Really high oil consumption- need ideas

[billncolo]

I built a high performance 3.0 L engine several years ago and I still have not been able to isolate the cause for the high oil consumption (~150 mi/qt). It smoked from the first time I started it up. I have rebuilt the heads and the guides are fine. Installed new valve guide seals. Replaced the rings with new Goertz on three occassions. Just had the cylinders replated to new condition by Engine Builders supply. Compression is 100 on all cylinders and the leakdown is between 2-3% on all. All ring gaps are within factory spec. There is some smoking when the engine is cold, but not much when hot, none at idle or when compression braking. After about 500 mi the plugs (all) are so fouled the engine barely runs. The only thing I haven't changed out are the J&E pistons (which were originally installed new). Has anyone had problems with these pistons, or have any ideas on what else could be wrong???
Thanks,
Bill

[Henry Schmidt]

My guess is that your rings / cylinder have an issue.
What is the ring gap?
What is the cylinder ovality ? It is not uncommon for replated cylinder to be out of round, sometimes as much as .002+
What is the piston clearance ?
100 lb of compression is very low.
Fouled plugs could also mean too rich. If the engine continually runs rich the ring may never seat.
What was your break in procedure ? how you break it in can be very important.

[billncolo]

All ring gaps were well within Porsche specs- I don't recall the specific readings. The cylinder were originally a bit out of round, but within spec. When I recently sent them to EBS, I asked them to check them out and recommend what I should do. They said that they were worm, but well within spec and recommended that all I do is rehone them. I decided to have them replated and bored anyway since at the time I really believed that they were the problem. I measured them when they came backed and was quite pleased at how round and close to 95.0 mm they were. The 100 psi compression reading is a result of my altitude (8500 ft) and the GE80 cams that I am using. Others in the area with similar engines report getting the same readings on their engines.
I am using an Electromotive TEC 1 engine management system which allows me to maintain good control of fuel mixture. To adjust and monitor A/F ratio I am using both dual A/F ratio meters and dual EGTs. During brekin I try to keep the EGT readings around 1300 deg. My breakin procedure starts with about 1/2 hour at 3000-4000 rpm at light load and then slowly increasing load levels and varying rpms without any hard accelerations for the first 100-200 miles. Then gradually start increasing the load and rpms. I don't know what J&E set the piston clearance to, but I am told that they have a much larger gap than the Mahle's.

[cstreit]

I'm gonna second Grady... Compression still sounds a little low... ...and Goetze rings do not like to be babied for break-in. An overly gentle break-in such as you described could result in the rings not seating properly. I actually beat the piss out of them (relatively speaking) to get them to seat. 4-5k RPM with the engine warned up, up through the gears while allowing the car to deccel in gear as well.

[billncolo]

Wouldn't poor seating of the rings lead to poor leakdown numbers?

[cstreit]

A leakdown is a relative comparison between cylinders... If the test was done at lower psi even poorly seated rings (if they were poorly seated evenly) would show acceptable leakdown numbers.

Bottom line is that your oil is going somewhere....

Your compression seems low to me, but I don't have experience in higher altitudes... ...what compression ratio are you running?

You say the valve guides are new and the engine isn't burning oil noticeably... ...but that your plugs are fouled. If it isn't leaking it, it's burning it.

[911pcars]

Cranking compression with many engines w/high lift cams. What is the compression ratio? If high, that should compensate.

Make sure the throttle is wide open, then crank through at least 2 complete 4-stroke cycles to get maximum reading.

Sherwood

[billncolo]

I'm running about 11.3 CR dual plug, with a GE80 cam. What is a typical oil consumption for unseated rings. Clearly I'm burning a lot of oil, even though it isn't always visible. As for the breakin, I have varied it a bit each of the 4 times I have tried new rings, always with the same result. This last time (after having the cylinders replated) I got the best compression and leakdown numbers I have ever had, and the worst oil consumption.

[911pcars]

Have you tried a "wet" compression test? Squirt some motor oil in the cylinder and see if the compression increases.

Sherwood

[billncolo]

No, haven't tried a wet comp test. Didn't think it would matter with all of the oil in the cylinders. I will try it though.

