I just bought a beautiful mess... care to express an opinion? - Page 3 - 986 Forum - The Community for Porsche Boxster & Cayman Owners

aneal000 · 05-19-2014, 08:49 PM

Bottom left - exhaust valves - of cylinder #3. Can't wait to get this apart and see what's going on in there...

healthservices · 05-19-2014, 08:51 PM

So wait a minute. Have you found the issue before tearing the valve cover off?

aneal000 · 05-19-2014, 08:51 PM

TDC found and held in place with an M8 bolt from an old jet ski project.

aneal000 · 05-19-2014, 08:52 PM

Just for fun... my garage and my project.

aneal000 · 05-19-2014, 08:55 PM

I believe I have. In a previous post I said that I found the two exhaust valves are not in sync with each other. One closes and the other stays open a bit when I spin the motor. Jake said that it is common for the lifters or the valve springs to fail. I've decided to pull the valve cover off and see what I can see. If it is a spring or lifter and I can replace in the car then that is my plan. If it ends up being more than that then I'll drop the engine and start reading...

healthservices · 05-19-2014, 09:03 PM

Ah!

Jamesp · 05-20-2014, 03:00 AM

This is looking a whole lot like a broken valve spring. To remove a broken valve spring without removing the head (and man do you want to avoid removing the head!) The idea is to use compressed air in the cylinder to hold the valve with the broken valve spring closed so you can put the new spring and keepers on the other end. As you have the engine locked at TDC (make sure it is TDC and not one of the other holes in the crank pulley) the valve train is unloaded and all of the valves should be closed. You'll need a special hose with one end a standard air compressor QD and the other a spark plug thread - I borrowed one once that looked home made - the best kind of tool. Pressurize the cylinder as high as you can and the valve will stick closed. Now you can replace the broken parts without further dis-assembly.

Do check with your bore scope to be absolutely sure there was not valve piston contact. If you can not determine 100% that they never touched, my advice would be to drop the head and replace the valve. If they touched, even a little, the valve is bent, and it will break and drop into the cylinder at the most inconvenient time.

Best of luck! looks like you'll be on the road in no time!

Jake Raby · 05-20-2014, 04:35 AM

With the M96 engine a valve can bend from bounce, not just piston contact.

You must also ensure that the seat wasn't damaged from the valve bouncing off it. In engine repair and assembly one must never assume anything and quantify everything.

If not, the issue will find you.

aneal000 · 05-20-2014, 05:00 AM

Thanks James... I was just talking to a buddy of mine yesterday who was explaining the same procedure. He even has a homemade spark plug to air compressor hose! I have looked very closely at the top of the piston over and over and I see no indication of the valve touching it so I'm excited about that as well.

Jake Raby · 05-20-2014, 11:20 AM

Quote:

Originally Posted by aneal000

Thanks James... I was just talking to a buddy of mine yesterday who was explaining the same procedure. He even has a homemade spark plug to air compressor hose! I have looked very closely at the top of the piston over and over and I see no indication of the valve touching it so I'm excited about that as well.

Before using the air to hold the valve closed to change the spring, use the same air to carry out a leak down test. Might save you lots of heart ache.

healthservices · 05-20-2014, 12:13 PM

Quote:

Originally Posted by Jake Raby

Before using the air to hold the valve closed to change the spring, use the same air to carry out a leak down test. Might save you lots of heart ache.

And this was the assumption I thought was already done. If it does not seal with just air pressure under a leak down... putting in a new spring is not going to help.

aneal000 · 05-20-2014, 02:54 PM

Ok, I just did a leak down test and I can hear/feel air out the exhaust. Should the air pressure alone be enough to force it closed? If this is the case how can a leak down test be used accurately if it forces the valves shut? This is my first experience with a leak down test. Just trying to understand. Is there a chance something else is holding the valve open slightly? I'm holding out hope that the spring is broke and something is physically holding it open slightly.

Ian c · 05-20-2014, 03:22 PM

Quote:

Originally Posted by aneal000

If this is the case how can a leak down test be used accurately if it forces the valves shut? .

With an air leak test you are basically pressurizing the combustion chamber to perform a pressure test to see what is NOT sealing .
A bit like ressurizing your water pipe system at home to find/check for a leak .

We knew you had a leak , the compression test told us that .

What the air leak (leak-down) test tells you where it is leaking from .

The inlet and exhaust valves and the piston give you a "closed space "

Air will either leak by the piston (bottom end problem) or the head (top end problem) or the gasket (head gasket problem)

You've now found where its coming from ....

aneal000 · 05-20-2014, 03:30 PM

Right, that makes sense, but I already knew the exhaust valve wasn't closing because I saw it with the bore scope. I totally get the fact that the leak down lets you know if you don't already know. Once I saw the valve not seating as flush as the other exhaust valve I decided to take the cover off and see what I can see. It just seems like the leak down test confirmed what I already knew. Not sure what else it is telling me? Thanks again for everyone's input.

healthservices · 05-20-2014, 04:34 PM

Quote:

Originally Posted by aneal000

It just seems like the leak down test confirmed what I already knew. Not sure what else it is telling me? Thanks again for everyone's input.

Now ask yourself this question. If air from the leak down test will not hold the valve closed. it tells you something...

The valve is bent.

If the valve was not bent the valves would seal and not leak when the cam has released the pressure off of the valves.

healthservices · 05-20-2014, 04:39 PM

Time to pull the head off.

aneal000 · 05-20-2014, 05:35 PM

Spring is broke and appears to be keeping the valve from closing. I'm not saying the valve is not bent, but I don't see how it could happen. I'm going to replace the spring - because I'm this far into it and it seems silly to not try. I'll then do another leak down test before I put it all back together. If it fails that test then the head comes off. Is that a fair line of thinking?

healthservices · 05-20-2014, 05:42 PM

Quote:

Originally Posted by aneal000

Spring is broke and appears to be keeping the valve from closing. I'm not saying the valve is not bent, but I don't see how it could happen. I'm going to replace the spring - because I'm this far into it and it seems silly to not try. I'll then do another leak down test before I put it all back together. If it fails that test then the head comes off. Is that a fair line of thinking?

If the valve is good you can do a leak down now with the cams out and the spring off of the valve. if it does not seal valve is bent.

Jamesp · 05-20-2014, 06:07 PM

Pull the valve back while pressurizing (be the spring). If the valve does not seal under pressure it's very likely damaged. If you put the motor back together and run it you stand a good chance of dropping the valve. As you have a very understanding customer, that may be an ok gamble for you, because there is a chance it could be fine. It really depends on your level of risk acceptance. Me? If the valve did not seal perfectly I'd drop the head. listening to the motor crump after all that work would be just too painful. Keep us posted

healthservices · 05-20-2014, 06:21 PM

What James said, sorry I assume a lot things when diagnosing and giving advice at times.

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