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New guy here...sort of. Been lurking for a while, but I finally signed up for the forum. I'm new to Porsche, but not new to German iron, and I have a fairly well-equipped place to work and store my jalopies.
Anyway, I now own a 2007 C4 with about 70k miles on it. I bought it with a skip at idle, and the understanding that the skip was compression related. A leak-down test confirmed that all cylinders were healthy but #6, which showed 20% leak-down and produced air out the oil cap.
At this point, the engine and the car are in separate locations, and heads are off the engine. The heads look great, as do the cylinder sleeves; no cracks or scoring. Which is great. However, I'm a bit stuck as to how to proceed. I guess I can split the case, which should lead me to a smoking gun (I hope), and probably to situation where I'm buying pistons and rings.
However, assuming that is what I find, I'm not quite sure how I would be able to get things back together again. It looks like I need a bevvy of Porsche tools to get the wrist pins back in on 4-5-6. So I guess I'm looking for suggestions, sympathy, resources, and money. Anyone have any of those they would be interested in contributing?
Thanks for reading. Looking forward to sponging up a bunch o' knowledge here.
Tom
PS - The dealer that had the car prior to my ownership swapped out the lobster forks for some turbo twists, so at some point I'll be wheel shopping too.
Your in deep enough at this point I would highly recommend saving your funds and doing a full blow rebuild. Sounds like your savy enough to tackle much of the work yourself. The machine work you can sub out and possibly the aspects of re-assembly your not equipped to handle. Hartech might be an option as well as they are active here and offer a comprehensive rebuild/large bore conversion for a reasonable price. At 70K miles your likely to get more out of a full blow conversion IMHO.
A full rebuild has occurred to me, and it's not off the table, but I'm not sure that the ROI is there. I can be pretty fickle, and so it's possible that I'll be in this car for a few years and about 10k miles. I want it fixed right, but not sure I need to go "whole hog" to make that happen.
I think the sleeve condition will drive the outcome. If the sleeves look good, I'll probably do pistons, rod and main bearings, IMS, and have the heads checked/cleaned by a machine shop. If I find a cracked sleeve, it's off the races. ;-)
When I saw the title with #6 and low compression I immediately thought bore scoring. But you removed the heads and say the cylinder walls look fine. Well that certainly is a relief. #6 is almost always the one to go with bore scoring. Check the piston skirts for wear too. Remove the oil pan and check the walls from below. You might be able to see something from there.
On non-pcars low compression is usually a head gasket or valve issue. Sometimes something simple like carbon deposits on the valves. Other times a valve can be stuck partially open. Bad lifters, bent valves (timing belt/chain failure), or so on. Since this is a pcar and are halfway there with the tear down, future proof it against bore scoring during the rebuild.
I agree with German888 - sub out the block work. Have #6 resleeved with nickies, maybe others too. Or go to a larger bore. Maybe sub out the heads too since the engine is open. I'm sure you can save a ton doing the rest of the work yourself compared to what others are paying for a turn key rebuild. RND, Hartech, Flat6 Innovations and the three that come to mind as pcar specialists. And don't be afraid to use a reputable local shop too. For example there's a local air cooled specialist near me that I'd be 100% comfortable sending my water cooled heads to for rebuilding. But the block I'd probably ship to someone who has done a 997 resleeve before.
Planning on splitting the case next weekend, so I'll update with results and maybe a few pics.
Definitely no scoring..especially nothing as nasty as the MB pic. Yikes.
Could it be a stuck intake lifter? They can mechanically stick and not move for low rpm operation causing a misfire.
Near 100% certain that it's a ring issue. With the heads off, we stood the block on the 1-2-3 side with 4-5-6 facing up, and dumped a small but equal amount of oil onto each piston. #6 leaked past the rings in a few hours; the others took a day or so to drain.
Good luck with it and please consider doing a full write up if you decide to tackle it. Would be great to follow along with your project. I'll be in rebuild mode before long myself.
Make sure you check that the cylinder is still in spec. I read somewhere that the #6 cylinder could slightly oval due to heat. I guess the location could lead to more heat because of the coolant channeling.
-jw
Make sure you check that the cylinder is still in spec. I read somewhere that the #6 cylinder could slightly oval due to heat. I guess the location could lead to more heat because of the coolant channeling.
-jw
That would be my concern as well at 70K... Lokasil coating may look ok with regard to scoring but maybe already beginning to oval? Hard to know without a thorough mic job.
03-25-2017, 10:59 AM
Low compression in #6 (new guy post)
