Help Interpreting Compression Test Results

[JoeCanada]

So I got this 88 2.0L that has been sitting for a year and a half, so it no doubt has gas varnish clogging up the carb. The guy says it had a leaking rear main, which is a straightforward enough fix, if that's all there is to it. Well, and cleaning the carb, I suppose.

I ran a (dry) compression test on it, and got these numbers
(Front) 60 110 110 90


My thought was bad valves, since the compression is not low in adjacent cyls, it likely isn't the head gasket. BUT, could this also indicate timing being off?

 

[Mark_88]

Could be valves, a cracked head causing the valves to leak...or a cracked piston like mine had, but my compression was actually pretty close to the 15% recommended...meaning the chambers should not be more than 15% difference between them...

Yours are closer to 20% on number 4 and close to 50% difference on number 1...two and three are within the specs that I got on my compression test.

The good news would be you can drop a 2.3 short block in there and be further ahead as long as the short block is in good shape...and doesn't need a rear main seal.

My suggestion would be to pull the head and check the bottom end visually for damage to the pistons...if they are in good shape you might be able to get away with just swapping a different head on it...or having yours rebuilt...if there is noticeable damage to one or more pistons then I'd consider swapping in a 2.3 and changing over the carb system also...the current carb/intake would work, but if it's anything like mine was you'd be better off going to a different setup...

Much of this probably depends on how much you want to spend...and/or how fast you need the truck running.

 

[fastbluetruck]

squirt some pb blaster or light motor oil in the cylinders crank it over a few times and reapply and crank it over a few more time make sure you are getting oil pressure and tehn run a compression check before you tear anything apart. then see what your #'s are and go from there

 

[Pistons23]

its been a while since i took autoshop in high school, but i beleive a leak down test will dtermine if its the valves or the piston rings.

 

[JoeCanada]

My suggestion would be to pull the head and check the bottom end visually for damage to the pistons...if they are in good shape you might be able to get away with just swapping a different head on it...or having yours rebuilt...if there is noticeable damage to one or more pistons then I'd consider swapping in a 2.3 and changing over the carb system also...the current carb/intake would work, but if it's anything like mine was you'd be better off going to a different setup...

Much of this probably depends on how much you want to spend...and/or how fast you need the truck running.

Yeah, pulling the head will probably be my next step after doing a wet test and perhaps a leakdown. I don't want to sink too much time and money into this thing, as a lifetime of neglect is evident from looking at it. I just found the compression numbers a bit strange, so I figured valves, but wasn't sure. (And won't be until the head comes off, I suppose.)

 

[Mark_88]

It may be a good time to just upgrade to the 2.3 if you can find one in your area...I was about to rebuild the 2.0 block but was advised by a few people on here to go with the 2.3...as long as you can find one with a distributor you can keep everything on the top end...or use the 2.3 head with a different intake designed for the oval port heads...

There are quite a few options...I'm still looking into getting the 86 FI intake and adaptor to put on a Holey 350 carb...but now that my Motorcraft 5200 is working again I may just stick with it for a while...

 

[JoeCanada]

Rings must be fried on this thing, new compression numbers (wet, this time)

120 150 150 120

Which, if I can find a 2.3 block at the j-yard, might not be a bad thing. I should be able to just bolt my 2.0 head and other bits onto a replacement shortblock.

I like the FI idea, Mark_88, but seems like a lot more work and parts without a donor truck available.