I've been having very smoky start ups and rough idling. The truck blows white (maybe a hint of blue) smoke for a few seconds out of both tailpipes, and then for a minute or two out of the right (passenger side) tail pipe. Once it's running it settles down and doesn't smoke much.

So I finally got around to doing a compression test. I didn't install the air intake crossover thing (whatever that is) that the Haynes manual mentions, so I don't know if these numbers are correct, but I don't see why they wouldn't be.

Right (Passenger) Side:
#2 350 psi
#4 310 psi
#6 290 psi
#8 380 psi

Left (Driver) Side:
#1 380 psi
#3 300 psi
#5 340 psi
#7 350 psi

On all of the cylinders, the compression guage gradually climbed to it's high point. I'd like some help interpreting these results and suggestions about what to do next

Also, the variation between sides doesn't seem drastic enough to account for so much more smoking on the passenger side. True??

Now that you have done a compression test once. Take her for a road test and work her a little to get her good and warmed up and do the test again. To me it is about repeatability. If your numbers come out close to the same you might try a leak down test to see if your rings are leaking or if it is the valves. 2 cylinders next to each other could have a head gasket starting to leak between the two. A healthy 6.5 should have around 350 psi all the way around within 10% between highest and lowest.:grd:

The 30% difference from high to low is quite a bit. The lowest cylinder could have a worn intake valve guide which could result in less than perfect seating. A worn guide will draw oil down the sleeve at startup until the engine parts warm up and expand. It is still cold in Colorado so smoke can be caused by extra unburned fuel at startup. If you manually jump the fuel advance solenoid at startup then that will reduce the smoke.

How many miles on the engine and how often have you changed the oil and filter?

The low cylinders may cause misfire while cold. You have two on the right bank which would show as more smoke for a longer period of time when cold. The cylinders have to warm up to be able to fire the fuel. There is not enough "heat of compression" upon initial startup.

My '82 Pickup has done this for years. Just not quite as severe as you describe. I live in a fairly warm area, so wouldn't see as much smoke. The problem with mine is definately loss of compression, due to normal wear on an old, tired engine.

My manual basically says to take it to a mechanic for a leak down test. But all I need to do is hook up the compression test adapter to my air compressor right? What else is involved in a leak down test? Can someone here walk me through the process?

Thanks

for a basic leak down test, you can just hook up air to your tester. Then listen for where the air goes, either out the crankcase vent, the intake manifold or the exhaust pipe. Bad rings will be the crankcase vent or oil fill (remove cap) test between know real good compression and lowest compression and compare the sounds. Was your engine good and warmed up when you did the compression test? Are all of your glow plugs working propperly?:grd:

The engine was not cold, but probably not all the way up to operating temperature either. I may drive it around for a while and then test again, but I figure that since I got 380 psi in two of the cylinders, it must have been fairly warm.

When I do the leak down test, I need to make sure that the valves are closed on the cylinder that I'm testing, right? How do I do this? Pull the valve covers? Are there marks on the flywheel or timing chain sprockets or somewhere else that will tell me?

Thanks

Oops, you're right, just tap the starter a little. You will know if you have an open valve, it will sound like a blast of air and you are only looking for a hint of air. My main reason for having you heat the engine up and retry is to see if the numbers come out the same. I have been fooled by bad compression tests before, tore down the engine and found nothing wrong. Now I always do 2 tests and look at the numbers. If the numbers come out close to the same, it would be safe to say it is time to look deeper. 6.5's don't usually have much problem with valves. Usually the problem is with rings or scratches in the cylinders for contamination.

How many miles are on this engine? What kind of oil do you use and how often do you change it? Is there any blowby when you remove the oil fill cap with the engine running? Are there any bubbles in the radiator with the engine running after it is up to operating temp, with the cap off? Does the engine use any oil and how much?:confused:

So I did another compression test with the engine fully warmed up. My numbers were all basically 10-15 psi higher than the first time. So I still have only 300 psi in the #6 cylinder. It also took 10-12 compression strokes for the guage to reach it's highpoint on all of the cylinders. I've been trying to do a leakdown test, but having difficulties. My compression test adapter has a check valve, so I took a 10mm x 1.00mm bolt and drilled an 1/8" hole through the center of the bolt. then I cut off the hex head and theaded it into the glow plug port. Then I clamped some hose on the end of the bolt and clamped the other end of the hose to my air spray nozzle. I alternatively spray air into the cylinder, hand crank the engine a half turn, spray air, crank, etc. when the valves close, the air just pushes the piston down and opens the valves again. I tried putting the truck in gear, but this doesn't seem to stop this from happening. What's going on?

Okay, finding TDC was pretty easy. I just figured out which way the compressed air wanted to push the piston (i.e., clockwise or counter clockwise), found the midpoint and that was TDC (or BDC). Then I extrapolated from there to find TDC on the compression stroke. I used that point on the #1 cylinder to extrapolate TDC for the rest of the cylinders based on the firing order. When the piston is at TDC there is not enough leverage for the air to force it down, so the engine stays put.

The rest of the leak test seemed pretty subjective. By comparing the four worst cylinders to the two best, I felt like (it was more a "feel" thing than being able to deduce) that the low compression cylinders were leaking more from the intake valves than from the rings. Blowby past the rings felt about the same for all the cylinders that I tested. The sound coming from the intake manifold seemed greater for the bad cylinders. I kept checking back and forth between good and bad, and it was kind of hard because it took a little while to set up each test, so I was trying to remember what the last one sounded like just before doing the next one. The thing is, they all leak significantly, so trying to judge more verses less is very difficult I found.

