<div dir="ltr">Absolutely correct, Jim. I realized my error on the drive to work, intended to post an update, but work as usual got in the way. I also figured as a first-pass approximation I wasn't off by much.<div><br></div><div>SO</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Apr 8, 2020 at 6:14 PM Jim Becker <<a href="mailto:mr.jebecker@gmail.com">mr.jebecker@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div dir="ltr">
<div style="font-size:12pt;font-family:Calibri;color:rgb(0,0,0)">
<div>Compression ratio is of the swept volume plus combustion chamber volume
divided by the chamber volume. It looks like you used swept volume divided
by chamber volume.</div>
<div> </div>
<div>If I ignore the bore, which is just a multiplier on top of
everything:</div>
<div> </div>
<div>If stroke is S, C is the average height of the combustion chamber, and R is
the compression ratio:</div>
<div>R = (S + C)/C</div>
<div>R = S/C + 1</div>
<div>R – 1 = S/C</div>
<div>(R – 1) * C = S</div>
<div>C = S/(R – 1)</div>
<div> </div>
<div>C = 92/(23 – 1) = 92/22 = 4.18</div>
<div> </div>
<div>A shorter rod increases C by the same amount to the new value C1.
Thus the new compression ratio R1 is:</div>
<div>R1 = S/C1 + 1</div>
<div>R1 = 92/(4.18 + 1) + 1 = 92/5.18 + 1 = 17.75 + 1 = 18.75 call it 18.8</div>
<div> </div>
<div>Back to the original problem, it isn’t clear to me that it matters whether
the ratio is 18.4 or 18.8. It seems that is low enough to cause a
misfire. If there isn’t enough compression to get ignition, it seem
unlikely the left over fuel from a misfire would cause preignition on the next
cycle. But who knows what all the behavior might be.</div>
<div> </div>
<div>I can’t come up with any way to identify a mismatched connecting rod
without disassembly. Once the head is off, it should be easy to find by
bringing each piston up to TDC and measuring the height relative to the deck of
the block.</div>
<div> </div>
<div>Jim Becker</div>
<div style="font-size:small;text-decoration:none;font-family:Calibri;font-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">
<div style="font:10pt tahoma">
<div><font size="3" face="Calibri"></font> </div>
<div style="background:rgb(245,245,245)">
<div><b>From:</b> <a title="soffiler@gmail.com">Stephen
Offiler</a> </div>
<div><b>Sent:</b> Wednesday, April 08, 2020 4:18 AM</div>
<div><b>To:</b> <a title="at@lists.antique-tractor.com">Antique Tractor Email
Discussion Group</a> </div>
<div><b>Subject:</b> Re: [AT] Kubota M5700 noise</div></div></div>
<div> </div></div>
<div style="font-size:small;text-decoration:none;font-family:Calibri;font-weight:normal;color:rgb(0,0,0);font-style:normal;display:inline">
<div dir="ltr">I just worked out some math. That engine is 87mm bore x 92mm
stroke. 23:1 compression. Swept volume is .547 liter, giving
combustion chamber volume of .0238 liter. Now, what-if the con rod was 1mm
too short? That adds .0059 liter to the combustion chamber, now .0297
liter, which drops compression down to 18.4:1
<div> </div>
<div>SO</div>
<div> </div></div>
<div> </div>
<div class="gmail_quote">
<div class="gmail_attr" dir="ltr">On Tue, Apr 7, 2020 at 7:02 PM Doug Tallman
<<a>dtallman@accnorwalk.com</a>> wrote:<br></div>
<blockquote class="gmail_quote" style="padding-left:1ex;border-left:1px solid rgb(204,204,204);margin:0px 0px 0px 0.8ex">
<div>
<p><font size="+1">The rod being too short can't change injector timing or cause
pre-ignition. It would just mean less compression because the piston wouldn't
come up as far. Doug T</font><br></p>
<div>On 4/6/2020 6:24 PM, Dave Maynard wrote:<br></div>
<blockquote type="cite">
<div>I know the piston is correct as we replaced it. But James makes a good
point to ponder, if the rod is too short, it may change injector timing.
<div> </div>
<div>Dave</div></div>
<div> </div>
<div class="gmail_quote">
<div class="gmail_attr" dir="ltr">On Mon, Apr 6, 2020, 6:03 PM Bo Hinch <<a>bohinch@gmail.com</a>> wrote:<br></div>
<blockquote class="gmail_quote" style="padding-left:1ex;border-left:1px solid rgb(204,204,204);margin:0px 0px 0px 0.8ex">
<div dir="ltr">Or the wrong Piston ( too short or tall ) .</div>
<div> </div>
<div class="gmail_quote">
<div class="gmail_attr" dir="ltr">On Mon, Apr 6, 2020 at 12:40 PM Dave Maynard
<<a rel="noreferrer">dave@themaplehillfarm.com</a>>
wrote:<br></div>
<blockquote class="gmail_quote" style="padding-left:1ex;border-left:1px solid rgb(204,204,204);margin:0px 0px 0px 0.8ex">
<div>Actually, did not check length of connecting rod and its clearance
from head at TDC. But it's not traveling to close to the head as there
would be damage showing. Just have this new concern about the wrong rod
being put in by mistake, but that would have been short, not long.
