2ndof2

I'm sure alot of us with cars that have more than 40 or 50K miles on them have had a leaky lower valve cover gasket and were knowledgeable enough (or their hired wrench was) to do the wiggle test on the valves when it was opened up.

What I'm wondering is whether anyone has actually experienced some kind of major engine failure as a result of worn guides. Many say the extra slop due to worn guides causes greater oil consumption and is a leading cause of an SAI fault on 96+ cars but if you are burning oil within factory specs how urgent is replacing guides?

I have yet to speak to a mechanic that wouldn't want the $$$$ that such a job would bring in. Whats the concensus on the "if its not broken don't fix it" approach to this?

Terry Adams

My oil consumption did an almost imperceptible creep up from about 1qt/2500 at 100K miles to about 1/1500 at the 120K rebuild. The valve guides at the rebuild were only "half way worn". Or something like that, I forget. Nothing broke from 100K to 120K, and no CEL came on. The pistons and cylinder heads had only moderate carbon buildup.

Don't know your miles or oil consumption, but it sounds like "ain't broke".

2ndof2

Miles are about 75 large and consumption is about 1000 to 1250 miles/qt.

Mike Murphy

You will eventually burn so much oil that the car runs poorly. Until that happens, you don't need to replace the guides, but you might be smokig profusely. If the car is run for too long, you could get some engine-damaging pre-detonation due to improper combustion and, over time, that could destroy the engine. But again, the car will be a smokestack long before then.

RallyJon

Good question. Worn valve guides can affect heat transfer from the valve stems, but most of the heat is dissipated into the head through the valve seats, not stems.

Have any 993s ever had worn valve guides result in broken valves? What other catastrophic damage can result from worn valve guides? I think I saw a picture of an older 911 engine where that has happened, but with hydraulic lifters, our valves are always perfectly adjusted, so that should be less likely.

If not, I figure you just let it go until the cloud of blue smoke behind you gets too big, or you're adding a liter of oil at every fillup.

Martin S.

be certain and come to the 993 Tech Session to be held at Tony Callas's shop. See the post above for specifics.

Also, be certain to read the November Excellence Magazine. There you will see Tony's check list for the 993.

If you are really worried, just do the valves in advance. Put in some heavy duty valve springs, and the latest valve guides recommend by the experts. Have the ports reamed out and all carbon removed...then join Porsche Owners Club and bring the car out to the track every month or so to blow out the carbon. That's my formula!

Steve Weiner-Rennsport Systems

Personally, I wouldn't worry about it until the oil consumption reaches 700-800 miles/qt.

At this time, the carbon buildups become serious enough to stick rings and lower the threshold of detonation.

I've seen engines with loose guides at 3K miles all the way to 100K+. The factory fitment tolerances were NOT very good resulting in wide variations in guide wear/oil consumption issues.

RallyJon

I wonder how many valve jobs are sold to meticulous Porsche owners who are worried, vs. those whose cars need them immediately?

gordo993

On mine, the guides were oval shaped causing the valves to slap extended, then seat properly when retracted. I hadn't owned the car long enough to know oil usage or any reduction in power, but the ticking noise got louder and louder until I got it fixed. My valves were fine, but my mechanic said it probably wouldn't have taken much to trash the effected valves.

She's run like a champ since I got her back from the shop nearly 3 years ago - I've never had to add oil.

fast_freddy

I went from 1qt every 2000 miles light/highway duty, 1 qt every 1300 miles heavy/city (lots of cold starts) duty to 1 qt every 1000 light/700 heavy all at once at about 93k miles. My engine is apart this week and every thing seems to be fine parts wise. However, I have been wetting my pants from time to time during the past 15k miles due to all of the alarmist write ups out there. The funny thing is now that it has happened is that there are very clear signs (to even a moderately circumspect person) when they need to be replaced. Of course it's easy for me to say that now that it's (finally) happened to me but again I did get some very clear indications that something was amiss. As Steve Weiner said in his earlier post to which he was kind enough to apprise me of many thousands miles ago, every car is different but you'll generally know by the rates of consumption when the time has come.

Edward

Yes, most wrenches will gladly take your dough.
Yes, if it ain't broke, indeed don't "fix" it.

The Porsche rec on oil consumption (as Steve W. mentioned) is 1qt/800 miles. Any consumption that's better than that is just not worth worrying about --assuming the car is running well, of course. Of course the OBDII cars are more sensitive, given the dreaded CEL problems which isn't, in itself, a "problem" in any way ...until you need to smog the car. And mileage itself is no predictor of valve-guide replacement. I'm at about 106K miles, with a considerable amount of track events in there, and I'm consuming about 1 qt/2000-2500 miles. So the moral of the story is drive it as she was intended to be driven and enjoy the miles

Edward

JChiles

So, in reality the valve guide "issue" especially for us in the rest of the world isn't that big. People less loving about 993's than we are usually tend to bring it up as a big flaw. But I guess it really is a PITA for those of you needing to pass a smog test if it's messing that up...

tj90

Just had my 95 in for california smog this week. 115k on the odometer, no OBD check, no rollers - according to the CA book (even though it is a 2wd) and only 2 RPM checks (idle and 2500 RPM). NOx were right in the middle of the range. Its nice to be able to sail thru the test without all the fancy checks that your exempt from~~ I believe most owners report that the cars are clean and iusually dont have emmisions problems (except for the sensitive CEL)...

BTW those rollers looked scary! Almost like the back of the car would bottom out in the gap between the rollers.

Edward

yes, it's a smog technicality with the CEL business. Those who have "failed" smog inspection did not fail due to emissions ...their cars ran as clean as all other 993s, which is to say very clean. They "failed" smog because their OBD reports a failure, and this is "reported" straight into the testor's machine. No "go around" for this AFAIK. You have to get your OBD to NOT report a CEL. Some pay the serious dough to have it addressed. Others disconnect the brain's power to clear it, reconnect and hurry over to the smog station before the damn thing detects the "failure." OBDII is ridiculously overzealous, IMHO.

Edward

mborkow

correct, the only problem with the plugged SAI ports on an obd2 equipped car is that you can't pass smog (well, not at first anyway...in CA there are referee stations)