Yellow Rose
Suspended
- Joined
- 22 November 2001
- Messages
- 2,256
There are at least two incidents where valve guide failure has occurred on an NSX with a CTSC. Coincidence? Don’t know, but something to think about this hot summer weekend, while sipping a cool one in the shade. The two situations are so strikingly similar, it should invoke thought among CTSC owners. Not meaning any flames of any sort, just stating factual knowledge. So before somebody suggests that this is speculation, hearsay or innuendo…it is not. What follows is a detailed story of NSX #1, which can be verified by several prominent members on this forum.
The supercharger was installed as a brand new unit January 2000. Comptech’s warranty is two years if installed on a used NSX and three years if installed on a new NSX. Why the distinction makes absolutely no logic, but that’s their policy. For about a month before the supercharger seized, at full throttle but only from 7000 RPM to 8000 RPM, the driver would sometimes hear a squeal. The driver thought it was the belt but it was tightened it but to no avail. March 2002 the unit seized. The owner paid for the labor but even though it was out of warranty, Comptech sent a replacement blower. When the original blower was removed, inside the intake manifold was a very fine layer of aluminum grit. Flip the blower over and it was evident the rotors were rubbing into the aluminum housing. The only way this could’ve happened is bearing failure, allowing the rotors to axially “float” instead of being fixed into position like they are supposed to be. Thus the source of the squealing noise.
The owner called an expert and he said before installing the replacement blower to perform a compression test and a leakdown test on the engine. Both tests failed.....not surprising considering that the engine had been inhaling aluminum grit for some time. The owner wrote Comptech a letter asking for assistance with engine repairs that the two tests proved was needed. The owner was told that Comptech would not pay for repairs to engine damage.
One month later the car was dyno’ed and the car was down on power about 20 HP. Again, not very surprising since compression was low because of the grit. Pondering the options, the owner (after consulting with one or two experts) decided that the damage is done but won’t get any worse so just drive the car with twenty less horsepower.
The next day driving 70 MPH the replacement supercharger seized. Two superchargers seizing on the same car within a month of each other. Well, surely it must be the owner / his mechanic / his car. When the owner stated that a Comptech-authorized technician installed the original blower and the replacement, they changed their tune…somewhat "blaming" the car as a jinx.
Unlike the first seized blower that had no loose pieces of metal, there were small bits of metal that did come from the second seized blower. Just like the first seizure, it was checked to ensure the factory air filter was not breached. It was in perfect condition. But that is good news and bad news. The good news is that it can be eliminated a foreign object like a rock being sucked up from the road. The bad news is that the only place the foreign metal could’ve come from is the engine. But how? If the inlet is filtered and the blower outlet feeds into the engine, how could metal be coming from the engine? More on this in a sec.
Unlike the first blower that Comptech sent to the owner then the owner returned the bad one, the owner had to ship them the blower for investigation before they would decide anything. Comptech did prefaced this by mentioning "valve guide failure" as a possibility even before seeing the unit. Upon receipt of the unit and the metal pieces, they called the owner back and confirmed the pieces were valve guide fragments. With this ruling / conclusion, Comptech’s position was that a foreign object entered their blower and they would not cover this one. The owner e-mailed an expert pictures of the metal pieces and he said that it looked like they could be valve guide bits. Sticking a finger into one of the intake runners, sure enough the owner could feel that pieces of one of the valve guides broke off. But how did they go up when air and gravity cause objects to go down into the engine? More on this in a sec.
Upon teardown of the engine all six cylinders were badly scorn by the aluminum grit caused by the original blower. Also, it was evident where pieces of debris larger than just fine grit had impacted the top of the pistons. Could this have been valve guides or pieces of the two seized blower? Who knows?
