Blew my s50

[savage217]

I was at the last NHMS event of the year and on my 3rd or 4th lap exiting the oval, my engine shit the bed. After further inspection there is absolutely a hole in the piston and it looks as though it has nothing to do with the valvetrain. No valves seemed to have dropped. This happened to cylinder # 4. It looks as though this was a result of pre ignition, based on the spark plug and what I can tell from looking into the spark plug hole.

My question is, what the hell would cause this, and why in only one cylinder?

The last thing I did to the engine was a headgasket job. At the same time I replaced my fuel pressure regulator, installed 24# injectors that were supposedly refurbished and tested, and a TRM chip programmed for the complementary modifications. Every now and then I would get a check engine light at 3k rpm on the street, under normal driving but it never seemed to occur on the race track ever. This is supposedly somewhat common on 95 s50 engines. The code said it was for knock sensor 4-6 IIRC. What could have caused this issue? It happened at WOT FYI. See spark plug picture. All the others came out perfectly fine and looked normal. This one would not budge, now I know why.

[magnetic1]

rod bearing failure or rod failure sending the rod up making contact w/ valves and hole in block.

Is your oil pump nut secured?

[99MPower]

FYI, but I have some friends in the area with good condition s52s... let me know what your plan is....

[JETninja]

Wow, bummer Dude! That is strange....

[savage217]

Why in cylinder number 4 though? Not doubting you but why that cylinder? In the past I dropped a valve in that cylinder when my retainers let go. Luckily it did not do any mechanical damage to the piston (just an imprint). Ever since then it seems like that cylinder has been where headgasket leaks have been or small amounts of pre detonation, based on what the machinist was telling me when he was inspecting and machining my head for reinstall.

Yes my oil pump is secured. I safety wired it a couple years back and to my knowledge I had normal oil PSI. I dont remember looking at the gauge on the track but on the way up it was always about 60psi under load or around 3k rpm.

Calvin, I am looking for good condition s52's. Definitely let me know. I do not want to spend a ton obviously but am looking for deals.

[rpob5t]

yeah definitely a bummer dude, unfortunately I've been there, myself:

http://www.flickr.com/photos/2815744...7622416444982/

Did she tighten up at all or just go bang and sound like a handful of change is a dryer (mine went bang)?

If you spun a bearing it'll usually tighten up and you'll develop a knock first but not entirely uncommon to just let go (esp at WOT).

My dead M20 I narrowed down to a broken valve, 99.9% of factory valves are 2 piece and can sometimes fail at the weld; basically the head pops of the valve, the piston and valve have a co-spacial event and the valve wins shattering the piston (esp so if its cast, if its forged it'll probably just punch a hole in it). Not sure what your head side of yours looks like if its anything like that you might have had a similar issue (esp if its high mileage or has been tracked for more than a few seasons).

[magnetic1]

No clue why it is cyl #4. Could just be random but when Ive blown these motors, it always seems to be #4 or #5. Take the block apart and you will likely find the root cause.

[jbrannon7]

I don't understand. If "no valves dropped" what beat up the spark plug?

If it was a peice of a valve that beat it up then a valve most likely dropped. Over rev? Valve stem to guide clearance? Who can tell now.

Pre ignition usually burns the end off the spark plug and burns a hole in the piston.

You need to provide more photos and information.

I was at the last NHMS event of the year and on my 3rd or 4th lap exiting the oval, my engine shit the bed. After further inspection there is absolutely a hole in the piston and it looks as though it has nothing to do with the valvetrain. No valves seemed to have dropped. This happened to cylinder # 4. It looks as though this was a result of pre ignition, based on the spark plug and what I can tell from looking into the spark plug hole.

My question is, what the hell would cause this, and why in only one cylinder?

The last thing I did to the engine was a headgasket job. At the same time I replaced my fuel pressure regulator, installed 24# injectors that were supposedly refurbished and tested, and a TRM chip programmed for the complementary modifications. Every now and then I would get a check engine light at 3k rpm on the street, under normal driving but it never seemed to occur on the race track ever. This is supposedly somewhat common on 95 s50 engines. The code said it was for knock sensor 4-6 IIRC. What could have caused this issue? It happened at WOT FYI. See spark plug picture. All the others came out perfectly fine and looked normal. This one would not budge, now I know why.

[Def]

Detonation will usually make the piston look like the exhaust side has been melted and eroded away on the ring lands. Sometimes it'll go straight through the middle of the piston, but that's pretty rare on an engine with oil squirters (the piston is cooler/stronger in the center).

[sak335]

Looks like the result of an over-rev to me. Valve probably got bent in a minor way a while back and fatigue finally set in, breaking off the head of the valve. It bounced around inside the cylinder until it vented the piston.

[savage217]

Looks like the result of an over-rev to me. Valve probably got bent in a minor way a while back and fatigue finally set in, breaking off the head of the valve. It bounced around inside the cylinder until it vented the piston.

I just had the head off earlier this year. I did not notice anything and I had the machinist check it over as well for cracks and had it shaved. I have never over revved this on a mis-shift however occasionally I will bounce it off the 7k rpm rev limit while autoxing.

