[SEL] Piston clearance

Thu May 25 05:51:03 PDT 2006

Grant,
You may want to reference this chart (it's very readable once printed) 
as it addresses the stepping of the diameter as you approach the crown.
<http://www.oldengine.org/members/holland/images/PistonClearances/PistSpec.jpg>
Curt Holland
Gastonia, NC

Grant Weir wrote:

>
> 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 at lists.stationary-engine.com
>>> http://www.stationary-engine.com/mailman/listinfo/sel
>>>
>>>
>>>
>>>
>>
>>
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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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