No compression on #1

This is strange. 2000 Blazer 4.3 runs great cold but when warm loses #1. Check when warm shows almost zero leakdown, but only 30 psi compression. Cold has 200 compression. The Old mechanic has never seen that before and I haven't either. In fact no one around here understands how it's possible. Heads just professionally done at reputable shop and engine doesn't smoke the bore looked great. Was torn down for head gasket between 1 and 3 everything was checked and decked. Got a whole crew here stumped you can see in the ports all clear what could be wrong with this thing other that it's a Blazer? :runaround:


Eric

When a valve lifter pumps up and does not release, it holds the valve open not allowing compression to build up. When the engine is shut down, the lifter gradually leaks down allowing the valve to close. Check both of the lifters and both of the push rods on #1 cylinder for a partial restriction. Or, the valve lash could also be adjusted too tight on one of the valves for #1, which would give the same results. Just a thought.

Well I don't see any thing wrong so far, got pushrods out and they seem clear. The rockers are not adjustable; they look more like Ford 302 style than Chevy. First day back after the Christmas Holiday so I'll know more in a bit. Thanks a million so far! :)

Might take the lifters apart and clean them out just to be sure. Should be able to blow through the push rods relatively easily. Torque the rocker arm nuts to 18 foot pounds.

Is cylinder 1 valves making a ticking noise from the hydraulic lifter?
Loose compression when hot!

Well, head's coming back off. #1 intake has good seal under leakdown. I now have the spring off with air in the cylinder under 25 psi so I can open, close, and rotate the valve at will. So here's the deal: valve is sealed well, spin the valve 90* and the seal goes away and leaks out the intake manifold. Turn back 90* and seals again. Head not off yet but I'm gonna guess the valve and seat are shaped like a stack of "Pringles". Strange. More to come. :)

Took a head to a shop for a new OHC, valve job, and they put the original valve stem seals in.
This car had plenty of hp, but smoked like a chimney.

Well, head's off. Sure enough, number 1 intake has a bit of a "Pringles" shape to it. Just about .006 on the lathe with an indicator rolling on the valve face. Head's gotta be out too. Back to the head shop for another checkup. Really wish I had my own valve grinding machine. Only $20.00 USD for a gasket and bolts so I can't really complain I guess, just a little more time. I'll let y'all know what happens next. :)

Well, head's off. Sure enough, number 1 intake has a bit of a "Pringles" shape to it. Just about .006 on the lathe with an indicator rolling on the valve face. Head's gotta be out too. Back to the head shop for another checkup. Really wish I had my own valve grinding machine. Only $20.00 USD for a gasket and bolts so I can't really complain I guess, just a little more time. I'll let y'all know what happens next. :)

Several things can cause a burnt valve.

Make sure machine does there job right.
Beside facing valves and seats good the seat should hit center of valve and not be to wide.
Also check valve guides and valve springs for proper tension.
Make sure the double check valve stem height after grinding valves and seats.

But also when putting it together first to check the valve stem height.
With the no adjustable valves rockers the valve stem height has to be set correct and all should all be even with other.

After engine is running you can feel push rods for being to tight.
If you can not twist them with fingers they are to tight.
If to tight Valve stem to high or lifter pumping up to much or rocker arm screwing down to much.

Let us know how it goes.

Heads going on right now. Got fingers crossed, which makes it a little harder to work...:)

friend had same problem and it had no compression in number 2 pulled head off it was cracked and broke a valve also.

Well, it's smooth as silk. Had to hold it wide open to get it to start, and it took a minute or so for #3 to start hitting right (lifters pumped up I reckon) but after crank cam correlation learn it couldn't run better. Thanks a million for puttin' up with me! I'm goin' for a nice long test drive WITH my phone! :)

allright! glad to hear you found and fixed it. thanks for posting back!