The Stovebolt Site Forums The Shop Area Engine Shop Compression???

My 49 3600 w/original 216 has been running fine, but in the last 3 weeks has
started to emit a fair amount of blue smoke. It seems worse when you let off
to shift, but a thin cloud is now always present. I bought a compression
tester and used it last night. The throttle plate was blocked wide open, gas
shut off and the engine had just been driven for 1/2 hour. The readings:
1 2 3 4 5 6
50 20 110 80 0 20
wet 70 20 110 80 0 20
I'm astounded. How can it run so well, it sounds like a sewing machine? The
plugs were all light brown with a little soot. I installed new plugs and
started the truck. Pulled off the plug wires 1 at a time. Number 2 and 5
elicit no change at all. I did the compression test to try to ascertain if
it was valves or rings. I don't know how to interpret these numbers. I was
planning to pull off the rocker assembly and check the rocker arms to see if
the contacts are flat, re-install and re-set the valves to see if that
would help, but I'd sure like some comments. I have a 235 that ran well when
I pulled it last year. I would like to keep the 216 if possible and wouldn't
mind doing a valve job, but I don't want to do a complete rebuild. How can I
tell if it is the valves or rings, and how can I do a compression test on
the 235 in the engine stand??

With PSI like Zero, I would think it would have to be a valve. Even bad rings would probably give you at least a little bump on the needle. Pull the valve cover and see whats up.

Exhaust valve is probably stuck open - which is weird because even then you should get a blip. Pull the valve cover, maybe one of the lifting rods is bent. The good news in that case is you can fix it without pulling off the head.

The bad news is if you run it too long like that, the valve may not seat properly if carbon etc get a chance to gunk up on there.

-Boyo

Little or no change on the wet test indicates valve problems. Have you done a valve adjustment recently? I'd check to be sure the valves are seating fully, then run an adjustment sequence and retest the compression. Worst-case scenario, you might need to do a valve job. How much mileage does the engine have right now? If it's a high-miler, valve work will probably do in the rings in pretty short order, due to the increase in compression.
Jerry

It seems to me that your rings have to be at least fairly worn, on account of the blue smoke. The increase in smoke when you let off to shift is probably from engine vacuum sucking air from the crankcase into the cylinder(s) around worn or broken compression rings. I'm not saying the zero reading isn't from a stuck valve, but it seems likely that a rebuild may be due even if/when you get some compression back after valve work.

You may have a burnt valve also. That's about the only way to get a "0" PSI reading, unless he piston has a hole in it of coarse.
Sounds major either way,
Scott

Thanks guys,
I will check the valve adjustment this weekend, probably end up pulling the head. I'm a little concerned that a valve job will increase compression and that will lead to the need for an O/H, which is not in the budget. I want to stay with the 216 if I can, but have a 56 235 that ran well last year and didn't smoke. If the 216 doesn't turn out well I'm trying to see how to run a compression ck on the 235 bolted to an engine stand. I'm thinking that the harmonic balancer is still on and run a pulley to an electric motor, or maybe epoxy an nut on the balancer and turn it with an impact wrench?

Shoot compressed air into each sparkplug hole. The air escaping will produce noticable noise at carb, exhaust, or road draft tube/valvecover depending on where the air is escaping.

You need a "leak-down tester". In fact you could check both engines with it. Here are two home made units I just found on the internet. [img]http://www.lafishmag.com/LeakTester.jpg[/img] Home made unit in photo
Another home made unit
Here is one that uses two gauges and has instructions to use even if you don't have a compressor that can maintain 100psi.
Longacre racing $100

I would think that no matter what you do with the head, the oil burning will not go away. You could probably install rings without spending a lot of money.

I think the leak down test is just what I need to do, so on the 216 I know I have to have each cylinder at TDC on the compression stroke. The 235 on the stand is not mounted with the bell housing and the rockers have been removed along with both manifolds. Even with all the valves closed, I'm assuming I need to bring each cylinder to TDC on the compression stroke to do the leak down test??

Not necessarily. The leakage will be a little more pronounced at the top of the stroke, where the most wear is, but on the one with the rockers removed, just pressurize the cylinder and let the piston bottom out. Then listen for leaks at intake, exhaust, and crankcase. With the manifolds off, you can even pinpoint which valve is leaking. A leak at the thermostat housing would indicate a blown head gasket.
Jerry

To add to what Jerry said, keep your hand away from the flywheel and front pullies. If you add compressed air to a cylinder at TDC, the engine will want to roll over to BDC.
Just a word of warning,
Scott

Of all things, Dave, remember this was designed to be a farm truck. A ridge reamer and a new set of rings should be plenty of O/H for the RPMs these trucks operate at.

I've assembled all the parts I need to build the tester to do the leakdown test(thanks for the links!). I need a simple primer on how to find TDC on the compression stroke for each cylinder. I've adjusted the valve's a couple of times using Oly's primer, but am unsure on how to ck each cylinder for TDC. If I watch the distributor rotor in firing order and the rotor is pointing to the place on the cap where the plug wire goes and the points are about to break, is that TDC on the compression stroke?

