Perhaps you could look at the exhaust valve seats and see if there is evidence of excessive heat. Or if there are other signs of excessive heat on the head, piston, or any area around cyl. #2. The piston should show signs.
My thought is that your engine went because of a mechanical issue versus a fuel/Air issue.
It is possible that a single cyl. went lean and burned up but it should have showed signs of that before imploding. You should have felt the cyl. dropping out or something.

This isn't entirely accurate. Lean burns do not cause excess heat. Lean burns can cause detonation, which forces the flame wave in unitended directions and consequently cause certain areas to run hot. Lean burning by itself, however, runs cool. If you don't believe me, grab a blow torch and max out the flame. Then start turning down the fuel knob and see what happens. A more objective proof of this lies in aerospace applications, where pilots have relied for many decades on cht and egt readings to monitor their engine status. Any pilot who understands these number will back up what I am saying here.

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I just RE-viewed the picture in post #15 you can see ring bits, valve head, and other bits.
If that hole got hot enough to cause a valve to drop you should see signs of excess heat on the ring pieces or valve bits. I don't see that.

The exhaust valve that is missing, the shaft is perfectly straight. I’m guessing the head fell off that one from heat, or possibly simple mechanical failure due to structural issues in the metal? The intake valves that are damaged, the valve shafts are bent, making me think this might be collateral damage from the exhaust valve?

I will get the head off this weekend and post more pictures of the carnage.

My main concern is ruling out anything that moves from old engine to new engine as the cause of the failure. Whether in the end it was the injector, the intake or a mechanical problem with the piston or head is not as important to me as keeping the new engine safe from a repeat performance.

Silber

Oh, and I read an interesting take on why people think an engine running lean is hotter.

A perfectly tuned engine usually runs richer than stoichiometric. So if you lean out from there it gets hotter till it hits stoich, then cooler after that.

So an engine running leaner than a slightly rich tune gets hotter but leaner than stoichiometric gets colder.

Does what I read make sense?

Silber

Silber,.

Fuel injected engines that run closed loop operations shoot for stoich. Nbo2 sensors actually only work around 14.7 because of their design. Always (unless manipulated ;) ). This is because of emissions.

Open loop operations are different. They run much richer (afr 12-13) for better power production, retaliation prevention, and cooler running. But open loop operations only happen under very few circumstances.

I have a wbo2 installed and can confirm that the 986/996 does run at 14.7 closed loop, 12.3-12.5 open loop)

Long before there were o2 exhaust sensors, pilots used cylinder head temp and exhaust gas temp readings for each cylinder to understand what was happening inside their engine at all times. It's a simple system that can tell you an exceptional amount of a running engine.

In terms of temp numbers, egt is representative of the combustion process and changes with each stroke. stoich is max exhaust temp. Max power is about 75deg lower than stoich (this is referred to as rich of peak, or ROP).

Cylinder head temps are different. They are closest you can get to measuring the actual cylinder temp. Much slower to react to changes because we're measuring the temperature of metal but still very important because it shows what's happening to the engine material.

For example, if you run lean and start to detonate, your head will often heat up because of improper flame wave propogation. However, less fuel causes a cooler burn, so you'll see a cylinders egt drop and cht rise.


Back to your problem though -

Ok looked at your pics. Was your gasket intact on cylinder 2? That pic is concerning but I don't know if that was the culprit.

The exhaust valves are sodium filled. Good luck melting one of those. A garage in ga with extensive m96 data who actually shares his data (NOT RABY) found the only valve related issues on the 2.7 and 3.2s to be related to lifter springs. Navarro mentions that on his website as well.

https://newsite.hamheads.com/2016/12/01/m96-m97-porsche-cylinder-head-specifications-and-general-info/

I guess I'm a bit confused though...How do you know what your valves look like if you have pulled your head yet?

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Thanks for the great explanation on lean versus rich in these cars. Very helpful!

I have pulled off the exhaust manifold and the intake manifold and I can look down in the ports and see that both of the intake valves are broken off and one of the exhaust valves is broken off. I found bent pieces of intake valve stem in the intake, but looking in the exhaust port the exhaust valve stem is in perfect shape other than missing the head.

Whatever happened it was isolated the cylinder number two, I don’t see any of the same problems on 1 or 3 leading me to believe it it was not a valve train issue.

The intake gasket looked relatively normal, but looking at the head it doesn’t look like it was sealing properly. Thus my theory that the intake was warped. I’ll post a picture of the gasket later.

Silber

From what I see in your picture in post #15 and what your describing here. (valves broken off). There was a mechanical issue. Broken wrist pin, broken rod, valve spring or lifter issue. will be interesting to see what you find with further disassembly.

I think you are onto the mark with the valve spring. One thing I did not mention is the car ran, but poorly, after it lost all power during a run. I started it maybe five or six times with no power and no expensive engine noise. But the last time I started it, it made all kinds of expensive engine noise.

So, if the valve spring failed partially maybe the valve would not hit the piston but if it later failed completely then it would and that would cause the damage chain to start.

