Valve Guides....Nightmare waiting to happen?
08-02-2006, 12:51 PM
#31
08-02-2006, 01:30 PM
#32
RL Technical Advisor
Originally Posted by Matt Davies
However, all theories about driving technique are peripheral to the main issue, which I believe is in the individual differences/tolerances between engines that were hand assembled.
From what I gather, some just came out of the factory prone to premature valve-guide wear, no matter how they were driven.
From what I gather, some just came out of the factory prone to premature valve-guide wear, no matter how they were driven.
I think you are right.
Recently, we did a valve job on a '98 C2S with 3800 miles (yep, 3800!) where the exhaust guides had almost .030 of sideplay even though this engine was, for all purposes, brand new. The exhaust valves wobbled all over the valve seats due to a poor fitment at the factory and this one would have been an early candidate for the SA issue due to oil consumption.
We replaced the factory soft guides with our own phosphorus-bronze ones and honed them to fit with closer tolerances so this will not recur. Further, we enlarge the AI passages in the heads & cam housings for a little more airflow as we've found that decreased their propensity to clog over the long term.
Frankly, Porsche (and other German marques) have all experienced guide wear issues for many years and IMHO, is no reason to ignore these otherwise fine automobiles. I've never seen any car that didn't have some problems at one time or another and 993's are well below the norm in this regard. I would tell any prospective 993 buyer not to worry and simply maintain some perspective when dealing with any used car.
08-02-2006, 04:03 PM
#33
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Originally Posted by Matt Davies
Hmmm...Mine's a tip. (And it goes all the way to redline too!)
08-02-2006, 09:12 PM
#34
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There is a lot of good info here. I have a 96' 993 and the CEL light has been on for months. I use about 1.2 quarts of oil per 1,000 miles. I know that a top-end rebuild is in my future. I gotta pass emissions by November. My recommendation to anyone thinking of buying a 993 is to pay the bucks for a leak-down test. I would never had bought my 911 if I had known to do that test...oh well. Does anyone out there know if I am doing any extra damage to my whicle by driving at the aforementioned oil consumption rate?
08-02-2006, 09:29 PM
#35
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Originally Posted by digdoug2001
There is a lot of good info here. I have a 96' 993 and the CEL light has been on for months. I use about 1.2 quarts of oil per 1,000 miles. I know that a top-end rebuild is in my future. I gotta pass emissions by November. My recommendation to anyone thinking of buying a 993 is to pay the bucks for a leak-down test. I would never had bought my 911 if I had known to do that test...oh well. Does anyone out there know if I am doing any extra damage to my whicle by driving at the aforementioned oil consumption rate?
Burning 1 quart of oil every 1.2k miles is not bad at all in my opinion. Figure out how many miles you drive per year and divide that by 1,200 miles, and multiply that by the cost of oil per quart. I'm sure it will come out considerably less than $5000-6000 for a top-end rebuild.
No, you are not doing any extra damage.
08-02-2006, 10:20 PM
#36
"All you have to do to pass the emissions test is to reset the codes, but you'll fail the ODBII portion of it, so then they'll put your car on their dyno with a sniffer. If the car is fully warmed up, and if there are no other problems such as a bad O2 sensor, you'll pass the emissions test."
Not in most states, e.g. CA, as the readiness states must be set (completed), i.e. at least 5 of 7.
Not in most states, e.g. CA, as the readiness states must be set (completed), i.e. at least 5 of 7.
08-02-2006, 11:40 PM
#37
Rennlist Member
Originally Posted by Lorenfb
"All you have to do to pass the emissions test is to reset the codes, but you'll fail the ODBII portion of it, so then they'll put your car on their dyno with a sniffer. If the car is fully warmed up, and if there are no other problems such as a bad O2 sensor, you'll pass the emissions test."
Not in most states, e.g. CA, as the readiness states must be set (completed), i.e. at least 5 of 7.
Not in most states, e.g. CA, as the readiness states must be set (completed), i.e. at least 5 of 7.
08-03-2006, 12:16 AM
#38
Rennlist Member
Originally Posted by Steve Weiner-Rennsport Systems
Matt:
I think you are right.
Recently, we did a valve job on a '98 C2S with 3800 miles (yep, 3800!) where the exhaust guides had almost .030 of sideplay even though this engine was, for all purposes, brand new. The exhaust valves wobbled all over the valve seats due to a poor fitment at the factory and this one would have been an early candidate for the SA issue due to oil consumption.
We replaced the factory soft guides with our own phosphorus-bronze ones and honed them to fit with closer tolerances so this will not recur. Further, we enlarge the AI passages in the heads & cam housings for a little more airflow as we've found that decreased their propensity to clog over the long term.
