually when you get rust in that type of spot it is because something has
>been moving around, making easily rusted powder.  The key was chewed up, as
>was the keyway in the crankshaft nose. Ed has made a wider key and is
>reassembling this weekend, with new key and new bolt. Ed saw no evidence of
>any locktite on the bolt. Also, very importantly, Ed said that the key was
>properly installed when he took it apart.
>
>The important thing here is that the crank bolt had never been touched in
>this car since Mazda built it.  Ed has done all of his own servicing, did the
>timing belt himself and did not do the front seal, so never had a reason to
>pull that bolt.  I suspect that it may be worthwhile for all of the '90
>owners (myself included) to pull that bolt and replace it with a new,
>locktited, properly torqued (whatever today's torque du jour is) bolt.
>
>This may dampen the "improper assembly" theory, unless the improper torquing
>was done by Mazda at the factory.
>FWIW.
>
>bill cardell
>Dealer Alternative
>1-800-FLY-MX5S
>
>
>

Based on my investigation to date regarding a failed crankshaft nosepiece
and bolt, it appears that the cracking initiated in the nosepiece, and while
the crank was cracking, the bolt started cracking.  Evidence of rust was
also apparent on the bolt.  As a preventative measure, since he saw the
pulley assembly wobbling, loading the crank, it is my recommendation that he
nondestructively test the bolt and the crankshaft using either dye penetrant
inspection (simple, easy, cheap) or magnetic particle (more expensive but
better).  The keyway on the crank SHOULD BE CHECKED!  Fatigue may have
already initiated, and is waiting until the crack propagates to a point that
it can not hold the crank together.  It's really cheap insurance.

I will keep you all informed regarding the progress of the failure analysis
of the crank and bolt.

Scott
D. Scott MacKenzie

"I believe that intelligence behaves like matter and energy - there is a
fixed quantity in the universe that can not be created or destroyed.
Unfortunately, the population is growing."