My 993 News: Top End Rebuild Looms
07-12-2017, 12:23 PM
#16
RL Community Team
Rennlist Member
Rennlist Member
Good question.
(1.)The idle is lumpier. The acceleration at around 4.5-5.5k seems a little rougher.
(2.)The exhaust valve on #4 is surrounded by crusty,crystal stuff. I noticed it a few years ago when I had the exhaust manifolds off.
(3.)Other than that, I am going on a hunch. I am by no means a mechanic, just a very interested enthusiast who likes to get his hands dirty.
--Michael
(1.)The idle is lumpier. The acceleration at around 4.5-5.5k seems a little rougher.
(2.)The exhaust valve on #4 is surrounded by crusty,crystal stuff. I noticed it a few years ago when I had the exhaust manifolds off.
(3.)Other than that, I am going on a hunch. I am by no means a mechanic, just a very interested enthusiast who likes to get his hands dirty.
--Michael
(1.)Lumpy idle indicates a potential dirty idle valve, easily cleaned. Mid RPM issues may simply be a vacuum leak or inoperative vacuum actuators on your intake if you have Varioram there are five involved if not there are three less. If Here is the testing procedure:
To test the overall Varioram system including the actuators and the solenoid valves that control them you will need a helper:
1. Have your helper start the engine and run it for a few moments, to build vacuum;
2. Shuts the ignition off;
3. Turns the ignition back on without starting the engine while you observe the engine;
4. Observe the three Varioram actuators on the engine going through an initial cycling, you will need a flashlight and push down on the rubber duct attached to the fan housing to observe the third actuator underneath the intake manifold;
5. With the ignition on press the air recirculate button on the Climate Control Unit (CCU);
6. Listen for the sound of the vacuum actuated recirculating air flap moving inside the dash;
7. Go back behind the car and observe the heater flap actuator located on the duct work on the lower left side of the engine;
8. Cycle the CCU thermostat setting from cold to hot and back to cold a few times while observing the actuator;
9. Observe the actuator retracting rotating the flap arm from the 7:00 o’clock (heat) to the 9:00 o’clock (cool air) positions as you rotate the **** on the CCU.
(2.) Not an issue, on occasion a little carbon gets stuck in a valve and it fails to seal fully. Reving the engine or just rotating the valve can snap it shut. This is an intermittent issue on, I suspect, all 993 engines, not an indicator of the need for a rebuild.
(3.) Hunches are generally not a good basis for a very expensive internal engine repair.
Excessive Oil Consumption - Is a reason owners consider a top-end rebuild under the assumption that the valve guides are worn to the point that excessive oil is slipping past them and burning. The logic in this seems sound. Then again I recently ran across the following comment in the 993 Rennlist Forum in reply to an oil consumption concern:
“How full do you keep the oil tank? When I kept mine at the full level I'd go through easily a qt. per 600 miles, now I keep it at min - 1/4 I use barely a qt. every 2500 miles. Even now, after spirited driving, the oil can expand to over 1/2 full.”
If your car starts easily, idles and runs reasonably wellthere is no reason to consider a top end rebuild. I put Techron in two consecutive tanks of gas once a year in the theory it keep injectors clean, that is about it.
Leak Down Testing - Cylinder leaks can be from a poorly seated spark plug, worn rings or a valve that does not seat properly. I hear lots of discussion about leak-down testing of engines as a validation of engine condition. From reading the comments I have come to believe that the conditions under which such tests are done , are in many cases, inadequately controlled, Results can vary widely making such tests unreliable as an absolute test of condition. They may be of some very very limited antidotal value in capturing variances between individual cylinders on an engine in the presence of other gross operating symptoms.
Here is a recent comment in reply to my Renlist posting questioning a potential valve leak, a common reason a top end rebuild is proposed:
My posting question:
“Thinking that there may be carbon debris in the valve seat, can one take a valve cover off and rotate the valve by its stem to possibly knock it free? Maybe put some choke cleaner or Techron in the cylinder to help with this.”
