Engine Diagnosis: 3.6L twin plug in 964 RSA

[Eric S]

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!

[Landjet]

Glad to hear you lucked out.

[MatP]

Freaky. Never heard of such a thing.

[Vicegrip]

Freaky. Never heard of such a thing.

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

[Rick Lee]

Subscribing

[Jase007]

ASG found that the #1 head had simply cracked.

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.

[markwemple]

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.

[Eric S]

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.)

[Jase007]

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).

[Eric S]

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.

[Eric S]

Here are photos showing the cracked head; I didn’t take photos of the timing chain housing or melted chain ramp.

As mentioned, there were cracks through the top of the head and up the sides to the intake, although the corner of the head was still connected and held in place by the head stud. However, one little rap and the entire corner of the head broke off. The portion of the head near the intake had not cracked all the way through and was physically snapped when rapping on it; the portion nearer the "notch" was obviously cracked all the way through and had been melted/carbonized and you can see where it had been vibrating against itself.

The biggest issue is trying to decipher why it happened. Most likely suspects are overheating due to a lean running condition or perhaps pre-detonation. Once we pull the cylinders we’ll take a good close look at all of the rings to see if any are broken (as occurred back in ’04). There are some significantly more knowledgeable people than me frequenting this site; I’d be interested in anyone else’s ideas.

It's been 15k track miles since my total rebuild, so from here it is top-end rebuild, including rings, head studs, valve fitment, Aasco valve spring checking, and injector cleaning/flow-matching; then we'll dyno it to check for anything out of the ordinary. If nothing, then it's track time!

[Lupin..the..3rd]

JB Weld.

[Landjet]

Since it will be apart, put some water cooled, 4 valve per cylinder heads on it Eric. With the twin plug design you already have, I bet you would like the results.

[Vicegrip]

Cool. Almost a clean path of least resistance. Around the valve seat and through one of the intake port stud holes. I wonder if the stud was the propagator? Cranked in too tight or through a bunch of existing crud stuck in the threads. Might answer why the crack wandered around the valve seat but did not include the spark plug hole. That little tear in the side of the sheet of paper. Just add heat and stress over many cycles.

[Richard Curtis]

The biggest issue is trying to decipher why it happened. Most likely suspects are overheating due to a lean running condition or perhaps pre-detonation. ... I’d be interested in anyone else’s ideas.


Eric: lots more knowledgeable folks than me hanging out on this board, but here's a long shot: I had the 6.5 hp Briggs & Stratton engine on my Billy Goat lawn vacuum go kaboom. Actually, it blew a head gasket, burned a valve, popped a valve seat out, etc. Needs a new engine.

Mechanic said cause was a mouse nest, hidden by the engine cover, which caused the engine to overheat. He found the dead (slightly fried) mouse, plus the nest materials near the head. He said he sees a lot of this on lawnmowers, snowblowers, etc., and I know from personal experience that rodents will nest in auto engine compartments.

Doubt seriously that this caused your problem, but should be a cautionary note to p-car owners who store their cars over long periods of time to look for rodent infestation. Sorry about your engine.

[Vicegrip]

..overheat tends to drop seats out too. Would be kind of funny, in a not funny way, for Eric's motor have gone kaboom from being messy.

i had a riding mower in a shed and after starting it up for the first time in the spring found the air driven governor was not helping to hold a steady RPM. I then noticed a mouse running out with a pink baby in her mouth. I shut the motor off and watched as she made 4 or 5 more trips in and then back out with another baby and under a nearby pile of firewood.
The air cooled motor was packed with mouse nest made from a nearby towel carried in thread by thread.

[VaSteve]

JB Weld.http://dorkiphus.net/porsche/showthread.php?t=22174&page=3

[VaSteve]

..overheat tends to drop seats out too. Would be kind of funny, in a not funny way, for Eric's motor have gone kaboom from being messy.



Like rain on your wedding day or a free ride when you've already paid.

[Clarke]

I wonder if the stud was the propagator? Cranked in too tight or through a bunch of existing crud stuck in the threads. Might answer why the crack wandered around the valve seat but did not include the spark plug hole.

This is what I was thinking as well.

[pjalexandre]

wow

[tdatk]

Sorry to see that Eric. Spooky to say the least, could be that cylinder was dropped at some point in it's life or maybe the casting had a flaw. That burn through is unusual, where you running race gas?

[smdubovsky]

Castings can have flaws. They crack due to thermal cycles. Happens to all other aluminum & iron heads all the time. Even if rare in the porsche world they aren't immune so I wouldn't beat yourself up over figuring why. Replace it, check everything else out, reassemble and be on your merry way.

Cool pics though :)

[Eric S]

Cool. Almost a clean path of least resistance. Around the valve seat and through one of the intake port stud holes. I wonder if the stud was the propagator? Cranked in too tight or through a bunch of existing crud stuck in the threads. Might answer why the crack wandered around the valve seat but did not include the spark plug hole. That little tear in the side of the sheet of paper. Just add heat and stress over many cycles.

Certainly could have been, but it's difficult to isolate the cracking sequence - it's obviously worst at the notch but that doesn't mean it started there. From looking at the intake stud and the threads in the chunk they are very clean and there is no indication of any crud but that is about the extent of my visual forensic capability; I'll bring the parts by some time and see if you find anything else. It also doesn't appear that the crack on the intake went all the way through (until we "helped" it) such that it could have been the source of an air leak. I have another view that shows how the crack went around the surface where the head stud nut was tightened; this also looks suspect to me.

Doubt seriously that this caused your problem, but should be a cautionary note to p-car owners who store their cars over long periods of time to look for rodent infestation. Sorry about your engine.

