OBD-II CEL : Carbon buildup issues (long)
10-10-2003, 01:42 AM
#61
Rennlist Member
please tell me oh great one- are you saying that excessive valve guide wear at 40,000 miles is only because of driving habits, and nothing to do with Porsche's valve guide material?? and/or choice of valve seals??
10-10-2003, 02:48 AM
#62
RL Technical Advisor
Thread Starter
Hi Loren:
Please forgive me as I meant nothing personal in my earlier post. Upon reading your reply, my feeling is that you might have somehow taken offense where none was intended and no disrepect was meant.
My apologies.
That said, I stand 100% behind everything I've written.
LOL,...you are assuming that Porsche has always made perfect and altruistic decisions about what they use and how they do things in the production environment. I cannot and will not change your mind if you think they are incapable of making a mistake or if you do not believe that economics/politics affects some of their selection of suppliers. The reality of this is what it is, and the facts stand. Talk to any machine shop who does lots of 911 heads.
For the record, Porsche has not always provided the most durable of engine parts over the past 40 years and the aftermarket has stepped in for those rare instances and provided much improved and more durable parts. Valve springs, rod bolts, head studs, valve spring retainers and valve guides are just a few. Although I have GREAT respect for what the Factory does, they are not perfect.
If you think Porsche hasn't and doesn't suffer some QC issues from time to time, once again I cannot change your mind. I can only respectfully suggest that you have more to learn.
I'm 55 years old, have been building Porsche race engines since 1976, and I'm happy to say that I'm still learning both from some of my peers and my customers. I try to keep an open mind,....
Lastly, I have not rebuilt all the 911 heads in the world for sure, but I've done several thousand over this time span and I can tell you that with very rare exception, the 911 valve guides have always been an issue and the root cause of the majority of oil consumption problems.
Send me some heads and I'll be very pleased to show you what we do,...
Please forgive me as I meant nothing personal in my earlier post. Upon reading your reply, my feeling is that you might have somehow taken offense where none was intended and no disrepect was meant.
My apologies.
That said, I stand 100% behind everything I've written.
LOL,...you are assuming that Porsche has always made perfect and altruistic decisions about what they use and how they do things in the production environment. I cannot and will not change your mind if you think they are incapable of making a mistake or if you do not believe that economics/politics affects some of their selection of suppliers. The reality of this is what it is, and the facts stand. Talk to any machine shop who does lots of 911 heads.
For the record, Porsche has not always provided the most durable of engine parts over the past 40 years and the aftermarket has stepped in for those rare instances and provided much improved and more durable parts. Valve springs, rod bolts, head studs, valve spring retainers and valve guides are just a few. Although I have GREAT respect for what the Factory does, they are not perfect.
If you think Porsche hasn't and doesn't suffer some QC issues from time to time, once again I cannot change your mind. I can only respectfully suggest that you have more to learn.
I'm 55 years old, have been building Porsche race engines since 1976, and I'm happy to say that I'm still learning both from some of my peers and my customers. I try to keep an open mind,....
Lastly, I have not rebuilt all the 911 heads in the world for sure, but I've done several thousand over this time span and I can tell you that with very rare exception, the 911 valve guides have always been an issue and the root cause of the majority of oil consumption problems.
Send me some heads and I'll be very pleased to show you what we do,...
10-10-2003, 03:07 AM
#63
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I think Steve has earned the respect and trust of every single Rennlist member on this board. I for one, would take Steve's advice over anyone else's on this board (especially over a non-Rennlist member) =).
10-10-2003, 03:17 AM
#64
RL Technical Advisor
Thread Starter
Originally posted by max911
please tell me oh great one- are you saying that excessive valve guide wear at 40,000 miles is only because of driving habits, and nothing to do with Porsche's valve guide material?? and/or choice of valve seals??
please tell me oh great one- are you saying that excessive valve guide wear at 40,000 miles is only because of driving habits, and nothing to do with Porsche's valve guide material?? and/or choice of valve seals??
IMHO, excessive guide wear at 40K miles is not related to how you drive the car unless you were racing it. Its a function of valve guide material, stem-to-guide clearance, and production tolerances in valve stems.
The latter item is why each and every valve stem should be hand fitted and honed-to-size during a valve job. This is something that simply cannot be accomplished economically during production. Its the difference between "production" and "custom". Anther word commonly used word is "blueprinting".
Porsche to their credit, uses an excellent valve guide material; Viton, and it does a superb job of oil control unless the stem-to-guide clearance is excessive.
