86 Bronco II - compression test results

[Marty86]

I obtained a 86 Bronco II that was sitting in my father-in-law's yard. He got it for parts, but only ever took one piece off and didn't bother with the rest.

He gave it to me to either resurrect or sell for parts. He was told when he got it, it was a bad engine.

After some playing, and a good battery, I got it to start. It runs, sorta, and has super low power. I changed the oil and fixed leaking valve covers, before getting it started. I decided to do a compression test. I found all of the spark plugs with oil on each of them, and the compression was 120 across the board. Searches have told me this is pretty low. I'm thinking bad rings (with the oil)?

Anyone have any thoughts? I can't decide if this should become a project or just to haul it off. But 120 is pretty bad for a 25 year old truck...

 

[88ranger89camaro]

depends on the condition of the rest of it, tell us more or post up pics of the outside and inside

 

[adsm08]

That doesn't sound horrible to me.

I tried to look up the spec in the shop manual but it doesn't give a definitive reading in PSI. It just says that the low reading must be within 75% of the high reading and gives a chart. Since you have 120 across the board that probably doesn't indicate a major compression issue.

If you want to check the rings, dump a table spoon of 50 weight oil in each cylinder and do the test again. If it doesn't come up, you either have valve issues, or no issues. Oil on the plugs can be a number of things, not just rings. Valve seals or seats could be leaking. It may also just be oil that has run down from leaking valve covers into the plug wells.

 

[kimcrwbr1]

As long as they are even 120 is ok. When you get it running put a vacuum guage on it if the vacuum holds steady within 1/2 hg anywhere above 17-21 hg is good. It wouldnt hurt to run some seafoam thru it and then do the compressdion test again for giggles. If it has good compression and vacuum pressure and still smokes when you start it you can change the valve guide seals without pulling the heads.

 

[88ranger89camaro]

oh dang i need to read better he said 120 PSI :icon_rofl:

yea heck i agree with the putting some heavy oil in and doing it again, but i doubt its compression, as said before valve guides can leak oil.

a really clogged cat could cause the super low power

 

[Marty86]

I'll try these out and get back to yall with the results, thanks gents!

 

[adsm08]

I'd put a vac gauge on the manifold and see what you have. If you have 20 inches, you don't have a clogged cat.