Found my missing Horsepower!

[eurocarrera]

This weekend I thought it would be a good time for a valve adjustment. One of the main reasons I started this project, was because I did a little "off the line" race with a buddy of mine the other day, and I heard this loud rattling sound coming from the rear of the car at high acceleration. Thinking that this could be: loose valves, loose exhaust, or who knows what, I went and adjusted the valves (1 loose and two tight), but nothing out of the ordinary.

Going a little further, I decided that it might be a loose cam tower, or head stud (praying that it was not worse....). After checking them all, I get to cylinder # 6, and lo and behold, I have 4 loose head stud nuts!!! Needless to say, after re-torqueing those down, adjusting the valves, and installing the cam line modification, it feels like a NEW car. Not bad for a car with 150K on the clock.

So, the next time you are in there for a valve adjustment this is one of those must do "while I was in there" things.

Happy motoring!

[Wayne 962]

Four loose head studs are a symptom of another problem - they typically don't just come loose by themselves...

-Wayne

[Kurt B]

okay, so he should check em each valve adjustment. NO problem... right?

[BGCarrera32]

I have 4 loose head stud nuts!!!

Agreed....sounds fishy....I'm hoping for the best....

[eurocarrera]

Wayne, what kind of problem. I mean the car was manufactured over 18 years ago, wouldn't this be just "normal". What else would cause loose head studs - the stud actually stretching? I would think if I contacted and expanded daily for 18 years I might be a little loose as well.

[82SC]

i think maybe the studs should be checked to see if they are backing out...

unless the threads are damaged, you can probably remove the entire stud...clean the hole, and reinstall iwth red locktite...

you may have just done a temp fix by tightening the nut/loose stud

good luck

MJ

[cegerer]

If the stud were broken, would you be able to torque the nut back down????????? -- Curt

[Early_S_Man]

Bill,

Depending on the setting of the octal [8-position] 'fuel quality' switch on the DME ... and the quality of the questionable Cali gas you have been feeding it ... might be a detonation problem!!!

[eurocarrera]

Is it possible to extract the stud without removing the heads, or am I looking at removing the engine and taking apart the right side of the top end?

I noticed Wayne used a stud extracting tool in his new book, but it looked like it was a bit big to fit in the hole where the head stud nut goes.

[eurocarrera]

Warren, what should the setting be on the octal [8-position] switch?

[Ruben911]

Bill, for what is worth, I just adjusted my valves over the weekend and I also ended up tightening all the head stud nuts anywhere from half to over a full turn to get them to the proper torque specs. I believe the car has gone at least 75,000 miles since the engine was completely rebuilt I have never experienced any symptoms from the loose head studs (some say it may be the classic pulled studs which was chronic in the 2.7 L engine). All I can say is that after adjusting the valves and correcting a problem with the WUR, the car now sprints and runs like a bat out of hell. I will be checking at the next valve adjustment to see if any further loosening is evident. Thanks

Ruben

[Early_S_Man]

Bill,

The '0' setting is the most conservative ignition advance map setting, and the '7' setting is the most aggressive.

No, the studs can't be replaced with the heads left in place ... and I believe suggestions about broken head studs are premature. Dilivar exhaust studs -- the bottom 12 -- are the ones subject to breaking, and when they break ... they is no doubt about it! So, four loose nuts on one cylinder is indicative of a different problem such as a stuck or leaking injector causing a carbon build-up on the piston crown and on the cylinder head ... leading to detonation because of carbon 'hot spots.'

The 'loud rattling' you heard during accelerationwas the #6 cylinder head banging on the top of the cylinder!!!

Have you looked at your spark plugs? I suspect you will find #6 to be carbon fouled.

[agabriel]

Just curious - are your sure the nuts backed off? Many of those parts are designed to stretch. If you pull the nuts off where is the discoloration on the bold? If its only deep in one place I wonder if things didn't rattle loose recently. This seems weird... I'm not a mechanic and I haven't rebuilt any Porsche engines but I have done a few bikes over that were older than 18 years and the stud bolts were tight when coming off. Could the bolts have (should be designed to stretch) have loosened over a rough ride?

[RickM]

OK, I'm in the dark. What "Cam line modification" needs to be done on a Carrera?

[eurocarrera]

Rick M, here is the thread.
new updated cam tower fitting

After changing out the fittings, I noticed a large increase in my oil pressure. If the factory recommended it, I can assume that they feel it is not harmful, but more beneficial to the engine. More pressure = better lubrication.

[eurocarrera]

Warren, I haven't been able to take a look at the spark plug yet, or the setting on the DME box, but I will tomorrow. I always use 91 octane gas (the highest I can get in California), and I do run Chemtool once a month. Do you think this could be attributed to dirty fuel injectors, or maybe is it that the DME setting is too agressive?

All of the rest of the cylinder head nuts were fine, and this only happened about 2 weeks ago (the sound that is). Maybe I should make plans to have the injectors serviced.

[Wayne 962]

I've added some comments on the head stud issue here:

http://forums.pelicanparts.com/porsche-911-technical-forum/113301-loose-head-nuts.html#post828571

-Wayne