Miata Mailing List: January 1996, Message #169
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   From: scannon@earthnet.net (Skip Cannon)
Subject: Engine Noise
   Date: Thu, 4 Jan 1996 00:23:02 -0500

Hi All:

While in SLC over the Christmas break, I spent some time with my 90 Miata
which lives there.  It has 108K miles on it and has developed a strange
noise in the engine.  I'm not too concerned about it yet, but my friend who
takes care of it for me is a very anal type and is far more worried about
it than I am.

The noise sounds somewhat like a dry roller or ball bearing but only
happens in a very narrow band at about 1,200 and again at 1,900 RPM.  It
doesn't always make the sound at these speeds.  I tried to localize it
using a long 3/8" extension as a crude stethescope (sp?).  To the unaided
ear, sometimes the sound appears to be at the front of the engine and other
times near the rear of the engine on the passenger side.

Unfortunately, I could neither pick out this noise with the stethescope nor
could I localize it.  The obvious candidate is the idler bearings on the
timimg belt (as discussed on the list several months ago) but the inability
to localize the noise in this area makes me wonder if something else might
be causing the problem.  The engine sounds/runs normally otherwise.  The
noise starts after the engine has warmed up.

Has anyone had a similar problem?  Does anyone have another candidate for
the source of the noise other than the idler bearings?  If it were the
idler bearings, I would expect the noise to be much more evident over a
wider RPM range.

Can the idlers be changed without removing the belt or disturbing the
crankshaft bolt or the Woodruff key?  This a 90 and I want to avoid
disturbing this area if possible.  The belt was changed at 85K by the
previous owner's mechanic so it doesn't really need a belt change yet.  I
checked the front pulley/dampner for possible looseness, but was unable to
detect any.

Someone on the list supplied part numbers for the improved idler
assemblies.  Would you please email me those part numbers again?

Thanks in advance.

Skip Cannon