No issues of this sort. :) As VaSteve referenced, "ironic" would be an understatement...

Sorry to see that Eric. Spooky to say the least, could be that cylinder was dropped at some point in it's life or maybe the casting had a flaw. That burn through is unusual, where you running race gas?

I experienced denotation that was bad enough that it broke rings in a cylinder back in late '04. There was no obvious cause but I had been on a trip to Canada where the highest octane fuel available was 91, and who knows if that was actually in the tank. As a result, after the total rebuild I made changes to the most likely contributing factors: replaced the chip with a "safer" one that can run on straight 93 octane, cleaned and flow-matched injectors, installed an auxiliary oil cooler, rebuilt the alternator, and started blending race gas to have more certainty of the quality and octane level. My average blend ratio is 1:1 race gas to pump premium; as low as 1:2 on really cold days, and 2:1 on really hot/humid days.

Castings can have flaws. They crack due to thermal cycles. Happens to all other aluminum & iron heads all the time. Even if rare in the porsche world they aren't immune so I wouldn't beat yourself up over figuring why. Replace it, check everything else out, reassemble and be on your merry way. Cool pics though :)

Certainly could have been a casting flaw, metal fatigue or improper torquing. However, the most common opinion is that it (1) ran lean, (2) overheated, and (3) cracked. While we might not be able to determine the initial cause, I want to do my best to figure it out so that if possible I can prevent it from happening again.

[EdsProject]

Hey Eric- what a shame. What did Steve W think? Coincidentally I was emailing him while you were on the phone with him the other night.

As per my email, I would send the 6 injectors out to have them checked. Especially if 2 other heads are showing cracks as well. I'd want to know if any of them were not flowing properly and causing a lean condition. Short of a pure mechanical failure, that would seem to be the most logical cause, though that cylinder isn't pure white like a lead condition might indicate unless oil was getting in there right before it broke.

Someone mentioned rodents nesting in these engines? I just completed the teardown of my recently acquired 3.6 last night and there was a big nest on top of #6, with all sorts of crap jammed down into all the fins of that barrel. Most certainly would have caused serious overheating problems on that cylinder if I hadn't torn it down.

So you going to have Steve W do the same valves and cams he's doing for me?

[Eric S]

Hey Eric- what a shame. What did Steve W think? Coincidentally I was emailing him while you were on the phone with him the other night.

As per my email, I would send the 6 injectors out to have them checked. Especially if 2 other heads are showing cracks as well. I'd want to know if any of them were not flowing properly and causing a lean condition. Short of a pure mechanical failure, that would seem to be the most logical cause, though that cylinder isn't pure white like a lead condition might indicate unless oil was getting in there right before it broke.

Someone mentioned rodents nesting in these engines? I just completed the teardown of my recently acquired 3.6 last night and there was a big nest on top of #6, with all sorts of crap jammed down into all the fins of that barrel. Most certainly would have caused serious overheating problems on that cylinder if I hadn't torn it down.

So you going to have Steve W do the same valves and cams he's doing for me?

I thought you were keeping your special project a secret...:)

Steve's opinion is that while bad casting/metal fatigue/improper torquing can occur, heads most often crack because they been overheated, and they nearly always get too hot because they ran too lean (pre-ignition, detonation, crack). Possible suspects not yet ruled out include insufficient fuel caused by a bad injector or faulty management system or an air leak.

All injectors are being cleaned and flow-matched. Point of clarification - the other two heads are not cracked at all; however, when the first head cracked the fitment between the heads and cylinders was compromised only enough that you could see that small tell-tale carbon indicating some exhaust gases had leaked between them. There doesn’t appear to be any damage to those heads, but one consideration is to replace them as well.

Visible evidence of the metal surfaces shows that the other cylinders are all burning perfectly; rather than the signs you would expect to see with a lean condition cylinder #1 is actually showing the blacker after-effects of the crack. It is possible that the lean condition happened in the past and the consequence manifesting now.

Glad you found the nest in your new/old engine! It certainly happens, but wasn’t the case in my failure.

I’ve thought about valves and cams, but want to continue with it in stock form. I’m basically doing rings, valves and head studs for a fresh to end, adding some reliability bits and replacing most of the rubber in the intake system. It's plenty capable as it is and doing it right means that I'll be happy with it for a long time...me or someone else should a 997 GT3 ever make it's way into my garage!

[EdsProject]

I thought you were keeping your special project a secret...:)

I am. You won't tell anyone will you? :D

Heads will be on their way to Steve tomorrow. I'll split the case in a week or so and get the rod on their way shortly thereafter.

Good to hear the other heads aren't cracked. I may have read between the lines based on your email a few days ago. So just one head and a fresh top-end to be good for another 15K miles? Good to hear.

But why limit your sights to a GT3, go for a GT3RS or a Cup Car. It's only money.

[Ryan]

Sorry to see, but maybe this is that sign your were looking for to make a change in cars? Good deals on tracked prepped GT3s out there this winter!

[Eric S]

Sorry to see, but maybe this is that sign your were looking for to make a change in cars? Good deals on tracked prepped GT3s out there this winter!

As much as I would love to have a 997 GT3, and I still plan to get one someday, I'm afraid this expense warrants keeping the RSA a little longer.

And for the good news: I picked the car up from ASG last week and put some break-in miles on it over the weekend. Had the oil changed this week and everything checked out, so the RSA is back in business!

Funny how not driving your car for four months makes it seem like it runs great. But it sure runs GREAT!

Now if I can just break away from work...Hello, VIR!!!

[KevinOyler]

Congrats on getting it running again. Enjoy.