Variocam Pad Replacement and Cam Deviation

[Jeremy Bruecken]

I have a 2000 911 Cab. The engine blew up on the previous owner at 85k. They replaced it with a MY2000 engine with 38k on it. 

 

I picked it up at just over 90k miles and drove it for a bit to feel comfortable it was a good candidate for some major maintenance. One finding was cam deviation of bank1: -9.4 deg and bank2: -3.8 deg. This was check when the engine was hot. So I added variocam pads to the to-do list.

 

Pulled the engine and replaced the RMS, IMS, WP, LT thermostat, AOS, variocam pads, and spark plugs and tubes. First run after getting everything sorted and up to temp showed cam deviation of -3 deg on both banks. Would that be normal for fresh pads? Should I expect less? I haven't been able to find any examples of people replacing the pads and then reporting cam deviation numbers post replacement. 

 

Bank 2 on the left and Bank 1 on the right. 

 

[Ahsai]

My understanding is with proper timing the cam deviation should be closer to 0 or even being positive.

[Jeremy Bruecken]

Very much appreciate the reply Ahsai.

 

So an added data point after ~ 70 miles of driving since the replacement and hot deviation is now about -3.5 on both banks. I'm thinking I'll drive it for at least a week and make sure it's settled in before attempting a re-time. My understanding of how the chains ride on the pads is that the chain teeth wear into the pad until the rollers are running on the surface at which point the wear stops (or at least slows significantly). I would assume that's where the extra -0.5 degrees came from. 

 

I used these tools to do the timing:

https://www.amazon.com/PMD-Products-Camshaft-Compatible-Replace/dp/B01MQMRHJ4

 

But I did mess up and miss the 360 degree turn between the banks. So I had to re-time bank 2 in the car. I did that the easier way by putting the engine at bank 1 TDC (which was incorrectly also bank 2 TDC at the time) and inserting in the cam lock tool from the IMS Pro Tool Kit on the bank 2 exhaust cam, unbolting the exhaust cam sprocket, and turning the engine 360 degrees. The tool fit perfectly, which I think indicates the timing should be spot on. 

 

Once I'm sure the deviations have settled, I'll put the cam plugs at TDC and re-fit the locking tool to see if any deviation is present at the exhaust cam. As I understand it, the DME deviation measurement is taken using a sensor on the intake cam. So the only other source is the drive system between the two cam (i.e. the typical variocam pad wear), but I suppose other items include stretched chains, weak actuator spring, etc. Seems unlikely with such a low mileage engine. 

 

Btw - here's the thread on rennlist if anyone is interested in the pictures:

2000 6MT Aero Cab - Page 2 - Rennlist - Porsche Discussion Forums

RENNLIST.COM

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996 Forum - 2000 6MT Aero Cab - I started this thread a few days ago: https://rennlist.com/forums/996-forum/1128827-possibly-buying-first-porsche-in-2-days.html And I'm happy to report, that I am now a Porsche owner. My 3 yo son rode in the back for the 2 hour drive home. He loved it...

 

[Ahsai]

Yes, the cam deviation value will go toward more negative as the pads break in (and wear down later on) so it's better to start with a zero or slightly positive value to begin with.

I suspect your timing is off just a little bit.