LSA/LS9 S/C Shaft Wear - Engineering Response
11-23-2009, 02:40 PM
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LSA/LS9 S/C Shaft Wear - Engineering Response I’m Ed Piatek and I’m the Program Engineering Manager on the CTS-V. I recognize that this forum represents the thoughts and experiences of some very passionate owners and enthusiasts, and appropriately many of us on the engineering team periodically review this and other forums to keep our finger on the pulse of this important group.
While we cannot respond or comment on every post or question, the number of comments and degree of inaccurate information around supercharger shaft wear on LSA and LS9 merits an engineering response to set the record straight, and assuage any concerns of our owners. Here is the response from our engine experts:
The torsional isolator is used in the CTSv LSA and ZR-1 LS9 engine to isolate potential gear rattle noise during idle. The isolator contains a torsional spring that fits over the shaft. Purpose of the shaft is to distribute the stresses in the torsional spring. As the spring goes thru its travel, the inside of the coils can contact the shaft. The spring material is intentionally harder than the shaft which by design results in visual witness marks and/or limited wear on the shaft. The witness marks and/or limited wear is expected and has been observed on all the Eaton component durability tests, GM engine and vehicle durability tests and on customer vehicles with no impact on the functionality of the spring and isolator. The shaft and isolator are in a sealed cavity, separate from the rest of the supercharger and engine.
Q: Will this shaft wear harm my engine?
A: No. The visible wear will not damage the engine. The supercharger and the engine were tested and successfully validated to meet all GM durability requirements…which are much more severe than any customer usage.
Q: What causes this wear?
A: The isolator contains a torsional spring that fits over the shaft. The purpose of the shaft is to better distribute the stresses in the torsional spring and prolong its life. As the spring goes thru its travel, the inside of the coils can contact the shaft. The spring is a harder material than the shaft…so that when there is contact, the spring will not potentially break. If the spring breaks, then the torsional isolator function is lost.
Q: Can the shaft wear all the way thru and broken pieces get into my engine?
A: No. The travel on the spring that is contacting the shaft is limited. It cannot wear all the way thru the shaft. The shaft and isolator are in a sealed cavity, separate from the rest of the supercharger and engine. It cannot be ingested into the engine.
Q: Can worn bits or wear debris from the shaft get into my engine?
A: No. Again, the torsional isolator is in a SEALED cavity inside the supercharger. The seals on the bearings have not been compromised and wear debris is fully contained in this cavity.
Q: Why is the isolator design better than a solid coupling?
A: The torsional isolator does precisely that – it isolates an even more objectionable gear rattle noise that was being heard inside the vehicle cabin at all times during idle. The solid coupling will not eliminate this noise.
Q: My car is now quiet after I replaced the isolator w/ a solid coupling…how do you explain that?
A: If the ONLY modification was the replacement of the isolator w/ solid coupling…then it’s unlikely that it’s completely quiet. Most likely, you WILL have the timing gear rattle noise inside the cabin. Initially, it may sound better because the random “knocking” noise outside the vehicle is reduced…but you’ve now traded that noise for the gear rattle noise. Now…if you also replaced the induction system and exhaust system w/ louder aftermarket/performance parts…then it’s no longer an accurate comparison because you may not hear gear rattle over the increased exhaust and other noises in the cabin at idle. By the way, the torsional isolator is not a serviceable part…and removing the front inlet to replace with another part has warranty implications.
Q: Will GM be releasing a service fix for the shaft wear?
A: No. The current torsional isolator design does not diminish or compromise the durability or longevity of the supercharger or the engine. It has been fully validated to that effect. It also provides a benefit to the customer in terms of reduced noise at idle inside the vehicle…where the driver and passengers will be located during vehicle operation.
While we cannot respond or comment on every post or question, the number of comments and degree of inaccurate information around supercharger shaft wear on LSA and LS9 merits an engineering response to set the record straight, and assuage any concerns of our owners. Here is the response from our engine experts:
The torsional isolator is used in the CTSv LSA and ZR-1 LS9 engine to isolate potential gear rattle noise during idle. The isolator contains a torsional spring that fits over the shaft. Purpose of the shaft is to distribute the stresses in the torsional spring. As the spring goes thru its travel, the inside of the coils can contact the shaft. The spring material is intentionally harder than the shaft which by design results in visual witness marks and/or limited wear on the shaft. The witness marks and/or limited wear is expected and has been observed on all the Eaton component durability tests, GM engine and vehicle durability tests and on customer vehicles with no impact on the functionality of the spring and isolator. The shaft and isolator are in a sealed cavity, separate from the rest of the supercharger and engine.
Q: Will this shaft wear harm my engine?
A: No. The visible wear will not damage the engine. The supercharger and the engine were tested and successfully validated to meet all GM durability requirements…which are much more severe than any customer usage.
Q: What causes this wear?
A: The isolator contains a torsional spring that fits over the shaft. The purpose of the shaft is to better distribute the stresses in the torsional spring and prolong its life. As the spring goes thru its travel, the inside of the coils can contact the shaft. The spring is a harder material than the shaft…so that when there is contact, the spring will not potentially break. If the spring breaks, then the torsional isolator function is lost.
Q: Can the shaft wear all the way thru and broken pieces get into my engine?
A: No. The travel on the spring that is contacting the shaft is limited. It cannot wear all the way thru the shaft. The shaft and isolator are in a sealed cavity, separate from the rest of the supercharger and engine. It cannot be ingested into the engine.
Q: Can worn bits or wear debris from the shaft get into my engine?
A: No. Again, the torsional isolator is in a SEALED cavity inside the supercharger. The seals on the bearings have not been compromised and wear debris is fully contained in this cavity.
Q: Why is the isolator design better than a solid coupling?
A: The torsional isolator does precisely that – it isolates an even more objectionable gear rattle noise that was being heard inside the vehicle cabin at all times during idle. The solid coupling will not eliminate this noise.
Q: My car is now quiet after I replaced the isolator w/ a solid coupling…how do you explain that?
A: If the ONLY modification was the replacement of the isolator w/ solid coupling…then it’s unlikely that it’s completely quiet. Most likely, you WILL have the timing gear rattle noise inside the cabin. Initially, it may sound better because the random “knocking” noise outside the vehicle is reduced…but you’ve now traded that noise for the gear rattle noise. Now…if you also replaced the induction system and exhaust system w/ louder aftermarket/performance parts…then it’s no longer an accurate comparison because you may not hear gear rattle over the increased exhaust and other noises in the cabin at idle. By the way, the torsional isolator is not a serviceable part…and removing the front inlet to replace with another part has warranty implications.
Q: Will GM be releasing a service fix for the shaft wear?
A: No. The current torsional isolator design does not diminish or compromise the durability or longevity of the supercharger or the engine. It has been fully validated to that effect. It also provides a benefit to the customer in terms of reduced noise at idle inside the vehicle…where the driver and passengers will be located during vehicle operation.
11-23-2009, 06:32 PM
#2
Thanks for the insight ED, and also thanks for willing to create a thread to address it to those outside of GM. It goes a long way to letting people rest easy if they ever had a concern.
