MarkRobinson

Just got off the phone with my 40-year experienced European machinest: My valve stem "popped" in half due to fatigue/defects beyond human eye or metallurgy issues.

I had just started up my race car & it had idled for about 30 seconds before I heard a brief clatter (like a tool had slide off the car & was falling through the engine bay), then the engined stopped. I checked the t-belt, was still on, so we tried to re-start in case it WAS a tool that had fallen, but a brief bit of noise while cranking & then it stopped. Then it was seized.

With the breaker bar, engine only turns 45 degrees either way before stopped.

We hoped it was the clutch, but after inspection ascertained it was probably in the rotating assembly or valve train.

A few hours later I had the cams out & saw an odd valve spring retaining assembly on the #4 where the spark plug came out with a mangled ground strap: the valve had snapped just past the retaining assembly: so tip of the valve, both keepers, & the retainer all still together as one assembly. The vavle was no where to be seen: all the way inside the combustion chamber.

I have the head mostly ready to come out tonight so will have ugly, UGLY pictures to share tomorrow.

FWIW, entire engine is stock/resealed 86.5 engine, no track time, head recently R&R'd by me. Machinest said he's seen it before but not very common: he highly doubts it was anything i could have done. I've performed a number of valve jobs before on 928/951 heads & never seen anything like this before. Bummed. I may have to give last rights to my engine tonight.

9x8

Daym Mark, that sucks.
Did you replace valves or it's the original one?

MarkRobinson

Originals, within spec out of 98k engine. I have extra heads, valves: more concerned about possible damage to the block/rotating assembly and the chance it happening again, though probably pretty remote.

9x8

Fingers crossed, but unfortunately the bore is very likely to be ruined.

BC

Amazing that this happens in an under .05% case basis after 25 years and 100k miles.

Simply amazing.

IcemanG17

it happens....... Sean had a stock 5.0 S4 engine suck an exhaust valve at Thunderhill a while back.....here is a video of someone following behind him....talk about SMOKE

BPG_Austin

Crap! Sorry to hear Mark. Hope its in better shape than you think when she's opened up..

MarkRobinson

Yeah, looks like it would have been a bigger issue than that. I was wondering why there was oil in my #4 when I pulled the spark plug: uh, because there's no valve stem to keep the oil out??? :/

86'928S MeteorGrey

Major bummer! I'm saying a little prayer for your cylinder wall...

IcemanG17

Seans engine was UGLY.....think crack in the oil pan from where the rod hit it ugly.... There are pics on here somewhere

SeanR

Dang Mark, sorry to hear about this, was looking forward to seeing it run.

GregBBRD

That sucks. Sorry about your problem.

Mike Simard had this happen to one of the TRW "aftermarket" 968 intake valves. Right at the base of the lower keeper groove.

If you look at these valves closely, under magnification, the keeper grooves are very chattered from being machined, which will allow a stress riser to form.

You should be able to see something that allowed the crack to form in your pieces.

MarkRobinson

A few ugly pics. Piston & ( won't chance the rod) are trashed, head can be repaired, block is reusable: just have a little scratch/gouge to fix: delighted about that all things considered. :/

Last picture: the 3" merge towards the turbo off the factory (prior-owner-mutilated cat-removal) Y-pipe.

Cosmo Kramer

Ouch! I guess not bad considering what it could have done. Can you tell where it broke or is the valve too badly mangled?

MarkRobinson

Yes the last keeper grove it appears is where it popped in half. The keepers, retainer, & tip of the valve are still one assembled unit. :/