What is this grinding noise at startup?
10-01-2012, 03:03 PM
#16
Race Car
10-01-2012, 04:32 PM
#17
Addict
Rennlist Member
Rennlist Member
Dell,
I think the sound comes from the side muffler valves (the ones bypassed by the Sport button). For these valves to be closed (quiet sound), they need 12v current on the solenoids and vacuum pressure to push the actuator rods and keep the valves closed.
There is a small amount of vacuum pressure left in the car when the car is no longer running, but after a long while this pressure is almost nil. When you startup the car, the solenoids are receiving a 12v signal, and send vacuum to the actuators which would push the rods and close the valves. While enough vacuum is being built, the rods don't have enough pressure to close the valves, and it is on this transition where the exhaust gases can make the valves shake (flapping valves) creating this grinding sound, as soon as enough vacuum pressure is built, the actuator rods fully push the valves closed.
A 996 GT3 would not make this sound, because it uses a traditional muffler.
When the 997.1 and 997.2 engines are started, these valves are in open position (the rods are not pushing the exhaust valves closed), and as soon as the car build vacuum pressure( less than 2-3 seconds), the solenoids have enough pressure to push the rods and close the valves.
It would be easy to test, put metal wire around the two valves if the car has been sitting for a long time, and start it up, that transition sound should not be there.
By the way, my Fiat had a very similar noise, it uses the same brand solenoids used by VW in the 997 Aero Beetles. The sound went away when I switched to a custom muffler that eliminates the valves. Recently I went back to a valved muffler, and the sound just came back.
I think the sound comes from the side muffler valves (the ones bypassed by the Sport button). For these valves to be closed (quiet sound), they need 12v current on the solenoids and vacuum pressure to push the actuator rods and keep the valves closed.
There is a small amount of vacuum pressure left in the car when the car is no longer running, but after a long while this pressure is almost nil. When you startup the car, the solenoids are receiving a 12v signal, and send vacuum to the actuators which would push the rods and close the valves. While enough vacuum is being built, the rods don't have enough pressure to close the valves, and it is on this transition where the exhaust gases can make the valves shake (flapping valves) creating this grinding sound, as soon as enough vacuum pressure is built, the actuator rods fully push the valves closed.
A 996 GT3 would not make this sound, because it uses a traditional muffler.
When the 997.1 and 997.2 engines are started, these valves are in open position (the rods are not pushing the exhaust valves closed), and as soon as the car build vacuum pressure( less than 2-3 seconds), the solenoids have enough pressure to push the rods and close the valves.
It would be easy to test, put metal wire around the two valves if the car has been sitting for a long time, and start it up, that transition sound should not be there.
By the way, my Fiat had a very similar noise, it uses the same brand solenoids used by VW in the 997 Aero Beetles. The sound went away when I switched to a custom muffler that eliminates the valves. Recently I went back to a valved muffler, and the sound just came back.
10-01-2012, 04:38 PM
#18
Rennlist Member
^^ Sounds like the answer.
10-01-2012, 04:55 PM
#19
Nordschleife Master
Thread Starter
Dell,
I think the sound comes from the side muffler valves (the ones bypassed by the Sport button). For these valves to be closed (quiet sound), they need 12v current on the solenoids and vacuum pressure to push the actuator rods and keep the valves closed.
There is a small amount of vacuum pressure left in the car when the car is no longer running, but after a long while this pressure is almost nil. When you startup the car, the solenoids are receiving a 12v signal, and send vacuum to the actuators which would push the rods and close the valves. While enough vacuum is being built, the rods don't have enough pressure to close the valves, and it is on this transition where the exhaust gases can make the valves shake (flapping valves) creating this grinding sound, as soon as enough vacuum pressure is built, the actuator rods fully push the valves closed.
A 996 GT3 would not make this sound, because it uses a traditional muffler.
When the 997.1 and 997.2 engines are started, these valves are in open position (the rods are not pushing the exhaust valves closed), and as soon as the car build vacuum pressure( less than 2-3 seconds), the solenoids have enough pressure to push the rods and close the valves.
It would be easy to test, put metal wire around the two valves if the car has been sitting for a long time, and start it up, that transition sound should not be there.
