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Smokey exhaust, compression test - now what?
Posted By: Red383
Smokey exhaust, compression test - now what? - 04/10/13 02:15 PM
Last year at the end of the season my car started smoking real bad at idle, and I would notice the smoke between gears while driving the car. Didn’t notice any miss or strange noises. I changed out all the valve seals, thinking that was the problem (they all looked new, but I swapped them anyway). I parked it for the winter and now am getting back to it. It’s a 383 .030 over with KB hyper. Pistons, 906 heads, hydraulic cam, performer RPM intake, Edelbrock 750. 4-speed Trans. Has around 7000 miles on it since rebuild years ago (don’t drive it much). Smoke was a blue/white color.
I pulled all the plugs last night, all the plugs look the same, except for #8 which appeared to be wet. I unplugged the coil and propped the carb wide open. I did a compression test on each cylinder.
#1 – 150
#2 – 150
#3 – 155
#4 – 150
#5 – 160
#6 – 155
#7 – 160
#8 – 95
So I put a couple squirts of oil in the #8 cyl and turned the engine over and then did the compression test again, and it showed maybe 10 on the gauge. So now what? I’m not much of an engine tuner, and I don’t know anything about carbs. What do these results tell me? What is the next step to take?
Thanks for the help.
Posted By: Red383
Re: Smokey exhaust, compression test - now what? - 04/10/13 02:16 PM
Other plug picture
Posted By: Kirby
Re: Smokey exhaust, compression test - now what? - 04/10/13 02:29 PM
is it gas or antifreeze? Stick on the tip of your tongue and you'll know-lol. Assuming you have spark on #8- almost has to be antifreeze.
Posted By: DaveRS23
Re: Smokey exhaust, compression test - now what? - 04/10/13 02:38 PM
If you can, take the guage off of the compression tester and replace it with a valve and air chuck. Then bring #8 up on compression stroke, hold the crankshaft in that position and put some air to that cylinder. It doesn't take a lot.
You can listen to the carb, exhaust, and breather to hear where the air is escaping the cylinder. Of course, hearing air from a valve cover breather means the biggest headache.
This is a simple and definitive test that will point you in the right direction.
Posted By: RapidRobert
Re: Smokey exhaust, compression test - now what? - 04/10/13 02:39 PM
Quote:
Smoke was a blue/white color.
What do these results tell me? What is the next step to take?
borrow a Stant radiator pump kit & pump it up to 15 lbs (when hot) & see if it holds pressure (may need to sit overnight with the tester on it). If good there it might be a burned ex valve on #8 (for the low comp) & the valley pan may be leaking (for the smoke)
Posted By: Red383
Re: Smokey exhaust, compression test - now what? - 04/10/13 05:06 PM
Thanks for the suggestions, I will give them a try and report back.
I didn't taste it, but it looked like oil.
What exactly is a burnt valve anyway? I've heard the term, just not sure what it means.
Thanks again.
Posted By: DaveRS23
Re: Smokey exhaust, compression test - now what? - 04/10/13 07:05 PM
The valve has a bad spot on the sealing ring, like a notch or chip, that allows the combustion gases to escape. More typical on the exhaust due to the higher temps. Refering to a burnt valve is refering to the way the bad spot was created. As in a spot was burned in the edge of the valve.
But there are other things that can cause a valve not to seal properly and allow the loss of some or even all compression on that cylinder.
Posted By: dogdays
Re: Smokey exhaust, compression test - now what? - 04/10/13 07:10 PM
Head gasket. That plug is unnaturally clean.
My
R.
Posted By: 340727dart
Re: Smokey exhaust, compression test - now what? - 04/11/13 04:30 PM
White smoke is from water.
Posted By: Red383
Re: Smokey exhaust, compression test - now what? - 04/12/13 02:18 AM
I had a few minutes tonight and put the cylinder at tdc (I think), and put air pressure on it (can I apply too much pressure?) and held the crank. I can feel air coming out of the valve cover breather above the cylinder, and I can hear the air at the exhaust tips, but not feel air. Nothing at the carb.
I may try it again to verify I had it at tdc.
Air at breather= rings? Air at exhaust = Burt valve?
The plugs in the engine a pretty new, less than 50 miles, and it really looks like that # 8 plug is new, maybe there is no spark in that cylinder? I'll have to check the wires for spark.
