Loud Rattle on Cold Start

[miscou]

I have a 2000 Carrera 2 that has a loud rattle on cold startups that lasts about two seconds. I cannot reproduce the rattle after the car has run for a few just a few seconds, leading me to believe that it is oil pressure related. After the car is run, even for very short periods of time, the car will have to sit for several hours to reproduce the sound on startup. An additional symptom is what sound like a "Lifter Tap" from a Chevy V-8 with the rocker arms out of adjustment. My initial thought was that it was the "Death Rattle" and I needed an IMS. I did a full engine-out last month. The car was on the original clutch, and I thought I needed an IMS. The engine had never been out of the car so I decided to give it a thorough going over and change all of the cooling hoses. They were 11 years old and I did not feel like pulling the motor again over a $20 hose so I did all of them while I was in there. I replaced the clutch, bearing, flywheel bolts, etc. and upgraded to a LN Ceramic IMS while I was in there. Everything went together fine and the car runs great, except I still get this rattle on cold starts.

I decide to pull the motor again and get to the bottom of it. The "tap" seemed to be louder on the passenger side, so I pulled that valve cover first. After a thorough examination, I could not find any sign of wear. My thinking was that I have a bad valve tappet, noting that they are hydraulic. This would explain the rattle on cold start up and the elimination of the problem with full oil circulation. However, I thought I would find some sign of wear upon close examination of the valve train. There was no visible wear on any of the cam lobes and no sign of excessive wear on the tappets (that does not mean the wear could not be visible from the bottom of the tappet that I cannot see). Just to be sure, I pulled the cover on the IMS to make sure the first row of the bearing was not showing signs of wear. The new IMS looks fine, so I am ruling that out.

As this is the first 911 I have owned, I was wondering if anyone with a lot more experience with these engine’s has encountered a similar problem, or has any thoughts on how to get to the bottom of this mystery. Any help or idea would be greatly appreciated.

....Chris

[Ahsai]

Have you checked the hydraulic chain tensioners?

Edited October 9, 2012 by Ahsai

[Dharn55]

Rattles on start up are often the chain tensioners on the IMS to crank chain or the IMS to cam chains. As they get old they leak down when the engine is off and take a second or two to pump up when the engine is started. This allows the chains to rattle. You can all three for only $200-$300 and they can be replaced with the engine in the car. The only one that is difficult to change is the one on the 4-6 side at the rear of the car on the top as you have to remove the AC compressor. As you have dropped the engine you know how to remove this.

Fairly inexpensive DIY that will probably fix the problem.

[miscou]

Thanks for the help! I pulled all three tensioners when I got home tonight (see pics). 1-3 is the softest and I can compress it fully with a good squeeze, with no oil coming out. 4-6 and the IMS only allow me to compress them about a half-inch with a good squeeze then they stop hard. Both of those are ejecting oil as I push. Based on the 1-3 being dry and compressing fully, I'm guessing that is the culprit. The difference in resistance across the three tensioners is reason enough to replace all three of them.

Thanks again for the help...........Chris

[surahman1]

Hi miscou,

 

Did the noise go away after you replaced the three tensioners  ? I have a similar rattle noise on start up but only seems to happen after the engine has been warmed up a little. SO I am considering replacing the tensioners as it doesn't seem to be a big job.. I made a shot video to show the difference https://youtu.be/9ZJ064bh7ko

 

[surahman1]

I did not expect a reply form  miscou, since this is such an old thread. So I got my local Porsche dealer to replace all three tensioners. I did not want to do the job myself as there was a risk I cold mess things up. Now I can confidently say loud rattle noise during start up is completely gone. The engine also seems to run quieter overall. 

[Campag]

Surahman1, what did it cost at the dealer ?

[surahman1]

38 minutes ago, Campag said:

Surahman1, what did it cost at the dealer ?

Parts + labour, about AUD 1170. We pay more here in Oz for parts...