Compression test

[dwsa]

Did a compression test on my 1995 SN with Ford 351, results were all cylinders between 130 - 140 psi. Is this considered good. I guess a lot depends on the gage accuracy, at least all cylinders came in approx same readings.

[97sport]

RE: Compression test

Yes gauges can be alittle off. Your readings seem to be normal. The good thing is that they are all about the same.

[ryanandrews]

RE: Compression test

how hard is it do do a compression test yourself? whats the cost of the tool(s)?

[ffmedic74]

RE: Compression test

All you need is a compression guage. Disconnect the main electric going to the plugs. Take out one plug, screw in the compression guage and turn the motor over a few revolutions. Take a reading for every cylinder and pray that they are all about the same.

[surroundsound64]

RE: Compression test

+ or - 10% or 30psi is acceptable. And it's always a little more accurate when you do it with a warm engine. You'll get lower compression on a cold engine due to blow by.

[Bob's2001]

RE: Compression test

That should be + or - 10psig instead of %. 30psig is 10% of 300. 130 to 140 psig is good compression, 100 is not.

[surroundsound64]

Re: RE: Compression test

+ or - 10% or 30psi is acceptable. And it's always a little more accurate when you do it with a warm engine. You'll get lower compression on a cold engine due to blow by.

10% is a pretty standard variation through out engines. A dealer told me on these as long as you're not more than 30psi difference you're fine. That is a substantial number, but apparently it's ok.

Either way, dwsa's compression is good.

[dwsa]

Thanks guys, good news, I'd much rather ski than pull the engine out.

[nautique95]

how hard is it do do a compression test yourself? whats the cost of the tool(s)?

ryan, the tester will run you around +- $25.00, and checking is just as ffmedic described.

[ryanandrews]

thanks for the help. im gonna try auto zone tonite to see id they have one!

[surroundsound64]

I got mine at autozone for like $17.

[97sport]

Ryan, I like to pull all 8 plugs out. Makes the engine turn over faster. make sure to pull the coil wire off and crank about 3-4 revolutions. Very easy to check, no more then a 6 pack job, or 8 being you have 8 clys.