Miata Mailing List: August 1994, Message #162
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   From: Jeff Maurer 
Subject: Re: Care and Feeding of my new baby (fwd)
   Date: Fri, 5 Aug 1994 10:46:08 -0400

Forwarded message:
> > I have a question about this one:
> > 
> > 	2: Run the engine over it's entire RPM range, but don't
> > 	hold any one setting for more than a minute or two.
> > 
> > Why does this matter?  For any given engine speed all the parts in 
> > the engine follow the same motion.  I have heard this for years 
> > from people who I thought were knowledgeable, but no one has ever
> > explained it.
> 
> As I understand it, at different engine speeds the bearings receive pressure at
> slightly different positions.  If this is the same position (same rpm, same 
> load) you can develop uneven wear in the bearing and will forever have a 
> funny rumble at that rpm.  I believe this is what happened to a car my mom
> owned once -- of its first 500 mi, 440 of them were at 3750 rpm.  Forever
> after the motor sounded funny at that speed -- faster ok, slower ok.
> 
> I've always broken in motors over a wider rpm.  That includes "breaking in"
> one by driving the 80mi to NHIS on a brand new motor and then racing it 120mi.
> It still runs great 1k track miles and 2k street miles later.

I've also heard that running at steady rpm's during break-in can increase
the chance of developing a ridge on the cylinder wall at the top of the
piston stroke.  This increases wear on the rings when higher rpm's force
the piston higher in the cylinder.
            _
            /        Jeff Maurer, Staff Analyst
     _  ___/ _ __   Manufacturing & Engineering Apps
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