Expert Opinion needed: Ring flutter or Valve Guides???

[vntgspd]

Over the past 1,000 or so miles I have noticed an increasing amount of smoke puffing from the tailpipe when driving. It kind of acts like valve guides except that it doesn't seem to smoke at all at idle and the smoke seems to be limited to the 3-4K rpm range. Meaning, if I accelerate slowly and short shift, I can stop it from smoking. Also, at WOT there is no smoke. If I drive down the freeway at 4500 rpm there is no smoke (or very little maybe) that I can see yet if I cruise at 3500 rpm I can see a light trail of smoke that is somewhat variable. If I accelerate to redline then coast in gear for a bit then nail the throttle, there is no obvious smoke.

I am beginning to think that it is ring flutter that only occurs at the 3-4K rpm under light to medium load. If it is in fact ring flutter, any thoughts on potential additional damage if I continue to run it this way?

Other details:
2.4E with Webers
43K miles on P/C (inspected by Ollies 5K miles ago without removing pistons from cylinders and advised to leave them alone)
40K miles on heads (inspected by Ollies 5K miles ago and determined to not need work)
Car generally runs well at low and high speeds
Cold leakdown showed 20-25% on all cylinders with air escaping through rings
Hot leakdown TBD

I'd love some thoughts from the experts before I begin taking things apart!

Thanks!

David

[Steve@Rennsport]

Hi David:

With 20-25% leak, you need to take things apart and measure ring gaps, closely inspect cylinders for scoring, scratches, roundness (top & bottom) and look VERY closely at the outer edge of the rings.

Ring flutter is a high-RPM condition and IMHO, this is not a problem unless you are not using OEM Goetze rings or there are other issues.

[vntgspd]

Okay. I will definitely double check leak down when hot before tearing anything down but it sounds from your post that the area to be looking is in the pistons/rings/cylinders.

If I read into this correctly, you are saying it is possible to have a failure point within the piston/cyl. system that would yield the symptoms of oil smoke at limited rpm ranges? Presumably the higher load at WOT/high rpm works to seal the rings?

I'm looking to solve this problem in the most efficient way and learn some more stuff along the way.

Thanks!

David

[Quicksilver]

Dave
Have you tried looking at the plugs to see if there is evidence of any specific cylinders oiling more then others? (With them all blowing 20-25% it seems likely they are all oiling somewhat evenly...) It seems really odd that everything has started to go at once.

The only things that I can think of that would cause a failure across all the cylinders is:
- 'Old age' (which doesn't seem likely unless the parts were used)
- Bad air filtration (which will kill an engine in a hurry)
- A carbon build up problem
- Defective/substandard parts.
- Bad valve seals (or guides)

If there was a sizable leak in the air cleaners it could wear out the rings, cylinders, and pistons in a hurry. I've seen how you maintain your car so I could only imagine this as a possibility if the air cleaner housings fit badly and you didn't realize it. I would also expect it to be worse on one side of another because of the separate air filters. (Check the plugs, but you said 20-25% so I'm assuming that it is all of them)

Carbon could mess up the ring's seal in the piston and that would cause all sorts of oiling problems. The rings actually seal by having the combustion pressure push down on the top of them so the bottom of the ring is sealed to the bottom of the ring groove. This allows the pressure from above to go into the groove across the top of the ring to the back of the groove behind the ring and press on the back side of the ring. This pressure causes the ring to seal against the cylinder wall. The addition of carbon buildup can cause this interaction to fail and this could definitely cause oiling and blowby.
I'm not sure of any methods to check this or remove this kind of carbon buildup. The 'coke bottle full of water' trick is meant to deal with carbon in the combustion chamber so I don't think it would work here. I wonder if an old fashioned water injection kit would help clear up this kind of problem...

Defective parts really means the same thing as old worn out parts. You have to tear it down to see and the only solution is replacing them. It would be nice to know before you do something drastic though.

I can't see it as a valve guide problem with the leakdown evidence you have but if it isn't a cylinder problem perhaps there is a valve seal problem. The smoke seems to really only come when you are running steady state which can build a little vacuum while throwing oil around a bit more vigorously around the valves. This would have to be an intake valve problem so I would also expect to see a consistent puff of smoke on startup after sitting for a bit.