Renlister reply:
“I've had mixed results when doing leak-downs on older motors. Sometimes I gotta tap the valve to get it to snap shut. During hand rotation the valve will hang open on carbon. During running operation it will snap shut [work properly] due to speed of the valve closing. I would not cry just yet. Warm the motor up well and pull the suspected valve cover and see if you can pull the rocker off and tap the valve stem slightly when doing the leak down. Don't run it up to 100 PSI. Start a bit lower when tapping the valve. You should hear the leak stop.”
Another shop that was conducting a Pre-Purchase Inspection (PPI) for a Rennlist member suggested that a “top-end” rebuild was needed. In investigation multiple cylinder leak-down percentages in the 75% range were found, however the dyno test of the same engine put output at 237hp at the wheels, allowing for drive train losses of 10% from the factory stated 270hp this number is quite good for a 16+-year-old car that in this case runs perfectly otherwise. If the leak-down results were to be relied upon the car should barely run, exhibit the check engine light, not be able to hold idle and should be blowing more blue smoke than Jerry Garcia did in his lifetime. Go figure? What appears as general low engine output, OBDC issues a rough idle or a tapping like sound at the exhaust can have many reasons that should be ruled out before considering cracking open the engine!
You know the line, “accept the things I should not fix, have the courage to fix the things I must and have the wisdom to know the difference”
Last edited by pp000830; 07-12-2017 at 03:04 PM.
07-12-2017, 12:32 PM
#17
Rennlist Member
Thread Starter
Excellent info here. I will run some tests and see what happens. I can't afford the rebuild now so I have an excess of time and a minimum of money. And a garage with a scissor lift and tools and a few friends!
Thanks!
--Michael
Thanks!
--Michael
Answers:
(1.)This may simply be a vacuum leak or inoperative vacuum actuators on your intake if you have Varioram there are five involved if not there are two less. If Here is the testing procedure:
To test the overall Varioram system including the actuators and the solenoid valves that control them you will need a helper:
1. Have your helper start the engine and run it for a few moments, to build vacuum;
2. Shuts the ignition off;
3. Turns the ignition back on without starting the engine while you observe the engine;
4. Observe the three Varioram actuators on the engine going through an initial cycling, you will need a flashlight and push down on the rubber duct attached to the fan housing to observe the third actuator underneath the intake manifold;
5. With the ignition on press the air recirculate button on the Climate Control Unit (CCU);
6. Listen for the sound of the vacuum actuated recirculating air flap moving inside the dash;
7. Go back behind the car and observe the heater flap actuator located on the duct work on the lower left side of the engine;
8. Cycle the CCU thermostat setting from cold to hot and back to cold a few times while observing the actuator;
9. Observe the actuator retracting rotating the flap arm from the 7:00 o’clock (heat) to the 9:00 o’clock (cool air) positions as you rotate the **** on the CCU.
(2.) Not an issue, on occasion a little carbon gets stuck in a valve and it fails to seal fully. Reving the engine or just rotating the valve can snap it shut. This is an intermittent issue on, I suspect, all 993 engines, not an indicator of the need for a rebuild.
(3.) Hunches are generally not a good basis for a very expensive internal engine repair.
Excessive Oil Consumption - Is a reason owners consider a top-end rebuild under the assumption that the valve guides are worn to the point that excessive oil is slipping past them and burning. The logic in this seems sound. Then again I recently ran across the following comment in the 993 Rennlist Forum in reply to an oil consumption concern:
“How full do you keep the oil tank? When I kept mine at the full level I'd go through easily a qt. per 600 miles, now I keep it at min - 1/4 I use barely a qt. every 2500 miles. Even now, after spirited driving, the oil can expand to over 1/2 full.”
If your car starts easily, idles and runs reasonably wellthere is no reason to consider a top end rebuild. I put Techron in two consecutive tanks of gas once a year in the theory it keep injectors clean, that is about it.
Leak Down Testing - Cylinder leaks can be from a poorly seated spark plug, worn rings or a valve that does not seat properly. I hear lots of discussion about leak-down testing of engines as a validation of engine condition. From reading the comments I have come to believe that the conditions under which such tests are done , are in many cases, inadequately controlled, Results can vary widely making such tests unreliable as an absolute test of condition. They may be of some very very limited antidotal value in capturing variances between individual cylinders on an engine in the presence of other gross operating symptoms.
