[Asahel]

I did a compression test on my 01 with 157k miles the other day.
There was only a 5.lb or 2% split between all the cylinders, very happy with that. Trying to find some poop on good compression numbers.
I got 380 psi low 385 psi high, I think they are good for a truck with this kind of mileage. Can some one confirm this? Also is there a good article or old post about this subject. I can't figure our search engine on this sight to save my life. Thanks

 

[dvtech]

a new eng. will have at least 410 to 420. a used one will have the readings you have as long as they are not between 25% from each other. a 25% drop means theres a mild dusting concern.

 

[Asahel]

Thanks for the reply dieselmech50s.
You said a 25% drop is mild dusting or dusted period?
At 25% drop that puts engine compression at 310 psi. Can 310 psi support combustion? /ubbthreads/images/graemlins/shrug.gif

 

[ITowBoats]

did you take these as cold compression readings?

for a true indication of compression we take firing readings with our big shipboard diesels. remember that your cylinder sealing is a function of the firing pressure forcing the rings against the oil film on the cylinder walls. firing readings can also indicate stuck rings, weak injectors, burned valve seats.

its very useful and gives a wealth of information.

just for a quick example. we have a 4-53 detroit diesel in the lab here that we do firing compression with. these engines have been beat on and tooled on by kids that have never turned a wrench before. they all run around 600# firing compression.

and a 4-53 detroit is very similar in bore/stroke to a 444e

 

[Asahel]

Thanks MMADieselTech, 3.5hrs after I parked it, I did the first cylinder which was #2. Which I did twice because of lower reading then the others. My first go around it read 375, after I did them all I went back to #2 cylinder and gauge read between 380-385. Lets call it a 7.lb difference, between a wet and dry cylinder walls, sound right?

 

[DieselDeaf]

[ QUOTE ]


just for a quick example. we have a 4-53 detroit diesel in the lab here that we do firing compression with. these engines have been beat on and tooled on by kids that have never turned a wrench before. they all run around 600# firing compression.

and a 4-53 detroit is very similar in bore/stroke to a 444e

[/ QUOTE ]

I am sure the detroit has a different compression ratio so not real sure that you're talking apples to apples.

I've always heard anywhere around 400 psi is pretty average on the 7.3's

On edit be careful about doing wet compression tests or you might be digging pieces of the compression guage out from the back of your eye sockets.