Model B Compression

[Duffy1]

How much compression should a model B engine with a C head and 60 over have ? I ran a compression check with two different gauges.

1) New gauge made in China 61 psi
2) 50 year old sears gauge 85 psi

Your respnose is appreciated.

[Duffy1]

OK, let me rephrase this post.Does any one know what the compression should be for a stock B engine. Does anyone have any idea why there is such a difference in the readings from the two gauges . New gauge defective? Old gauge defective ?
Appreciate your input.

[James Rogers]

B engines would have the same compression readings as a Model A with a comparable head since the deck, pistons and, stroke is the same, Oversize pistons would make a negligible difference so, you can discount that. I have run compression checks on many engines with many different heads and suspect the sears guage is closer to correct. I find a motor with any oversize piston and a Snyder 5.5 will read between 95 and 100#.

[Duffy1]

James ;
Thanks for the response .
So with the stock "C" head ( 4.6 to 1 ) your are saying the 85 lb reading from the sears gauge is probably more accurate than the 61 lb with the new china made gauge which is more in line with a stock model A compression .

[James Rogers]

If the head is truly a 4.5-1 then 65-70 would close. You need to check the compression gauges against a known good one to be sure of calibration.

[Duffy1]

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James ;

Thanks for the response .