Having followed you down the freeway it would be real nice if you could knock this problem down. It can get a bit hard on the lungs behind you.

[vntgspd]

Okay, finally got to spend more time with the car today and gather more data.

I found that I was not checking the leakdown correctly. So I warmed the car up to normal temp then tested all cylinders. While the plugs were out, I checked compression. Here is what I found:

Cylinder Leak Compression
1 0% 155psi
2 0% 160psi
3 0% 160psi
4 0% 155psi
5 0% 155psi
6 0% 150psi

I suspect that the cylinders had SOME leakage, but nothing measurable on the gauge.

I also took pictures of the plugs. Notice how #6 seems to have a bit more oil on it and #3 seems to be dark as well but may be due to running rich. The others look okay to my novice eye.

On a July 4th drive, a friend driving behind noted that most smoke seems to be coming from the right pipe of the sport muffler. Also, I have noticed when cold, there is no visible smoke from inside the cockpit but when the car is fully warm like after a long drive (total engine temp, not just oil temp) the smoke is much more prevalent.

Any more input anyone???

Thanks!

[vntgspd]

Anyone out there have input or experiences to share???

Thanks.

[911pcars]

Leakdown percentage change from 25% to 0% (cold to hot) begs the question as to the method you used to determine leakage.

Not sure any engine can have 0% leakdown, but others can confirm their experience.

Sherwood
http://members.rennlist.org/911pcars

[vntgspd]

Originally posted by 911pcars
Leakdown percentage change from 25% to 0% (cold to hot) begs the question as to the method you used to determine leakage.

Not sure any engine can have 0% leakdown, but others can confirm their experience.

Sherwood
http://members.rennlist.org/911pcars

Sherwood,

Excellent question. As I mentioned I performed the first test erroneously. My tester has a check valve of sorts that has to be compressed to allow air in or out. I was pressurizing the gauge and setting to "zero", and THEN compressing the check valve thereby filling the last 6" of hose and combustion chamber with air. This process resulted in a 15% to 25% drop on the gauge.

When I correctly set the gauge with the combustion chamber pressurized, I could detect no leakage while holding it for 20-30 seconds. To verify my method, I tested the gauge with the hose venting to the atmosphere (instead of combustion chamber) and the gauge steadily dropped to about 30-40% after 20-30 seconds.

I suppose I could still have an oil ring issue but it appears that the compression rings and cylinder bores are okay.

A teardown seems inevitable but how much and how soon it needs to be done are things I'd like to get a better feel for. Since my budget won't allow a serious teardown with headwork etc. right now I'm really trying to determine whether I need to park it or continue driving it (about 200 miles per month).

Sorry for the long-windedness (is that a word?).

Thanks.

David

[911pcars]

It sounds like you're using a single gauge-type leak tester, like this



...and how to use here:
http://www.650motorcycles.com/LeakDownTester.html

A commercial tester typically uses two gauges; one to monitor the source air (100 psi for ease of calculating); the other to observe air pressure inside the cylinder.



In both cases, if you're starting out with 100 psi source air and the cylinder (@TDC end of compression) only holds 80 psi, the leakage is approx. 20%. That right?

It's possible for the oil rings and/or worn valve guide(s) to allow excess oil into the chambers yet compression still be good. Do you observe (hear) air leaking into the crankcase via the oil filler tube and other air escape paths?

Sherwood

[vntgspd]

The one I have looks like the second picture but not as nice as the Longacre one unfortunately. Only, the second gauge is marked (clockwise) 100, 90, 80, 70... in 5% increments. So you fill the gauge and combustion chamber with compressed air then use the regulator to dial the second gauge to "0", or 100 as on the Longacre gauge, then read the leakdown.

One issue is that my guage operates at 10-20 psi when performing the test, not 100 psi. I don't know if this would exacerbate a leaky ring due to a lack of pressure to "seat" the ring or return a faulty reading due to a lack of pressure to force the leak? Or, make no difference at all??

All leakage is heard in the crankcase (rings) when using a hose/stethoscope arrangement. Intake and exhaust are pretty quiet except for what is likely ambient noise.

Now I have a whole new set of questions and will have to double check my readings with another gauge I think.

[RWebb]

while the tests are intellectually interesting, you are still going to have to pull the thing apart.

you should look at all cylinders.