10-10-2003, 03:19 AM
#65
Rennlist Member
Loren-
Porsche -over a decade to get the stud situation "cured", with several different tries.
Porsche -over a decade to get the collapsed chain tensioner "cured". also with several interim solutions.
I do not know very much about the 996/ Boxster watercooled engines, but i always see a stack of failed ones when i peek around the dealers off limits areas.
Is that Porsche perfection??
Obviously perfection must always be pursued. If you ever think you have achieved it....you're kidding yourself...
Loren, hopefully you can rewind enough starters to pony up for a membership soon.
max
Porsche -over a decade to get the stud situation "cured", with several different tries.
Porsche -over a decade to get the collapsed chain tensioner "cured". also with several interim solutions.
I do not know very much about the 996/ Boxster watercooled engines, but i always see a stack of failed ones when i peek around the dealers off limits areas.
Is that Porsche perfection??
Obviously perfection must always be pursued. If you ever think you have achieved it....you're kidding yourself...
Loren, hopefully you can rewind enough starters to pony up for a membership soon.
max
10-10-2003, 06:20 AM
#66
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Steve, not meaning to exhaust this topic much further, but from your comments I am now wondering whether I should be concerned regarding the oil consumption of my low mileage 98 Cab.
I know little about the previous Florida owner's driving habits other than he put on only 6k miles and likely drove short distances. Initially I was getting only 750m/quart, now after two oil changes and 10k miles, comsumption has improved to about 1300m/qt.
Is it conceivable that the car could have eccessive valve guide wear despite the low mileage?
I first assumed that seals may have gone bad but i see no visible leaks(pan removed), and oil consumption is lessening rather than worsening. Should I still be concerned? Thanks
I know little about the previous Florida owner's driving habits other than he put on only 6k miles and likely drove short distances. Initially I was getting only 750m/quart, now after two oil changes and 10k miles, comsumption has improved to about 1300m/qt.
Is it conceivable that the car could have eccessive valve guide wear despite the low mileage?
I first assumed that seals may have gone bad but i see no visible leaks(pan removed), and oil consumption is lessening rather than worsening. Should I still be concerned? Thanks
10-10-2003, 08:10 AM
#68
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Carbon build up/valve guides
Is it me,or is the guy that specs the valve guide material,sleeping with the woman who is in charge of rear tire compounds?
But seriously,I have found the problem of carbon build up is almost always associated with worn valve guides.The problem is evident in not only high oil consumption,but also with a degraded idle and decreased power.Left unchecked,it will lead to the valves themselves requiring replacement do to stem wear and face damage to the point where when ground,the margins are under spec.As for 964's,I think the spring retainers break before the guides wear out in many cases.We replace the valve spring retainers as a precaution after approx.75k on most cars track driven.The failure is very ugly if it occurs,i have seen too many of those too.
But seriously,I have found the problem of carbon build up is almost always associated with worn valve guides.The problem is evident in not only high oil consumption,but also with a degraded idle and decreased power.Left unchecked,it will lead to the valves themselves requiring replacement do to stem wear and face damage to the point where when ground,the margins are under spec.As for 964's,I think the spring retainers break before the guides wear out in many cases.We replace the valve spring retainers as a precaution after approx.75k on most cars track driven.The failure is very ugly if it occurs,i have seen too many of those too.
10-10-2003, 12:21 PM
#72
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One of my favovite sayings: "When you don't have a valid argument to make, resort to personal attacks".
Steve:
Add my name to the list of those very appreciative of your efforts here. One question: On page 4 of this post you mention that in your opinion "spirited" driving has very little effect on oil consumption. My '96 has seemed to use considerably more when I've done some extended aggressive driving on twisties or in an autocross. As an example, I autocrossed a few weekends ago, made sure my oil level was at midrange before the event and when it was over it was pretty much off the scale low again. It seemed to correspond to about 0.5 quart which is much, much faster consumption than during more normal driving.
Does this seem normal or does it sound like I've got significantly worn guides? History: I've had the car since February and consumption during normal driving is ~1qt/1000 miles which seems on the high side already.
Thanks
Brad
Steve:
Add my name to the list of those very appreciative of your efforts here. One question: On page 4 of this post you mention that in your opinion "spirited" driving has very little effect on oil consumption. My '96 has seemed to use considerably more when I've done some extended aggressive driving on twisties or in an autocross. As an example, I autocrossed a few weekends ago, made sure my oil level was at midrange before the event and when it was over it was pretty much off the scale low again. It seemed to correspond to about 0.5 quart which is much, much faster consumption than during more normal driving.
