Compression check

S

SLEMMON

Member
Im getting ready to do a compression check on my 304. Granted this engine has been overhauled. New pistons and rings but not bored out. Heads rebuilt. Composite gasket. What psi numbers should I be looking for.
The engine has been ran acouple times but never driven. It has been sitting for a couple of years due to frustration and job overseas.
 
Actual number is not really important as different gauges and altitude will change things. That said somewhere around 130 -140 is typical. What's most import is consistency between the cylinders. A variation of <10% between the min and max cylinders is considered good.
 
Okay, sounds good. I started on the odd number bank and was getting weird numbers, until I realized I didnt disconnect the fuel line and open the throttle. The dizzy is removed right now so no chance of spark. All of the plugs are removed, but what has me wondering now is after I caught the fuel line and disconnected it I turned the motor over and the #6 cylinder was spitting a lot of fuel out. None of the others were at all!
I am thinking something might be wrong with the carb.
 
Don't crank it with the dizzy removed. Yes I'm yelling! The dizzy turns the oil pump. Cranking on dry bearings is not good. Also check your oil and see if the level has risen due to gas leaking past the piston rings. If so please drain the oil and use a drill to prime the pump then do your compression test.
 
Omg, I totaly forgot about that. At least it was only for a litle bit. Fingers crossed. I did check the oil and it was way full with gas. So I drained the oil and removed the filter. Just got back from getting new oil and filter. Will put the oil in and filter on after dinner. I will prime the motor with the drill and do the compression check. Will check back tomorrow with the numbers.

Thanks steve
 
Alright, everything that fdchappie said to do, has been done. Now I have a problem with my compression gauge I believe. When I turn the motor over you can see the needle on the gauge jump up to about 90 psi. But as soon as the compression stroke is over it drops to 0 psi. So it isnt holding pressure.
Is there another reason this would happen or is my gauge toast?
 
There is usually a small tire type valve in the end of the gauge. Remove it with a tire valve tool and clean it. Then try again and see if it works.
 
Did that and also replace the teflon tape where the gauge and the air chuck meet.
When I hold the gauge you can feel the air coming in, and I dont feel any leaks
 
Sooo, there was another shrader valve in the end of the hose. I guess I bent it when I was changing the tip around. Problem solved. So onto the cylinder #'s.
1-120. 2-115
3-125. 4-115
5-125. 6-120
7-115. 8-120

these are dry numbers. Didnt think wet ones were needed due to the numbers being very close.
 
Try opening the brass plug on the passenger side of the float bowl and see if the float level is to high while running.
 
I would if I could, it isnt running. Im trying to isolate what is going on with this engine. So I tore everything off except the carb. Did the compression check, old plugs were realy black with carbon, a lot. So got some new plugs to go in. New coil, new wires, new cap and rotor. I had a dui dizzy in it but I gave me alot problems with fitment. So im going back to old Holley dizzy (points). I'm going to put all of that on today. Only thing left is the carb, which has got to have a problem, with the amount of gas it was dumping in there. It has sat for awhile. So im thinking the ethanol might have got to it. I tried to rebuild this card awhile ago for the same thing. Dont think I did a very good job. Never did it before and nobody to help.
 
It sounds like the primary issue is the float level. It can be checked after cranking for a bit. Do you know how to adjust the float level on that carb?
 
It is done with the neddle valve on the top of the fuel bowl right? Last time I had it off, I believe, I set it to what the Holley manual said to do. Turn it upside down and turn it until float was level with something, can remember what right now. Then re-installed it.
The fuel level should be right at the bottom of the sight hole right?
 
I think those numbers are on the low side. I've rebuilt two of these engines (both 196s) and right out of the gate the numbers were not lower than 140 psi. If it's been sitting a long while, maybe rings stuck? If that's the case, I'd treat it to sea foam.
 
I don't know how much fuel you found in the oil or how you determined that it was a lot but if it came from the carb and it was running relatively normally prior, the most likely culprit is the fuel pump diaphragm. If the diaphragm is porous, the fuel goes straight to the oil pan.

For the fuel to come from the carb it has to get past the rings and it has to be running like a drowned pig and belching black smoke from the tail pipe. Very heavy oil dilution is fuel pump related on a normally running engine.
 
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