Here is a recent comment in reply to my Renlist posting questioning a potential valve leak, a common reason a top end rebuild is proposed:
My posting question:
“Thinking that there may be carbon debris in the valve seat, can one take a valve cover off and rotate the valve by its stem to possibly knock it free? Maybe put some choke cleaner or Techron in the cylinder to help with this.”
Renlister reply:
“I've had mixed results when doing leak-downs on older motors. Sometimes I gotta tap the valve to get it to snap shut. During hand rotation the valve will hang open on carbon. During running operation it will snap shut [work properly] due to speed of the valve closing. I would not cry just yet. Warm the motor up well and pull the suspected valve cover and see if you can pull the rocker off and tap the valve stem slightly when doing the leak down. Don't run it up to 100 PSI. Start a bit lower when tapping the valve. You should hear the leak stop.”
Another shop that was conducting a Pre-Purchase Inspection (PPI) for a Rennlist member suggested that a “top-end” rebuild was needed. In investigation multiple cylinder leak-down percentages in the 75% range were found, however the dyno test of the same engine put output at 237hp at the wheels, allowing for drive train losses of 10% from the factory stated 270hp this number is quite good for a 16+ year old car that in this case runs perfectly otherwise. If the leak-down results were to be relied upon the car should barely run, exhibit the check engine light, not be able to hold idle and should be blowing more blue smoke then Jerry Garcia did in his lifetime. Go figure? What appears as general low engine output, OBDC issues a rough idle or a tapping like sound at the exhaust can have many reasons that should be ruled out before considering cracking open the engine!
You know the line, “accept the things I should not fix, have courage to fix the things I must and have the wisdom to know the difference”
(1.)This may simply be a vacuum leak or inoperative vacuum actuators on your intake if you have Varioram there are five involved if not there are two less. If Here is the testing procedure:
To test the overall Varioram system including the actuators and the solenoid valves that control them you will need a helper:
1. Have your helper start the engine and run it for a few moments, to build vacuum;
2. Shuts the ignition off;
3. Turns the ignition back on without starting the engine while you observe the engine;
4. Observe the three Varioram actuators on the engine going through an initial cycling, you will need a flashlight and push down on the rubber duct attached to the fan housing to observe the third actuator underneath the intake manifold;
5. With the ignition on press the air recirculate button on the Climate Control Unit (CCU);
6. Listen for the sound of the vacuum actuated recirculating air flap moving inside the dash;
7. Go back behind the car and observe the heater flap actuator located on the duct work on the lower left side of the engine;
8. Cycle the CCU thermostat setting from cold to hot and back to cold a few times while observing the actuator;
9. Observe the actuator retracting rotating the flap arm from the 7:00 o’clock (heat) to the 9:00 o’clock (cool air) positions as you rotate the **** on the CCU.
(2.) Not an issue, on occasion a little carbon gets stuck in a valve and it fails to seal fully. Reving the engine or just rotating the valve can snap it shut. This is an intermittent issue on, I suspect, all 993 engines, not an indicator of the need for a rebuild.
(3.) Hunches are generally not a good basis for a very expensive internal engine repair.
Excessive Oil Consumption - Is a reason owners consider a top-end rebuild under the assumption that the valve guides are worn to the point that excessive oil is slipping past them and burning. The logic in this seems sound. Then again I recently ran across the following comment in the 993 Rennlist Forum in reply to an oil consumption concern:
“How full do you keep the oil tank? When I kept mine at the full level I'd go through easily a qt. per 600 miles, now I keep it at min - 1/4 I use barely a qt. every 2500 miles. Even now, after spirited driving, the oil can expand to over 1/2 full.”
If your car starts easily, idles and runs reasonably wellthere is no reason to consider a top end rebuild. I put Techron in two consecutive tanks of gas once a year in the theory it keep injectors clean, that is about it.