[Tom R]

did you change the valve seals when did your HG change. old seals can allow oil to enter the combustion chamber. Oil in the combustion chamber lowers effective octane rating of fuel mixture.

just a thought since you report no over-revving and some knock sensor problems.

wont really know until you tear into it. post pics.

[magnetic1]

I just had the head off earlier this year. I did not notice anything and I had the machinist check it over as well for cracks and had it shaved. I have never over revved this on a mis-shift however occasionally I will bounce it off the 7k rpm rev limit while autoxing.

Maybe a retainer or spring let go. That's what happened to mine:

[mtrsprt]

Here's my guess.
You say you dinged the top of piston #4 earlier and left the piston in? How big was the ding? Did you make an attempt to repair that ding, by sanding it, or smoothing it out in anyway?
If not, then it is entirely possible that the edge of that ding created a "hot spot" in the cylinder combustion chamber. That would then create a situation of preignition, and could've destroyed the piston that way.

Or, like what happened to me on my 2.5 S14 years ago, it was just a lean condition in that cylinder because of a failing injector (also rebuilt 45 minutes of track time earlier... same age as the motor). I melted through my piston like that, in cylinder 3. That went at WOT and ended in a bang and puff of smoke, on track.

The first scenario, with the hot spot, happened to me in a 911 turbo I had. That was due to an improper install of a retrofit factory head gasket, by a lazy Porsche Tech. Part of the S.S head gasket for that cylinder remained in the combustion chamber... Picture a ring in the shape of a D, rather than an O. The part in the combustion chamber was always glowing and causing preignition... Until the rod bearing spun and shot the rod through the crank case... The motor stopped instantly with little noise, if any (at least not louder than the ridiculous exhaust sound), at about 65 miles per hour on the highway in 5th gear. Since it is a dry sump motor, there was no oil on the ground for easy diagnosis.

Sorry to hear it, though.

[savage217]

Maybe a retainer or spring let go. That's what happened to mine:

Wow it definitely could be that. Inititally that is what I thought happened but I thought I would have seen other evidence to steer me more towards that. It does make the most sense though. I need to just pull the damn head off and see.

Mtrsprt, thanks for the info. At this point it could have been anything you decribed. I do not think the dinged up piston was an issue as it was minor but anything is possible. The injector is an interesting idea too.

[csr]

Dropped valve head. The spark plug looked chopped off just like yours.

[fsmtnbiker]

A dropped valve is what causd a failure like that in one of our cars as well. Bummer that it happened, but at least it was at the last event of the season and not the first!

[Def]

Yea, sounds more like a dropped valve with that much spark plug carnage. Both the head and block are usually trashed, although sometimes the block survives if the cylinder walls aren't gouged too badly.

[odortiz]

i dropped a valve once at vir and was lucky enough to feel the instant loss of power, shut it down and coasted to a stop. no real damage besides a bent valve. it happened months after a friend over-reved the engine. i've gotten 2 free engines that did the same, except they kept driving till the valve head found its way to the oil pan through the piston.

[JS154]

rod bearing failure or rod failure sending the rod up making contact w/ valves and hole in block.

Is your oil pump nut secured?

yeah that's piston to plug contact alright. Check your other rod bearings for signs of detonation, but I agree with Wonger.

[magnetic1]

yeah that's piston to plug contact alright. Check your other rod bearings for signs of detonation, but I agree with Wonger.

Yea. If there is a hole in the block itself, the rod had to have failed. Either by way of rod bearing failure, connecting rod bolts, connecting rod itself, or something.

If no hole in block, then valve dropped or made contact w/ piston somehow to muck up the spark plug like that.

Only way to tell is to remove head and/or block.

let us know!

[savage217]

Thanks guys. I plan on starting to pull the engine this weekend. Hopefully will have an s52 in it within a month. I will take it apart once it is out of the car. Anybody need any s50 parts

[///M3Augy]

I want updates Nick!

[JS154]

yeah that's piston to plug contact alright. Check your other rod bearings for signs of detonation, but I agree with Wonger.

now that is see the other photos it looks like a dropped valve head.

so why? is the neighboring valve bent? the rod bearings may help, but they are probably pretty hammered if they weren't already wasted.

if the other valve is not bent, sounds like the valve head let go. if the other one is bent, than it was probably caused by detonation killing the rod bearings and the rod reachsing the valves. one went before the other, and the plug was collateral damage. that doesn;t look like a detonantion melted hole to me.

[jimmypet]

As another data point (non S5X), on one of my S14s, a piece of a piston top broke off, just above top ring (probably due to detonation via possible failing injector, I'll never really know) and rattled around in the combustion chamber wreaking all kinds of havoc looking very much like you have shown (actually Eric Wong was passing me at Summit when it let go).

When I pulled the engine apart, piston top was broken (about a 3/4 - 1" long piece along the radius just above ring #1 missing).
The piece was gone (ejected out a valve presumably).
Had a peppered head, some beat up valves, mashed spark plug).
Other than that no evidence of what or why it had happened.
The other 3 cylinders were perfect (still are, the short block is sitting in my basement awaiting its turn at rebuild).
I drove it in, a whole lap at Summit Point running on 3 cylinders.
Cheers
jimmy p