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<p>Back when I could overhaul a 350 chevy for $100 in parts, I tore
one down to find out what the knock was and never found it!!
Later I had a bad scar in a 305 cylinder wall and bored it out
with an old old T model era cylinder hone. The bore had a .004
taper from bottom to top. I installed a 0.010 oversize piston.
It knocked, but used no oil. Ran good. After about 15K miles I
sold the pickup to a couple buying it for their 16yr old son's
birthday. The kid drove it all through high school and part of
college. He sold it and bought a later model. The engine that
knocked, still knocked at over 150K miles... Sometimes a knock
is not too bad...<br>
Cecil<br>
</p>
<div class="moz-cite-prefix">On 4/5/2020 10:35 PM, Thomas Martin
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:1510730565.141589.1586144123073@webmail.xtra.co.nz">
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<p>I was wondering about a errant piston, too. Have struck once on
an AC crawler engine.<br>
</p>
<p>Also came across an over length con rod once, how that was made
was a bit of a mystery.<br>
</p>
<p>Have you thought about a compression test?<br>
</p>
<p>Tom<br>
</p>
<blockquote type="cite">On 06 April 2020 at 14:42 Roger Moffat
<a class="moz-txt-link-rfc2396E" href="mailto:rogerkiwi@gmail.com"><rogerkiwi@gmail.com></a> wrote: <br>
<br>
<br class="">
<div><br class="">
<blockquote type="cite">
<div class="">On Apr 5, 2020, at 9:59 PM, Dave Maynard <
<a href="mailto:dave@themaplehillfarm.com" class=""
moz-do-not-send="true">dave@themaplehillfarm.com</a>>
wrote:</div>
<br class="ox-0a017db5fe-Apple-interchange-newline">
<div class=""><span style="font-family: Helvetica;
font-size: 12px; font-style: normal; font-weight:
normal; text-indent: 0px; text-transform: none;
white-space: normal; word-spacing: 0px; text-decoration:
none; float: none; display: inline;" class="">Have
cracked injector lines one at a time, and it gets
quieter on #5</span></div>
</blockquote>
</div>
<br class="">
<div class="">But only on #5?</div>
<div class=""><br class="">
</div>
<div class="">When you crack the others the engine misses, but
the noise remains?</div>
<div class=""><br class="">
</div>
<div class="">I wonder if something about cylinder 5 is somehow
different so that the compression is higher, and so it’s
igniting (pre-igniting) too much before top dead centre in
just that cylinder?</div>
<div class=""><br class="">
</div>
<div class="">Eg #5 piston slightly higher than the other 4?</div>
<div class=""><br class="">
</div>
<div class="">Roger</div>
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