Headed out to the garage in a few minutes will know more tonight hopefully.

Silber

yup with that info certainly sounds like a mechanical issue rather then heat.

:eek::eek:

uhh, sorry to hear that.

You and me both! When it had low power but would run, I was thinking some sort of easy to fix valve train issue. once I heard all the crunching I knew it was probably not going to be as easy as I had hoped LOL

On the good side the crunching happened basically idling in the garage so the damage is not as bad as it could’ve been if I were going at high RPMs.

I got the valve cover off the 1-3 head tonight:

https://adobe.ly/3kmd1Vc

I found a loose valve keeper, but the cams look to be in very good shape. May have the magnafluxed just to be sure.

My garage is kind of a mess I need to pick it up and build a workbench to keep all the engine parts sorted out on. Will probably come back to this Sunday morning.

Regards,

Silber

Broken Valve Spring.

https://adobe.ly/2XAyy3y

I guess the moral of the story is if I hadn’t keep running the car after it stopped putting out power, I might’ve gotten away with just a valve spring. Since I kept running the car until I heard expensive noises now it’s a rebuild. Maybe there’s a lesson in that I don’t know LOL

Edit: Kept going with the tear down and got the 1-3 head off. As expected there were three valves broken off, the head was kind of munched, Cylinder walls were cracked, and there was a small chunk missing out of the bearing carrier. now I have to try to source one of those.Got a lead though we’ll see what happens.

Silber

If cylinder walls are cracked, this isn't a rebuild any longer...



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I have a spare block and wasn’t really planning on using this one anyway, however when LN sleeves the block they machine out the entirety of the cylinder walls, and replace them, so cracks may not have disqualified it.

Interesting video:

https://youtu.be/ebxkhGTyL9w

Silber

Found a 28,000 mile crank/bearing carrier, on its way here.

Plans to travel to LN Engineering this week to drop off my spare engine block for 101mm Nickies conversion.

Finish tear down of bad engine hopefully tonight!

Regards,

Silber

Got the 4-6 head off. Cams are good, but lifters have some pretty obvious circular wear patterns. Lifter holder on this side looks pretty worn as well. Fairly surprised there is such a pronounced difference side to side. Almost seems like two different engines.

Ok, so I can’t sleep and I’m thinking a bit crazy:

https://www.fvd.net/us-en/100105986002/sport-camshaft-set-986-boxster-s-32-l-m9621-engine-schrick-hydraulic.html

My thought is, a 3.8 with 3.2 heads is going to be a real stump puller due to the large displacement and small valves. This kind of setup really builds low down torque, but chokes off the high RPM breathing.

Would the Schrick cams give me the best of both worlds? Sacrifice a little stump pulling to get some top end back, or would I end up with a flat low end and still be choked off high RPM, basically gaining nothing and losing my low end boost.

Any engine gurus want to weigh in? And, up front I should say that I know the 3.2 heads on a 3.8 isn’t ideal, but it is what I am doing and I’m going to try and make the best of it, So advice to go buy different heads won’t be very helpful.

Appreciate everyone’s time so far. You maybe wouldn’t think it would be, but tearing down a mostly dead flat six has been pretty fun so far.

Silber

EDIT: The cams on the FVD website are SUPER agressive, high lift. May have found a better set. First image is the milder set, second image is the set with the high lift, third set is a compromise with the same degrees as agressive set, but less lift. Not sure the stock valve springs could handle the high lift cam.

In the light of day my camshaft idea seem a little extravagant, probably just going to go with new lifters and my current cams.

Got the 4 to 6 case half taken off, going to lift out the crankshaft cradle tomorrow. LN Thursday. Confirmed the part number On my new crank box matches the part number on my current one, seller is shipping tomorrow.

Hopefully my ramblings are helpful, I’m going to try to post less frequent updates with more substance So as not to clog up the board with my rantings.

Silber

I seem to recall that the crank carrier and crank are matched to some extent. I'm guessing you would need to measure the bearing clearance and consider an align hone

Just thinking about it, main bearings are a standard size. They have to fit the crank on the inside, and the carrier on the outside within thousandths of an inch. If there was much wiggle room there the whole system would fail, so my expectation is I’ll be fine.

That being said, My plan is to:
- check the crank for runout with a dial gauge in old carrier
- Measure main bearing clearances in old carrier with plastigauge
- check rod tolerances of old rods with plastigauge
- Check crank endplay in old carrier with dial gauge
- have crank magnafluxed
- check main tolerances with new bearings in new carrier with plastigauge
- check rod tolerances of new rods with plastigauge
- check crank endplay in new carrier with dial gauge

If I pass all those tests I think I will be OK, if any of the tests fail then I will have to figure out why and get back to the drawing board.

Does anyone happen to know the main bearing and rod bearing tolerances offhand?

EDIT: apparently rod and main measurements on these engines is a big secret, added steps to measure what I have first. My crank carrier damage is out by the cylinder, and relatively minor, so the measurements at the journals should still be good.

Silber