ChicagoSpeed996

Van, where did you go? Any updates?

Jon Moeller

He's probably getting in his racing fix, while he can. I suspect we'll see a lot more progress on the engine, when the snow starts flying.

Pat Grahek

@Van what was the outcome of the engine inspection? Bore scoring? Your action? Some advice for other 996 and 997 owners experiencing similar issues? Thank you kindly!

wildbilly32

Uh last time Van shows activity here was Dec 2019 and this thread is over 5.5 years old...

Van

Yes, this is an old thread... (and I do miss my 996)

Teardown inspection showed the cylinders were pretty badly scored up. My best guess is this was from extreme cold starts, since I was commuting in the car all year-round. The pistons would heat up faster than the case and the metal would expand to the point where it was an interference fit with the cylinders. I wasn't ready for the expense of an engine rebuild, so I sold the car as-is to someone who felt they could do it cheaper. I don't know what the final outcome was.

As much as I'd love another 996, I've had a job change and now work from home. I rarely drive anywhere - unless I go to the track, in which case I'm driving a truck and trailer!

Mike Murphy

So what are your lap times with the truck and trailer? And does it bother you the trailer can never seem to take first, despite almost identical lap times?

Flat6 Innovations

The cold start theory was one of the first we had, many moons ago.. What you have to understand is the underlying conditions that exacerbate the issues related to any adverse environment, including cold weather.
Cylinder finish is one of those conditions.

dougn

That was my guess too.... at least the primary cause. I think in some pics I've seen scoring on just one side of the cylinder. Not sure how that could happen...a distorted cylinder and piston growth maybe. my question to you though is.... How did you drive it? Did you baby it till it warmed up (small throttle openings and let it spin up) or did you extract torque right away?

Van

At home, it would always be parked in the garage, so it would never get that cold. But I would have to leave it parked outside at work (2-days at a time) - it was not uncommon for me to have to do a cold start at zero degrees. I think the coldest I saw was -15. I would let it warm up a few minutes before driving, and I'd never go over 3k RPMs until the water temp was up to operating temperature. But in that extreme cold, I think the damage happens very quickly.

Mike Murphy

I never let mine warmup because I hear knocking and rattling when I do. If I drive off right away and keep revs between 2,000-2500, no knocking. Been this way for 4 years now.

dougn

just looking at expansion numbers roughly. A 100 mm piston could expand .004 inch for a 50 degree c delta

Van

That's pretty significant. I'm sure someone could do the math: start with a cold engine at -20C, if you know the thermal mass of the piston and the thermal mass of the case/coolant/oil and apply a 2000C temp in the cylinder to warm it up, how far apart do the thermal gradients get? My guess is you'll get the piston up to at least 30C before the case is up to -19C.

dougn

Also I bet the cylinders go through a distortion on the way up to temp. I wonder what the piston to cylinder clearance is on a new factory motor...

dougn

thats why I was asking about driving style. when you extract torque, you dump much heat into the piston. rpm, not so much