My Valve Guides: How long do I have Doctor?

[RandalJ]

If it's any help, I bought an '86 with 70k almost two years ago with similar compression readings during PPI, but with #6 exhaust valve showing 28% compression loss during leakdown.

The owner of this very reputable shop where the PPI was done, advised that a top end job was on the horizon, but that overall the engine seemed very strong, and that he would have no qualms about driving the car to the East Coast (from Phoenix) and back. "on the horizon" to him meant drive it and check it again at 85k, 100k, etc., and see if there was any degradation. Unless, of course, it threw a valve through the lid, in which case we check it right away, if not sooner.

Since everything else in the PPI was very good, and the price was right, I decided to go through with the purchase. The only issues I noticed as I settled in with the car (which were probably there from the start), were a large puff of smoke sometimes when I pull up to a stop, and high oil consumption, maybe a quart every 500 miles.

This car has been my daily driver, and I've so far added 15k miles to the clock. The engine seems very robust, performance-wise, at least compared with others I had driven. I even did a DE a couple of months after I bought it, with no ill effects. There has been no degradation in performance or anything noise-wise that would indicate impending doom. And I do not hesitate to mash it up to 6k every now and then, which is the whole point, after all...

In March, I decided to have a major service done, and the same shop owner decided to try some major carbon busting. Following this, he said he was able to get the leak-down back to normal! This did not solve the oil consumption problem, but did seem to alleviate the smoke when coming to a stop - but just temporarily. My hunch is that carbon build-up is fast when guides are loose.

Anyway, he set the right expectations during the PPI in terms of how soon major work would be required. I have had the equivalent of more than TWO round trips to the East Coast, and I still seem to be OK for the time being. Of course, you mileage may vary...

My advice would be to do the work now if you can afford to, otherwise keep feeding it oil and just be very attuned to unusual noises or changes in performance. Just anything out of the ordinary.

Had to write this in a hurry, but I hope it helps.

[Paul Franssen]

I've had my '88 ROW Carrera between km 188000 and 211000 so far (117500 to 131875 miles). It's always had ticking valves, even after having them set by a reputable independent Porsche mechanic. When I had her changed to new Bilsteins, that person (not a Porsche mechanic) mentioned the ticking valves to me, too. I've recently done 2700 miles in 8 days and oil consumption was less than 1 quart per 625 miles...and the valves keep ticking. The engine is strong, there's hardly any smoke (yes, a bit of white smoke just after startup, said to be condensation water...) and I've never experienced "smoke on decelleration". Next weekend, I'm having the valves adjusted by another independent Porsche mechanic, and I'll ask him to pay particular attention to the valve stems. But many Porsche owners and some mechanics have already told me, "yes, some of them tick, and others don't, and if you don't have any problems with the engine, then don't bother doing anything, it's one of those things".
I also get the impression that the "Carrera early valve guide wear" issue is more prevalent in the U.S. than over here (but I'm not sure, it's just an impression). Any case, I'll report back next week, when the valves have been set...

[Wayne 962]

I just read through this thread, and I think there's an important point that has been missed. Compression and leakdown tests will not tell you if your valve guides are shot - they can't be used to determine this.

The leak down test is performed with the valves closed - no interaction with the guide. Likewise, the compression tester measures compression, which is done when the valve is closed.

Your oil consumption is high. 1 qt per 500 miles is what I call "area of concern." Worn valve guides will tend to overheat the valves, which can cause them to wear more, and possibly break off, destroying the entire engine. This, of course, is an extreme case - your guides would have to be seriously worn to have this happen.

Read this, lots of good info on the subject:

http://www.pelicanparts.com/techarticles/mult_Engine_Rebuild/mult_engine_rebuild-1.htm

-Wayne

[JDaniel]

valves can loose their heads dropping them into the cylinders to do mechanical grief.

At 59k miles I had a top end done to fix premature valve guide wear. Note the word premature... I noticed an increase in oil consuption @ about 51k.

The car ran fine. It "appeared" to smoke very little. Oil consumption was around 1qt/ 400 mi. Sometimes more, sometimes less. Besides the oil consumption another dead giveaway was the constant fouling of the plug in #6.
My compression and leakdown numbers were fine.