Anyway, is it likely that I have bad intake valves on all of the low compression cylinders? A mechanic buddy told me that the middle cylinders tend to wear more, so it's most likely rings since those are the low ones.

I'm just trying to figure out what to do next. Pull the heads and mic the cyliders? If the cylinders are good then get a valve job and call it good? If I could just stop the excessive smoking on start up I could live with the engine the way it is for a while. I use the truck for work, just around town mostly, but I drive it daily so the start up smoking is really annoying. Could valve seals be the problem? Should I get the injectors pop tested/rebuilt? I guess I'm just trying to figure out the next logical step to take.

Thanks a whole lot for any help/ideas.

I realized that I haven't answered the several questions you all have asked me.

I was told by the people I bought the engine from that it had only 70k miles on it, but I'm skeptical of their veracity now -- they were dishonest about other things I later realized

I'm using Amsoil sythetic 15w-40 and I've changed it every 2-3k.

I have not checked for bubbles in the radiator while it's running-- you do this when it's hot and running???

Blowby has alway seemed so subjective to me. What is acceptible and what is too much?

The engine consumes about one quart of oil for every 600-700 miles, but this is doing short trips of 10 miles or less. On the one long drive of 600+ miles that I did, the engine did not consume any oil.

I am going to guess that you have some wear going on in the cylinders. Hard to know how the engine was taken care of before you got it. If it was me, I would switch to dino oil, Delo 400 or Rotella and save the extra coins for a rebuild. These engines respond fairly well to re-ringing, as long as there isn't too much taper. When re-ringing, throw out the factory specs because you won't even be close, you will be a little loose, but the engines tend to run better, because it is like being broken in. Blow by tells a lot on these engines about the condition of the rings. Very little blowby means great engine. Lots of blow by means a little tired. If you change to a manual glow plug system, you could give a little longer glow time and some after glow to get the smoking to stop. Make sure you are using A/C 60 g plugs or equivilent.:grd:

Thanks for the reply,

I'll definitely switch to dino oil now that I know I'm not hoping for another 200k out of this engine. I've got manual glow plugs now. How long would you say I can cycle them without burning them out? The plugs are Autolite 1110 10.5V H2.

Do you think it's worth it to re-ring without doing a full rebuild? I'm assuming I'd have to pull the engine to do a re-ring.

I am not familair with the characteristics of the auto lite glow plug, maybe you can find the info on the internet. With A/C 60 G's you can vary your initial glow time anywhere from 10 seconds to 1 minute without any problems. The glow plugs are thermally self limiting so they won't burn out. After the engine starts, I like to give some after glow, several seconds at a time until the smoke clears. You can do the after glow as many times as necessary. This is basically just duplicating original systems except their after glow was only for about 1 second, but they were using the easy to burn out 9G plug.

As for a re-ring, cost is a lot less than a rebuild, no machining on the block, assuming everything looks good. The biggest savings is not having to buy pistons at 400.00 +. If money allows, by all means go the distance and bore it. There is a company that has been selling engine kits on ebay for around 800.00 and it uses good quality pistons. They don't include a camshaft, but I have yet to ever see a bad cam in one of these engines, so to me that isn't an issue.
You might also consider putting in some marvel mystery oil with a fresh oil change and keep an eye on that low cylinder, maybe the rings are gummed up and stuck. You could also find that maybe that one piston has a broken compression ring. Lots of guesses, but my gut feeling is that the engine wasn't very well cared for before you got it and there is some cylinder wear. I have seen these engines that were neglected(long time between oil changes) have severe cylinder wear. Hope this helps.

Yes, thanks again. One last question: Do you have to pull the block to do a re-ring, or can you push the pistons up and out from underneath?

I have done it in the vehicle before but it is a PIA. Best to yank engine and do it on a engine stand. The big thing is cleanliness and in the truck it is hard to get rid of the honing debris. Also if you do take out the engine, inspect pistons and block carefully. Pistons you are looking for cracks and block you are looking for main web cracks esp. in the #1 main outer bolt area, not trying to scare you here, but better to look first before you go to a bunch of work.

D, thanks for all your input. I started it cold today and cycled the glow plugs longer than before. Started up much better. A lot less smoking. I was told a while back on this forum not to cycle the plugs for more than 10 sec, so I've been doing 5 on, 1 off, 5 on and start. Today did more like 8 on, 1 off, 8 on start. From now on, I'll push the plugs harder and get A/C 60 Gs when the autolites burn out. Perhaps I can live with the engine a little longer in it's present condition -- at least through the summer.

But it's good to know more about its condition and what I'm eventually in for. I do look forward to rebuilding it someday -- I'm developing a perverse affinity for this beast. :)

See if you can find some info on the glow plugs you have, if they are self limiting you are safe to let them glow about as long as you want. I sometimes used to glow my 18:1 6.5 for 30 seconds when it was really cold and I also had a marine glow heater in the manifold. I wouldn't do a tear down until things got a little worse. Keep an eye on the coolant, looking for little bubbles when the engine is running with cap off will clue you in if your head gaskets are starting to leak.:cool2: Also I am pretty sure that since your glow plugs say 10.5v you are safe to do extended glow cycles. The old 9g's were 6v plugs that had 12v going to them and thats why they would burn out if over glowed.:grd:

How much end gap would you guys say in ok for a rering on a 6.5? Piston to wall clearance with the used pistons? What about the clearnances on the bearings?

Everything is relative. On a rering you are starting with a worn block and then you are honing it to clean it up. So, your clearances are going to be a little on the loose side, over all it won't last as long as the factory designed but being a little loose, you won't stick pistons in the holes from running a little warm and horse power will be up. Have you ever seen a race engine that was set up tight?

As for bearings, you want between .0015 and .003 on mains and rods.:cool2: