mojieboy

Hi All,

I posted a message on Saturday about my 944 s2 that had started vibrating badly and making strange exhaust noises. Well, I bit the bullet and took it down to the nearest Porsche specialist I could find (I am currently several hundred miles away from home for a few days and can't drive the car back home)....

I am not a techy but think the diagnosis is not good. According to the mechanic there is no compression on cylinder 4! I have left the car with them and from what I can gather they need to establish wether the inlet valve has burned out and how much needs to be fixed/replaced. Have any of you guys had experience of blowing a cylinder/replacing valves?

Should I be crying into my furry dice?

Any advice on what I can ask the mechanic to appear like I know about these things?

Jfrahm

Unless it's a head gasket that's pretty strange. It would be good to know where it is leaking compression.

ljibis

A "dead hole" as they call it is what ended up killing my car last spring. My problem ended up being a broken ring that gouged several 2-4 mm deep depressions into the cylinder wall. I ended up replacing that engine with a completely fresh 2.5 liter that I built up from a bare block.

You need to have them determine if it is a valve problem or if it is a cylinder/piston problem. That will determine next steps. Ask if it is losing compression through the crankcase into the sump or if it is losing compression through the valves. They'll be able to figure all that out.

Be very thankful if it is a valve problem. A competent machine shop can rebuild the head with all new valves, guides, seals, etc. They will also clean it and machine it so that it looks like brand new. Replacing the head can be done without removing the engine from the car. It's not an easy job, but it is not the end of the world either. An experienced home mechanic could easily have the head off in a day.

If it does turn out to be a problem with the head, IM me and I'll send the contact information for the machine shop I used. They do excellent work, and since they don't exclusively work on Porsche stuff they are about 50% cheaper than some of the other places I contacted. They are here in Minnesota but do work through FedEx all the time.

Good luck! Don't worry about it...this is a great opportunity to learn more about your car.

Oddjob

I think a burned valve, especially an intake valve, is very unusual on a non-turbo. I suppose it is possible if the injector failed and that cylinder ran very lean. But that would still be more likely to take out an exhaust valve. Broken valve spring would be possible.

They should be able to do a leakdown test to determine source of the leakage. But regardless, the head will need to come off.

Makis

If it is what happen to me it will be a burned exhaust valve caused by brocken valve spring. On the S2 there are 2 valve springs per valve. When the main spring brakes the valve will still work but at higher rpm the valve operation becomes ineffective and valve float is experienced. As a result of this the exhaust valve will overheat because it cannot cool properly (not closing properly to release heat into the head). Inlet valves cannot burn because they are cooled down by the inlet air/fuel mixture. Evidently I replaced all the valve springs when I replace the burned valve. It is expensive but worth doing this job.

mojieboy

It looks like 2 valve springs have gone - this does not sound as bad as it could have been then?
The valves and head are being sent to the machinist for inspection and presumably a skim of the head. The head gasket is on it's way out too and will be replaced.

When carrying out this work would it be normal to check all the valves across all cylinders while the head is off - or would this be thought unnecessary and just to look at the faulty cylinder?

Either way, breaking down on holiday is a nightmare. the car won't be ready for a few days, so, where did I put that train timetable to get back home to Scotland.?.. )

ljibis

You should have them check all the valve guides for wear, and then check the spring tension on all the remaining original springs. A good machine shop will check the whole head out to find any trouble spots while it is off...presumably your mechanic will ask them to give the head a complete once over.

Not at all as bad as it could have been! Your luck is holding up well.