[911pcars]

If you can, increase the test air pressure closer to what the engine normally creates, around 100 psi. 20 psi is probably too low to ID potential sources of combustion chamber leaks.

Sherwood

[Steve@Rennsport]

Originally posted by RWebb
while the tests are intellectually interesting, you are still going to have to pull the thing apart.

you should look at all cylinders.

Randy,..that was the basis of my suggestions,...

Assuming for the moment that the valves, guides, and guide seals (Viton, I hope) are all in perfect shape doing their collective jobs, its time for Brother David to pull the cylinders and start checking the ring clearances, surfaces, bore dimensions and concentricities.

I've had perfectly good pistons with new rings in otherwise OK-looking bores just smoke like the dickens and the cure was always new P/C's.

Oftentimes, the bores are no longer round and new rings don't really seat well under such circumstances, even after extensive de-glazing.

[RWebb]

"that was the basis of my suggestions,.."

- yup -- just seemed like they didn't penetrate -- I was trying to tap the head of the nail to drive it in a bit deeper. We all have hurdles to start in on a very large task....

[vntgspd]

Ha Ha guys. I did get your suggestions and ideally they are spot on.

The reality is that I have three small children and other responsibilities that take most of my time and money. The result is that a valve job or new p/c are not an option right now. Since this car is a hobby for me, it would have to wait.

So, I am trying to determine from the experience of those around here where the problem may be so that I can determine if it is okay to continue to drive the car. If it's valve guides that are starting to leak, I can likely drive it for another year (1500 miles or so) before tearing it down and correcting it. If it is a broken ring, maybe that is not an option and I will therefore put it in longterm storage until I can deal with it.

From the feedback so far, it seems that I could be dealing with valve guides, out of spec P/C, or maybe a bad oil ring. All of which would probably not result in catastrophic failure if driven another 1500 miles - or would they.

Thanks for all the input so far. Please don't think I am ignoring you...

David

[RoninLB]

wild guess.. based upon 40k heads, P&C

and that it's grey oil smoke, not black gas smoke


confirm valve guide wear is ok and check exhaust valve guide seals. Actually i'd probably just replace the seals and feed the gas and oil a few doses of Sea Foam afterwards before opening up the engine without hard info..

i also feel that a 911 leak down test isn't the most reliable for hard info.

[vntgspd]

Well, finally pulled the engine apart after the smoke screen behind me while driving spoiled any enjoyment for the car I once had.

The main concern at this point is some moderate scoring/scratches on the piston skirts and the cylinder walls. Nothing really deep except for a couple cylinders showing 1/4" long scratches in the cylinder at the very top (above the compression ring line). The heads look okay with no obvious signs of oil leaking past the guides. There is a LOT of carbon buildup on the pistons and combustion chambers considering I cleaned all of that up less than 7000 miles ago. I will evaluate my carb settings and ignition components as part of this process.

All parts go to Ollie's on Tuesday for evaluation - I'll keep you posted.

[vntgspd]

Bad news and more bad news...

Looks like metal particles in the oil have contaminated everything. I'm not 100% sure but I think it comes from a TMP replica oil cooler that came with metal chips inside. I cleaned it but really have no way of knowing if I did this well enough - I'd guess not.

We think the metal went into the system and led to rapid wear of the oil rings (which were probably already worn anyway). This proceeded to wear the rings down past the "scrapers" and begin wearing a .001 to .002" low spot on the cylinders.

This likely added more metal to the oil that proceeded to go through the system damaging all 6 intake valves, two valve guides, cam surfaces, pistons and cylinders, and most likely the main and rod bearings. I haven't had time yet to split the case to survey the damage.

So, the heads will be rebuilt, pistons replaced with 85mm JE, cylinders bored, crank and case thoroughly flushed including piston oil squirters, cam reground with rockers, new bearings and seals, oil system flush and probably a few other things while we are at it.

Should be a bit over $3k - thank God I can do my own labor!!!


Overall it's definitely a bummer but at least I can look forward to a very healthy engine when I'm done. It's deteriorated over time and I definitely felt that it went soft so I'm really looking forward to getting back to the quick revving spirited motor I remember.

[calling911]

This is an old thread but I found metal shavings inside this same cooler... not good!