Persistent Rattle, need expert
12-07-2016, 02:35 PM
#1
Thread Starter
Persistent Rattle, need expert
Hello again.
I'm looking for experienced insight again. I've done everything obvious, and I'll list everything I've already done to moving parts in the engine bay below. I'll try to be very thorough, but I've done a lot of work on this car, and I'm going to leave out unnecessary lists..
This issue happens when starting from a dead stop. In reverse or first, as I let the clutch out, and let the RPM's drop, a loud, hollow rattling / knocking starts, and gets louder as the revs drop further. The rhythm matches RPM. I'm not talking about stalling, I'm talking about 800 ~ 1100 RPM. If I keep the revs up (1200 - 1500) and slip the clutch, there will be no noise, but the less I slip the clutch, the louder the noise is. The noise does not happen while moving in any gear, unless I let the revs drop below 1100 (think rolling in gear near idle in stop&go traffic.) Related: when the car is rolling in gear, if I get on or off the gas, I can hear a faint, single, "clunk"
What I know:
The noise is from the engine bay.
The engine consumes no oil and runs fine throughout the entire rev band and power band. VTEC works just fine.
No compression or leakdown problems, all sensors function. The MAP sensor is pre-TSB and I should replace it but I believe it's unrelated
I ran the car on a Dyno Dynamics dyno, and there's an odd "bump" on my dyno plot which moves with varying loading, gearing, temp, and time. I believe it's clutch slip. There's some variation in the road speed/RPM graph.
I do have clutch buzz, and a little bit of discernable clutch drag at low/mid-RPM.
It's a bone-stock '03 AP1, and basically everything is original factory parts. It is abundantly clear to me that the previous owner never replaced anything under the hood except oil.
The shifter shakes quite a lot when on the gas. Seems like more than should be normal.
What I've found so far:
Idler pulley bad bearings - replaced
Tensioner pulley assembly binding and bad bearings - assembly replaced
Couldn't feel any other bad bearings in accessory drive, but I know that AC compressor just starting to go bad. I do not believe it's related. The issue happens regardless of whether the AC clutch is engaged. The AC compressor makes a bit of a gravel-in-a-coffee-grinder noise when it's running at idle, and drags the idle down a bit, but not audible at higher speed/rev...
TCT replaced, but I think it's the wrong noise for TCT, and replacing the TCT with a Billman unit didn't change the noise.
Valves adjusted to spec. Not too tight. Valvetrain sounds excellent.
Mounts are not leaking fluid, but they are very old
I can't see anything on the engine or trans hitting any part of the car, and I can't feel anything tapping on the frame, though I won't rule it out.
Theories of mine from best to worst:
1. Some sort of clutch chatter... Maybe the clutch disk hub springs are so old and shot that they're rapidly/repeatedly bottoming out when loaded at very low RPM. At higher RPM / load they stay bottomed out, causing the transmission to shake more than normal.
2. More bad bearings in accessory drive, specifically the water pump.. I can't load them sufficiently by hand to feel it, but the shuddering of low RPM is causing classic pulley alignment wobble and the associated noise. Can't be the alternator because it has front and rear bearings and spins too fast to make a noise with a frequency this low. Besides, the alternator is making its own paper-in-the-wind bearing whirr-noise and I'm going to have to rebuild it.
3. I can't see the mounts leaking because they already leaked dry years ago, they're slopping around like a wet noodle (dry noodle?), and something is hitting something... I doubt this one.
4. It's a normal S2000 noise and I'm worrying about nothing.
I'm in Miami, but I will drive this car all the way to Billman in NY if I have to.
I'm looking for experienced insight again. I've done everything obvious, and I'll list everything I've already done to moving parts in the engine bay below. I'll try to be very thorough, but I've done a lot of work on this car, and I'm going to leave out unnecessary lists..
