pcar964

For those of you who followed my earlier thread on the strange clattering noise my 993 is making...

The engine has a split personality - either it runs absolutely perfectly, sounds tight as a drum, no noise except the beautiful flat six sound.... or, it starts up with a louder than normal "click" and runs with what I can only describe as similar to valve lifter noise.

Last winter, on cold mornings, my car would sometimes not start - the starter wouldn't even engage - and that was diagnosed by some on this forum as being the starter solenoid not engaging.

My question is this: Is it possible that the strange clattering noise I'm hearing - could it be the starter solenoid getting stuck and holding the starter gear against the flywheel gear? I would think the starter would be destroyed in a short time if this was the case? But it would make a lot of sense, because every single time the engine makes that noise, the starter sounds different as well.

Mike J

From my understanding the starter works as follows:

- if the solenoid is activated it will "push" the starter gear towards the ring gear on the flywheel

- the the starter gear get gets far enough (i.e. the solenoid pin moves far enough) it will power up the starter by closing contacts in the solenoid

- once the current on the solenoid is stopped (i.e. the ignition switch is not in "start" the starter gear will disengage, resulting in the starter motor power being shut off as well as the internal contacts open.

Its totally possible, that during a start cycle, the shaft gets stuck and the starter remains engaged. This would result in a loud whining sound since the starter would be rotated by the ring gear on the flywheel. If you rev the engine in this state its very hard on the starter! On my starter which I recently replaced the shaft was corroded and the starter gear did not move very well on its sliding shaft.

If the solenoid does not activate nothing will happen.

A clattering noise is a bit weird. Does it continue while the car idles or is it just for a short while? If you turn the engine off and start again does it repeat or is it hit and miss? Could it be the chain tensioners not pressurizing (that would give a clattering noise like chains being dragged on metal).

Its the starter original and what is the mileage on the engine?

Cheers,

Mike


- as the solenois continues to shut off a spring will

viperbob

Greg, you may have a bad DMF... When they start going bad, they will sometimes rattle.

pcar964

Mike,

I'm not sure if the starter is original, I'll have to dig through the records. But the noise has been occurring enough that, if the starter would be damaged like you say, I think that eliminates that possibility, because there's no whining sound and the starter still works normally.

The timing chain tensioners not pressuring up, THAT sounds like a possibility... is there an easy way to confirm this? What would be the culprit? And would the fix be very expensive? Would running the engine without fully pressurized tensioners damage the engine in any way?

Thanks!

Mike J

I had not thought of that...!

Greg, did you try engaging and disengaging the clutch while its rattling? If the noise changes (ie you can do it at idle) then the flywheel is making noise..


Cheers,

Mike

pcar964

Bob, if the DMF is the culprit, that would give me a good excuse for a LWF I just wish there were an easy way to know for sure...

pcar964

I feel like an idiot for not trying that sooner, I just assumed it was an engine issue and not a clutch/flywheel issue... So I'll just rev the engine with the clutch disengaged, then with the clutch engaged, and see if there's any difference?

I'll try it tonight, fingers crossed!

pcar964

But when you said chain tensioners, that got me thinking - it really does sound like a faint chain-rattling against-chain guides-sound.

MarkD

+1

I just replaced my DMF and clutch. ONE of the symptoms was a nasty rattle sound on startup.

Do you feel a moderate (hard to quantify) vibration in the shifter or the pedal? Pedal was more of a pulsating feeling of course. Vibration was particularly noticeable when I eased off of the throttle slightly when between 3K and 4K rpms. Sort of coasting a bit, little tension on DMF... neutral power. Know what I mean? That was the other symptom.

In comparison, the new DMF and clutch feel like buttah. Honda-like. Scary smooth and light.

Good luck!

EDIT: BTW, that rattle appeared to be the starter ring gear contacting the trans bell housing. I noticed contact marks when I had it apart. At first I actually started looking for a piece of metal or something that might have been rattling around in there before I figured it out. Tolerances are pretty tight in there.

Garth S

To repeat my earlier comment ...
Corrosion can prevent full retraction, leaving the drive just touching the ring gear without being engaged.

Re the DMF, FWITW, BMW units can make a distinctive clatter when the engine is shut off with the clutch depressed. This noise is absent when repeated by engaging the clutch in neutral prior to shutdown. I have not tried this with the 993 unit.

pcar964

I don't feel any noticeable vibration in the shifter or clutch pedal, no matter the engine load. That's why I never thought to check the DMF as the cause of the noise.

MarkD

Then I'd lean towards another source too. If it is vibrating at startup I would think it would also be felt while running. Would think it would have to be felt if it could move that much while starting to spin up.
Disclaimer: This is only based on my one issue and experience.

pcar964

One more thing: The noise is only really noticeable IN THE CABIN, and you can't really hear it outside the car.

I think the key to this problem is, it occurs for an ENTIRE drive cycle at a time - i.e., if it starts up with the noise, the noise will be there until I shut it off. If the car starts up normally, the car will run normally until I shut it off. Doesn't matter if the drive is 5 minutes or 4 hours. Hence my hunch that the starter had something to do with it.

vjd3

Does it sound like it's coming from the passenger side rear of the car?

pcar964

I've tried to isolate it, but it just sounds like it's coming from behind the rear seats (firewall ?), and since I can only hear it inside the cabin, it's hard to say which side it's on.