I will double check my findings, maybe after putting it back together and running it for a while.
Posted By: DaveRS23
Re: Smokey exhaust, compression test - now what? - 04/12/13 03:02 PM
Air test another cylinder or two so that you can get a comparison to judge by. Make sure that the exhaust valve is closed, there shouldn't be any air out the exhaust.
There is often some air past the rings, especially the more pressure you use. But not a lot, which is why I suggested to do another cylinder or two for comparison. Use about the same amount of air pressure.
If the air continues out the exhaust, loosen that rocker to be sure that is not an issue.
Air out of the breather indicates a cylinder sealing issue, not necessarily the rings. And the exhaust air points to the exhaust valve sealing, not necessarily a burnt valve.
A little more driving probably won't hurt anything, but it is looking like pulling that head is becoming more and more likely.
Keep us posted.
Posted By: GTX MATT
Re: Smokey exhaust, compression test - now what? - 04/12/13 03:13 PM
Quote:
Air test another cylinder or two so that you can get a comparison to judge by. Make sure that the exhaust valve is closed, there shouldn't be any air out the exhaust.
There is often some air past the rings, especially the more pressure you use. But not a lot, which is why I suggested to do another cylinder or two for comparison. Use about the same amount of air pressure.
If the air continues out the exhaust, loosen that rocker to be sure that is not an issue.
Air out of the breather indicates a cylinder sealing issue, not necessarily the rings. And the exhaust air points to the exhaust valve sealing, not necessarily a burnt valve.
A little more driving probably won't hurt anything, but it is looking like pulling that head is becoming more and more likely.
Keep us posted.
I agree check another cylinder or two for comparison on whats leaking into your crankcase. Something is always going to leak past the rings. As noted there should be NO air escaping the valves.
Posted By: dogdays
Re: Smokey exhaust, compression test - now what? - 04/12/13 05:16 PM
NO, the #8 plug isn't new, unless you haven't driven the car after installing it. That's wishful thinking.
Water in the combustion chamber cleans things up like the picture. Even 50 miles of driving in a non-computer-controlled car will have some deposits on ceramic or electrodes.
Head gasket.
R.
Posted By: Red383
Re: Smokey exhaust, compression test - now what? - 04/15/13 04:09 PM
I wasn't saying the plug was new, I mant that it looked new (really clean)
I put the plugs back in the engine, checked for spark on the plug wires (I had spark). I took the car for a little spin and it really is running good, but halfway through I noticed the smoke while sitting at a stop sign.
Came back to the shop, let it idle in the driveway and checked the temps of the header tubes at the head. #'s 3,5,4,6 where in the 400 degree range, #'s 1,2,7 where in the 300-325 range, and # 8 was around 150 degrees. (Not sure what this tells me, just thought I check it)
I pulled the plugs (#8 really clean and wet with oil) and did the compression test after it cooled a bit, and #8 was very low on the compression, around 30 PSI. It was also spitting oil when I was turning it over.
I am going to try the air in the cylinder to listen for leaks on a couple cylinders again, and then start pulling the head.
Posted By: Red383
Smokey exhaust, compression test - now what?*UPDATE* - 02/14/14 05:36 PM
I know it's been a while, but I finally got around to pulling the engine. When I pulled the intake, I looked down the head on the #8 cylinder and could see coolant sitting on top of the valve. Dogdays was right. How does coolant get on top of the valve? Must be a crack? I pulled the head and found the exhaust valve on that cylinder is clean compared to all others, I assume this is from the coolant cleaning it.
So do I have the head checked for cracks? Is it worth putting any money into iron 906 heads for a street car?
.jpg "8039356-IMG_1828(640x431).jpg")
Posted By: GTX MATT
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/14/14 05:47 PM
Yeah sounds like you've got a cracked head, referring to your later posts from last April it makes sense. Car got hot and compression went lower as the crack expanded.
As far as what to do, there are hidden expenses in switching to aluminum heads that people won't mention when they tell you that you're money ahead going aluminum. That said you'll gain some power, and if you've got the money and want more power then go for it.
Posted By: RapidRobert
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/14/14 07:16 PM
might be head gasket/warped block/warped head. I'd have your machinist check the block deck for flatness, same with the head. I've never seen an unported 906 that was cracked but I have not worked with an abundance of em so you could very likely be an exception to my (limited) exp in that area. Wouldn't hurt to check long shots like thread depth while you are there. Holler how it goes.