This issue happens when starting from a dead stop. In reverse or first, as I let the clutch out, and let the RPM's drop, a loud, hollow rattling / knocking starts, and gets louder as the revs drop further. The rhythm matches RPM. I'm not talking about stalling, I'm talking about 800 ~ 1100 RPM. If I keep the revs up (1200 - 1500) and slip the clutch, there will be no noise, but the less I slip the clutch, the louder the noise is. The noise does not happen while moving in any gear, unless I let the revs drop below 1100 (think rolling in gear near idle in stop&go traffic.) Related: when the car is rolling in gear, if I get on or off the gas, I can hear a faint, single, "clunk"
What I know:
The noise is from the engine bay.
The engine consumes no oil and runs fine throughout the entire rev band and power band. VTEC works just fine.
No compression or leakdown problems, all sensors function. The MAP sensor is pre-TSB and I should replace it but I believe it's unrelated
I ran the car on a Dyno Dynamics dyno, and there's an odd "bump" on my dyno plot which moves with varying loading, gearing, temp, and time. I believe it's clutch slip. There's some variation in the road speed/RPM graph.
I do have clutch buzz, and a little bit of discernable clutch drag at low/mid-RPM.
It's a bone-stock '03 AP1, and basically everything is original factory parts. It is abundantly clear to me that the previous owner never replaced anything under the hood except oil.
The shifter shakes quite a lot when on the gas. Seems like more than should be normal.
What I've found so far:
Idler pulley bad bearings - replaced
Tensioner pulley assembly binding and bad bearings - assembly replaced
Couldn't feel any other bad bearings in accessory drive, but I know that AC compressor just starting to go bad. I do not believe it's related. The issue happens regardless of whether the AC clutch is engaged. The AC compressor makes a bit of a gravel-in-a-coffee-grinder noise when it's running at idle, and drags the idle down a bit, but not audible at higher speed/rev...
TCT replaced, but I think it's the wrong noise for TCT, and replacing the TCT with a Billman unit didn't change the noise.
Valves adjusted to spec. Not too tight. Valvetrain sounds excellent.
Mounts are not leaking fluid, but they are very old
I can't see anything on the engine or trans hitting any part of the car, and I can't feel anything tapping on the frame, though I won't rule it out.
Theories of mine from best to worst:
1. Some sort of clutch chatter... Maybe the clutch disk hub springs are so old and shot that they're rapidly/repeatedly bottoming out when loaded at very low RPM. At higher RPM / load they stay bottomed out, causing the transmission to shake more than normal.
2. More bad bearings in accessory drive, specifically the water pump.. I can't load them sufficiently by hand to feel it, but the shuddering of low RPM is causing classic pulley alignment wobble and the associated noise. Can't be the alternator because it has front and rear bearings and spins too fast to make a noise with a frequency this low. Besides, the alternator is making its own paper-in-the-wind bearing whirr-noise and I'm going to have to rebuild it.
3. I can't see the mounts leaking because they already leaked dry years ago, they're slopping around like a wet noodle (dry noodle?), and something is hitting something... I doubt this one.
4. It's a normal S2000 noise and I'm worrying about nothing.
I'm in Miami, but I will drive this car all the way to Billman in NY if I have to.
Last edited by Spartarus; 12-07-2016 at 03:40 PM.
12-07-2016, 07:02 PM
#2
Post a vid, or I can help you out, at least get a good listen and point you in the right direction.
12-07-2016, 08:20 PM
#3
Thread Starter
It's plenty loud, but I can't get my cell phone to pick the frequency out from ambient. Engine noise washes out the entire low range..
I'm around Miami all day tomorrow.
I'm around Miami all day tomorrow.
07-25-2019, 12:11 AM
#5
Take a look at your motor mounts, make sure they are not ripped, When I replaced my damaged engine mounts it fixed a lot of issues with noises from stopping and accelerating, going over bumps and gear shift shaking to name a few.
Thread
Thread Starter
Forum
Replies
Last Post
