Race motor *major* Hand-Grenade - doing forensics & need help.

[jeffstev]

My new 3.4L race motor blew up while on track at Fontana - a complete loss. I'm doing the forensics on it right now. It appears that the wrist pin failed on the JE piston at about 8000rpm and caused a chain reaction - basically it's a complete loss. Looking at the Motec log file, everything appeared normal right up until the hand grenade. the wrist pin bushings look normal but the rod bearings are a bit worn. This new motor had a total of about 6 hours on it when this happened.

full story and pics are here:
http://www.bushwackerracing.com/blowup_index.html



What doesn't make sense is the damage that happened to the right lower chain ramp. I am only guessing but it appears that ramp in question was about to fail anyway - there's no way it could have failed as a result of the blowup because cyl #3 hand grenaded (left bank) and the right lower chain ramp is the one in question. Looking at Motec it tells me that 2.5 seconds elapsed from the time the motor blew to the time I had 0 revs - not enough time to create this kind of damage to the tensioner AND have all the filings work their way down and into to the oil pump mesh.

I seem to recall pulling the tensioner out of the bottom and looking at the markings on it which said "Links" which means left in German. Is it even possible to put these tensioners in reversed (this is a late model 993 motor)? And if they were reversed, would it make sense that this type of damage to the ramp would occur? There was also a ****load of plastic debris stuck in the bottom of the oil pickup mesh which might explain an oiling problem - all of the rockers were pitted and are now useless.



If anyone has comments/ideas, let's hear them.

I'm also looking for 3.2 parts - I need to start over and it looks like a 3.4L motor based on a 3.2 case is the best way to go right now. Basically I need EVERYTHING. What do you have that I can use?

Jeff

[snowman]

Wrist pin failure?????

just looked at your pictures

COOL MAN!!!!

Lovely pictures. Those rods really looked nice before they were bent up so much.

On a more helpful note, What were a whole bunch of things before it blew up? ie piston to head clearence, valve to piston clearences, did you measure EVERY one? How high did it REALLY rev? do you have anything concrete or just drivers memory?

Take the rods apart. any excessive clearence? any scoring? or signs of lack of oil? What do all the piston tops look like? The pitting in the rockers is bothersome. What does the cam look like? take many more good pictures and maybe there will be a teltale sign somewhere. the broken wp, is it scored? Did you check valve spring bind? How much clearence did you have? What about the valve springs, any broken? Did you check all the spring pressures? if so how much?


The thing that is most suspisious at this point, not having all the information, is the pitting in the valve followers. How and why is it there?

With the additonal problem with the seemingly non connnected chain guide, I would strongly suspect a valve train problem(s).

[jeffstev]

Don't think you'd be saying "COOL" if it was your motor...

[snowman]

Yes I would say cool. Been there done that (non Porsche motor though).

[ChrisBennet]

That so, soo sucks. My condolences.
-Chris

[911pcars]

You obviously have much work and heart in this project. That sucks. Sorry to hear (and see) the aftermath. One might think that's one of the chances one takes when racing, but still, when it happens, it's disheartening.

The pitted rocker arms might be an independent incident. How's the cam lobe side of things? The broken valve head looked fairly healthy. Though I suppose should be as it's going up against mere aluminum. The broken valve might have been the beginning point of the big bang or perhaps a faulty wrist pin boss. How many hours on this 8000 rpm engine? What was the expected life expectancy? What's the weight comparison between JE and equivalent Mahle pistons? Perhaps others with more engine failure experience can contribute.

If forensics doesn't reveal anything concrete, all you can do is check and recheck, magnaflux and Zyglo until you're satisfied everything is the way it should be during assembly.

Sorry couldn't help more,
Sherwood Lee
http://members.rennlist.org/911pcars

[350HP930]

I'm assuming that a 3.4 liter motor has a 2.75" or greater stroke, correct?

That being the case 8K RPM would seem to be an excessive RPM for the piston and rod assembly.

Does JE even recommend using those pistons at that high of an RPM?

Even in a race motor there are still limits to the strengths of aluminum and steel.

[jeffstev]

All good questions and since I didn't do the assembly, I can only answer what I know for sure:

69.4mm destroked 3.0L crank. 102mm pistons. This is a "short stroke/over square" motor - high revs are supposed to be possible. JE was consulted on the motor design.

Revs: honestly, 8200 was the rev limit, and I rarely visited that spot. About 6 hours total on the motor, including idling, dyno, etc.

Piston Tops - there are signs that valves were coming VERY close to the valve pockets, based on the shadow of the exhaust gas left in the top of the piston. No "scoring" but you can see a perfectly round shadow on several of the pistons in the exhaust pocket.