Watch for plug fouling, and plan for a top end in the near future. Also consider a new clutch and the g-50 upgrade.

Or... selling your motor and upgrading to a 3.6. I wish I'd done that (damn).

[axl911]

How would you know a plug fouled without pulling it out?

[HarryD]

Originally posted by Wayne at Pelican Parts
I just read through this thread, and I think there's an important point that has been missed. Compression and leakdown tests will not tell you if your valve guides are shot - they can't be used to determine this.

The leak down test is performed with the valves closed - no interaction with the guide. Likewise, the compression tester measures compression, which is done when the valve is closed.

Your oil consumption is high. 1 qt per 500 miles is what I call "area of concern." Worn valve guides will tend to overheat the valves, which can cause them to wear more, and possibly break off, destroying the entire engine. This, of course, is an extreme case - your guides would have to be seriously worn to have this happen.

Read this, lots of good info on the subject:

http://www.pelicanparts.com/techarticles/mult_Engine_Rebuild/mult_engine_rebuild-1.htm

-Wayne

Wayne Good point.

I will say that I carefully monitored my oil use and listened to my car to keep an eye on it's health. I knew I was living on "borrowed time" and when I was able, I addressed the problem. I got somewhat lucky in that my cost was probabbly a few more worn valves then if I had done it sooner but I could have had a very expensive error as well.

Like I noted, you have to weigh your chances and make a choice. If I was him, I would get my valves adjusted to verify that they are set properly and watch my oil consumption. I would be saving my $$ and prepare to do the work when I was able. If the oil use suddenly changed, I would advance my plans.

[jwmc1]

hey, is there a tech article on valve guide replacement?

[HarryD]

Originally posted by jwmc1
hey, is there a tech article on valve guide replacement?

Everything you need to know can be found here:



and in the factory manuals.

[jwmc1]

I have the book....it is a good one, but though I might have better luck with something more specifc...thanks

[HarryD]

Originally posted by jwmc1
I have the book....it is a good one, but though I might have better luck with something more specifc...thanks

Are you looking for the information on how to machine the heads themselves?

To replace valve guides you need to tear the engine down to the point that the heads have been removed. You then "machine" the heads to remove the old guides, install new ones, maybe a flycut, and grind the valves to fit. you then reassemble. The steps are in Waynes book except for the machine shop work.

[geof33]

Originally posted by JDaniel
Also consider a new clutch and the g-50 upgrade.

G-50 upgrade???

Bruce Anderson makes the point that the Carrera engine is good to go if you make it through the 85-90K zone. There was an article by him stating that the valve guide issue is really not all that prevelent in these engines, but some do fail early. The basic attitude of his was that, in general, the issue was overblown to some degree and it wasn't really too big of a deal for most. He also went into the reasons for the failure, and if I recall, only a few of the motors were in jeapardy....

Mine just ticked 100k and sometimes smokes a little on start up... burns maybe a quart per 1000 and runs great... My mechanic says these motors can drive flat out, cross country and back with no problem and an oil change.... Basically, a 250,000 to 300,000k motor...

[jwmc1]

Mine burns oil at start, but not when it is warmed and driving. When I pull away from a light there is no smoke and it burns about a quart every 900-1200 miles...

[caliber60]

Don't waste your $$$ on so call "preventive maintenace". That's only for the aircraft. Drive the car until you

"When you start fouling plugs - under 400 miles a qt - that's when you get it done"

My mechanic toll me drive my '87 until 200,000 miles. He will check to see if it needs a rebuild. Porsche are over-engineered car. The mechanic toll me they had opened up a 911 engine with 200,000 miles and still see the machining mark on the pistons.

[Kurt B]

200,100 miles and my Carrera does not blow smoke at all. Not on start up, not at high revs, not at medium revs. I'm just lucky or what?

[jrdavid68]

Originally posted by Kurt B
200,100 miles and my Carrera does not blow smoke at all. Not on start up, not at high revs, not at medium revs. I'm just lucky or what?

Same as Kurt B - almost 176,000 miles, no smoke, 1 qt per 1000 miles (a little higher consumption at the track), engine has never been open.