IMSF8

I had the engine in my Cayman S rebuilt two years (and 2,500 miles) ago to address incipient IMS bearing and bore scoring problems. I started to hear ticking on clutch depression soon after I got the car back but I attributed it to the new flywheel and clutch. The noise has gradually increased since and I'd like to identify the source.

The usual suspects in a case like this are the clutch release bearing and the crankshaft thrust bearing. It can't be the former because I just replaced the clutch and flywheel (again) and the latter seems very unlikely because the crank endplay is within spec.

Here are my observations. I should warn you that hypotheses come to this problem to die!

• Ticking / rattling are only audible when the clutch is depressed
• Degree of clutch engagement doesn't matter
• Clutch switch doesn't matter (I bypassed it)
• The noise isn't observed when the engine is cold. It only begins after a few minutes.
• The ticking is periodic at the camshaft frequency suggesting it's associated with a single valve and not a piston
• The amplitude of the noise is variable and sounds somewhat like a rock tumbling in a tin can!
• The amplitude of the noise is variable over long timescales as well and sometimes I don't hear it
• Sudden deceleration (front or back) and front/back inclination on a steep hill make no difference

I've attached two audio files. The first one (Pside) begins with the clutch depressed. The noise is very audible until the clutch is released about 2/3rds of the way through. The other is the rough restart I've noticed when the car is warm (in case it's related).

The aspect of this problem I have the hardest time reconciling with is its connection to the clutch. I've considered four possibilities:

1. Inertia - Depressing the clutch disconnects the transmission and reduces the total moment of inertia
2. Slip - The release and pilot bearings slip when the clutch is depressed instead of simply spinning [X - clutch replaced]
3. Force - Force applied to the clutch goes to the crankshaft through the housing and flywheel
4. Pressure - The hydraulic clutch line stiffens when the clutch is depressed

What am I missing? Maybe force increases the oil flow through the thrust bearing causing a marginal valve lifter to stick?

I think the answer is in the unusual sound of the ticking. I hope someone here has heard this before!

Waveform of the ticking in the time domain after applying a high-pass filter

-Rick

harveyf

Wow!
Uh, welcome to Rennlist. That is one impressive 3rd post. I'm guessing you might be a scientist
I'm going to tag @KevinGross (our resident transmission expert) as he may spot your problem without breaking a sweat but it is indeed a curious set of circumstances.
What year is the car?

Not that you haven't supplied more clues than most but have you poked around with a mechanics stethescope to see if you can better isolate where the noise is coming from? While you are doing that, I would check all the bolts that attach the bellhousing and I would check the bolts that attach the clutch slave. The thinking is that with 2500 miles on your rebuild, something fastener wise may be coming loose.

IMSF8

Harvey,

Thanks for your comments! In fact I am an engineer and I've always loved unraveling hard technical problems.

I appreciate your tagging Kevin. The owner of the shop that did my rebuild also suspects the transmission. I've been looking elsewhere because the transmission is static when the clutch is depressed.

My car is a 2006 Cayman S, originally 3.4L and now 3.8.

My great regular mechanic (Dan Heinrichs, owner of RMG Enterprises) tried to locate the noise with a stethoscope but it sounded like it was coming from everywhere. I had expected it to come from the transmission housing around the clutch, but to my untrained ears it sounded loudest near the passenger side cylinder head (bank 1-2-3). Another way to locate the source would be to measure relative time delays with a set of accelerometers mounted in various positions on the engine casing with something like this: https://www.tequipment.net/Extech/VB...r/#description. I may try to rent one of these.

Something I forgot to mention before is that none of these problems are apparent in normal driving. I only hear the noise when the car is stopped with the clutch depressed. If I lived in a rural area, free from the scourge of traffic lights, I might not even notice it!

-Rick

KevinGross

Hmmm... so the problem occurs when you're pressing the clutch pedal, but no noise if your foot is off the pedal. A few suggestions, but no certainty as to the issue. I'd begin by making sure the bolts connecting the transmission to the engine are all tight. I would want to check the clutch release: the t/o bearing, the release lever, the "intermediate piece" the lever pivots on, and the clutch slave bolt fastening it to the transmission.

IMSF8

Kevin: Thanks for looking at this. I kept the all the part you mentioned when Dan H. replaced my clutch and flywheel last month, so I don't think they could be implicated. I'd also expect anything that ticked in the clutch to tick at the crankshaft frequency or one of its harmonics. As much as I wish the transmission was the source of the problem I think the signs still point to the engine. However I really appreciate your sharing your expertise with me!

-Rick

Deaton

Stock OEM clutch, throw out bearing, fork, pressure plate, flywheel?

IMSF8

Deaton: The original flywheel and clutch were replaced during the 2022 rebuild with OEM parts. Dan at RMG replaced the parts again at the end of February ('24) with another LUK dual-mass flywheel and a Sachs clutch kit that contained everything (clutch, fork, pressure plate, throw out and pilot bearings). The only things we didn't touch were the transmission and the slave cylinder.

-Rick