By the way, my Fiat had a very similar noise, it uses the same brand solenoids used by VW in the 997 Aero Beetles. The sound went away when I switched to a custom muffler that eliminates the valves. Recently I went back to a valved muffler, and the sound just came back.
I think the sound comes from the side muffler valves (the ones bypassed by the Sport button). For these valves to be closed (quiet sound), they need 12v current on the solenoids and vacuum pressure to push the actuator rods and keep the valves closed.
There is a small amount of vacuum pressure left in the car when the car is no longer running, but after a long while this pressure is almost nil. When you startup the car, the solenoids are receiving a 12v signal, and send vacuum to the actuators which would push the rods and close the valves. While enough vacuum is being built, the rods don't have enough pressure to close the valves, and it is on this transition where the exhaust gases can make the valves shake (flapping valves) creating this grinding sound, as soon as enough vacuum pressure is built, the actuator rods fully push the valves closed.
A 996 GT3 would not make this sound, because it uses a traditional muffler.
When the 997.1 and 997.2 engines are started, these valves are in open position (the rods are not pushing the exhaust valves closed), and as soon as the car build vacuum pressure( less than 2-3 seconds), the solenoids have enough pressure to push the rods and close the valves.
It would be easy to test, put metal wire around the two valves if the car has been sitting for a long time, and start it up, that transition sound should not be there.
By the way, my Fiat had a very similar noise, it uses the same brand solenoids used by VW in the 997 Aero Beetles. The sound went away when I switched to a custom muffler that eliminates the valves. Recently I went back to a valved muffler, and the sound just came back.
10-01-2012, 05:20 PM
#20
Admin
Lifetime Rennlist
Member
Lifetime Rennlist
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Dell,
I think the sound comes from the side muffler valves (the ones bypassed by the Sport button). For these valves to be closed (quiet sound), they need 12v current on the solenoids and vacuum pressure to push the actuator rods and keep the valves closed.
There is a small amount of vacuum pressure left in the car when the car is no longer running, but after a long while this pressure is almost nil. When you startup the car, the solenoids are receiving a 12v signal, and send vacuum to the actuators which would push the rods and close the valves. While enough vacuum is being built, the rods don't have enough pressure to close the valves, and it is on this transition where the exhaust gases can make the valves shake (flapping valves) creating this grinding sound, as soon as enough vacuum pressure is built, the actuator rods fully push the valves closed.
A 996 GT3 would not make this sound, because it uses a traditional muffler.
When the 997.1 and 997.2 engines are started, these valves are in open position (the rods are not pushing the exhaust valves closed), and as soon as the car build vacuum pressure( less than 2-3 seconds), the solenoids have enough pressure to push the rods and close the valves.
It would be easy to test, put metal wire around the two valves if the car has been sitting for a long time, and start it up, that transition sound should not be there.
By the way, my Fiat had a very similar noise, it uses the same brand solenoids used by VW in the 997 Aero Beetles. The sound went away when I switched to a custom muffler that eliminates the valves. Recently I went back to a valved muffler, and the sound just came back.
I think the sound comes from the side muffler valves (the ones bypassed by the Sport button). For these valves to be closed (quiet sound), they need 12v current on the solenoids and vacuum pressure to push the actuator rods and keep the valves closed.
There is a small amount of vacuum pressure left in the car when the car is no longer running, but after a long while this pressure is almost nil. When you startup the car, the solenoids are receiving a 12v signal, and send vacuum to the actuators which would push the rods and close the valves. While enough vacuum is being built, the rods don't have enough pressure to close the valves, and it is on this transition where the exhaust gases can make the valves shake (flapping valves) creating this grinding sound, as soon as enough vacuum pressure is built, the actuator rods fully push the valves closed.
A 996 GT3 would not make this sound, because it uses a traditional muffler.
When the 997.1 and 997.2 engines are started, these valves are in open position (the rods are not pushing the exhaust valves closed), and as soon as the car build vacuum pressure( less than 2-3 seconds), the solenoids have enough pressure to push the rods and close the valves.
It would be easy to test, put metal wire around the two valves if the car has been sitting for a long time, and start it up, that transition sound should not be there.
