Engine issue

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72CS

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Hi,

Just want to get some opinions on the following: My engine shows some blue smoke at high rpm (not on overrun), compression check seems to be ok (at around 18opsi) but the engine fails the leak down test miserably. I can hear the hissing sounds clearly from the dip stick hole, I can't really hear it from anywhere else. I'm guessing piston rings, but what seemed a bit strange to me is that all cylinders came up more or less equally bad (I did the test on a warm to hot engine).

If it is the rings what is the best repair procedure if we assume the top end is good?

Thanks,

Fabio
 
72CS said:
Hi,

Just want to get some opinions on the following: My engine shows some blue smoke at high rpm (not on overrun), compression check seems to be ok (at around 18opsi) but the engine fails the leak down test miserably. I can hear the hissing sounds clearly from the dip stick hole,
Fabio
Click to expand...


hi, some questions to try to help you:

1- can you please explain what is the "leak down test" in detail ?

2-what hissing sounds do you mention ? you suspect them comming from ?

3- if you check this what is the result ?: climb up a mountain and then down (a 6 to 8% of slope will be good, and more than one mile long) using "brake motor" at more than 3000 rpm, when you arrive to the end of the slope, accelerate and look through the mirror !, if you do so what do you see ? nothing or a big clowd of blue-white smoke for 2 to 5 minutes ?

regards
 
Engine ID

Fabio,

Could you tell us all that you know of the engine ( age, condition, modified, etc.) and what rpm/speed you experienced the occurence?

In general, 180 compression is excellent for a standard 9 to 1 stock M30.

Leak downs can be alarmingly low for reasons not usually common especially if there all very close readings and make no sense whatsoever.( did you rock the crank to make sure the valves were fully closed for the highest readings?)

Things to consider:

1) Oil consumption and grade. - are you using a 40w.?

2.) Age/ use. If the engine has been rebuilt and never broke in fully.. some times cars get driven very little. For example- heads/ valves sometimes don't completely seal or settle for 3-5k miles; that's why you adjust valves.

3) Other effects - carbs overly rich, vac. secondaries that don't open, timing off, etc. can almost mimic similar effects.

4.) Usually one or two cylinders would be lower; but not across the board.

5.) There are analyzer tests for oil, etc. that are pretty inexpensive. A sample is taken and sent to a lab.

It sounds like the engine is sealing fine though and you want to work on whatever is causing the smoke?
 
I did the leak down test by applying pressued air throught he spark plug port while all valves are closed.

When I did the test I did it with the valve cover off to make sure I was TDC on each cylinder. I listened for air leakage at the valves and there was none that I could detect, but tons comming from the dip stick port.

Unfortunately I don't have the history of the engine. It is a 3.5L "replacement" block, I believe it was replaced/restored to a high standard (at least judging by the fittings and polishing etc...) in the early 90s. I don't have any info on the engine internals. I am running 38/38 webbers. I adjusted the valves a couple of months ago. Spark is by Petronix conversion.

The engine runs and revs fairly smoothly, it is possible that the carbs are set a bit on the rich side but I don't think all that much based on the condition of the plugs. I am running 10w30 oil.

I see blue smoke through the rearview mirror on high rpm (4k-5k) and wide open throttle but I think it is also burning oil at other times, it's just not as obvious.

You're right, I do want eliminate the smoke. I also seem to have some re-ocurring oil drips under the car that would be nice to eliminate as well!
 
Smoky and the Bandit

First, change your oil to a heavier weight. Owners for years have reported what a difference it makes when they thought the same.

Find the engine ID and check it. You still have great compression.

Find the year stamped on the head. But how did everything look when you had the cover off? Nice and clean, honey colored? Maybe someone put an earlier head on a later block and the valve stem seals are hard.

Plugs- all pretty clean when you pulled them? Any of them different? If you were really burning oil it would show up somewhere on them.

Leaks- find them. Especially anything that under high vacumn conditions that could find it's way into the intake/ carbs that might be leaking slightly. Tighten everything up again ( intake manifold, carbs, anything that can let something in). Clean the engine off and see what if anything changed. M30s like to leak in front; two part timing cover, etc. Losing and brake fluid? Check the line that goes to the booster.

