Green93

Saturday I decided to do a little maintenance on my truck. New cap, rotor, upper rad hose and pcv valve. Since I had the plugs out to check the gap and clean, I decided to do a compression test. The measurements I took were pretty scary. 2 cylinders had almost no compression and one was way low, at about 60 psi. This is far from the 147 that the FSM lists as minimum.

I did the compression test as described in the FSM. Engine warm with all plugs out and cold start injector plug unhooked. When I saw the low results I tested each one again with a little oil. The readings were pretty much the same. This, to me, points to valves. I have just redone this whole engine. It has about 10,000kms since rebuild. I shimmed the valves with my father-in-law. We were pretty careful but we were both learning. Is it possible that the valve seats seated themselves far enough that the valve isn't closing at all in a couple cylinders?

Basically what I'm looking for is someone to tell me that this is common and all I need to do is re-shim the valves and all will be good. It scares the crap out of me that I might have to pull the engine out again.


Jason

abecedarian

did you do the compression test with the throttle propped wide open?

abecedarian

and if you're concerned the valve adjustments aren't correct, measure them again.

Green93

No, I didn't have the throttle wide open. As soon as I saw your reply I remembered seeing that in the FSM. Damn. Ok, that would obviously account for a low reading per cylinder. It wouldn't give me near 0 on a couple cylinders though would it? That would mean I still have another problem. Does my theory with the seats setting in make sense???

Jason

abecedarian

lol, sorry.

don't forget to remove all the spark plugs too.

near 0 could be valves being held open...

...but can't be sure until you do a proper compression test.

and if you still read near 0, check in to doing a leakdown test.

Green93

Ok, thanks for your help. I'll try to get a proper comp test done tomorrow after work and then I'll post here. I guess a leakdown test would be better than just tearing off the plenum and checking valves right away.

Thanks,
Jason

Green93

Ok I just did a proper compression test but the results are still terrible.

#5 145psi 128psi #6
#3 75psi <50psi #4
#1 <50psi 130psi #2

I guess a leakdown test would be next? I'll have to scrounge up the tools to do that. Is there a proper psi to fill the cylinders or do I just fill with compressed air and listen for air escaping? I guess air would escape to the intake, exhaust or crank case. Would I hear it if I removed the oil fill cap?

No wonder it is running rough. Should smooth out once I address these issues. Hopefully I just botched the valve shim adjustment and it's nothing serious.

Any help and direction is appreciated.

Jason

Bigblock

Put the plugs back in and fire it up and hook up a vacuum guage.Needle moving wildly or perfectly still?Any hint of a misfire will show up on a vacuum guage.Pull the plug wires one at a time and replace them until you find one that changes the engine idle.then you have somewhere to start checking your valve clearances.
Bigblock

Green93

I haven't had a chance to look into this any further. I'm sick, workin' overtime this weekend, and have some wedding thing to go to. No time till next week I guess. Will I hurt it running it like this? Assuming it's the valves that are the problem. I've just been taking it easy back and forth to work.

Jason

abecedarian

likely it won't hurt it much. it's been running like this for how long already?
catch my drift? but that doesn't mean that this weekend won't be the weekend it decides to blow, either.
but I'm fairly sure another 100 miles won't kill it.

Green93

Well I finally made time to rip the plenum off and check the valves. On my 3 low compression cylinders I found that the intake valve has no clearance at all. On the other 3, the clearances aren't too far off though, so I don't know what is causing lower compression in them.

These are the clearances I just measured:

#5 in. .011---------#6 ex. .012
ex. .013-------------in. .010

#3 in. dead tight---#4 ex. .012
ex. .011------------in. dead tight

#1 in. dead tight---#2 ex. .017
ex. .016-------------in. .012

I checked the clearances after the truck had been sitting for about 2 hours. Does this still qualify as warm? Obviously when I work on it in the morning it's going to be cold. Do the clearances tend to close or open when it gets to operating temp? I'm just not sure on what side of the scale I should set them up. I don't want noisy valves but I want them to open and close all the way.


Jason

Green93

Finished up the valves tonight. I had an extra shim from before which fit one cylinder perfect. The other 2 I had to order. What a difference it made. She's nice and smooth now, no more having to shift into park at stop lights. Now on to the next issue on the list.

Jay351

So how does it run now? More power?

Green93

Noticeably more power now. Of course that is just the "seat of the pants" dyno. After I got it running last night I went out for a highway run and she pulls alot harder. Idles nice and smooth also. Was a little disappointed that my rumbling idle is gone though.

After this snow lifts we will have to take our trucks out and see how they compare. Sometime when we can go more that 12km/hr on the #1.

Jason

PS. how's that locker in the snow?

abecedarian

a few thousandths can make a difference in compression. have you rechecked it after getting the valves all straightened out?

Jay351

Sweet! Our trucks felt pretty darn close in the power department last time, hopfally yours can blow mine out of the water now
I have to admit, the idle yours had before. That just sounded Badass! I loved it!

The locker isnt THAT bad, but let me put it this way. Any amount of throttle in 2wd will break the back end loose. But im used to it, when I get into hairy situations I just pop it into 4wd and the front end pulls it back straight (or gives me some traction)

I have mastered lock to lock drifts

Green93

No, I haven't re-checked the compression yet. I still need to time it again too. I just had time to get it back together for work. Maybe when I get a few days off over Christmas I'll do some testing and fine tuning.

Jason