Hey all, thanks in advance for ideas, I've gone as far as I can and now I need some help. I recently bought a '79 pickup with a 20r. It runs great, no smoke, no power loss or any issues. Just out of curiosity, I did a compression test and found that cylinder 1 is low. Specifically, I found:

1: 100
2: 165
3: 155
4: 160

I put a little oil in and tested again, but the numbers did not change. So, I pulled the valve cover off and found the #1 exhaust valve needed some adjustment, but when I performed the test again the numbers did not change.

There are no indications of a headgasket problem: no water in the oil or anything like that. So I'm out of ideas and need some help. Thanks!

 

 

Yup, time for a leak down test. You can buy a cheap tester at Harbor freight or make your own with parts you can buy there. If you don't already own a compressor, the 6 gallon oil-less model at HF is pretty decent for the price.

 

Thanks for the info. 111db, yes I did the valve adjustment after everything was warm and toasty. And thanks gsp4life for the tool advice.

I did another quick test with a piece of paper over the exhaust and it sucked back in. Soooo, now I'm pretty sure it's a burnt valve. I bought the whole thing for a few hundred bucks to use for projects as needed and now I'm starting to think it's not worth pursuing the issue further. Maybe that's dumb but it runs well enough for occasional use. Maybe I would feel different if it was a 4x4 but I'm just not sure how wise it is to start pouring money into this.

 

It'll probably run for a surprisingly long time on 3 cylinders. I'd pull the head and rebuild it myself, but it's your time and money to do with as you please.

 

Hmmm, well I'll have to give it some consideration. I don't have a shop space (or money really) to do a full rebuild right now, but maybe it'd be a good summer project when the rain stops. In the meantime, hopefully I won't damage it too much by driving it occasionally.

 

It is probably more like 3-1/2 cylinders. The low cylinder 1 will still make power, just less than the other cylinders. It is not ideal, but much better than 0 psi.

I would try to fix the issue also, but I would basically say that to any classic Toyota I see... It is hard to see them not get fixed up!