Compression Test help 400

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Nov 26, 2005 | 07:09 PM

78f250_rls

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From: Lake Havasu, AZ

Compression Test help 400

Just ran a Compression testdoes this numbers sound right

1 = 160
2 = 151
3 = 150
4 = 155
5 = 155
6 = 150
7 = 152
8 = 154

I was going to replace all the gaskets and the valve seats. Just want to make sure that I had good comp. so I didn't start blowing by the rings.

Thanks

Nov 27, 2005 | 01:40 AM

sparky69

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From: Wisconsin

it's hard to tell what the cylinder pressure should be. this can change from engine to engine due to cam timing. the best way to interpret these numbers is by comparing the highest reading with the lowest. you want the lowest pressure to be not less than 75% of the highest pressure recorded. your numbers are all pretty close to each other. don't think i'd even bother doing the math (but you can if you want). i'd say your in good shape.

Nov 27, 2005 | 05:58 AM

Greg 79 f150

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From: Kentucky

My newly rebuilt 351m read 150 -152 psi on all cylinders. Those are good numbers. Sparky is dead on, I wouldnt worry about what isnt broken. If a person is seeing engine problems in the compression area though and wants the total test of valves, rings, etc, do a leakdown test also.

Nov 27, 2005 | 11:13 AM

78f250_rls

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From: Lake Havasu, AZ

I am have some white smoke at start up and every once in awhile on accel. Do you think this good be from worn valve guide or seat?
Thanks

Nov 28, 2005 | 07:00 AM

danlee

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From: Delaware

It is from worn valve guides or bad valve stem seals. You can inspect your valve stem seals to see if they are brittle or broken. They can also be replaced without removing the heads. Of course if you remove the heads for new seats the guides can be checked and seals replaced. From your compression test, I would just replace the seals 'on the motor', and leave the seats alone.