Hey guys, I have a 1983 720 with the z24. I noticed my compression was low when I parked my car on my driveway and left it in first gear without the parking brake and came out an hour later to find it further down the driveway than I left it. I watched it for a little and the weight of the car is literally turning the engine on a hill. So I ran a compression test and go around 80 psi, but it runs just fine! Curious if you guys had any thoughts on that. Thanks!

Hendersoncj,

Hey, Hey, Welcome Aboard. Not too familiar with the Z24, but I believe the standard/when new compression ratio should be around the 165 to 175 mark. So you are at half of that.

Yes, it may "run" fine or idle fine, but I would say you are probably burning a little oil - hopefully blue and not white. Excess fuel and oil are mixing in the combustion chamber due to low compression and not totally detonating, leaving a moist oil gas mix. Spark plug is probably black and moist. This is the beginning of the end as the other cylinders are not far behind. I'd smell your dipstick, it might smell of fuel. Which means your oil is now diluted and this mix is circulating throughout your entire engine - not good - as the oil is not doing it's job - the viscosity piece.

I'd change the oil pretty quick and clean the spark plugs while looking for anything suspicious. Like really runny/thin oil or maybe beads of "water/anti-freeze" in the oil - what's it smell like. Once complete, check the compression again of all cylinders. You could have a leaky head gasket or worse a cracked head - just help my brother through his rebuild due to a crack head. I could not believe it was cracked.

I'd limit your driving or placing a load on the engine - like going up a steep hill. Where you will realize something is not right due to the low compression.

Hope that help and keep us posted

v/r
Li'l Truckie

Thanks Li'l Truckie, The weird thing is I know its not burning oil, ive done an oil change twice and everything smells/looks good. I have gone from Utah to colorado and then back to idaho in it will a full load in my truck and it did fine! ITs odd, it doesnt pass cylinder leak down test but shows no signs of burning oil or struggling under load. Coolant isnt leaking into oil either.

Well shoot. And there is no sound/wisp like there is a burnt exhaust valve. With that I might think there is a crack somewhere around the valve guide area or somewhere between the two valves or maybe a broken compression ring? With your symptoms I'd lean towards the "something is broken/cracked" versus warn out to fair wear and tear.

Really would need to tear it down to get better look. But if you are not burning oil and there is no anti-freeze or fuel in the oil, I'd just leave it alone.

thats whay I was thinking lol hopefully nothing gets too bad haha. Thanks!

It's actually not too bad to pull the head and check things out. I recently had to replace mine and it only took 2 hours to tear it all down and another 3 hours to get it all back together. In order to pull the head, you'll end up disconnecting the timing chain, and since you need to take it all apart anyways, you might as well install a new timing chain set. They are very affordable and will ensure engine operation for thousands of miles to come. Check out my build thread if you need pics of the process or any help.

Cheers,
~Peter

Hi.
I was searching the forums for info on pulling a head for a gasket replacement and came across this thread.
I wanted to ask if the head can be pulled without removing the front cover/water and oil pumps etc.
Is it possible? Never done a head gasket on this engine and want to avoid more work than strictly necessary as I am on a tight budget for this little truck. Thanks.

It is "possible" to leave the front cover in-place, but more than likely the instant you remove the timing chain to pull the head off, your spring tensioner down behind that cover will come loose. That or your chain will fall down or jump a link. In the long run, pulling the front cover isn't that big of a deal since it makes the re-assembly process much easier. I replaced my oil pump, timing chain, and all front gaskets while I was at it. I think it took me an extra 2 hours to get the front cover off, cleaned, and re-installed. Once you have the engine torn down this far, you might as well do some preventative maintenance.

^All my personal opinion and experience.
~Peter