Intake seat let go. Ended up resting at angle to valve (odd location, usually they sit flat if loose?) which ended up taking a chunk from top of piston and scuffing cam lobe from pressure created. Much work ahead of us this weekend :-(Click to view attachmentClick to view attachmentClick to view attachment

Oops! Yup, doesn't look good, probably didn't sound good either.

time for two new heads, these things are now 50 years old and repairing is expensive and then with bad luck another seat will let go

That looks wrong in a few ways.
Valve,,, obvious
Top of piston pitting, root cause?
Lots of white in head, possible lean condition?

Rich

Looks like it could of been lean as mentioned
Too much head temps and seat would of became loose

The top of that piston looks really bad. Did you wire brush off all the carbon deposits before you took the photo? If not, then it looks like the metal of that piston has gone bad and the metal is disintegrating.

It’s possible that detonation may have caused this.

Thank you for the eye. Great questions. I’ll grab and post more photos this week.

Top of piston - this is untouched, as it was when opened up.

Ancient Heads - LN Eng would be nice. Not much out there for options that don’t break bank.

What budget do you have?
I think AA makes new heads, then LN remachines them.
So….buying direct from AA May cost less

Or, shop for a used head and piston

Eric Shea made a great statement.
Don’t need to over think a type 4 motor.

I’m guessing it was not running right ?

Be interesting to see if the rod bearings are beat to death. The tops of the piston have all the hallmarks of detonation/preignition.

Yes, running with “ no issues”. Ha! What a mess.

Looks to me like that valve seat did a dance in there and pitted the piston. I'm guessing that pieces of the head chipped off and also added to the pock mark party. I'm guessing the big dent was caused by the valve being held open and the piston hitting it.

Dropped valve seats are often caused by poorly executed valve jobs where the shop didn't take into account the expanding nature of an air cooled head and didn't fit the seat with enough interference. Or there was a crack or some other event that kicked the seat out of there.

If the other cylinders all look good maybe just replace that piston and head. Very unlikely that the rod bearing is damaged unless you can see that the rod got bent. Once you reassemble, check if that piston sits low at TDC because that could mean a bent rod.

I'm surprised the cam got damaged without bending the pushrod or bending other valvetrain parts. Check that too!

I had an intake valve seat drop in a Corvair Turbo under boost..
Parts of the seat ended up in other cylinders on that side and some
went down the exhaust and ended up in the turbo blades.

That was a real mess…

Happened to me a week and a half after I bought my first 914. Got to learn how to remove an engine, with my previous mechanical experience being replacing a Camaro water pump.

Again, reminds me of the importance of AFR and CHT gauges in these cars.

engine original fuel injection or carb?

Proper tuning will do.

I’m not against technology but setting timing properly and reading plugs goes a long way, doesn’t cost much, and doesn’t require exhaust mods and wiring.

If technology is wanted to prevent this, need to start looking at knock sensing. On almost every modern vehicle.

One of the problems with air cooled engines is all the noise they emit. Very easy for someone not familiar with knock / detonation to think it is a “normal” noise that air cooled engines make. Detonation kills engines fast.

What do the other pistons look like?

I disagree...
I can read plugs just fine and did high performance builds and tuning before simple O2s sensors were common. It was a PIA to really know just which air correction jets or emulsions tubes were needed until wide band O2 sensors came onto the scene.

Now days if you DON"T use a wide band you deserve whatever happens to your car
.
I'm a wizard at this and I'll install a wide band BEFORE I put our 75 back on the road.
Wide band is far, far more important than a knock sensor.
I will not install a knock sensor until I install a complete stand alone digital ECU.
At this time I may install more than one knock sensor.

Knock sensor saves you when you have a failure. Wide band allows you to actually see the mixture in real time.
I've never had a cylinder head temp sensor on anything but they look seriously important and I will add this well before the digital ECU.

Agree that a wideband sensor is important, especially with all of the rebuilt MPSs out there that may not have been calibrated for the engine they are being used with.

How do the other cylinders look? It's possible that just one hole had a clogged injector or something that caused that pinging but it's unlikely. I think it's just the valve seat falling out and the resulting carnage that caused all that piston damage. Detonation erosion that I've seen usually shows up in the ring lands and sometimes gets so bad that you can see the top piston ring with the head off because the piston wore away.

What's the head look like? Is the exhaust valve burned?

Pulled it apart and this is what we found, remember this is an original 2.0 head on 96mm pistons In a motor I’ve been running a long time.
- no lean condition. The pistons in 1/2/3 look slightly rich, plugs the right colour, no signs of stress on piston tops, valves, rings.
- lifter rod was smashed on end, enough material removed to shorten rod by half inch.
- we assume the seat worked loose and then bounced around for many miles (perhaps I should have been listening!) before finally resting on angle and smashing piston top
- we assume material from seat and piston caused the piston top pitting prior to landing on angle, this explains the metal condition.
- no metal in crankcase
- number four liter and cam lobe “scuffed” due to piston contact. We will replace all internals
New Build:
- we have 039 heads from Jonathan at AA (would love to have them… but don’t have the budget for Ken’s $5k heads). 78mm crank counterweighted, 96 pistons, stock rods, everything balanced including flywheel and alternator.

Thank you everyone for questions, comment, opinion and advice on all of the above.

Cheers,

Dayum! That's a crazy failure.

Lean, detonation evidence on the other cylinder.
When you get it redone, you must address A/F mixture and timing issues

That looks depressingly familiar.

Could be caused by heat as well.

If so, the other intake seats are likely getting ready to do the same thing. (Don't ask how I know that.)

--DD