What engine oil do you run? Hard to think the bearings would be damaged with the winged sump setup. What do the valve springs look like?

oil pressure has been good in all the data logs, usual dip in the left hander at Barbagallo but nothing noteworthy. I usually run 10W-?? or 5W-??. I recently install an accumulator which has smoothed the pressure humps out a bit.

I haven't taken the valves out yet, don't have a OHV spring compressor. However from what I can see they looked pretty good.
One exhaust valve was black instead of burned brown colour like the other seven, this might be the lifter that is not holding pressure. Couldn't see evidence of this when hand cranking the engine, but again it might be something that requires a greater rotation speed for it to happen.
Can't hear the noise when cranking only when running.

Anyway new lifters are a must, the bores look worn and there is damage to No.4 cylinder bore, piston and head, so might pay to invest in a rebuild now.

found the problem after some more teardown.
No. 3 piston below....
Unsure what went first, but suspect the noise is piston slap.
Gudgeon pin split and cracked in two. Rod gudgeon pin bush rotated, blocking oil hole. Piston cracked in gudgeon pin bore. Evidence of ring landing scraping side of bore.
Big end bearing looked a little worse for wear but not showing signs of oil starvation which is good.
Anyway Time for a rebuild. Will bump up the static compression ratio on this one too.
Looking to go up to 10.5 to 11:1... Have some ideas on how to achieve this and keeping the flat-top pistons.

wow. lucky you didn't go for the full run at the track then. Any ideas how it happened. over rev?

Yeah agreed, although with the helmet on I only heard a noise when I got back to pit lane.
Unsure what failed first, but it wasn't due to an over rev, my engine is set to 7200 redline, with shift points well below that and anyway these numbers are well below any valve bounce issues.
I suspect it is not a one thing happened total failure type of event, maybe subtle issues over time have grown to this end result.
I'll get the injectors flow checked as this is a probable cause, maybe leaned out slightly and overheated No.3...
It could have been a pre-existing fault in the gudgeon pin?

Would it be worth checking the rest to make sure it wasn't a batch fault???

Will be replacing all pistons and rods, with the bore damage to No. 3 & 4 (Pre-existing damage in 4 due to a bolt ingestion a long time ago) will oversize the lot to 84mm.

Quick update.
Engine iwas dropped off at the machinist today.
On the cards for a rebuild:
Block bored, decked and torque plate honed
Head pressure tested, stripped, cleaned, valves seats reground, new seals, rebuilt
New oil pump
Exhaust cam on inkale side, adjustable cam gears
Custon high compression pistons
Ross racing balancer
New rods
New bearings
Balanced
Injectors cleaned
Retune

Took the other 3 pistons/rods apart the other week and found another bush spun, with it spun there is no oil feed to the bush/pin, which would have caused the failure.
Only way that can happen is if the clearance wasn't correct/checked when the engine was put together originally. Oh well, will get it right this time.

rebuild is turning into a monster build.
Hoping to net about 10-20% extra torque out of this build.
Machinist seemed to think last build it wasn't torque plate honed and a couple of bores were very slightly out of round, he has fixed that this time.

Most parts are now ordered.
Custom CP high compression pistons 4 weeks lead time are the next thing I need to progress.
Order thicker Gudgeon pins on this as well.
Decided to re-bush the rods in lieu of buying new ones. This way I can get the gudgeon clearance spot on and hopefully not have the same problem. Was significantly cheaper then new rods too.

Will keep you posted when things start to come together. Looking forward to the rebuild phase on this one.

Ok quick update as a few bits have arrived.
Block and heads are complete and ready to be picked up.
Now I have the pistons, the small end bushes can be replaced.
Not pictured is a new oil pump, crank timing gear, ACL race bearing and gaskets.
hopefully if maddat get back to me I will do a steam pipe exhaust manifold as well.

New CP Pistons below, this should take the compression ratio up to around 10.5:1.



Ross Racing Balancer, needs to go back as it didn't come with timing marks :(



Adjustable Cam gear, going to run two exhaust cams so need to adjust inlet timing.



did some work to fix the broken dump pipe, added a divider, enlarged the wastegate area to allow it to open further.



Also fixed the cracked section and added a stiffener between the flange and the O2 sensor mount, will also put a flex pipe in the exhaust to further reduce the load on the dump pipe.



Inlet manifold went on a diet with all excess mounts removed (close to 400grams removed from this heavy beast).



Ka24de throttle body attached. easy bolt on upgrade.



Sump started to be modified ready for wings and gate



Threaded insert machined to replace welsh plug on back of head for head drain.