Let’s put all of this aside and solve the problem of the foreign object. There is a conceivable manner in which broken valve guide could get into the blower inlet. It’s a stretch, but read along. At the exact instant the valve guide breaks off, the intake valve is going closed. As the debris falls down, the valve is coming up, meets the debris and impacts it into the opposite direction with enough force to knock it up the intake runner into the bottom of the intake manifold. Given the light mass of the debris falling down onto a valve with substantially more mass which is traveling much faster than the rate at which the debris is falling, this is entirely possible. Probable? Not particularly good odds. Possible? Yes. That explains how the debris ended up in the bottom of the manifold but not how it gets from the manifold to the inlet side of the blower? All supercharger kits have some sort of boost divert valve so that boost is not fed into the engine while it is at steady-state driving such as cruise control on the highway. The CTSC boost valve diverts to the throttle body inlet in a completely close loop system. The boost valve closes as manifold pressure rises and the forced induction begins, and is controlled by a small rubber vacuum line that senses boost within the intake manifold chamber. Guess where this boost divert valve is on the CTSC? You got it.....on the bottom of the intake manifold that is the absolute lowest part of the chamber. Remember how mechanically the debris was knocked into the manifold? Well from here it gets sucked into the throttle body by vacuum. Driving around, the vibrations will eventually “rattle” the debris to the opening of the boost divert valve connection. Under hard deceleration it is possible for the engine to create enough manifold vacuum to suck the small debris up the bypass tube through the throttle body and right into the entrance of the blower. This is exactly how the scratches on seized blower #2 indicate the debris traveled, ultimately lodging into the rotors.
This theory of what happened is sound but very difficult to prove. The owner has talked with four different lawyers and they all said it would be a tough case since there is no substantial evidence and it boiled down to (a) did the blower hurt the engine or (b) did the engine hurt the blower or (c) did the engine hurt the blower because the blower hurt the engine or (d) did the blower hurt the engine because the engine hurt the blower. Go against Comptech and their contention is that regardless of which of the above four, they were kind enough to provide the first replacement blower which was out of warranty so there is no way they are obligated for engine repair cost. Go against Acura and they will say that the increased heat from a blower thermally stressed (aftercooler is a good thing to have on an FI’ed engine) the valve guide and it failed at a temperature it was not designed for. Besides that, the engine was modified, which is a warranty no-no as far as they are concerned. Either way the owner was stuck with the repair bill. Caveat emptor.....how fitting.
The supercharger was installed as a brand new unit January 2000. Comptech’s warranty is two years if installed on a used NSX and three years if installed on a new NSX. Why the distinction makes absolutely no logic, but that’s their policy. For about a month before the supercharger seized, at full throttle but only from 7000 RPM to 8000 RPM, the driver would sometimes hear a squeal. The driver thought it was the belt but it was tightened it but to no avail. March 2002 the unit seized. The owner paid for the labor but even though it was out of warranty, Comptech sent a replacement blower. When the original blower was removed, inside the intake manifold was a very fine layer of aluminum grit. Flip the blower over and it was evident the rotors were rubbing into the aluminum housing. The only way this could’ve happened is bearing failure, allowing the rotors to axially “float” instead of being fixed into position like they are supposed to be. Thus the source of the squealing noise.
The owner called an expert and he said before installing the replacement blower to perform a compression test and a leakdown test on the engine. Both tests failed.....not surprising considering that the engine had been inhaling aluminum grit for some time. The owner wrote Comptech a letter asking for assistance with engine repairs that the two tests proved was needed. The owner was told that Comptech would not pay for repairs to engine damage.
One month later the car was dyno’ed and the car was down on power about 20 HP. Again, not very surprising since compression was low because of the grit. Pondering the options, the owner (after consulting with one or two experts) decided that the damage is done but won’t get any worse so just drive the car with twenty less horsepower.
The next day driving 70 MPH the replacement supercharger seized. Two superchargers seizing on the same car within a month of each other. Well, surely it must be the owner / his mechanic / his car. When the owner stated that a Comptech-authorized technician installed the original blower and the replacement, they changed their tune…somewhat "blaming" the car as a jinx.