Does this seem normal or does it sound like I've got significantly worn guides? History: I've had the car since February and consumption during normal driving is ~1qt/1000 miles which seems on the high side already.
Thanks
Brad
10-10-2003, 12:45 PM
#73
RL Technical Advisor
Thread Starter
DrZ:
Your case sounds more like the rings have not yet fully seated. Higher than normal oil consumption in the first 10K-15K miles is usually due to an owner babying the engine and the rings will be slow to seat. Try to drive the car with short blasts of wide-open throttle in 4th gear from 2000-5000 and back down again to help the rings to seat. Oil consumption will stabilize when this process is complete.
Lorenfb:
I could not agree more, Sir.
Brad:
You did not indicate how many miles are on your car but 1000 miles/qt seems high to me, as well. Autocross & track use can increase oil consumption especially when the car has not been driven aggressively for awhile. This is due to periods of higher RPM at closed throttle which pulls oil past the rings and down the guides.
How many miles on the car right now?
Your case sounds more like the rings have not yet fully seated. Higher than normal oil consumption in the first 10K-15K miles is usually due to an owner babying the engine and the rings will be slow to seat. Try to drive the car with short blasts of wide-open throttle in 4th gear from 2000-5000 and back down again to help the rings to seat. Oil consumption will stabilize when this process is complete.
Lorenfb:
I could not agree more, Sir.
Brad:
You did not indicate how many miles are on your car but 1000 miles/qt seems high to me, as well. Autocross & track use can increase oil consumption especially when the car has not been driven aggressively for awhile. This is due to periods of higher RPM at closed throttle which pulls oil past the rings and down the guides.
How many miles on the car right now?
10-10-2003, 01:47 PM
#74
Oh-oh,.......Perhaps I should make a reservation,....
10-10-2003, 01:51 PM
#75
Passed On
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Steve, thanks for your insighful post and follow-on to other's comments. Now, gotta think about what I get eventually to replace my aging 993.
My '95 has 75K miles on it; getting about 3K miles/qt of Mobil 1 0W-40. I guess I'm still of the opinion that puttering around town isn't the greatest thing for a 911. All my 911's (first '76 911S, then '84 Turbo-Look, now '95 993) are largely weekend fun cars - the 993 sees track and autocrosses but street driving is generally get on a back road and go for a "spirited" sprint for 1-3 hours, or else is expressway/interstate cruising. I have not seen excessive oil consumption exc. for burning more when at a track event.
Somehow I thought the valve guide problem was "cured" way back in the SC days. I know the '84 had a engine teardown at 120K miles due to a snapped spark plug (happened at PPI when I was selling it; Murphy's law!). Shop indicated valve guides were worn to just within the Porsche tolerances; not bad at all for the mileage. Cam chains, sprockets, and tensioners were worn but not bad; bottom end of engine was "like new" (shop's words). This experience plus the 993 oil consumption made me think that the valve guide premature wear was no longer a problem. Apparently not.
I'm not going to worry about the 993 engine until something indicates a problem. However, will try to ensure a thorough PPI if I ever decide to get a OBD-II 993.
My '95 has 75K miles on it; getting about 3K miles/qt of Mobil 1 0W-40. I guess I'm still of the opinion that puttering around town isn't the greatest thing for a 911. All my 911's (first '76 911S, then '84 Turbo-Look, now '95 993) are largely weekend fun cars - the 993 sees track and autocrosses but street driving is generally get on a back road and go for a "spirited" sprint for 1-3 hours, or else is expressway/interstate cruising. I have not seen excessive oil consumption exc. for burning more when at a track event.
Somehow I thought the valve guide problem was "cured" way back in the SC days. I know the '84 had a engine teardown at 120K miles due to a snapped spark plug (happened at PPI when I was selling it; Murphy's law!). Shop indicated valve guides were worn to just within the Porsche tolerances; not bad at all for the mileage. Cam chains, sprockets, and tensioners were worn but not bad; bottom end of engine was "like new" (shop's words). This experience plus the 993 oil consumption made me think that the valve guide premature wear was no longer a problem. Apparently not.
I'm not going to worry about the 993 engine until something indicates a problem. However, will try to ensure a thorough PPI if I ever decide to get a OBD-II 993.