Leak Down Testing - Cylinder leaks can be from a poorly seated spark plug, worn rings or a valve that does not seat properly. I hear lots of discussion about leak-down testing of engines as a validation of engine condition. From reading the comments I have come to believe that the conditions under which such tests are done , are in many cases, inadequately controlled, Results can vary widely making such tests unreliable as an absolute test of condition. They may be of some very very limited antidotal value in capturing variances between individual cylinders on an engine in the presence of other gross operating symptoms.
Here is a recent comment in reply to my Renlist posting questioning a potential valve leak, a common reason a top end rebuild is proposed:
My posting question:
“Thinking that there may be carbon debris in the valve seat, can one take a valve cover off and rotate the valve by its stem to possibly knock it free? Maybe put some choke cleaner or Techron in the cylinder to help with this.”
Renlister reply:
“I've had mixed results when doing leak-downs on older motors. Sometimes I gotta tap the valve to get it to snap shut. During hand rotation the valve will hang open on carbon. During running operation it will snap shut [work properly] due to speed of the valve closing. I would not cry just yet. Warm the motor up well and pull the suspected valve cover and see if you can pull the rocker off and tap the valve stem slightly when doing the leak down. Don't run it up to 100 PSI. Start a bit lower when tapping the valve. You should hear the leak stop.”
Another shop that was conducting a Pre-Purchase Inspection (PPI) for a Rennlist member suggested that a “top-end” rebuild was needed. In investigation multiple cylinder leak-down percentages in the 75% range were found, however the dyno test of the same engine put output at 237hp at the wheels, allowing for drive train losses of 10% from the factory stated 270hp this number is quite good for a 16+ year old car that in this case runs perfectly otherwise. If the leak-down results were to be relied upon the car should barely run, exhibit the check engine light, not be able to hold idle and should be blowing more blue smoke then Jerry Garcia did in his lifetime. Go figure? What appears as general low engine output, OBDC issues a rough idle or a tapping like sound at the exhaust can have many reasons that should be ruled out before considering cracking open the engine!
You know the line, “accept the things I should not fix, have courage to fix the things I must and have the wisdom to know the difference”
07-12-2017, 03:29 PM
#18
This low leakdown (and I assume you did a leakdown instead of a compresson test) on one of the cylinder also happened on my former 993.
One cylinder (can't remember which one off top of my head) had a leak down loss of 25% out the exhaust valve. I put a bag on the end of the exhaust pipes and can see it inflate up when I applied air pressure at the sparkplug with both intake and exhaust valves closed at TDC.
After several weeks of denying the truth by pouring in fuel cleaners, driving it hard to dislodge stuck carbons, changing and reseating sparkplugs, and blaming my poor eyesights for misreading 25% instead of 5%.....I came to the inevitable conclusion that the exhaust valve is worn and a top end is needed.
From my reading, poor exhaust valve seating can cause hot spots which may lead to pieces breaking/cracking.
So...instead of trying to deny it and ignore a sick symptom, I did a top-end rebuilt. And it gave me 10 years of driving pleasure rather than a bigger bill/headache down the road.
One cylinder (can't remember which one off top of my head) had a leak down loss of 25% out the exhaust valve. I put a bag on the end of the exhaust pipes and can see it inflate up when I applied air pressure at the sparkplug with both intake and exhaust valves closed at TDC.
After several weeks of denying the truth by pouring in fuel cleaners, driving it hard to dislodge stuck carbons, changing and reseating sparkplugs, and blaming my poor eyesights for misreading 25% instead of 5%.....I came to the inevitable conclusion that the exhaust valve is worn and a top end is needed.
From my reading, poor exhaust valve seating can cause hot spots which may lead to pieces breaking/cracking.
So...instead of trying to deny it and ignore a sick symptom, I did a top-end rebuilt. And it gave me 10 years of driving pleasure rather than a bigger bill/headache down the road.
07-12-2017, 03:39 PM
#20
Welll....if it makes you feel better, the hit to your wallet by the top end rebuild is recoup when you sell the car. The top end also takes care of the valve guide issue. And also any oil leaks.
