Have the heads off - what now?

gabenheimer · 07-01-2007, 09:50 PM

I took the heads off my '87 3.2 to replace suspected worn valve guides. I've never pulled the heads on a Porsche before and I was surprised to see so much carbon on the pistons. Here are my questions:

Is this normal or simply a result of burning oil?
I found some scoring on the number 2 cylinder (see pic). Do I need to address this?
What should I use to clean the cylinders before reassembly?

The car has about 125K miles.

Thanks!
Randy

ChrisBennet · ChrisBennet's Garage

That carbon is normal in my (limited) experience.
That scoring may be the result of a broken ring..
-Chris

Mo_Gearhead · 07-02-2007, 07:05 AM

Agree with Chris.

Because of the flat cyl. (boxer) configuration, these engines do tend to allow more oil into the combustion chambers. That plus the mileage you indicated, does not look out of the norm however.

I too would be concerned about that scoring. ONE scratch may have been a stray piece of something. But that looks like a possibly broken (sharp) ring edge(s)??

You can clean piston tops with carb. cleaner (soaking) and a Dremel tool with wire brush.

gabenheimer · 07-02-2007, 07:33 AM

Thanks for the advice. I guess I'll have to take the cylinder off and inspect the rings.

Believe it or not, this entire project started with a clutch job! But I fell into that "while I'm in there" trap. Now, of course I'm in deep.

Randy

Eagledriver · 07-02-2007, 08:32 PM

While you're in there.....it's not that hard to pull the cylinders and pistons off to remove the carbon, check the ring condition and wear, and clean up the cylinders. A dishwasher works well for most of this (assuming the wife is not home). Make sure to keep track of which piston goes with which cylinder and keep the rings on the same pistons.

-Andy

Eagledriver · 07-02-2007, 08:33 PM

Heat the pistons for about 1 minuit with a propane torch to make the pins push out easy.

-Andy

CliffBrown · 07-04-2007, 02:20 PM

Randy

Did you do a leakdown on the motor before the tear down? I'm asking because it would help diagnose if the rings were leaking.

I wouldn't be alarmed by the amount of oil on the pistons but I'd plan on replacing the rings if it were my motor.

88911coupe · 07-05-2007, 12:18 PM

Getting ready to do a similar project and was wondering what the collective wisdom was regarding rings. Is it better to leave them alone if they don't appear amiss? Do you just measure them and reinstall in the same orientation or should they be replaced with new as a matter of course?
Sorry to hijack thread but I thought this may be useful.

starlifter1 · 07-05-2007, 07:22 PM

What spot on the piston do you heat to make the pin slide in easier?

MBAtarga · 07-06-2007, 06:27 AM

The top/bottom studs look different. Are the exhaust studs dilavar?

gabenheimer · 07-06-2007, 08:35 AM

Quote:

Originally posted by CliffBrown
Randy

Did you do a leakdown on the motor before the tear down? I'm asking because it would help diagnose if the rings were leaking.

I wouldn't be alarmed by the amount of oil on the pistons but I'd plan on replacing the rings if it were my motor.

Unfortunately I didn't do a leakdown test - poor planning on my part. I never intended to get into the engine but the project took on a life of its own. A local shop is checking the valve guides and seals.

I'm going to repair/replace the no. 2 cylinder which has the scoring.

Randy

gabenheimer · 07-06-2007, 08:45 AM

Quote:

Originally posted by MBAtarga
The top/bottom studs look different. Are the exhaust studs dilavar?

I know the exhaust studs on the 3.2 engines are different from the intake. I'm sure someone on this forum can elaborate on the make of the studs.

Randy

ChrisBennet · ChrisBennet's Garage

The bottom studs are Dilavar (sp?) on a 3.2. They have the same breakage issues as the 3.0 studs before them - they are just newer so the breakage isn't as common. I've seen enough of them break that I would replace them with steel 993 studs (the very cheapest Porsche stud).
-Chris

Eagledriver · 07-08-2007, 09:22 AM

About the heat question...I heat the dome of the piston, playing the flame around in a circular motion. I have driven some of my piston pins out with a dowel on cold pistons but I feel guilty about the side loads on the rod especially if I'm not planning to replace the bearings.
I would absolutely replace the bottom row of headstuds. I use old steel studs recovered from other engine rebuilds from the machine shop I use.

-Andy

efhughes3 · efhughes3's Garage

I'd try to take the pins out without heat first. Mine came out pretty easily.

gabenheimer · 07-09-2007, 08:11 PM

I removed the cylinders and pistons over the weekend. The rod pins came out easily without heat. It looks like only the number two cylinder has scoring. The cylinders are SK, can these be honed or do I need to get a new one? Also, what steps should I take to replace the rings?

Thanks!

Eagledriver · 07-10-2007, 04:56 PM

I'm not familiar with SK cylinders. Do you mean KS? There is a (very) long thread on re-ringing alusil (KS) cyinders. I just finished a rebuild with alusils and new rings and so far so good. You just need to buy the rings and prep the cylinders. I don't think you can hone the cylinder enough to remove the scoring without enlarging the cylinder too much but a machine shop should be able to tell you if they can do it or not. You could send the whole set to EBS racing and they will recondition the cylinders and evaluate the scratches. If you need a new cylinder you'll need to get the correct group for size and height.

-Andy

gabenheimer · 07-11-2007, 07:22 PM

Thanks Andy, after I posted my question I found the long thread about re-ringing Alusil cylinders. I'm going to try finding a used cylinder with the right height group. There is a great porsche shop here in town and they are happy to work with customers who are taking the do-it-yourself route.

Randy

TibetanT · TibetanT's Garage

Buck:

IMHO if you are this far into an engine project, I would purchase new rings and install them. Might be a couple hundred dollars versus, putting everything back to gether only to find out 2,000 miles down the road you have an engine failure and a $20K budget needed. you know the drill...penny wise and pound foolish.

As far as this thread's project, I agree with everything said here above +1.

88911coupe · 07-12-2007, 02:17 PM

Thanks Ed. I have not started yet but was just trying to get a feel for what I should do about the rings. Sounds like replacing them is cheap insurance...for some reason I thought I'd read replacing them can cause problems with seating or something. I'll do more detailed research when I actually get started...I have both of Wayne's books.