Posted By: Cab_Burge
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/14/14 07:46 PM
Quote:
I know it's been a while, but I finally got around to pulling the engine. When I pulled the intake, I looked down the head on the #8 cylinder and could see coolant sitting on top of the valve. Dogdays was right. How does coolant get on top of the valve? Must be a crack? I pulled the head and found the exhaust valve on that cylinder is clean compared to all others, I assume this is from the coolant cleaning it.
So do I have the head checked for cracks? Is it worth putting any money into iron 906 heads for a street car?
Try to find a machine shop that can pressure check that head to find the crack, it might be fixable, maybe not. I would pull the #8 piston out and look real hard at it, especially the top and 2nd ringlands, look for corrosion, wear and damage to the piston including a collapsed skirt 
As far as replacing one 906 head versus buying new aluminum heads that is a decision you will have to make 
Posted By: JohnRR
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/14/14 08:57 PM
Did the oil look ok before you pulled the head ? What does the head gasket look like ?
As far as putting money into a 906 ... only if you race in a class that requires you to run 906's , otherwise it's scrap ...
Posted By: Red383
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/14/14 11:25 PM
Oil looked a little dirty, and smelled a little gassy.
Here's the cylinder with the gasket still sitting on it.
Posted By: RapidRobert
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/14/14 11:43 PM
Steel shim OE gasket. Just me I'd either clean the surfaces up & use the thin composition gaskets that are available & button it all up or clean it up & have the surfaces checked for flatness & use steel shim gaskets with alum spray paint which steel shim ones require flatness. Probably be better to check for flatness since you're already apart & you dont want to have to go in there again & I think I would go with the thin composition ones. Holler how it turns out
Posted By: JohnRR
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/15/14 07:06 AM
Quote:
Oil looked a little dirty, and smelled a little gassy.
Here's the cylinder with the gasket still sitting on it.
Take a close look at the head surface and the block surface , hard to tell but it could have been leaking under the gasket , was the head surfaced during the rebuild ? How about the block ?
Posted By: BSB67
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/15/14 03:31 PM
Like John said. Inspect that, and everything else closely.
Keep your antenna up. You need to find the problem before you start making assumptions or fixes. Even if you get new cylinder heads, and use a better gasket, you still need to find out exactly what is/was going on, IMO
The evidence is pretty convincing that water/coolant was getting into the combustion chamber, but if the source/cause is not obvious, I'm kinda wondering where all the cylinder pressure went. My very limited experience with small crack/water in the combustion chamber did not present the kind of cylinder pressure drop that you experianced.
Keep looking. Be sure to pull that piston as well.
Posted By: JohnRR
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/16/14 11:30 PM
Quote:
Like John said. Inspect that, and everything else closely.
Keep your antenna up. You need to find the problem before you start making assumptions or fixes. Even if you get new cylinder heads, and use a better gasket, you still need to find out exactly what is/was going on, IMO
The evidence is pretty convincing that water/coolant was getting into the combustion chamber, but if the source/cause is not obvious, I'm kinda wondering where all the cylinder pressure went. My very limited experience with small crack/water in the combustion chamber did not present the kind of cylinder pressure drop that you experianced.
Keep looking. Be sure to pull that piston as well.
Posted By: Red383
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/17/14 09:05 PM
More findings:
Exhaust Lifter is missing it's plunger retainer
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Posted By: Red383
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/17/14 09:10 PM
Pulled the lifter and found it is damaged. as is the cam lobe.
This may have been what started the problem. Amazing how well the engine ran like this, if it wasn't for the smoke, I wouldn't have know there was something wrong.
.jpg "8043235-IMG_1832(469x640).jpg")
Posted By: JohnRR
Re: Smokey exhaust, compression test - now what?*UPDATE* - 02/18/14 10:33 PM
Quote:
More findings:
Exhaust Lifter is missing it's plunger retainer
whoops ... I was just telling you to check that , I had the same thing happen.
Time for complete disassembly and a rebuild , the pistons below that lobe got all that metal on them and are not scratched up along wit hthe cylinders ...
Look inside your oil pump , it's be all gouged up also ...