[cstreit]

A lot of overlap in the cams will drop your compression test numbers, however not that much. My race engine runs 10.5:1 and has a cam similar to a GE60 and still gets 180psi compression....


You mentioned a lot of oil in your cylinders... How do you know this? When your heads were done, what valve guides were used? Do you know the tolerances set? WHat about valve stem seals? (Teflon, Viton, or none?)

[billncolo]

I am really puzzled by the concern over my "low" comprssion numbers. As I mentioned, I have been told by several PCA racers in the area that they get similar numbers. I'll get some more opinions on that. I am also curious why if the compression numbers are way low, then why would I still be getting leakdown readings in the 2-3% range? The plugs after about 500 miles are coated with so much oil they are actually wet. It isn't fuel because a flame doesn't cause any burning of the residue. The tops of the pistons are similarly coated I'm not sure what guides were used. The heads weredone by CMW. When I recently installed valve guide seals (originally had none) on the intakes, I coulod not detect any lateral movement of the valve stems in the guides. They really seemed tight to me, but I'm not an expert on this. I used factory Viton seals. Adding them didn't make any noticeable difference.

[cstreit]

Again, what sort of air pressure was used for the leakdown test? (Think on it, if you used 10 psi vs. 100psi your leakdown percent would change dramatically with unseated rings).

It's got to be your rings or your guides.

You mentioned replacing the rings several times already, why did you do that?

[Steve@Rennsport]

Bill:

Two questions:

1) What are your leakdown numbers? compression testing tells little about diagosing these issues due to camshaft profiles

2) Precisely what are your piston-to-cylinder wall clearances as measured at the top ring lands? Off-the-shelf JE's are notoriously loose and thats always been a problem for us. We have them made to our spec to control noise, oil consumption, improve leakdowns, and extend top ring longevity.

[cstreit]

Steve,

He mentioned 2-3% leakdown on all cylinders... While that sounds good "off the cuff" I am thinking that at low pressures, his "leakdown" may be good at low psi and consistent across cylinders, it may still be off at higher pressures.

In other words, while it's consistent, it may still be consistently bad. I would expect that even poorly seated rings could show low leakdown at low pressures. What do you think?

[Steve@Rennsport]

Chris:

LOL,..Sorry, I missed that. Thanks for pointing that out,...

2-3% sounds like the compression rings are initially seated but the oil control rings can take longer to seat and that causes higher than normal consumption.

I'd still like to know the piston-to-cylinder wall clearances at the head lands, tho.

[billncolo]

Hi Steve,
Been a while since we talked. I was hoping you were still around helping all us P mechanic wanna-bees.
I talked to a tech rep at J&E yesterday and he focused in on the same thing- what is my piston to wall clearance. He indicaed too much gap could cause my symptons. I'll will drop the engine and go measure the gap. From what Chris said, I take it that some, but not necessarily all the rings can seat. Never heard that before. Also, I have never heard what the "typical" breakin period symptoms are. What does the oil consumption start out at (100 m/qt) and end up at ? Also, how long does it typically take. I have heard everything from 50 to 5000+ miles. I have also heard wide variations in what the breakin procedure should be, from go easy to drive the crap out of 'em.
Your thoughts would be appreciated.

[Steve@Rennsport]

Hi Bill:

Indeed, long time, no talk,... I'm still kicking and I try to help people when I get time.

Leakdown testing simply shows compression sealing and doesn't reflect how well the oil control rings have seated. In most cases, its not a concern but when oil consumption doesn't stabilize, it a factor to be considered.

Break-in time depends on a LOT of things such as these few:

1) Cylinder wall finish

2) Ring type, gaps, and material

3) Oil

4) Technique,.....this is a biggie!

5) Ring tension

I use dino oil to break-in a new engine and we usually do that on our engine dyno to control temperatures, load and monitor compression. Its a 2-day affair.

[billncolo]

Steve,
I would be very interested in whatever you could share with me regarding what specs need to be given to J&E to insure their pistons work ok in P engines. If you prefer you can send the response directly to billncolo@hotmail.com.
Thanks in advance,

[john walker's workshop]

it's gotta come down again, regardless, so you might as well get rolling. teardown to the case and completely disassemble the heads. then get out the measuring devices. something will show up.