Really high oil consumption- need ideas

billncolo · 09-27-2006, 03:29 PM

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

Early_S_Man · 09-27-2006, 03:54 PM

Bill,

Three questions:

1. Were the JE pistons sent along with the cylinders, or measured so the correct amount of material could be built up as required to assure proper clearances between cylinder and piston skirts?

2. What oil did you use during most recent ring break-in run?

3. What was the measured clearance between compression rings and piston ... land gap?

My concern is that excessive clearance is present between either piston and cylinder, or rings and lands ... both the low compression and the plug fouling with new rings point to some kind of 'flutter/slapping' phenomenon going on with the pistons or the rings.

billncolo · 09-27-2006, 05:21 PM

The pistons were purchased without sending in the cylinders. My mechanic ordered them so I don't know what specs he gave J&E. I used 30 wt non-det oil on all 3 of my breakin tries. All ring gaps were within the Porsche specs. I don't remember the specific numbers. When I recently sent the cylinders to EBS, I asked them to report back to me on their condition and recommend whether they needed to be replated. They said they were worn but well within spec and only recommended rehoning them. I decided to have them replated and bored anyway since at the time I felt that they were the problem. I have had several mechanics drive my car and they all commented that they couldn't hear any signs of piston slap. The "low" compression readings are a result of my altitude (8500 ft) and the GE80 cam that I am using. These readings are very similar to what others in the area see. The J&E pistons do seem to have quite a bit of room for lateral movement inside the cylinder, but I am told this is normal since they are not made from the same alloy as the Mahle's and therefore are built to different dimensions.

ianc · 09-27-2006, 06:41 PM

Did you actually replace the guides? How about the valves? These and the rings are the only possible explanation for the problem. I take it you're torn the thing down a couple of times? Notice any difference between the cylinders as far as the presence of oil in the combustion chambers go?

If your compression rings are OK but you have a busted oil control ring or two, that could be an issue...

ianc

billncolo · 09-28-2006, 10:35 AM

The guides were replaced as part of an overall rebuild (+twin plugging and porting). The valves were machined and reused. Two different shops have verifed that the heads are fine. I have tried 4 different sets of rings. In each case all cylinders, combustion chambers & plugs looked identical. I have never encountered a broken ring. The first set were Totalseal rings. I sent them to the factory for inspection and they said that they looked like they had broken in fine. Not sure how they determined that.