Dave The way I check # 1 TDC is remove valve cover roll the engine until #3 intake valve in full open #1 will be at TDC. roll engine until #6 intake valve is full open #5 will be at TDC, #2 intake full open #3 at TDC, #4 intake full open #6 at TDC,#1 intake open #2 at TDC, #5 intake open #4 at TDC..Hope this will help

Dave
I put links to two different home made leak down testers, plus the one from Longacre. I was just looking at the one in the photo and I don't think that one would work. If you compare the gauge location to the drawing in the second link, you will see that the gauge is on the wrong side of the restriction orifice. The orifice has to be between the 100psi supply and the gauge that you read the pressure loss.
If you built the first one, I am sorry for the confusion. Add a "T" fitting between the orifice and the female quick connect and move the gauge or even better add a second gauge. The gauge on the regulator does not have to be a 100psi gauge. Anything over that will work fine. Set the regulator at 100psi and take the reading on the other gauge on the engine side.

Nope, haven't built it yet, just gathered all the parts and was planning on assembling tonight. Thanks for the heads up, I was planning on modeling mine on the 2nd post by Mike Nixon, which shows the damper valve AFTER the regulator and before the guage. Are you saying the dampner needs to be before the regulator and before the guage?? i.e. quick connect, damper valve, regulator, guage. quick connect, grease pump hose , spark plug fitting??

No. Build it just like the the guy shows in the drawing. Orifice(damper as he calls it) is between regulator and gauge that you take the reading from.
The reason for having a second gauge on the regulator is for a more accurate reading. After you make the connection and the air is escaping through the burnt valves or broken rings, the pressure on the supply side of the orifice may blead off a little below 100. You adjust that back to 100 even and the reading on the other (100psi) gauge will represent a more accurate % leak. The single gauge unit will work just fine. Just not quite as accurate.
I took another look at that setup in the photo(that I posted) and read his write up again. I had assumed that the pipe nipple between the quick connect and the regulator was an epoxy filled orifice like the other guy had. Wrong. He makes no mention of it. He is using the restriction in the hoses and connectors between the compressor and his test unit for the pressure differential. He is setting the compressor supply at 100psi. Pressure is lost in the supply hose and the regulator on his tester can't regulate what it doesn't have so you get a reading on the gauge showing the pressure loss in the hose. If he uses a different supply hose that is shorter, longer, smaller, he would get a different reading on the same cylinder.

One thing that might not have been made clear is the supply air pressure. The Longacre site tells you how to use the tester and they say to set the supply(at the compressor) air pressure to 110psi to 125psi with a max of 175. You just have to have enough so that the tester regulator is set at and can maintain 100psi.
Of course, that doesn't apply to the tester in the photo I posted.

Ok, I have a regulator and a guage on my compressor just before the air hose attaches, so that could function like the first guage shown on the Longacre site. I can set that regulator to @115lbs. max too.

No. I think.
The model 73010 is a two gauge unit. It would be used with a shop air supply hose connecting the tester to the compressor that would have its own regulator and gauge. A third gauge if you would.
The gauge on the compressor or shop supply line is set at 115psi to 125psi. Then a 20 foot hose or what ever you need to reach the tester and engine. The left gauge in the Longacre tester is adjusted to 100psi with that regulator and the reading for leakage is on the right side gauge. IE, compressor gauge is 115; left Longacre gauge is 100; right longacre gauge is 93; = 7% leak. With this setup, the short hose is already connected to the spark plug hole and to the tester.
With the single gauge unit you said you were building, it's done a little differently. 115-125psi at the compressor. Then 20 feet of hose. The regulator(has no gauge) is used to adj 100psi on the gauge(that is on the "T" between the orifice and female connect). Then the short hose is plugged into the testers connector. The gauge reading will drop at this time. If the gauge now reads 90psi, you have a loss of 10%.
Hopefully the regulator will maintain 100psi on the other side of the orifice. If that regulator had its own gauge, then you would know for sure. That's where the two gauge unit would be considered more accurate.
The two gauge unit would not necessarily have to have a detachable short hose, but it makes it easier to thread into the spark plug hole. You can also make up two short hoses for two different plug threads.

Update:
I built the leak down tester as described by Mike Niday??. The result on the 216 was NO cylinder over 60lbs and most under 20. 1 and 5 were about 5 lbs and were obiously leaking past the exhaust valves, as I could here it only at the tail pipe. #4 had sixty lbs and this was the only cylinder that had good compression (#110). The rest had some leakage thru exhaust valves and the crankcase. I slipped a piece of heater hose over the dipstick tube to ck for air in the crank case. I ran these test 3 times to make sure I was at TDC on all cylinders when tests were made and the results were the same each time. I then tested the 56 235 on the engine stand with no rockers installed. All cylinders were above 90 except 1 which was at 76. I could hear some air in the exhaust in this cylinder. I wanted to find out if the 216 had just head/valve problem or ring problems. I'm fairly convinced that it is worn out, and that I should concentrate my efforts on the 235. I am going to pull the head on the 235 and have it checked for cracks etc. I may try to lap the valves and install new seals. Since it is on the stand, I plan to pull the pan and ck the bottom end, install an new rear main and decide after I inspect the cylinders where else to go. I do not want to do a complet O/H unless I see something that really warrents it. I'm hoping that doing the valves will suffice, but I understand that disassembly will tell the tail.