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RPM higher when cold? - 3/25/2012 5:37 PM   
Scota4570


 

Posts: 800
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From: Salinas, CA, USA
Status: offline 		It is not the needle settings.

I have been playing with my OPS maxi conversion. The Bowman ring has about 1-hour on it with synthetic oil. Yes, I know he suggests regular oil for break in. I am thinking that the compression is a little better when the oil is colder thus giving slightly higher compression. It is a matter of about 200 RPM. Not a big deal but interesting. Anyone seen this too?

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RE: RPM higher when cold? - 3/25/2012 6:11 PM   
av8tor1977



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From: Lukeville, AZ, USA
Status: offline 		Yes, I have frequently seen this; a sort of a "flash" reading of a couple of hundred rpms higher when an engine is cooler. It could be due to the viscosity of the oil helping ring seal, but I always attributed it to the crankcase being cool, and the engine getting a denser fuel/air charge than it does when the crankcase is warming the mix before it gets to the combustion chamber.

AV8TOR

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If it is not SCARY, it is NO WHERE NEAR powerful enough!!

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RE: RPM higher when cold? - 3/25/2012 6:13 PM   
SrTelemaster150



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From: Brasher Falls, NY, USA
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quote:

ORIGINAL: Scota4570

It is not the needle settings.

I have been playing with my OPS maxi conversion. The Bowman ring has about 1-hour on it with synthetic oil. Yes, I know he suggests regular oil for break in. I am thinking that the compression is a little better when the oil is colder thus giving slightly higher compression. It is a matter of about 200 RPM. Not a big deal but interesting. Anyone seen this too?


quote:

ORIGINAL: av8tor1977

Yes, I have frequently seen this; a sort of a ''flash'' reading of a couple of hundred rpms higher when an engine is cooler. It could be due to the viscosity of the oil helping ring seal, but I always attributed it to the crankcase being cool, and the engine getting a denser fuel/air charge than it does when the crankcase is warming the mix before it gets to the combustion chamber.

AV8TOR



I've seen similar results on all of my Saito 4 strokes even when running glow fuel.

I think the assumpsions regarding ring seal & denser charge are correct.

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Club Saito #785 - FA91S CDI, FA150 CDI, FA180 CDI, FA180HC CDI/BBC, FA200TI, FA300TTDP CDI

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All Forums >> Glow Engines, Gas Engines, Fuel &amp; Mfg Support Forums >> Engine Conversions >> RPM higher when cold?
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