I did another compression test today and now I'm getting 80-78-85-80 after installing a new head gasket and cleaning the valves. The I&T manual says the compression ratio is 6:1, do you multiply this by 14.7psi (atmospheric pressure) to come up with new compression of 88psi? Another post at a car site has a table that calculates PSI by PSI=(compression ratio-1) X 14.7. Using this method, 6:1 would give you 73.5 psi.
Also, in the I&T manual below the line for compression (standard) is 3 more lines of compression specs, what are these?
Gerry
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SA compression test
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- Gerry Powell
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Re: SA compression test
The lines following standard compression ratio, 6:1, are for other pistons that were originally available for the tractor. The next lower line in my I&T for the SA is a 5:1 compression ratio followed by two blank lines.
Conduct the compression test dry, then wet (oil added to piston).
Your current figures are a bit on the low side. The C-60, Cub engine has a standard compression ratio of 6.5:1. You would normally see compression reading of 120 psi or a bit better on a freshly rebuilt engine after a couple hours of run time (break in).
Kind of an aside. I have a WC Allis Chalmers with low compression pistons, either 4.2:1 or 4.5:1 compression ratio. This engine has compression readings, hand cranking, very close to your SA readings. The WC parts books lists 9 different compression ratio/piston sets that were available from the factory.
Edit: Wikipedia. Generally, cylinder pressure for common automotive designs should at least equal 10 bar, or, roughly estimated in pounds per square inch (psi) as between 15 and 20 times the compression ratio.
Conduct the compression test dry, then wet (oil added to piston).
Your current figures are a bit on the low side. The C-60, Cub engine has a standard compression ratio of 6.5:1. You would normally see compression reading of 120 psi or a bit better on a freshly rebuilt engine after a couple hours of run time (break in).
Kind of an aside. I have a WC Allis Chalmers with low compression pistons, either 4.2:1 or 4.5:1 compression ratio. This engine has compression readings, hand cranking, very close to your SA readings. The WC parts books lists 9 different compression ratio/piston sets that were available from the factory.
Edit: Wikipedia. Generally, cylinder pressure for common automotive designs should at least equal 10 bar, or, roughly estimated in pounds per square inch (psi) as between 15 and 20 times the compression ratio.
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