By the way, my Fiat had a very similar noise, it uses the same brand solenoids used by VW in the 997 Aero Beetles. The sound went away when I switched to a custom muffler that eliminates the valves. Recently I went back to a valved muffler, and the sound just came back.
https://rennlist.com/forums/996-gt2-...le-on-gt3.html
We have to wait for the 991 cars to stop the terrible noise from the obsolete Mezger engines.
Dell I heard your clip, it's the normal noise probably coming from the tensioners..
At one point I had an email exchange on this issue with a UK friend and he brought up the Variocam theory. Basically the revised system of the 7 cars enhances the cold start noise when the car is sitting for a long time and the oil dries up and loses pressure.
You can read a short version courtesy of Pistonheads.com
"GT3 start-up rattle
Aside from chain tensioner and chain drive noises on start-up (similar to the other versions of the engine type) the GT3 engine uses 'Variocam' - a system that enables active adjustment of valve overlap by changing the position of the Inlet camshaft in relation to the Crankshaft and Exhaust camshaft. The electro-hydraulic system on the inlet camshaft sprocket has oil pressure fed to both sides of the sprocket element to fix it in place; adjustment is effected by changing the pressure on either side of the sprocket to rotate the element (left or right).
On the 9x6 and 9x7 models with second generation Variocam the sprocket is mechanically fixed until oil pressure builds and takes over sprocket control after start-up and it is from here that the noise emanates - In the GT3, the sprocket element isn't fixed so as the engine is cranked the sprocket is free move in its designed adjustment range (stop to stop / rotationally left to right) - as the cam loads against the next set of valves to open the camshaft moves to its 'left stop' (potentially with a 'clack'), as the engine continues to rotate the camshaft reaches peak valve lift and the lobes begin to ramp back off of the valves; at this point, because the sprocket isn't at full tension / pressure, the camshaft is helped round by the valve spring pressure and can rotate to its 'right stop' (potentially with a 'clack' - see where this is going??)
As oil pressure builds (almost instantly) the 'clack, clack' sound is lessened to eventual 'silence' (maybe not the right word!!)
Depending on the oil temp, how long the engine has been left to stand, the position of the cams when the engine was last stopped etc the noise is more or less apparent - in no way does the noise suggest a fault, more just a characteristic of the system.
I have seen one case on a Mk1 GT3 where the oil valve in the camshaft housing worked loose which allowed faster pressure loss / loss of oil retention once the engine was stopped (the valve could not have failed completely but the relative movement around where the valve should have been fixed was enough to make the above noises more prevalent)."
Aside from chain tensioner and chain drive noises on start-up (similar to the other versions of the engine type) the GT3 engine uses 'Variocam' - a system that enables active adjustment of valve overlap by changing the position of the Inlet camshaft in relation to the Crankshaft and Exhaust camshaft. The electro-hydraulic system on the inlet camshaft sprocket has oil pressure fed to both sides of the sprocket element to fix it in place; adjustment is effected by changing the pressure on either side of the sprocket to rotate the element (left or right).
On the 9x6 and 9x7 models with second generation Variocam the sprocket is mechanically fixed until oil pressure builds and takes over sprocket control after start-up and it is from here that the noise emanates - In the GT3, the sprocket element isn't fixed so as the engine is cranked the sprocket is free move in its designed adjustment range (stop to stop / rotationally left to right) - as the cam loads against the next set of valves to open the camshaft moves to its 'left stop' (potentially with a 'clack'), as the engine continues to rotate the camshaft reaches peak valve lift and the lobes begin to ramp back off of the valves; at this point, because the sprocket isn't at full tension / pressure, the camshaft is helped round by the valve spring pressure and can rotate to its 'right stop' (potentially with a 'clack' - see where this is going??)
As oil pressure builds (almost instantly) the 'clack, clack' sound is lessened to eventual 'silence' (maybe not the right word!!)
Depending on the oil temp, how long the engine has been left to stand, the position of the cams when the engine was last stopped etc the noise is more or less apparent - in no way does the noise suggest a fault, more just a characteristic of the system.
I have seen one case on a Mk1 GT3 where the oil valve in the camshaft housing worked loose which allowed faster pressure loss / loss of oil retention once the engine was stopped (the valve could not have failed completely but the relative movement around where the valve should have been fixed was enough to make the above noises more prevalent)."
