Pat:
This could be a variety of things. Some of them quite serious,
others
are nothing to worry about.
If it is piston slap, then it is nothing to worry about. Piston
slap is usually (but not always) more like a rattle. Properly fitted
cast pistons should not do this, but if you or a DPO fitted forged
pistons, then it is more common. Forged pistons require a looser fit to
allow for the greater expansion of a forging. As the piston warms, it
expands to the proper tolerance. This may be safely ignored for as long
as you can stand to.
If it is truly coming from the bottom of the engine, then you
have a problem that should be addressed ASAP. Most likely it is a bad
rod bearing, and what you hear is the rod hammering the journal on which
it is riding. The longer you wait, the more likely it is you are looking
at having to drop the crank and have it turned, and refitting oversize
bearings (i.e. a full overhaul). If you catch it early, you might be
able to skate by with a fresh bearing. If it is a rod, the noise will
get steadily worse, and will do so with surprising rapidity.
Very few things fix themselves, and if this is something that
started rather suddenly, you best get it checked.
Cheers,
Vance
-----Original Message-----
From: owner-6pack@autox.team.net [mailto:owner-6pack@autox.team.net] On
Behalf Of webb@daikin-america.com
Sent: Wednesday, December 24, 2003 1:32 PM
To: 6pack@autox.team.net
Subject: Engine knock
I noticed a regular "knock" that sounds like it is coming from the
bottom of the engine when it is cold (disappears after it reaches normal
temp, about 10 - 15 min). The noise speeds up with the engine rpm.
The engine has about 140K miles and I don't know the history, just that
it has had little or no maintinance the last 2 yrs. The engine has good
oil pressure and smokes a little when first started up but not after
warming up. I think it runs a bit rich; I bought it recently and haven't
tried to tune it yet.
Does this sound like a serious problem? I don't have experience
diagnosing engine noises beyond excessive valve lash. Any guesses on the
likely cause? I intend to pull the sump to inspect the thrust washers
very soon - what should I look for? Is it easy to spot bad crank
bearings?
Thanks and Merry Christmas!!
Pat
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