Since you're running 38s, do you have anything left of the emissions/ vac. lines pulling vacumn in the motor? Plug it if you do. Are the throttle/ secondaries causing the mixture to go way rich too early? Plugged air jet? Not the same but when Zeniths hang up they do the same thing- smoking....

When you do a leak down; sometimes you have to rock the crank to get to the exact spot were everything is closed; don't just look at the valves. Valves in static conditions do not always close exactly since you're missing the force of compression.

Go back to the compression test- try a little oil and see if the numbers go up if at all.
 
Last edited:
Smoke

Sounds like possible cracked piston to me...but wait...all cylinders pushed air to the crankcase? Weird...let me contemplate a bit
just my 2 cents
 
72CS said:
I listened for air leakage at the valves and there was none that I could detect, but tons coming from the dip stick port.

The engine runs and revs fairly smoothly, it is possible that the carbs are set a bit on the rich side but I don't think all that much based on the condition of the plugs. I am running 10w30 oil.

I see blue smoke through the rearview mirror on high rpm (4k-5k) and wide open throttle but I think it is also burning oil at other times, it's just not as obvious.
Click to expand...

Hearing air leakage at the dipstick is not necessarily a good thing, but it is not necessarily abnormal. Virtually every engine has a wee bit of leakage at the rings. Since you did not quantify your leakage, it is difficult to make a long distance diagnosis solely on the basis of sound.

Running 10W30 oil may have something to do with your oil burning problem since this is thinner than recommended. (20W-50 is the norm). Of course, if you also have problematic oil rings, or you have been chronically dousing your cylinder walls with an extremely rich petrol mix, that might also account for having acceptable compression along with poor oil control. Worn valve guides and seals and/or a plugged crankcase vent may add to the oil burning equation. What do your plugs look like?

Sight unseen, the easiest thing for you to do might be a change of oil to 20W50.


From http://www.wcengineering.com/articles/leakdown.html

leakdown.jpg


If air is leaking past the rings, or the valves, or the head gasket, we can directly read the amount of leakage and can easily find the leak. If there is air blowing out the PCV, we have a ring leak, if it's coming out of the exhaust, we have an exhaust valve leak, and so on...


A leak down test is especially good at discovering leaky valves. We use much less pressure (about 80 psi) than is normally in the combustion chamber (several hundred psi). If there is a valve that is slightly off its seat, the actual combustion pressure may have helped close it, but the lower testing pressure won't exert as much force and the leak will be apparent.


This test is very time-consuming with the engine in the car. To do the test, each cylinder must be tested one at a time, they must be at TDC compression, and the crank must be held in place to prevent rotation. A freshly rebuilt engine should have less that 4% leak down on each cylinder and if leak down is above 10%, service should be performed. All cylinders should be within 2 percentage points of each other. NOTE: These figures are for performance engines. Stock production engines may have as much as 10% right off the assembly line.
Benefits:
Direct reading of each cylinder's condition
Pin points any problem areas
Drawbacks: Difficult to perform
Time consuming
Requires source of steady air pressure
 
Here is some more detailed info:
The plugs have light grey deposits on the tips and bit of carbon black on the insulator. No oil is present.
The valve train and inside cover are more blackish than honey colored.
The leak down test gave me 90 to 100% leakage across all cylinders. Judging by the sound I think the leakage I heard through the dip stick overwhelmed any potential leakage there might be throught the valve guides.
When I had originally done a compression test on a cold engine with no oil put in the combustion chamber I was getting around 135 to 145psi
Brake fluid level is stable.
Not much left of the emmisions on this car so less vacuum lines to worry about, the ones I do have look ok. (also I am definitely not on the lean running side)
I also noticed that the carb that is connect by hose to the valve cover (I presume for venting purposes) seems to be oily, I wonder if I'm getting more oil than I should through this hose and in to the carb? Is there supposed to be a valve of some sort on this hose? (I've seen other motors with nothing more than an small filter on this vent)

I will make the switch to a heavier 20-50 oil as suggested and I will look into how rich I might be running.

Does anybody know what a jetting baseline might be for Webber 38/38 carbs?

If there are any othes suggestions please pass them on.

Thanks for the input.
 