Oh...btw....when I asked the shop that did my valve job, they said the valve was only a little bit worn. Guess just a little bit worn is enough to cause the lower leakdown.
Oh...btw....when I asked the shop that did my valve job, they said the valve was only a little bit worn. Guess just a little bit worn is enough to cause the lower leakdown.
07-13-2017, 10:00 AM
#21
Rennlist Member
Thread Starter
Welll....if it makes you feel better, the hit to your wallet by the top end rebuild is recoup when you sell the car. The top end also takes care of the valve guide issue. And also any oil leaks.
Oh...btw....when I asked the shop that did my valve job, they said the valve was only a little bit worn. Guess just a little bit worn is enough to cause the lower leakdown.
Oh...btw....when I asked the shop that did my valve job, they said the valve was only a little bit worn. Guess just a little bit worn is enough to cause the lower leakdown.
--Michael
07-13-2017, 12:07 PM
#22
Did the top end rebuild a couple of months ago to address some seeping exhaust valves and the SAI light on my car. Wasn't cheap, but I figure it's worth it since I plan on keeping and driving the car for the foreseeable future. Had 121k miles on it when it went under the knife.
https://goo.gl/photos/pwkvefTCnNikDM6P9
Also got new piston rings, rod bearings, rod bolts, clutch kit, and other odds and ends.
https://goo.gl/photos/pwkvefTCnNikDM6P9
Also got new piston rings, rod bearings, rod bolts, clutch kit, and other odds and ends.
07-13-2017, 02:06 PM
#23
RL Community Team
Rennlist Member
Rennlist Member
This is great and always the way to go in my book.
What running issues caused you to investigate in the first place?
Andy
07-13-2017, 06:17 PM
#24
After the rebuilt, it made the 270s stock horsepower again.
07-14-2017, 06:06 AM
#25
Rennlist Member
Last time around 2 of mine were off by 8-10%. That's almost a full point AFR. I had less than 10k miles on them. Cars that sit have bigger issues with clogging than those that get driven regularly.
Last edited by MarinS4; 07-17-2017 at 07:43 PM. Reason: Added info
07-14-2017, 09:21 AM
#26
RL Community Team
Rennlist Member
Rennlist Member
07-20-2017, 11:59 PM
#27
What is a cost range for a top-end and a full engine rebuild?
With a Testarossa, it's easily $50K. Hopefully it's much less with a 993?!
With a Testarossa, it's easily $50K. Hopefully it's much less with a 993?!
07-21-2017, 01:25 AM
#28
I'd budget at least $10K, if you're letting shop do all the work. Thing is, once you're in so deep, you're always gonna do all the "while you're in there and the engine is already out stuff", so that will usually add thousands more, unless, of course you do it all yourself.
07-21-2017, 01:53 PM
#29
I'd budget at least $10K, if you're letting shop do all the work. Thing is, once you're in so deep, you're always gonna do all the "while you're in there and the engine is already out stuff", so that will usually add thousands more, unless, of course you do it all yourself.
These engine are incredibly robust. Piston & cylinders usually look new @ the 100K mark. Just do seals, bearings, rings, valve guides, etc.
Resist the attempt to go 3.8 or cams!!!! Or supercharge or turbocharge!!!
07-21-2017, 02:06 PM
#30
I would try to resist ALL attempts of while you're in there with only ONE exception...that is to split the case which doesn't add that much more to the cost.
These engine are incredibly robust. Piston & cylinders usually look new @ the 100K mark. Just do seals, bearings, rings, valve guides, etc.
Resist the attempt to go 3.8 or cams!!!! Or supercharge or turbocharge!!!
These engine are incredibly robust. Piston & cylinders usually look new @ the 100K mark. Just do seals, bearings, rings, valve guides, etc.
Resist the attempt to go 3.8 or cams!!!! Or supercharge or turbocharge!!!
I just did a complete engine rebuild including splitting the case, and as long as my car was gonna be gone for a few months and I was in deep, I told my mechanic to go ahead and replace any and all seals, bushings or any wear items he could find that needed to be replaced. That decision made my car mechanically as new when the job was done, but added substantially to my final bill.