<div> </div>
<div>Dave</div></div>
<div> </div>
<div class="gmail_quote">
<div class="gmail_attr" dir="ltr">On Mon, Apr 6, 2020, 1:01 PM Mike M <<a rel="noreferrer">meulenms@gmx.com</a>> wrote:<br></div>
<blockquote class="gmail_quote" style="padding-left:1ex;border-left:1px solid rgb(204,204,204);margin:0px 0px 0px 0.8ex">
<div bgcolor="#FFFFFF">When you had it apart, did you check all the
piston,ring and bearing clearances?<br><br>Mike M<br><br><br>
<div>On 4/6/2020 11:35 AM, Dave Maynard wrote:<br></div>
<blockquote type="cite">
<div>No sleeves in this engine. Someone had this engine apart before
and #5 had a new piston and rod and bearings. The seller said it was
his father's tractor since new and never been apart....he lied!
There was more RTV on oil pan than you could imagine and obviously
that piston and rod and bearings had been replaced and I thought
they had been chasing the noise. Unless there was some other reason,
but dont know.
<div> My friend and mechanic help has a
Jacobson mower he's is rebuilding that has a 4 cylinder version of
this motor that appears identical except the number of cyl's. He
found the rod to be the same except it a tweak shorter by an almost
immeasurable amount, maybe .005 or .010. Part number is almost the
same except last digit and now I'm wondering if that could be
someone's mistake. Would shorter rod cause preignition? By the way,
there is no part number on the rods so they would have to be
accurately measured.</div>
<div> It's going to be a bit before I can
get this back apart again, but hoping to have this fixed in time to
plow.</div>
<div> </div>
<div>Dave</div></div>
<div> </div>
<div class="gmail_quote">
<div class="gmail_attr" dir="ltr">On Mon, Apr 6, 2020, 9:08 AM Cecil
Bearden <<a rel="noreferrer noreferrer">crbearden@copper.net</a>> wrote:<br></div>
<blockquote class="gmail_quote" style="padding-left:1ex;border-left:1px solid rgb(204,204,204);margin:0px 0px 0px 0.8ex">
<div bgcolor="#FFFFFF">
<p>That was one of my thoughts, but my experience has been that
the liner movement was a double "thud" once on down stroke and
once on upstroke. <br>Cecil<br></p>
<div>On 4/6/2020 1:12 AM, <a rel="noreferrer noreferrer noreferrer">k7jdj@aol.com</a> wrote:<br></div>
<blockquote type="cite">
<div style="color:black;font:10pt arial,helvetica,sans-serif">
<div><font size="2">Cylinder liner loose. Don't know if this
engine even has cylinder liners if it does and that liner is
moving you would get click. Did you look carefully at the head
when you had it off and look for any sign of head
distress?</font></div>
<div><font size="2">I would do a compression check as
well.</font></div>
<div><font size="2"><br></font></div>
<div><font size="2">Gary</font></div>
<div><font size="2"><br></font></div>
<div><font size="2">Renton, WA.</font><br></div>
<div> </div>
<div> </div>
<div style="font-size:10pt;font-family:arial,helvetica;color:black">-----Original
Message-----<br>From: Roger Moffat <a rel="noreferrer noreferrer
noreferrer">mailto:rogerkiwi@gmail.com</a><br>To: Antique
Tractor Email Discussion Group <a rel="noreferrer noreferrer
noreferrer">mailto:at@lists.antique-tractor.com</a><br>Sent:
Sun, Apr 5, 2020 7:43 pm<br>Subject: Re: [AT] Kubota M5700
noise<br><br>
<div id="gmail-m_-4530146076711159888gmail-m_-8610138368857045324m_4006388287010896440gmail-m_1943752252575946901m_2085109996553918962m_-2421004768206050369yiv0933957868">
<div>
<div> </div>
<div><br clear="none">
<blockquote type="cite">
<div id="gmail-m_-4530146076711159888gmail-m_-8610138368857045324m_4006388287010896440gmail-m_1943752252575946901m_2085109996553918962m_-2421004768206050369yiv0933957868yqtfd88006">
<div>On Apr 5, 2020, at 9:59 PM, Dave Maynard <<a shape="rect" rel="noopener noreferrer
noreferrer noreferrer
noreferrer">dave@themaplehillfarm.com</a>> wrote:</div>
<div> </div>
<div><span style="font-size:12px;text-decoration:none;font-family:helvetica;white-space:normal;word-spacing:0px;text-transform:none;float:none;font-weight:normal;font-style:normal;display:inline;letter-spacing:normal;text-indent:0px">Have
cracked injector lines one at a time, and it gets quieter on
#5</span></div></div></blockquote></div>
<div> </div>
<div>But only on #5?</div>
<div> </div>
<div>When you crack the others the engine misses, but the noise
remains?</div>
<div> </div>
<div>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> </div>
<div>Eg #5 piston slightly higher than the other 4?</div>
<div> </div>
<div>Roger</div></div></div>
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