Engine Diagnosis: 3.6L twin plug in 964 RSA
 

The last DE event of my 2009 season was NNJR VIR Nov. 6-8. The weather was outstanding and the track was perfect. While feeling under the weather I rode with a White student that hadn’t been to VIR before, and then felt okay in my first session. Second session; not so much. After about 3 laps heard something in the engine and felt it go down on power; started to hear a knock and within three corners got a meatball flag at Oak Tree so I checked my mirror and seeing no one there darted over to the South Course pit lane. Saw a little smoke and started to hear what sounded like an exhaust leak. Shut it off immediately, got towed back to the North Paddock, stowed everything in the trailer and went to the B&B where I was sick and in bed for 48 hours with Type A flu-like symptoms. Talk about a double whammy! But in one way, probably fortunate that my car broke; I didn’t realize just how sick I was and I probably would have “toughed it out” and kept driving – with potentially far worse consequences.

Imagining all sorts of things, from dropping a valve to worse, ASG found that the #1 head had simply cracked. It created an exhaust leak that formed a mini-plasma cutter that burned a hole in the chain housing (magnesium!) and started melting a timing chain ramp. No obvious signs of precipitators; perfectly clean/even burning in all cylinders with no signs of running lean, and the valve train was perfectly intact with no improper contact of any kind. This could have been pure mechanical fatigue or a result of contributing factors; I’ll post some photos when I take some next week so maybe someone will have additional ideas of what caused this to happen and what to look for/test.

So it looks like my New Year is off to a good start; it’s a simple and straightforward repair and I’ll be ready for the 2010 track season!

Glad to hear you lucked out.

Freaky. Never heard of such a thing.

No kidding? I have seen a lot of folks get the flu this season...

Subscribing

Please post pics when you can.

Seen lots of aerated cases and overheated cracked cylinder top and bottom surfaces (and fins) but not a crack-ed head.

Twin plugged? (assuming yes)

Thanx.

I too would like to see where the head cracked and how that may have happened. Sorry about the news and glad it wasn't worse.

I stopped by to see it yeserday but didn't have my camera with me; I will post photos later this week.

It is very interesting - at least two cracks in the head, the biggest went from combustion chamber to the rear outside edge of the head where it mated to the cylinder and down. It created a fairly large fissure that at the edge was v-shaped creating a little cutting torch. The escaping gases also damaged the top of the cylinder, burned a hole in the timing chain housing, and started melting one of the timing chain ramps.

The second crack went from the top side of the head to the intake. If not for the head stud sandwiched between the cracks that secured a corner of the head it looks as if and entire chunk of the cylinder could have come off! Good thing both the corner worker staf and I were paying attention and I got it shut off pretty quickly; damage done but it could have gotten much worse.

Still researching possible causes, from mechanical failure to perhaps running lean or other source of predetonation. No signs of any contact whatsoever; valve train and piston tops fine (haven't pulled cylinders to check the rings yet). They should be fine but I want to look for any signs of predetonation.

(Jase - yes, it's a '93 RSA with twin-plugged 3.6L.)

Over the years I've had to get the heads on my 356/912 motor(s) welded up. Very fine cracks in fins, etc... work done at Ollies, Competition Engineering and Anchor Atlantic IIRC.

Unlike your motor, I'm running high compression, CAM2, single plug and the thing lives between 5,500 and 7,800+ whenever it isn't idling. Top end is weak part ... and expected to fail at X hours use.

Wonder if it was a lean condition ... fuel delivery related to that cylinder. Gonna get your injectors cleaned and flow matched? (while motor is getting repaired).

Thanks for the reference re welding; wouldn't have thought that was possible, but unfortunately given the extent of damage it won't help in this case.

Absolutely sending the injectors for cleaning and flow matching. I also had that done when the engine was rebuilt in 2005.