nomadic_addict

I finally did a compression test... the results from 1st to 4th cylinder in pounds per square inch:

#1 - 25 psi, #2 - 65 psi, #3 - 100 psi, #4 - 75 psi

Tried to do a cylinder leak-down test today, but my air compressor maxes out at 115 psi and could not keep up with how bad it was leaking. Once I connected everything, I then turned the regulator knob on my compressor in an attempt to get to the recommended 100 psi, but it would only get to about 70 before it would end up stabilizing at about 50 with the compressor running. So bascially, I had to test at 50 psi due to a small compressor and what seems to be really bad exhaust leaks on all 4 cylinders.

First question is: How important is it to test at 100 psi instead of 50 and could anyone possibly explain why as well? I could try again with someone else's larger compressor if readings at 50 psi really are far less accurate for some reason.

Here are my results from the leak-down test I attempted by regulating with my air compressor and attaching the air hose to a tee that has a pressure gauge on it before it connects to the spark plug hole with a fitting from a regular compression gauge:

Cylinder #1: reg. @ 50 psi -> held 25 psi on leak gauge
Cylinder #2: reg. @ 50 psi -> held 27 psi on leak gauge
Cylinder #3: reg. @ 50 psi -> held 28 psi on leak gauge
Cylinder #4: reg. @ 50 psi -> held 30 psi on leak gauge

That's about 40% leakage on all cylinders with almost all the air blowing out of the tailpipe on all 4.

So you know, I tested each cylinder with the piston at the top of its stroke but just barely starting to move downwards and with the distributor rotor pointing to that cylinder. To my understanding, this would be top dead center of the power stroke which is what is needed. I even tested one at both this position AND at top dead center of the compression stroke for comparision (tested cylinder 1 after testing cylinder 4 without turning crankshaft). It does seem obvious that it leaks more without being on the power stroke, but was still not a huge difference since I am leaking bad anyways.

By using a piece of hose for a stethoscope I could hear air making it to the crankcase through the dipstick hole, but I believe this is probably normal... and because I have never tried this before, I was probably taking long enough for the engine to cool even though I tried to get it to operating temp beforehand. Also, is it normal to have some leakage out of the other cylinders when testing one? I ended up plugging the others with spark plugs to hopefully see where else it was going, but almost all leakage was through the tailpipe regardless.

Leaking did not seem apparent out of the throttle body nor was the coolant bubbling in the radiator when testing any of the cylinders, however... I could feel it blowing out of the tailpipe like it was running except it was a steady stream of air. This was the result I got on all 4 cylinders... and I can't help but to wonder how much air would even end up anywhere else regardless, due to the exhaust leak being the path of least resistance.

Now to my main questions: Should I try this again with a bigger compressor that can hold 100 psi going into the cylinder? Are there any other diagnostics worth doing while the truck is still operational? I am thinking it is time to pull the valve cover... see what the clearances look like on the valves and inspect the camshaft lobes... then pull the head to actually see what the valve seats look like, as well as the pistons and cylinder walls.

The truck still runs, but won't crank or idle due to such bad compression. I have to roll it and pop the clutch to get it going, but seems to drive fairly decent for running on 3 cylinders with exhaust leaks... I just can't take my foot off the throttle when in neutral or it dies.

The engine was a complete long block installed by Yodaman less than 3 years ago and only has about 30,000 miles on it and does not burn any oil, so I am hoping that all my problems can be fixed by replacing or servicing the cylinder head only. I suspect that I also have a blown head gasket, but the oil and coolant are not mixing. I recently saw that my radiator leaks and the fan blows the coolant onto the front of the engine, which had me thinking it was leaking from around the water pump gasket at first. Radiator still holds coolant to where you can see it with the cap off, but will not stay full to the top of the neck. I already took the thermostat out suspecting it was stuck closed.

Thanks to anyone taking the time to read this, and all advice and suggestions are welcome and appreciated. My main concern is to hopefully exhaust any diagnostic procedures that can help me discern that only the cylinder head needs to be rebuilt to correct my engine problems. If ALL of my exhaust valves are not seating, then it seems to me that either they were all left to tight after the install, or... well, maybe you can help me here. Perhaps ALL of the camshaft lobes for these valves are worn? I would doubt the timing chain skipped a tooth this soon without me knowing it.

