I just tested the compression and three are at 180. One is at 70 and I put oil in, it stayed around 70. Another is at 120 and with oil it went up to maybe 123.

The coolant is fine, the heads are fresh. What should I check next?

Symptoms: Had my '88 at the track. Started to have smoke, oil coming out of the dipstick. Ran fine on the way home, told that there is smoke when cutting the throttle.

 

Head gasket....

 

Old School: If both wet and dry compressions are low and about the same look for a problem with the valve train. Pull the valve covers for a look-see.

 

Andrew,
With no change in wet comp. test.It could be a few things.
Possibly broken rings and/or bad intake valve seating indicating a burnt or bent valve. Bad intake seating will put increased pressure to the manifold creating increased crankcase pressure as will broken rings maybe causing the dipstick tube oil venting. Broken rings could also be a reason for exhaust smoking on deceleration.Could also be bad valve seals causing smoke,but you said the heads were refreshed.
Rick

 

Gotta pull the heads first. That'll give you the answer. Hopefully just the gasket.

 

When I pulled the plugs #7 looked very different. Flat black on the porcelain rather then light gray like the rest. I pulled the V/C and checked things over but didn't see anything amiss.

The engine had the intake changed this spring along with ported heads and new head gaskets. Plus rockers. It ran well all summer till now.

 

How many miles on the shortblock? At 110K miles Im in the same boat with exessive blow by, oil out the dipstick and burning it through the PCV/Throttle Body. I need new rings and possibly an overbore.

 

Same mileage for mine. I'd be happy if it was just the gasket. Both sides? I don't find any signs of coolant amiss.

I'll get started pulling the drivers side head.

By the numbers:

#1 180
#3 180
#5 142
#7 70

#2 180
#4 120
#6 160
#8 180

The oil smells like gas.

 

To me it sounds like you have bad rings on #7. The black could be a sign of running too rich or burning oil and sadly the latter fits better. Either bad valve seals or worn/cracked ring could be causing it, but since the heads were just refreshed I am pretty sure you will find a bad ring.

Is the smoke all the time, but worse on acceleration?

 

Andrew,
It looks to me like you have bad rings. Multiple cylinders down on compression and high crankcase pressure.

 

Shouldn't the numbers go up with oil though?

 

Fluid follows the path of least resistance so if there are worn rings not allowing a complete and perfect seal between the piston, rings, and wall the fluid will run scared at the attempt made to compress it by slipping by the piston and rings down into the pan. Same concept applies to a cracked ring.

Also, in my past experiences, I have found it to be somewhat bad practice to refresh the heads with out refreshing at least the rings on engines of this age because when you restore the top end to normal power after all these years and don't restore at least the same power/integrity to the bottom you are bound to have the simple yet aggravating ring failure. If you don't, you're one lucky SOB and I envy your luck.

 

Yes, If rings were in trouble but no (or little) change in pressures with oil is indicating you probably don't have a ring problem. Broken rings are rare, I don't know that I have ever seen one.

If you had a valve problem the symptoms would be different than you are describing. A leaking valve will not pressurize the crankcase and blow oil out the dipstick. A leaking intake valve (they don't burn but they could get bent from not enough piston to valve clearance after bolting in a big Steak N Shake cam) will just blow combustion into the intake manifold and make noise out through the air cleaner. A leaking exhaust valve will blow combustion out in the exhaust. You have to determine where the pressure path to the crankcase is. I would put compressed air through an adjustable regulator or a cylinder leakage tester into cylinder #4 and #7 and see where it is leaking. I would not be concerned what the the tester says as you already know you have a problem, you just want to locate it. Listen for air leaking out through either the oil fill cap opening, or at the exhaust tips or the air cleaner to locate the source of the problem.

You say the car ran normal on the way home? The problem went away?

 

If it has burned a piston (and #7 cyl runs pretty lean in a SBC) no amount of oil in the cyl will help out compression. Bad rings are one thing but broken rings or a cracked ring land on a piston are quite another.... Dosent mean that is what happend but all the blow by and gas in the base pan you've described point heavily to it. This is my number 1 suspect.

A valve bent bad enough will kill that much compression as well but won't casue the other 2 symptoms.

A head gasket will also but, I'd be surprised if your not getting coolant in the hole or compression in the cooling system. It very well could be blown between the #5 and #7 cyls - but I'd expect the #5 hole to be a bit weaker... still this is a real possibility and would be my number 2 suspect.

With only 70lbs on #7, I'd say it's pretty bad whatever it turns out to be.

Sorry to hear about the trouble.
Will

 

Air up the cylinder, and see how bad it blows into the crankcase. My guess is broken ring.

 

Broken ring? Not very likely... He has two different low compression readings... 120 on #4 and 70 on #7. A ring problem could possibly be responsible if he only had the indication he is seeing on #4 but the 70 lbs he also has on #7 is far too low to be a problem with a ring. He would have to have two broken rings on that piston which is highly unlikely. The second ring is not only an oil scraper but a back-up compression ring.

How can a ring break unless you break it putting it on or taking it off? I have never seen a broken ring except as secondary collateral damage from an engine failure which originated somewhere else.

 

I have.
Just because you have not seen it, does not mean it cannot happen. I have seen it 3 times. 2x it was the top ring only, 3rd time is was a cracked land and it resulted in a broken ring. Valve was able to pass the small broken chunk of piston, and it was not even know until the engine was freshened.

 

Outside of a mechanical failure originating from somewhere else in the engine there are no forces in a running engine which can break a ring except high speed operation with excessive ring to ring land clearance or sustained pre-ignition which is often incorrectly called "detonation." It appears you can rule those out in this case.

 

It can. I've seen several engines where rings have broke and no
other damage to the engine.
I can't say what caused it, but I've seen it happen.

 

OK, well I posted a poll in a new thread where you can go vote yes. Let's find out how common this one is. Factory cast iron rings with inclusions, impurities or stress risers I guess, who knows?