Cams: lobes are perfect. I've had this problem before w/ the rockers - it was a problem with the oil squirters the last time. we changed them to the early style and got rid of the 993 ones which restrict the oil flow.

Wristpin: it's a mess from the explosion but you can see in the picture that it is actually very clean and was fine right up until it was hurled out the top of the motor. The final test on this was looking at the wristpin bushing which looks perfect - no scoring or discoloration on either surface. all rod bearings looked ok although there were some signs of wear. Journal sizes were close to within spec on the failed rod - 53.0mm but my micrometer isn't perfect.

And re: the valvetrain - my question remains - is it possible to interchange the chain ramp tensioners on a 964/993 motor?

Jeff

[TimT]

Ive seen a similar failure in a high compression 3.4 race engine, also with JE pistons. The engine I saw that had a failure like this was based on a 3.2L case, 8000 rpm redline etc.

We determined that there wasnt enough head/piston/valve clearance. One of the pistons pounded the head enough that it fractured, The piston skirt broke away, the rod pulled from the piston. And we had a pic that looks kinda like yours. It sucks when its a total loss..

This engine also had low hours on it... so figure a JE can last about 6 hours pounding the head till it fails....Its not the wrist pin that fails, its the piston that ends up cracking.... and then all hell breaks loose..



dont know about the chain ramp..

[john walker's workshop]

was the valve spring broken? i just tore down a 3.6 hot rod that must have run with a broken spring long enough to pull the keepers thru the retainer, resulting in the valve head getting bent sideways by the piston, and breaking off, punching a hole in the piston and bending the rod. luckily on decel @ 3500. i was going to use J&Es on the rebuild. now you're scaring me.

[juan ruiz]

That REALLY REALLY REALLY SUCKS BIG TIME! BUT guys when I did my research I have hear at least 15 different hand grenades ALL of them with JE Pistons coincidence ? Im not sure but I did stay away just for the fear.

[TimT]

John, Juan....... dont dismiss the JE pistons

I have them in two of my cars. One of which is a 7800 rpm engine..My 2.2 is a high compression zero clearance engine..no problems with piston failure. We have engines that have been in service many years using JE's

My 914 is tame at about 9.3:1..........

Juan my friends monster turbo engine making over 700rhwp uses JE...

Im going to post some ugly pics now.............This piston failed because of valve train problems....not problems with the piston..

[TimT]

another pic

[juan ruiz]

Tim, I know that you use them is just weird that all the ones I hear all had JE Pistons.

[ChrisBennet]

Originally posted by juan ruiz
Tim, I know that you use them is just weird that all the ones I hear all had JE Pistons.

Maybe it's a stastical thing? If most people use JE pistons, most failed pistons will be JE's or something like that.
-Chris

[jluetjen]

Judging by the posts that I've read on the BBS (and most of the responses on this thread so far), most of the people who do build "full-race" 911 motors use JE's. Chris is right, given that piece of information, I'd be shocked if most of the situations like this DIDN"T involve JE pistons.

But then did anyone else noticed that all of the "grenades" discussed here so far involved a 911 motor??? Maybe they're not fit for racing???

[911pcars]

"If most people use JE pistons, most failed pistons will be JE's or something like that."

I dunno. Do most amateur race folk use JE's versus Mahle's? What do most pro teams use? JE's, Mahle's or ?? The statistical sample on this thread/forum may be a bit too small to determine.

Sherwood Lee
http://members.rennlist.org/911pcars

[TimT]

I could post some pics of Mahles that bought the farm....

I believe in the pics I posted, and in the pics Jeff posted. The pistons failed because of some outside influence, ie insufficient clearance, valve train issues, broken valves etc.

You can also hole a piston if you let it run to leans for extended periods..or burn the top ring lands...all of which suck.


The engine that toasted the piston I showed was 12.5:1 with a monster cam (huge lift) 8200 redline 375 at the wheels.. We know this engine has been over revved (missed shifts, downshifts),

If the JE'd were such a potential problem, I dont think they would be so widely used in the racing circles..

[cstreit]

I keep coming back to this thread, like slowing down for a highway wreck. Sorry to see this mess man!

[Wayne 962]

How were the rod bolts on this engine? Was the piston / head (deck height) checked before assembly (documented in the book). All of the checks that are detailed in the book need to be done, especially on close-tolerance engines like these.

I think that most 'custom' engines use JE pistons, which means that these 'experimental' high-output engines would tend to show more failures...

-Wayne