Leakdown.. eye of the beholder?? VALID?
 

So I have a 2.0l I am testing trying to find out whats up with mosquito fogging.. It has sat for about 3 yrs so I need to drive it BUT....

First thing I did was adjusted valves.. they were all damn close.. 2 were tight by .001.. no big surprise..

Did a compression and found #2 at 140psi and the high was 165.. this was not terribly good in my book..

They I found the timing was WAY off.. and it was retarded severely... like 10-15degrees.. so I set it correct.. ok.. NOW we have a problem.. SEVERE smoke.. So Im guessing someone retarded it to reduce smoke maybe.. (I just bought the car 3 yrs ago and never drove it much and didnt do much of a PPI.. )..

Ok.. now getting to the point...

so then I figure, lets do a leakdown and see waz up..

I recorded:
#2 at 15% (the "bad" cylinder)
and the rest from 10-30% (2 at 30%)..

BUT... I could EASILY have recorded much better results.. what do I mean by this? Well.. if I tap my crankshaft slightly I can make the rings seal better.. much better.. and if I wiggle the crankshaft (the wrench I have on the crank) I can reduce leakage further.. or make it worst for that matter.. but usually better..

Which leads me to... what good is this test?

I also played around with monitoring two cylinders thru the entire compression and power strokes.. which was rather interesting.. +- 8% was noted on one cylinder thru out the 2 strokes..

As one example:
#3 (which I recorded 150psi compression):
bottom of compression stroke: 30%
mid compression: 30%
top of compression: 38%
top of power: 34%
mid power: 35
bottom power: 35

Okay now that makes no sense really to me.. cept that the rings are sealing better going up than down.. and the 38% at the top??? I better recheck that I guess.. But what was alarming was when I set TDI and did the test it showed 30%.. so which is it? 30%? 35%? 38%?


While I am somewhat depressed at these results (all leaks were in the crankcase) I found this interesting.. and alarming..

Now i have to decide whether pulling the engine and doing the valve guides is worth the risk or not.. I guess I need to flog this car some first and see what happens with the smoke..

BTW.. all of these results were in the green "good" on my guage... but I keep reading if you are above 10% its time to tear down... is there anything from Porsche on this matter??

You have broken rings in all likelihood.

The leakdown doesn't lie. I measured 45% leakdown in a couple jugs of my 2,0. I scratched my head and said, "wonder why that is?" Maybe I'll repeat the test! Repeated the test, same thing.

Tore the engine down and. . . broken rings. Either caused by a "rebuild" in 1982 in which the rings were replaced even though the ring grooves had worn beyond spec, or by detonation caused by WAY too much advance from the worn-out distributor. Or both.

4% Leakdown is good. 10% is borderline. 30% is teardown time.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/214288-leakdown-results-1966-911-normal.html?highlight=leakdown

I'd be tearing down now if I were at 45%. I really dont think 30% is teardown time.. I think its marginal and I think I need to drive.. broken rings should be reproduceable as far as the readings.. Im not getting reproduceable.. I also noticed you didnt mention a compression test. Mine is pretty close to be in spec... one cyl off.. Did you do a compression test too?

BTW.. did you end up with new pistons and salvaging the holes?

Excellent advice (as usual) from Professor Cramer,.....:) :)

That thing needs to come all apart.

I think its good advice but I am seeing some discrepencies... and my tests are not necessarily repeatable... depends on exactly where I position the cylinder and whether I rock it at all before I do the test.

If the italian tune up doesnt work I guess I'll be pulling it regardless... while the engine sounds and runs just fine I cant be fogging the road as I drive.. Ill piss off too many people :)

Might be time to find a 2.7l motor and set this one aside.

JP,

There is only one position for the piston in the cylinder for a leakdown test, that's TDC. The test was not designed to be performed with the piston at, for example, BDC. The cylinder taper could throw things off. So there's not really any technical literature that we can draw from that correlates engine health to any measurements taken anywhere other than TDC-- you're on your own.

I don't know what you mean by "where I position the [piston]"-- are you saying that you get different values on the leakdown if you rotate the crankshaft away from TDC? Well sure, you can do that if you are cracking a valve open, but again, that's not the methodology of the test. The results are only valid if you have it set EXACTLY to TDC, with the appropriate crank pulley mark lined up with the notch in the blower housing.

Anyway, the most telling piece of information from your tests is "all leaks were in the crankcase." To paraphrase the great Johnny Cash, "I hear that breather hissin' "

I did not do a compression test, I think they are imprecise.

i would think a broken ring could give inconsistant readings, not just consistantly bad.

with the piston going down, without the power behind it, that may be keeping the rings from seating properly.

id drive it, mine is in need of a rebuild and i am still driving it, but i have a 3.0 on the stand.
get it nice and hot and put some sea foam in it and run it and check it again, just curious if anything changes.

It doesn't seem unusual for an engine that has sat for a long time to smoke. I'd drive it for several hundred miles and see what happens after that. If it has broken rings it won't get better. You are taking a chance on scratching the cylinders but they are probably already scratched so they would need work or replacement anyway.

-Andy

I would disagree with that.. you can test a cylinder for leakage in ANY position that the valves are closed.. what this showed me is I probably have some wear towards the top the of cylinders.. as opposed to consistent readings all the way up and down.. this is after some thought. In fact, you can whatch the gauge as you move the cylinder around.. well Im not strong enought to move it on the compression stroke much but the power stroke is interesting.