Frankly, Porsche (and other German marques) have all experienced guide wear issues for many years and IMHO, is no reason to ignore these otherwise fine automobiles. I've never seen any car that didn't have some problems at one time or another and 993's are well below the norm in this regard. I would tell any prospective 993 buyer not to worry and simply maintain some perspective when dealing with any used car.
I think you are right.
Recently, we did a valve job on a '98 C2S with 3800 miles (yep, 3800!) where the exhaust guides had almost .030 of sideplay even though this engine was, for all purposes, brand new. The exhaust valves wobbled all over the valve seats due to a poor fitment at the factory and this one would have been an early candidate for the SA issue due to oil consumption.
We replaced the factory soft guides with our own phosphorus-bronze ones and honed them to fit with closer tolerances so this will not recur. Further, we enlarge the AI passages in the heads & cam housings for a little more airflow as we've found that decreased their propensity to clog over the long term.
Frankly, Porsche (and other German marques) have all experienced guide wear issues for many years and IMHO, is no reason to ignore these otherwise fine automobiles. I've never seen any car that didn't have some problems at one time or another and 993's are well below the norm in this regard. I would tell any prospective 993 buyer not to worry and simply maintain some perspective when dealing with any used car.
Following the dreaded CEL, I recently had an engine rebuild on my 96 Targa. My mechanic used the guides that came with the kit - ie factory equipment. Is this a problem, and what do you recommend I should do now to avoid another rebuild in future?
08-03-2006, 12:25 AM
#39
RL Technical Advisor
Originally Posted by Leander
Following the dreaded CEL, I recently had an engine rebuild on my 96 Targa. My mechanic used the guides that came with the kit - ie factory equipment. Is this a problem, and what do you recommend I should do now to avoid another rebuild in future?
Keep track of the your oil consumption and do everything you can to contain oil temperatures in the 180-200 F range and that will help ensure a long life of your engine's components.
08-08-2006, 07:43 PM
#40
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Originally Posted by Jack of Hearts
He said cars with tiptronic and those driven by non-sporting drivers got clogged. .
your mechanic hasn't seen me drive my lowely Tip at the track
no clogs here
08-08-2006, 08:18 PM
#41
Ok, so here's a question
Since the SAI valves are only open for the first 30 seconds or so on cold starts and pump shuts down after that to inactivate the passages, would it be a good idea to drive a bit aggressively every once in a while for the first minute to blow the valves out?
Obviously driving hard before the car is warm is not good, but it does have a dry sump.
Feel free to chime in, but I definately want hear Steve Weiner's oppinon.
Since the SAI valves are only open for the first 30 seconds or so on cold starts and pump shuts down after that to inactivate the passages, would it be a good idea to drive a bit aggressively every once in a while for the first minute to blow the valves out?
Obviously driving hard before the car is warm is not good, but it does have a dry sump.
Feel free to chime in, but I definately want hear Steve Weiner's oppinon.
08-08-2006, 08:24 PM
#42
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"driving your car over 4500 rpm before the engine has reached operating temprature will affect the service life of your 911" from the owner's manual of a 3.2 carrera I believe
08-08-2006, 08:49 PM
#43
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I would not rev your engine over 4,000 RPM before it reaches operating temp. ie the 8:00 position. The time the SAI control and check valves are operational are not really the issue. The burned oil enters the ports from the opposite side in the exhaust port. So this will only create excessive engine wear and possibly a quicker way to clog up your SAI ports.
08-08-2006, 10:24 PM
#44
Ok, just a thought.
So Tony, it seem there is really two issues here right?
1 - CEL for clogged SAI, which is really no big deal except for getting the smog inspection. It doesn't harm the car at all. Only reason some prefer the OBD 1 over the OBD 2 is that it doesn't detect the clogged port and therefore they don't have the inspection issue.
2 - Worn valve guides, which is an issue and effects '95 as well as later models equally.
So how does the clogged SAI effect the valve guides?
So Tony, it seem there is really two issues here right?
1 - CEL for clogged SAI, which is really no big deal except for getting the smog inspection. It doesn't harm the car at all. Only reason some prefer the OBD 1 over the OBD 2 is that it doesn't detect the clogged port and therefore they don't have the inspection issue.
2 - Worn valve guides, which is an issue and effects '95 as well as later models equally.
So how does the clogged SAI effect the valve guides?
08-08-2006, 10:30 PM
#45
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The worn valve guides are the reason for the clogged SAI ports. The burned oil from the worn valve guides enters and carbons up the SAI ports from the exhaust valve ports right next to the exhaust valve guide. By cleaning the ports out you are merely putting a bandaid on the problem.