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Tractor Talk Discussion Forum

Piston Dome, Compression Ratio Revisited w/pics

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Aaron Ford

11-20-2006 19:14:42




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third party image


third party image


Heres the pics.


And here's the details of my engine within a quote taken from an earlier post...

"Not really all that well. The reason for the measurement is that the engine was damaged by the previous owner by detonation, preignition and the like. It broke ring lands, broke the top rings on all cylinders, and actually dented the liner on number 3. Number 2 piston was recently changed. I thought a valve had come apart in the past, but my machine shop seemed to think it was preignition.

So with the history of the engine known, it caused great concern when the replacement pistons had a considerable dome. I needed to know if my new setup was going to require 93 octane or would be able to live on 87.

The last thing I want to do is purchase a second $869 dollar kit...

Here's what I have. 3 37/64 bore, 4 3/4 in stroke, .050 in head gasket with a 3 3/4 in cylinder holes, 110 cc combustion chamber. I measured a 22cc dome at zero deck. It is a 4 cyl engine.

I came up with a 9.0649:1 or rounded to 9.1:1.

Original engine had flat tops at zero deck and approx 120cc combustion chamber.

The engine should measure 176 cu inches, but tht's not what I get when I cipher it out.

Whadya'll get?"

Thanks Aaron

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jdemaris

11-21-2006 08:27:22




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 Re: Piston Dome, Compression Ratio Revisited w/pic in reply to Aaron Ford, 11-20-2006 19:14:42  
Maybe I missed some earlier posts, but what engine are you working on, and what sort of application? Just at a glance, those high-dome pistons remind me of what Deere was selling during the 60s and early 70s for high-altitude use in gas tractor engines. My neighbor put Deere high-altitude pistons in his 2020 - and what a mess! We're are in central New York - not real high elevations. The goal with using the pistons was more horsepower. Even with high-test gasoline, the tractor pinged, detonated, it was just about useless. Finally had to pull it apart and redo with standard pistons.

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dr.sportster

11-21-2006 07:51:08




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 Re: Piston Dome, Compression Ratio Revisited w/pic in reply to Aaron Ford, 11-20-2006 19:14:42  
You also need to know how close the valves are coming to the new dome if the dome is under them.[.o4o"min.]Without knowing the swept volume there is no way of accuratly calculating the compression.More swept volume into the same size combustion chamber is an increase in compression.Math vs reality.



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Jerry/MT

11-20-2006 19:41:43




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 Re: Piston Dome, Compression Ratio Revisited w/pic in reply to Aaron Ford, 11-20-2006 19:14:42  
Based on the dimensions you quoted, I got the compression ratio as 9.06, V1 = 53.683 in3 and V2 =5.923in3



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fred from wyo

11-20-2006 19:29:29




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 Re: Piston Dome, Compression Ratio Revisited w/pic in reply to Aaron Ford, 11-20-2006 19:14:42  
quick calculation came up with 191 cuin, and the extra cubes should drop the comp ratio, based on your figures, to about 8.5 WAG. Sounds like a good candidate for propane



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Aaron Ford

11-20-2006 19:34:11




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 Re: Piston Dome, Compression Ratio Revisited w/pic in reply to fred from wyo, 11-20-2006 19:29:29  
Funny you should say that cause I 'spect these are the LP pistons....

Aaron



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Trkr

11-21-2006 13:33:01




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 Re: Piston Dome, Compression Ratio Revisited w/pic in reply to Aaron Ford, 11-20-2006 19:34:11  
What engine and what make pistons are those.Look like M+W.



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aaron ford

11-21-2006 14:46:57




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 Re: Piston Dome, Compression Ratio Revisited w/pic in reply to Trkr, 11-21-2006 13:33:01  
These pistons are stock Tisco replacements. The engine is a G176 Continental in a MF65. I am trying to avoid preignition that damaged this engine in the past. Stock pistons were the flat tops, but popups came in the rebuild kit. HTH Aaron



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aaron ford

11-21-2006 14:40:29




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 Re: Piston Dome, Compression Ratio Revisited w/pic in reply to Trkr, 11-21-2006 13:33:01  
These pistons are stock Tisco replacements. The engine is a G176 Continental in a MF65. I am trying to avoid preignition that damaged this engine in the past. Stock pistons were the flat tops, but popups came in the rebuild kit. HTH Aaron



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