Thanks again for any help offered.

spokane.yota.man

After seeing numbers from the compression test that low I wouldn't even bother with any more testing. Something is obviously wrong. Start by removing valve cover and checking valve lash. Also visually inspect everything well such as timing chain.Assuming you don't find a major problem I would then pull the head and check the valve seats and inspect the cylinders. Good luck.

fierohink

You could redo the compression test after squirting some oil in each of the cylinders. If the compression results improve, then the oil is sealing something up i.e. rings. If the compression results don't change then you can eliminate the rings and bottom end almost entirely as your problem, I don't want to say completely because you could have something crazy like a hole in the piston that isn't going to be solved with a squirt of oil.

toyrunnerns

by putting piston at tdc , this should close both valves .meaning the only leak points would be hg ,piston rings or the head(crack or warp). if the valves are out of adjustment that could cause some leaks. i would say that the #1 cyl has busted rings or a hole in the piston . did you do the compression test with tb wide open? i would check valves first then redo comp test. those comp # to me mean a motor rebuild, but maybe a new head and hg will fix

nomadic_addict

I did the compression test with the throttle wide open. I used my grandfather's old push-in style guage since it was too difficult to use the newer screw-in type from the parts store. My Chilton manual states that the older style is less accurate, but there are no corners to use tools and no room for my hands to screw the hose into the fitting from the newer gauges. I believe the gauge I used was probably top of the line when it was made, but I'm not sure how much this all factors in. I paid for a compression test from a shop once and got similar numbers, but I'm not sure how what kind of gauge they used.

If my piston or rings were busted or had holes in them, wouldn't my truck be smoking when its running? I've already pulled the radiator to be patched, but I guess I could reinstall it and refill with the coolant I drained just to get it up to operating temp one more time for another compression test... then I'll try the squirt of oil trick. Or... will it at least be obvious that my block is okay or not by visually inspecting it? I'd rather just keep disassembling once I drain the oil and pull the valve cover, but I don't want to put a new or rebuilt head with a new gasket on a bottom end that is failing in some way.

Thanks again for the replies.

TNRabbit

Sounds like your valves are nowhere CLOSE to seating.

nomadic_addict

I was going to drain the oil and then remove the valve cover today, but hit a snag...

I removed the drain plug from the oil pan after removing the filler cap first, but even after it was done dripping from the bottom... the valve cover was still full of oil on top.

I even turned the engine more than one whole revolution by hand to see if it would drain from the top, but it never budged. I tried adding a little more oil and sure enough, it would just keep filling more.... like it would spill out the top before I could ever even get more oil down in the pan. I wished I could have measured how much did drain out, but I didn't anticipate something like this and drained it into a big pan that wasn't empty like I normally would.

Anyone know what would make the valve cover stay full of oil like this? When I took the filler cap off after driving it the last time... the oil level was just as high as it is now... and has been sitting several days since then... and is that way now with the drain plug out for over 5 hours.

Also, what would be the best way to get the cover off now while making the least amount of mess? Maybe try to pump some oil out the top... then lots of rags around the sides? Starting to worry about how much worse this is gonna keep getting the further along I get.

nomadic_addict

First off, it only appeared to be oil sitting in the valve cover... guess it was thick enough to seem that way. Also, the cylinder head is in the machine shop now... and just like the leak-down test indicated, all 4 exhaust valve seats were burnt and not sealing properly. Only 2 of the intake valves didn't need to be reseated. The headgasket did not look like it had failed even though a shop tried to tell me it was leaking. Luckily, I decided to tackle this repair myself... otherwise, I would still be taking someone's word as to what's up with my engine. Oh yeah, the pistons and cylinder walls looked great... should be a good engine now when it is back together.... and I will def. be keeping an eye on the valve adjustment from now on.

Sportsmanphil

There is a chart to follow during a compression test. Its based upon needle reaction and will give you an idea where the leak is (valve, guide/seal, ring, valve spring etc) I have this in my shop (somewhere......maybe)

Problem is I cannot remember off the top of my head what to look for but im sure a quick internet search will find that chart.

If I find that I will post the instructions.

