I posted on here the other day about getting blue smoke out of the exhaust. I had been toying with the notion of buying a long block from autozone until I read all the horrible reviews and got some advice on here. So here is the results going 1-8. This is a 79 F250 with a 400m

110
110
113
113
80
120
110
110

Seem a bit low to me overall but looks like #5 is the main problem. Looks like a full rebuild is in my near future............

 

Not necessarily. You need to investigate why the one cylinder is low.
Ford doesn't publish actual compression figures because there are too many variables to consider. The only thing they say is the lowest and highest cylinders should be within 25% of each other. I personally like it to be 20% or less.
If it's rings causing the low compression, then I would say it's time for a rebuild. If it's a valve problem then I would consider doing a valve job. 110-120 isn't particularly low.
Pull all the plugs and squirt oil into the low cylinder. See if it comes up substantially. If it does, then the rings are probably bad. If it doesn't come up much or at all, then the low compression is probably valve related.
After you check the one cylinder, do the other seven to check them too.

 

Any machaine work you have done should be done by a reputable shop in my opinion

 

I agree, seems a bit low. The bad one could be just a valve - I had two like that, one at 40 and one at zero. With new heads my thoroughly whipped 352 has 130 across but still runs ok and gets around town. I hope for 175 after 10:1 pistons.
Eric

 

If i was seeing compression #s in the low 100s the engine would be coming out for either a rebuild or replace. There is no sense in trying to bring one cylinder up from 80 to 110psi you would be wasting time and money unless you had no other option in which case id just run it as is and keep my eye out for another engine to rebuild as funds allowed

 

OP. Listen to this sound advice.

Considering the low static compression of the engine in the first place, 110 seems about right.

 

I agree, Mike is one of the more knowledgeable people on here, and yes 110 is pretty good compression for this engine

 

Personally I would like to see the compression at 130+ but, and this is why Ford doesn't publish specific cranking compression figures, there are too many variables when doing the test.
Remember, we're dealing with an engine that has a static compression somewhere in the area of 8.5:1. The two biggest factors in the compression test other than the problem you're troubleshooting is the battery and condition of the starter. A low battery or weak starter will have a big effect on the readings.
Compression in the 110-120 PSI area doesn't alarm me, that's why I said to check the other cylinders with the wet test too.
If the compression comes up significantly in the weak cylinder, no need to go any further, rings are bad. If, however, the reading doesn't change much then, in that cylinder it's probably valve related although it could be a head gasket problem too.
Test the other cylinders, if the compression goes up significantly then the rings are probably worn along with whatever problem is causing the low reading in that one cylinder and time for a rebuild. If there's no significant change then it's basically a sound, although probably high mileage, engine.
If the OP is looking for an excuse to rebuild, then go for it. If he's trying to troubleshoot and repair the engine, then he can fix the problem and get many more miles out of the engine at minimal cost.
Armed with this knowledge, the OP can make an informed decision on what's best for him.

 

Thanks for the suggestions everyone! To be a little more clear I DO NOT want to have to rebuild this motor. I usually just assume the worst. I would like to save some $$$ for other things for the truck. So I am hoping (and maybe praying) that the problem isn't the rings.

 

So have you done the wet test to see the results?

 

Not yet. Hopefully tomorrow I can find some time to get it done!

 

Crap saw it was a M not an FE.
But,
Don't spend money till you have to or want to.
These are tough engines. Run it.
Good luck.