abecedarian

cam timing, as in the chain is off a tooth or two or three or... you get the idea- basically the camshaft is not turned to the correct position to operate the valves at the right time when the piston comes around.
if the cam timing is off, one scenario could be the intake valve may be open as the piston comes up the bore on the compression stroke thus pushing air/fuel back out through the intake. when the valve finally closes, there's not enough air in there to build up to full compression.

DupermanDave

When we did the timing after the head job, we made sure all was aligned perfectly. We made sure the proper psiton was top dead center, and the hole in the timing chain sprocket was TDC as well. The chain was good. Only thing I can see being off is the distributor.

My girlfriend's dad was helping me with it and he ensured everything was done right. He used to be an aircraft mechanic, so he's very particular about how a job should be done. Doing it right cost me an extra week to do this, but it got done.

abecedarian

did you align the marks on the chain with the marks on the crank and cam sprockets?
sorry if it sounds like I'm beating a dead horse.

DupermanDave

Yup. we did that. Engine has 235k miles on it, so I wouldn't be surprised if it was the rings. But this was my first compression test I've ever done, so I may have done it wrong. It seems so easy to do, though. What else could be a source of bad compression?

-edit-
I even made sure to do the compression test while the engine was hot. Burned myself quite few times on the spark plugs

abecedarian

low compression is usually caused by:
worn or broken rings or damaged pistons
head gasket issues: failed, under-torqued, etc.
incorrect valve adjustment
burned or otherwise damaged valves or seats
cam timing or wear
physical damage to the head or block
slow cranking speed during compression test
obstructed intake or exhaust (throttle closed, plugged converter, etc.)

usually, if compression test numbers are low but there is no obvious cause as is your case (oil in the cylinders did not affect compression reading) a leakdown test would be performed- the cylinder in question is pressurized and the engine is checked for any obvious air leaks. hissing in the intake and/or exhaust would point at valve train issues, audible hissing in the crankcase would indicate piston/ring problem, bubbles coming up in the coolant/radiator would indicate head gasket or cracked head / block, etc.

DupermanDave

I think the gauge was faulty. The pressure reading never stayed on. IT had a pressure release button, but every time a reading was taken the needle would drop down again on its own. I had to angle the gauge so I could see it while cranking the engine.

I'm thinking about just taking it in and having a professional reading done. That way i can sleep without worrying.

drew303

If its doing that LOL then ya the guage isnt working right. It'll reach full pressure after a few revolutions and max out.. the guage is designed to only increase its reading and hold it.

=) Just rent one from a parts store.

DupermanDave

I did. Autozone, since there's one like right across the street from the neighborhood I'm currently living in. I'll probably just look at buying one, since it's cheap and good for future use.

DupermanDave

With the engine having 235k miles, and shooting smoke ONLY on startup, would it be reasonable to assume it's piston rings?

When i poured oil into cylinder #1 to to a wet test, the oil remained in the cylinder long enough for me to startup the truck and have it shoot out smoke immediately. Immediately is the key word. When i normally start up the truck, it usually takes it 20-30 seconds before it starts to smoke out the tailpipe.

Also, when I had oil in cyl. #1, and took it for a test drive to return the compression gauge, it was spewing smoke even as I drove, something my truck isn't doing now. As I've said, only on a cold startup will it smoke.

But back to the original question: piston rings...reasonable to assume it's those? or given the new information, could that point to something else?

DudeBud

i bet that the gauge doesn't have the valve in the end of the hose that's why its not holding pressure.