Unlike the first seized blower that had no loose pieces of metal, there were small bits of metal that did come from the second seized blower. Just like the first seizure, it was checked to ensure the factory air filter was not breached. It was in perfect condition. But that is good news and bad news. The good news is that it can be eliminated a foreign object like a rock being sucked up from the road. The bad news is that the only place the foreign metal could’ve come from is the engine. But how? If the inlet is filtered and the blower outlet feeds into the engine, how could metal be coming from the engine? More on this in a sec.
Unlike the first blower that Comptech sent to the owner then the owner returned the bad one, the owner had to ship them the blower for investigation before they would decide anything. Comptech did prefaced this by mentioning "valve guide failure" as a possibility even before seeing the unit. Upon receipt of the unit and the metal pieces, they called the owner back and confirmed the pieces were valve guide fragments. With this ruling / conclusion, Comptech’s position was that a foreign object entered their blower and they would not cover this one. The owner e-mailed an expert pictures of the metal pieces and he said that it looked like they could be valve guide bits. Sticking a finger into one of the intake runners, sure enough the owner could feel that pieces of one of the valve guides broke off. But how did they go up when air and gravity cause objects to go down into the engine? More on this in a sec.
Upon teardown of the engine all six cylinders were badly scorn by the aluminum grit caused by the original blower. Also, it was evident where pieces of debris larger than just fine grit had impacted the top of the pistons. Could this have been valve guides or pieces of the two seized blower? Who knows?
Let’s put all of this aside and solve the problem of the foreign object. There is a conceivable manner in which broken valve guide could get into the blower inlet. It’s a stretch, but read along. At the exact instant the valve guide breaks off, the intake valve is going closed. As the debris falls down, the valve is coming up, meets the debris and impacts it into the opposite direction with enough force to knock it up the intake runner into the bottom of the intake manifold. Given the light mass of the debris falling down onto a valve with substantially more mass which is traveling much faster than the rate at which the debris is falling, this is entirely possible. Probable? Not particularly good odds. Possible? Yes. That explains how the debris ended up in the bottom of the manifold but not how it gets from the manifold to the inlet side of the blower? All supercharger kits have some sort of boost divert valve so that boost is not fed into the engine while it is at steady-state driving such as cruise control on the highway. The CTSC boost valve diverts to the throttle body inlet in a completely close loop system. The boost valve closes as manifold pressure rises and the forced induction begins, and is controlled by a small rubber vacuum line that senses boost within the intake manifold chamber. Guess where this boost divert valve is on the CTSC? You got it.....on the bottom of the intake manifold that is the absolute lowest part of the chamber. Remember how mechanically the debris was knocked into the manifold? Well from here it gets sucked into the throttle body by vacuum. Driving around, the vibrations will eventually “rattle” the debris to the opening of the boost divert valve connection. Under hard deceleration it is possible for the engine to create enough manifold vacuum to suck the small debris up the bypass tube through the throttle body and right into the entrance of the blower. This is exactly how the scratches on seized blower #2 indicate the debris traveled, ultimately lodging into the rotors.
This theory of what happened is sound but very difficult to prove. The owner has talked with four different lawyers and they all said it would be a tough case since there is no substantial evidence and it boiled down to (a) did the blower hurt the engine or (b) did the engine hurt the blower or (c) did the engine hurt the blower because the blower hurt the engine or (d) did the blower hurt the engine because the engine hurt the blower. Go against Comptech and their contention is that regardless of which of the above four, they were kind enough to provide the first replacement blower which was out of warranty so there is no way they are obligated for engine repair cost. Go against Acura and they will say that the increased heat from a blower thermally stressed (aftercooler is a good thing to have on an FI’ed engine) the valve guide and it failed at a temperature it was not designed for. Besides that, the engine was modified, which is a warranty no-no as far as they are concerned. Either way the owner was stuck with the repair bill. Caveat emptor.....how fitting.
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