[SEL] Piston clearance

Wed May 24 22:37:31 PDT 2006

I knew you guys would have the answer!  About a thou per inch of bore sounds 
perfect to me - thats about 6 or 7 thou of clearance which is right between 
my own guestimate of between 0.005 and 0.010.  Too little is what was 
worrying me.

The sleeves came with a 6.705" bore so that they would clean up to 6.750 
once pressed in.  I did not bore them once they were in, but only honed them 
instead.  I used a 'real' bore hone - not one of those "deglazer" things - 
so the bore is nice and round.  The new hole size is 6.720 which leaves me 
about 0.010-0.015 to take off the pistons for a primo fit.  I don't think 
thats enough to worry about breaking through or weakening materials etc.  
The ring grooves are rather worn as well so I've got to widen and probably 
deepen them some too.  Happily I have all new rings.

When I pulled this engine apart I was totally amazed by how badly the bore 
was worn.  I could actually look down past the piston and see the first 
ring!  Just for fun I checked and it was almost 0.10" of clearance - wow.  
The fellow I bought it from claimed that it ran when he parked it (30 years 
ago...), but it was getting "...damn hard to start."  No doubt!

I guess if it ran with a hundred thou of piston clearance, anything more 
than 0.007 should be just fine. :-)

Sorry to ramble on...  Thanks for the info gang!

Grant Weir
Saskatoon, SK.
Canada

>From: Judge Tommy Turner <lcjudge at scrtc.com>
>Reply-To: The SEL email discussion list <sel at lists.stationary-engine.com>
>To: The SEL email discussion list <sel at lists.stationary-engine.com>
>Subject: Re: [SEL] Piston clearance
>Date: Wed, 24 May 2006 21:16:34 -0400
>
>Arnie and Grant,
>    I don't know what the proper "engineered" dimension should be but I 
>always use the rule of 1/1000th clearance per inch of bore. So, my piston 
>would be .00675 undersize.  Its always worked for me but I don't know how 
>close it would be to what the "book" says.
>
>Tommy Turner
>Magnolia, KY
>
>
>
>>Hi Grant,
>>
>>I don't have that clearance handy (but others will).  Have you checked how
>>much "meat" you'll have left at the bottom of the ring grooves after you
>>turn down the piston and re-cut the ring grooves?
>>
>>See ya,  Arnie
>>
>>On Wed, 24 May 2006, Grant Weir wrote:
>>
>>
>>
>>>I've sleeved my 29' John Deere D and left the bore slightly undersize of 
>>>the
>>>stock 6-3/4" size so that I can turn my worn out pistons down to fit.  I
>>>think it will work.
>>>
>>>
>>
>>
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>>SEL mailing list
>>SEL at lists.stationary-engine.com
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>>
>>
>>
>>
>
>
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>Arnie and Grant,<br>
>    I don't know what the proper "engineered" dimension 
>should be but I
>always use the rule of 1/1000th clearance per inch of bore. So, my
>piston would be .00675 undersize.  Its always worked for me but I 
>don't
>know how close it would be to what the "book" says.<br>
><br>
>Tommy Turner<br>
>Magnolia, KY<br>
><br>
><br>
><br>
><blockquote
>cite="midPine.BSF.4.51.0605241623520.59223 at vegeta.city-net.com"
>type="cite">
>  <pre wrap="">Hi Grant,
>
>I don't have that clearance handy (but others will).  Have you checked how
>much "meat" you'll have left at the bottom of the ring grooves after you
>turn down the piston and re-cut the ring grooves?
>
>See ya,  Arnie
>
>On Wed, 24 May 2006, Grant Weir wrote:
>
>  </pre>
>  <blockquote type="cite">
>    <pre wrap="">I've sleeved my 29' John Deere D and left the bore 
>slightly undersize of the
>stock 6-3/4" size so that I can turn my worn out pistons down to fit.  I
>think it will work.
>    </pre>
>  </blockquote>
>  <pre wrap=""><!---->
>
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>SEL mailing list
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