Sportsmanphil

^^OOps,, not a compression test, but a vacuum test^^

You should always follow a bad compression test with a detailed vacuum test. Here are some results to look for and what they mean.

Vacuum gauge checks and diagnosis:

The pump's vacuum gauge readings give indications of possible mechanical problems, but they are not foolproof. Observe the gauge carefully and follow the vacuum readings with further tests, where possible, to confirm your diagnosis. Do not look for the engine to produce specific (numerical) amounts of vacuum. Much more important than specific numbers is the range of the vacuum readings and the movement of the needle. Important things to notice about the needle movement are HOW the needle moves (in a smooth or jerky manner, erratic, etc.), what direction it moves, whether movement is regular or varying, and how far the needle moves.

Normal engine

Run engine and connect the pump to an intake manifold vacuum port. Watch the needle's movement on the gauge. At idle, the vacuum gauge reading should be 19-22" Hg and steady.

Burned or leaking valve spring

At idle, burned or leaking valves will cause the pointer on the gauge to drop to a low reading and return to normal at a regular interval. The needle will drop from 1" Hg at regular intervals whenever the defective valve attempts to close.

Sticking valve

A sticking valve will exhibit a rapid, intermittent drop from the normal pointer indication. This is unlike the regular drop that characterizes a burned or leaking valve. A sticking valve condition may be pinpointed by directly applying a lightweight oil to each valve guide. When the sticking valve is reached, the situation is temporarily remedied.

Weak or broken valve spring

Weak valve springs are indicated when the pointer of the vacuum pump gauge fluctuates rapidly between 10" and 21" Hg at idle. The fluctuations increase with engine speed. A broken valve spring will cause the needle to fluctuate rapidly at a regular interval. Again this will occur every time the valve attempts to close.

Worn valve guides

Worn valve guides admit air which upsets the air/fuel mixture. The vacuum gauge reading will be lower than normal and will fluctuate rapidly in a range of about 3" Hg. As the speed of the engine is increased, the needle will steady.

Leaking piston ring

Vacuum at idle will be low but steady at about 12" to 16" Hg. Open the throttle and allow the engine to pick up speed to about 2000 RPM. Then, close the throttle quickly. The pointer should jump 2" to 5" Hg above its low steady reading. A lesser gain may indicate faulty rings, and a complete cylinder leakage or compression test should be done.

Blown cylinder head gasket

At idle, the vacuum gauge pointer will fluctuate between normal and a low reading. The needle will drop sharply about 10" Hg from a normal reading and return each time the defective cylinder or cylinders reach firing position.

Exhaust restriction test

An exhaust restriction will cause normal or near-normal performance at engine idle but cause very poor engine performance under load, or at higher speeds.

1) Connect the pump hose to an intake manifold vacuum fitting.
Operate the engine at idle and note the vacuum reading and
needle movement. Compare readings and movements against
descriptions listed for burned valves and late ignition or valve
timing.

2) Watch the vacuum gauge as engine speed is increased
to approximately 2500 RPM.

3) An increase in vacuum over that obtained at idle indicates
an exhaust system that is free of restrictions.

4) If the needle drops toward zero as engine RPM is increased,
either an exhaust restriction or an over-active EGR valve is
causing the problem.

5) Test the EGR valve separately. If it is found to be in good
condition, the problem is a restricted exhaust. Check and
replace if necessary.

Incorrect idle air/fuel mixture

When the needle on the gauge drifts slowly back and forth at idle, over a range of 4" to 5" Hg, the fuel mixture is too rich. A lean mixture will cause an irregular drop of the needle over about the same range.

Intake manifold or air induction leaks

If there are any air leaks in the air induction system, the pump's gauge needle will be about 3" to 9" Hg below normal but will remain steady.

Late ignition or valve timing

An extremely low but steady reading at idle indicates late ignition or valve timing, or a uniformly close setting of the valve lash. Perform separate tests to determine which of these problems, if any, have affected the engine.

nomadic_addict

Thanks for the help... the vacuum test was still a little over my head at the time... but I will probably try to utilize it the next time around... hopefully not anytime real soon. The leak-down did turn out to give pretty acurate results though... I'm just glad I didn't have to pull the whole engine... or replace the head. Maybe now I can start getting some miles out of this engine so that the initial investment no longer seems like a waste.