Miata Mailing List: May 1996, Message #128
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   From: Dlralt@aol.com
Subject: More data:90 cranks.
   Date: Thu, 2 May 1996 19:13:52 -0400

In a message dated 96-05-02 15:06:23 EDT, you write:

>The crank pully on my 1990 didn't appear to have a perceptable wobble until
>I installed an outer pully to run the supercharger about 10000 kms ago.  The
>car now has (77000 kms, 48000 miles).  I disassemlbed the unit and
>reassembled it to make sure the installation was not faulty, and still the
>wobble.  The outer crank pully is of a very high quality, low weight
>aluminum and precisely concentric.
>
>Am I to worry?  I've driven the car for 10000 kms with 50% more horsepower
>and no change is evident. Should I attempt to torque the crank bolt to the
>80-87lbs to make sure the bolt won't break?  I'm sure if my crank breaks,
>Mazda will attribute it to the supercharger (but I'm off warranty anyway).
>Or should I replace the bolt for preventative maintenance?
>
>
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