72CS said:
Here is some more detailed info:
The plugs - have light grey deposits on the tips and bit of carbon black on the insulator. No oil is present.
The valve train and inside cover are more blackish than honey colored.
The leak down test gave me 90 to 100% leakage across all cylinders. Judging by the sound I think the leakage I heard through the dip stick overwhelmed any potential leakage there might be throught the valve guides.
When I had originally done a compression test on a cold engine with no oil put in the combustion chamber I was getting around 135 to 145psi
Brake fluid level is stable.
Not much left of the emmisions on this car so less vacuum lines to worry about, the ones I do have look ok. (also I am definitely not on the lean running side)
I also noticed that the carb that is connect by hose to the valve cover (I presume for venting purposes) seems to be oily, I wonder if I'm getting more oil than I should through this hose and in to the carb? Is there supposed to be a valve of some sort on this hose? (I've seen other motors with nothing more than an small filter on this vent)

I will make the switch to a heavier 20-50 oil as suggested and I will look into how rich I might be running.

Does anybody know what a jetting baseline might be for Webber 38/38 carbs?

If there are any othes suggestions please pass them on.

Thanks for the input.
Click to expand...

Assuming your initial 180 lb./in.2 compression readings were accurate, it is a good bet that thicker oil would have addressed most of the blue clouds in your rear view mirror. However, unless I am misinterpreting your latest report, 90% to 100% leakage suggests an engine that barely runs under its own steam. Compression readings of 135 lb./in.2 are poor. It is doubtful that any oil viscosity increase will fix this unless you are comparing no oil with any oil. Alas, engines do not last forever and your latest findings seem to bear this out. Rings and related items (cylinder wall honing, pistons) are probably in your future. Rebuilding is one obvious choice as is looking for a transplant - which seems to have been a choice once taken in your car's history.

Apart from double checking your earlier test results, you might also consider double-checking valve lash and valve timing. (I did not ignore that the hissing is coming from the dipstick tube and not the carbs. Nevertheless, improper valve adjustments can easily affect compression readings.)

One also wonders if you do not have some simple plumbing issues. The crankcase typically vents via the valve cover into the carb filter housing. No valve regulates this blow-by and maintenance usually involves periodic cleaning. If the vent is plugged, the blow-by can find its way to the dipstick or elsewhere. From your description, your setup appears to be functioning, but your symptoms warrant double checking this.

Another remote possibility is that your emission controls have been poorly disabled or rerouted. Later US models were fitted with an EGR and had added means of affecting ignition timing to reduce Nitrogen Oxides. Both systems involved intake vacuum plumbing and even porting into the exhaust manifold. After a few decades, your car’s original date of manufacture is no guarantee that odd equipment wasn’t used as evidenced by your apparent replacement engine block. If your car has or had any of this equipment and it was not properly plugged or rerouted, it can easily interfere with normal engine operation.

Carb jetting?
http://www.e9coupe.com/forum/showthread.php?t=1589
http://www.e9coupe.com/forum/showthread.php?t=406
 
Sometimes

Are all the cylinders compression relatively similar? If you really were on the lowest side ; it wouldn't start easily. Not enough velocity in the intake.

Crankcase breather tube- let it run free for a test.

OK, let's try something else- grey tip plugs- check your timing and coil. As the motor ages, the timing chain streaches and results in timing too far advanced- say 5-7 degrees. Also Pertronix sometimes are installed too far advanced. Still using the ballast resistor? Try bypassing it. Check the coil resistance on the primary.

You didn't say where the carbon was on the insulator- even, tip, or up high? At 4-5k rpm your ignition should be singing; dumping more fuel on it when it's singing and it might not like it. Add to that timing which is off and you've got a good recipe for smoke or unburned mixture being lit off out of optimum sequence.
 
I checked the crankcase breather (I assume that this the poorly named vent on the cam cover, if it's something else please let me know)), it was not blocked but certainly showed signs of oil in it. There is definitely some oil making it to the carb although I don't know if this is normal or not.

I also changed over to 20/50 oil last night but havn't driven the car yet.

One other odd observation; my car has an oil pressure guage installed and was registering a very high oil pressure at 3-4k rpm: almost 80psi. I don't recall it ever being that high, I usually see well under 20psi when hot and idling for a while and maybe 40psi to 60psi when driving normally. ????

Over the next little while I'll do complete tune up; timing, valves, mixture etc...
 
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