compression test bad??

[topgunn]

1992 has 340,000 and tired. Ran test and all cyclinders were close, first hit was around 175 then up to 300 plus or minus. Engine was run for a while befor removing most of items in way as either engine comes out and slight rebuid or replaced. Of 4 books on ford diesels, one said 440 is good number. I removed injectors and used adapter for test. glowplugs were left in. I can reinstall injectors and use glowplug adapter and try again ,if that gives better reading. What is the best way to do test and what numbers should there be. Engine smoked when started but cleared up, so I though it was vaves or seals and had spare heads rebuilt. I appreciate all answers as this site has a large and smart pool of knowledge.
Thanks

 

[icanfixall]

Doing a compression test with all the glow plugs removed will give a better result. When the motor is allowed to spin over easier the numbers are closer to being right plus... The starter wont be working so hard.

 

[topgunn]

Thanks for imput, but with having glowplug removed, cause leakage and give lower reading? Do you know if the 440 reading is correct for worn engine or just for new or rebuilt. If my readings are really low, then pulling engine and doing a ring job (if cyclinders are not to far out of round) also checking lower end is not the way to go. I wanted to use truck to pull my 32" fifth-wheel this summer. I have a 1986 6.9 to rebuild for replacement, but it will take me about 6mos. to have money to build the 6.9 the right way. Again thanks for reply.

 

[91crew]

Take out the glowplugs on all the cylinders except for the one you are testing. Run the 7.3 and get the 6.9 freshened up for a quick swap when you are ready. 440 is a really good number. My 7.3 was in good shape and had 400. My current 6.9 has 425 all around and I am very happy with it.

 

[icanfixall]

Removing all the glow plugs and just taking the readings with a glow plug adapter on one cylinder gives best results. Doing the test from the injector hole has not been done here before. Where did you get the tool? If the injector hole is the way you must do the test then remove all the glows from the other 7 cylinders but leave the plug in the cylinder being tested. Sorry for any confusion.

 

[topgunn]

Thanks for replies. The compression tester came with about a dozen adapters, one of my books said to use injector opening. I will put injector back in and use glowplug opening this time. Are the low readings within proper range to do a minor rebuild. It wasn't useing oil. We used Slick 50 for years befor changing to Lucas about 5 years ago. I am (actually my wife is) pulling to engine to check lower end and swap the rebuilt heads if the pressure is within safe range.

 

[Diesel JD]

I'd say 300 and up +- a little is in the fair to good range with that amount of mileage. I wouldn't even mess with working on that motor unless it was making some scary sounds from the valvetrain or bottom end. Instead I'd run it and call it good realizing it may be a bit on the smokey side and not have the power of a brand new happy engine. I'd save my money to build a killer 6.9...yeah.

 

[icanfixall]

My rebuild has 530 lbs of compression for 10,000 miles of use. My high mileage other 7.3 had 480 lbs of compression and either 280,000 or 380,000 miles on it. It even had an original head gasket on it for all those miles. The last 180.000 was with a turbo too..