engine smokes but compression is good what next??

I have a 75 cj-6 with the 232 inline six (confirmed by engine code on the block and fsm), with what is supposed to be 90k original miles. It was originally a Texas forestry service vehicle that was used and maintained by a state park for all but the last 4 years. Then it was sold to a buddy of mine that didnt really have time for it so i aquired it from him. Since i got it, it has been sitting for about 2 years until i had the time to get to it (too many projects). Now on to the problem, at an idle it has grey smoke coming from the tail pipe. Under a load it does the same thing, constant smoking, not enough to fog the neighborhood for mosquitos but definitely noticeable. There is no blow by when you pull the dip stick or remove the filler cap and pcv valve. It has recently had a tune up, oil change, converted to hei ignition, and swapped over to a 2bbl intake and carb. I checked the compression and it was as follows ( each cylinder checked three times as outlined in the fsm using the highest of the three attempts) #1 150, #5 150, #3 145, #6 155, #2 155, #4 155. According to the fsm, the 232 is supposed to have 140 lbs of psi per cylinder. I have no idea if the engine has been rebuilt in the past, cylders bored, or who knows what. Could the higher than normal compression be from a bored over rebuild or just years of carbon build up on the pistons? Could the smoking be from worn, stuck, carboned over valves? Im just not sure where to look next or how exactly to test it, so im not just changing parts or doing unnecissary service.

 

If you had valve/ring problems, the compression usually isn't that high.
Could be hard or brittle valve guide seals letting oil run down the valve stems into combustion chamber.
A leakage test could expose more detailed information about the rings and valves.
Compressed air is introduced into each cylinder when that cylinder is at TDC (valves closed, piston at top of compression stroke)
A gauge would then show the pressure being introduced and the amount of air pressure the cylinder is holding/retaining.
The difference between the two readings is the leakage. If 150lbs is introduced and the cylinder is holding only 75lbs, then you would have 50% leakage (very bad, and this is a very generic example). While the air is still being introduced, you can then determine, by several means, if the air is escaping by the piston rings, intake or exhaust valve for that particular cylinder.
The simpleset is just to listen for air escaping: out the tailpipe (exhaust valve), thru the carb (intake valve), thru the crankcase (rings).
It should be noted that cylinder leakage in the range of 10% or less might be considered normal.
This is a very basic description of the procedure, and it takes a "leakage tester" to get the most accurate results.
Certainly this is to not keep you from adapting air and introducing into the cylinder and just do the listening test on your own. However, sometimesw it can be difficult to keep the piston at TDC, as the air pressure can push the piston down, which means you get to try again at TDC.
A compression test used with a leakage test is a good test/indicator of the engines overall health.

Also, simply changing the oil from a multi-grade back to a straight weight can change oil consumption values as well.

 

COuld be valve guide seals. They get old and hard and often ride up the stem or crumble away entirely. With valve guide seals the engine may smoke worse upon startup then taper off to some lesser amount.

Also, a worn out, misassembled, or broken oil scraper ring could be the problem but if the compression rings are in good order your pressure will be unaffected.

I would encourage you to not spend too much on a 232, unless they are parts that can be transferred to a 258. But don't give up on a 232 that runs well just because it's a small engine, unless it's not enough to turn bigger tires.

 

Good advice from Jim (jpflat2a) - start with the compression test, and post up your numbers here. A compression test is really simple to do, and very easy on an inline engine.

Yes, the 232 has very little value as an engine. But there's nothing wrong with it - it's a very durable and reliable engine. If the engine is in really bad shape, I'd suggest upgrading to a 258 or 242 (4.0L). Or look around for a cheap or free replacement used 232.

But do the compression test first.

 

Are you running fresh gas, old gas or a mixture of old and new? Picked up an AMC Eagle a couple years back that had sat for at least five years and I added some fresh gas to the old, smoked something awful until I eventually got the tank off and cleaned it out. There was no white smoke which would indicate anti freeze or blue smoke which is generally what you get with oil. Didn't smell real nice while it was running either.

 

I did the compression test with the following results. ( each cylinder checked three times as outlined in the fsm using the highest of the three attempts) #1 150, #5 150, #3 145, #6 155, #2 155, #4 155. According to the fsm, the 232 is supposed to have 140 lbs of psi per cylinder.

 

I let it run until it was almost empty before rebuilding/swapping to the 2bbl carb and intake. Then I added 13 gallons of premium to the tank and some Lucas fuel treatment prior to running it with the freshly rebuilt carb. It has been run/ driven enough to get down to almost a 1/4 tank according to the gauge which seems to be accurate.

 

Sorry, I overlooked your numbers in the first post. Those look very good.

Does the engine lose oil? Do your plugs show signs of oil fouling? I would expect both of those if there were a lot of oil getting into the cylinders.

That kinda sounds backwards to what I'd suspect if oil were leaking down the guides. A leak around the valve stem would change with engine vacuum, ie at full load, vacuum is low and less oil would be pulled in through the guides. Back off the throttle and manifold vacuum goes up, increasing the fog. Sounds different from what you see.

So where can oil get into the fuel? I know that you can get fuel in the oil from the fuel pump, but I've never heard of the reverse. Maybe your PCV valve is stuck open, and you're pulling oil from the crankcase into the carburetor. Or maybe there's a crack in the block that lets oil into one or two of the cylinders? Then I'd expect to see one or two very oily plugs, and the others clean.

How convinced are you that its oil? Do you have power brakes? Sometimes the MC will leak into the booster, and it will be drawn in by manifold vacuum. Similar thing happens with a leaky modulator on an automatic transmission, but that does not apply here.

 

It hasn't been driven much so I will take it down the road when I get home from work tomorrow morning to reconfirm the amount of smoke under a load. I forgot that when I looked at the plugs after pulling them they all had a light oil residue on them. About the same amount as if you dipped your finger in oil and rubbed a light coat on them. It doesn't have power brakes and the pcv is new. It also did the same thing prior to changing out the pcv valve. Could there still be a ring issue even with the compression as good as it is? I'm guessing the leakdown test would be the ultimate tell all to determine if it's an issue in the head or in the block???

 

If it been rebuilt and the ring have not set in yet. or it has chrome rings , chrome rings take forver to set in. It will smoke just like that.

 

If the rings refuse to seat, an old-time cure is to put Bon Ami down the carburetor. There's even a Chevrolet SB that recommends this, from the 50s. Something of a last-ditch effort, but the price is certainly right. Search the net and you'll find dozens of references.

 

If the rings weren't seated properly wouldn't that affect the compression?

 

Well, I don't know. Maybe not, since this is an oil control problem, not a compression problem. There are two compression rings above the oil control ring (it's usually a composite ring of two thin bands and a wavy separator), and the oil ring could be the problem. Back in the day, the first Chevy V8s had a terrible problem with oil burning, and I presume that they ran ok and had good compression. You might find some stories on the 'net about this issue ... could be helpful.

I know that SOP is to hone the bores so that the rings will seat. The cross-hatch helps to wear-in the rings. Relatively soft cast iron rings are recommended if the bores aren't perfectly round (ie a re-ring using the old pistons). Since we weren't around when the engine was rebuilt, we can only speculate what was done.

 

My 1973 CJ5 with the 258 was doing the same thing. Good compression, no leaks, burned oil like crazy (about a quart every 150 miles)and left an oil/ash residue on the plugs. Vacuum was good. Vac gauge showed nothing different than a perfectly normal engine would at idle or under acceleration/decelleration. I installed new valve seals for less than $10 and the problem is solved. No more smoke, no more oil consumption, better mpg's and power. Four hour job.