The "instructions" for leakdown will read TDC.. but you can take it many steps further to explore things.

I agree with the other gentleman.. I need to flog this car.. however, I did do a cold start and it smoked right on startup which is not a good thing. lol..

As far as the compression test.. well.. hmm now which is imprecise.. I dont know if you caught it or not but my WORST cylinder during the compression test was my BEST cylinder during leakdown.. this is what really blew me away.. Compression is an overall test... whereas leakdown, as you stated is one position.. TDC.. so which is more important??? TDC or overall? I suspect maybe TDC?? but Im not sure..

I just found this test interesting... the car idles VERY well and drives with what I think is the usuall power (although this is the ONLY 2.0 car I've ever driven).. which is more interesting.. in fact, it idles like a kitty cat purring.. I just stood there listing for a few minutes :) Although I couldnt breath well.. :) I really want to put webers in my my 76.. I think I have a few more years before it doesnt need inspection in my state however.. :)

All of this being said.. I'm fairly certain I'll be pulling this motor and digging in.. but am hopeful still that I need to clear it out some.. and even more hopeful that its just the guides causing the smoke... I really think someone retarded the timing to reduce smoke... ugh.

I would suggest to do your leakdown and/or compression tests AFTER EVERY DAYS' RUNNING to avoid a sudden sharp decline in your engines' health i.e. a possible broken ring breaks off into pcs or possibly a valve guide wears excessively fast for lack of lubrication or something that would KILL your engine more severley than what is looming inside now.
Possibly, you have just some sludge build up needing to be burned off... however, as it sounds like you suspect, there is more going on bad inside this engine or should we call it a mosquito fogger...
Best of luck what ever you do and please keep this thread updated on how things progress & what you find out and do to remedy the determined situation.
Good luck!
Bob

Just put a "Green Diesel Powered" sticker on the back and drive the wheels off of it.....
That ought to keep the environmentalist of your back! ;)

I will.. trust me this will be remedied... I'll keep ya'll up to date.

2 experts have replied...
hmmmmm I think I'd take a pro's advice instead of refusing it
if you already know what you want to do, then don't bother posting...
enjoy the carnage... please don't try to sell me that oil cooler or any parts for that matter when you tear down.

Start over with a compression test and give us the results for all 6 cylinders please.

I think you're over-analyzing the situation with the leakdown tests at various piston positions. Like John said, there are established guidelines for leakage tests, and the specs are only valid for TDC with valves closed.

Since the engine has been in storage for awhile, there's a slim chance the rings are stuck due to corrosion and not fully able to seal the cylinder.

I could suggest pouring a tablespoon of Marvel Mystery Oil in each spark plug hole, add some to the fuel supply and change the oil, then run the engine for awhile and see if the compression/leakage numbers change for the better.

If these efforts don't improve the situation, you can either operate in a limp mode or decided to repair it and enjoy the full Porsche experience.

Sherwood

UPDATE:

Drove the car for about 70 miles.. some highway.. lots of on and off the throttle to hurry things along..

Results:

Less smoke but yet still a significant amount especially after a closed throttle and then application.. which tells me guides..

The new leakdown test is equally dissapointing from a diagnostic stand point.. whole the results were significantly better some of the results were sort of baffling.. there were two at 30% originally and one of them is now 10%.. (the other is at 20%).. however one that was 10% is now 22%.. which is the worst cylinder..


My guess: if I keep driving the #"s will get better.. I need valve guides. Just a guess.

911pcars: REALLY good advice, something that I never thought about.. I'll try it.

It could be academic at this point since you realize engine repair is needed at some point in time. However, oil can still be drawn into the chamber via the oil rings. Did you complete the compression test yet? Do a wet and dry test (wet = a couple of squirts of oil into the chamber).

Sherwood

calling911

Based on your posts and the good advice I gather that you are expecting things to change for the good, unfortunately it won't happen. On the other hand you do have a point based on the inconsistencies of your measurements and hopefully I can help you find your answer.

Compression Test

First the engine should be warm
Pull the relay for the fuel pump so as to not spray fuel into the cylinders
Open the throttle valve and lock it open
Check compression on all cylinders and record

With a syringe and a long piece of tubing, squirt 5 cc's of oil into each cylinder
Check compression on all cylinders and record.

Compare the two compression tests, if the values increase as I would expect there is blow by past the rings. The sources are many such as: worn rings, out of spec ring lands which allow the rings to "rock" as the piston moves, cylinder out of round, gummed rings and of course broken rings amongst others.

Small differences in compression between cylinders are not a good indicator of valve sealing, unless there is a badly burned or broken valve. Hence, the advent of the leak down test.

Leak down Test

This can be done following the compression test if the engine is still warm with each piston at TDC and not allowing the crank to rotate while doing the test. The readings will indicate leakage via one of three potential paths; the rings, the intake valve and the exhaust valve.

In order of the most likely problem I would go with exhaust valves (heat/air cooled engine), rings (mileage, gummed) and intake valve. In some extreme instances one could find a hole or crack on the piston (detonation or turbo lean out).

john_cramer’s rule for leak down; 4% good/10% marginal/30% teardown is an excellent starting point.

Last but not least, the smoke you are experiencing during deceleration, to read, engine vacuum is, as you suspected, excessive clearance on the valve guides or bad valve seals, albeit the original alloy of the valve guides didn't prove too durable.

So, in closing, the engine needs some attention and might make a good project if you have the inclination to go after the rebuild.

Best of luck and keep us posted.