Compression check troublehshooting.

[squealingtires]

'93 4.0L engine w/ 85,000 miles; 900' elevation; 85degree tempurature; cold engine; wide open throttle; all plugs removed; 6x4 engine revolutions. Here are my compression checker readings which seem a bit low from what I've read. I'm not sure how much these readings would go up if the engine were hot but unfortuneatly I didn't do that test or add any oil to the cylinders. I'm going the have the heads decked to eliminate the posibility of a bad gasket surface and have the valves vacume checked for sealing but I suspect neither of those are true issues. If they check out fine then that only leaves the rings as being suspect. Should the engine rebuilt based upon these cold compression readings? Your thoughts?

Cylinder #1 = 135
Cylinder #2 = 115
Cylinder #3 = 120
Cylinder #4 = 120
Cylinder #5 = 100
Cylinder #6 = 115

 

[cr_the_machinist]

I know my 4.0 OHV was all around 150lbs (105,000 miles at the time). You can take it to a shop and have a leak down test performed for a more accurate assessment of each cylinders health. Hope things turn out well.

 

[squealingtires]

Well, I picked up the heads from the machine shop yesterday--They milled 10 thousandths and ensured the valves were sealing. So my next think is to measure the cylinder bores for taper. Based on my conversation with the machinist that did my heads, Ford didn't put very high quality rings into into these motors and by 90K miles they are shot. Anybody know how to relate cylinder taper to ring-wear?