Best,
John
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Robocop305 (01-19-2023)
10-01-2012, 06:54 PM
#23
Nordschleife Master
Dell,
I think the sound comes from the side muffler valves (the ones bypassed by the Sport button). For these valves to be closed (quiet sound), they need 12v current on the solenoids and vacuum pressure to push the actuator rods and keep the valves closed.
There is a small amount of vacuum pressure left in the car when the car is no longer running, but after a long while this pressure is almost nil. When you startup the car, the solenoids are receiving a 12v signal, and send vacuum to the actuators which would push the rods and close the valves. While enough vacuum is being built, the rods don't have enough pressure to close the valves, and it is on this transition where the exhaust gases can make the valves shake (flapping valves) creating this grinding sound, as soon as enough vacuum pressure is built, the actuator rods fully push the valves closed.
A 996 GT3 would not make this sound, because it uses a traditional muffler.
When the 997.1 and 997.2 engines are started, these valves are in open position (the rods are not pushing the exhaust valves closed), and as soon as the car build vacuum pressure( less than 2-3 seconds), the solenoids have enough pressure to push the rods and close the valves.
It would be easy to test, put metal wire around the two valves if the car has been sitting for a long time, and start it up, that transition sound should not be there.
By the way, my Fiat had a very similar noise, it uses the same brand solenoids used by VW in the 997 Aero Beetles. The sound went away when I switched to a custom muffler that eliminates the valves. Recently I went back to a valved muffler, and the sound just came back.
I think the sound comes from the side muffler valves (the ones bypassed by the Sport button). For these valves to be closed (quiet sound), they need 12v current on the solenoids and vacuum pressure to push the actuator rods and keep the valves closed.
There is a small amount of vacuum pressure left in the car when the car is no longer running, but after a long while this pressure is almost nil. When you startup the car, the solenoids are receiving a 12v signal, and send vacuum to the actuators which would push the rods and close the valves. While enough vacuum is being built, the rods don't have enough pressure to close the valves, and it is on this transition where the exhaust gases can make the valves shake (flapping valves) creating this grinding sound, as soon as enough vacuum pressure is built, the actuator rods fully push the valves closed.
A 996 GT3 would not make this sound, because it uses a traditional muffler.
When the 997.1 and 997.2 engines are started, these valves are in open position (the rods are not pushing the exhaust valves closed), and as soon as the car build vacuum pressure( less than 2-3 seconds), the solenoids have enough pressure to push the rods and close the valves.
It would be easy to test, put metal wire around the two valves if the car has been sitting for a long time, and start it up, that transition sound should not be there.
By the way, my Fiat had a very similar noise, it uses the same brand solenoids used by VW in the 997 Aero Beetles. The sound went away when I switched to a custom muffler that eliminates the valves. Recently I went back to a valved muffler, and the sound just came back.
same noise
10-01-2012, 07:02 PM
#24
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So glad to hear LVDell's account of the grinding noise during start-up. Have the same issue when my .2 GT3 is parked for the entire week.
I must admit that the intermittent smoke and grinding noise during cold start is not fun and down right embarrassing.
Thanks to NJ-GT and 911Slow for the possible explanations. So it's fair to assume this comes with the territory and should be classified under behaves as expected?
I must admit that the intermittent smoke and grinding noise during cold start is not fun and down right embarrassing.
Thanks to NJ-GT and 911Slow for the possible explanations. So it's fair to assume this comes with the territory and should be classified under behaves as expected?
10-01-2012, 07:51 PM
#27
Rennlist Member
When the car sits for an extended period of time, the hyrdraluic chain tentioners bleed down a bit.
wait, that was all in the quoted piece from pistonheads in your post
Nevermind...
I recall having the power to delete a post in the past... seems to be gone now.
Last edited by MarkD; 10-01-2012 at 08:06 PM.
10-01-2012, 08:41 PM
#28
Rennlist Member
My car sits for weeks at a time and I do not have the bees in a can sound. Getting close to 30k on the clock and it's been quiet to this day. Hmmm, maybe something is wrong with my car.
10-02-2012, 06:54 AM
#30
Intermediate
If you listen closely you'll hear the rattle just as the oil pressure starts to come up. I decided over the years that the rattle must be air purging from the oil galleries. It's probably making the oil pressure regulator internals rattle as the air passes through.