J&E Piston failure
 

Anyone else have a J&E piston (95mm) rip apart?

Has J&E improved their pistons since this 96P model? I'm not going to use 96P again in any case.

http://forums.pelicanparts.com/uploa...1362797481.jpg

Could have been worse. Broke two rockers, bent both valves. Maybe the head can be saved. Cracked the cylinder - that's a new one on me, though much better than my several previous engine blowups, where the rod with wrist pin attached broke the cylinder apart and then started in sawing slots in the case. Here it just cut grooves in the cylinder. At the moment I can't get the cylinder out, due I suppose to its having been hammered to a larger spigot OD, or the crack did that. Remains to be seen if the Pauter rod is still straight.

Happened on the chassis dyno last spring. Engine had only chassis dyno time from a year earlier. Took me a while to get around to taking the head off to see just what had caused the problem.

Walt,

Ouch! I am so sorry to see that.

One word: Mahle

Scott

I've seen several of those before,....dyno only time, too.

Ouch x 2!! Sorry Walt.

What are the circumstances of the failure? High load/ high revs, like Steve has seen on the dyno failures, or engine at constant load?

Walt

Thanks for starting this thread.

I am beginning a 3.4 build for my wife's '72T using a 3.2 from an '86 Carrera. I have Mahle barrels but not the pistons.

Build will include twin plug, 993 SS cams, extrude honed intake, Steve Wong throttle body and chip, 1-3/4" exhaust and magna flow mufflers.

Do you or Steve have any recommendations for pistons outside of JE's as I don't need the same results as Walt? Or are their 98's ok. I plan on using 10.5:1 CR units or 9.8:1 for better streetability.

John

Really sorry to see this Walt :(

What are other good options for custom pistons? Soon I'll be rebuilding my 911 motor that has an unusal configuration 93mm x 66mm. I have Mahle pistons in it currently and have been happy with, but I can only get 10:1 compression due to my motor's short stroke (the pistons give 11.5-12:1 with 70.4mm stroke).

I know there are other custom piston manufacturers, e.g. Wiseco, Ross, Arias, etc. Or a different model piston from JE? I think I've seen some mention of that in other threads.

Scott

Scott,

You can add CP to that list as well. Nothing off the shelf that I know of but they can build you nice custom pieces for sure. Make sure they know what you need it to do, endurance is the word I use.

Walt,

J.E. updated the forging for the 95-98mm forging some time back. Were you running tapered wristpins?

Scott, the only pistons that had issue were the one's walt was running. We ran 93's from J.E. to 8700 rpm with no issues.

Wow. How many RPM? Scary.

Wasn't 95mm.... another from the collection of horrors. With the exception of this, and on other failure I can remember we have had great success with JE pistons.

Not really sure what caused the failure in the pic I posted, did the piston sieze in the barrel and then the rod pull out and flailed around? or did the piston fail first.. or did the rods seize on the crank... etc...I cant find the pics but the rod that mated to the piston pictured was twisted up like a pretzel..

http://forums.pelicanparts.com/uploa...1362870833.jpg

Could this be a symptom of the inertia of the rollers on the dyno?

Well, I ran it up to 8,000 or so (EGTs and AF looked OK), and then backed off and started a recorded run. Some way into that run (I think we were using 4th, looking to start at 4000 or 5000, and don't recall if I had gotten to 4th or not) I got the shut down signal from the dyno owner and my wife. Smoke out of the right rear megaphone. After shutdown, oil dripped out also.

After this happened I recalled the buddy who had it happen to him on two engines in a row at the track.

The pin boss (if that is a suitable term) is only about 4mm wider than the pin, leaving 2mm per side at the pin centerline to hold the forces trying to yank the cylinder down during the intake stroke. The pin does not extend out beyond this part of the boss - the groove for those horrible clips is right at where the skirt part starts.

I'll have to check to see what pins I have - whatever came with it.

These pistons, after I had them recut for larger intakes, and again to get enough valve clearance, were 12 to 1 CR measured, on a 66mm stroke with 3.2 heads. I'm debating going back to 10.5/1, but CR didn't seem to affect this. No signs of detonation. Nothing special to indicate this was caused by this piston sticking up around TDC. Top two rings look pretty good, considering (lands a bit compressed in spots, so they don't want to slip out

Re: J&E Piston failure
 

Wow. Interesting. Looking at the piston I would say the design just doesn't have enough material between the wrist pin and dome.

Walt,

One word: Mahle

Scott

I've heard rods usually let go if they're going to at high rpms right when the throttle is lifted after hard sustained running or acceleration. Did that piston let go under full load and full throttle or right when you let off?

I've also heard Mahle pistons and cylinders are more reliable and last longer than any of the alternatives placed into 911 motors.
That makes sense to me knowing they were made for each other from the beginning by incredibly good German engineers.

JE had a problem with that forging which affected their 95mm & 98mm pistons a few years back. AFAIK, its been fixed with an entirely new design.

I saw a good number of failures using the 98mm ones so we switched to a custom Omega piston.

It was under full load, accellerating the drum of the chassis dyno (inertial type).

Letting off the throttle at full load at high rpm is pretty common on a race motor under normal track conditions. Like about for every corner of any significance. I am dubious that this is related particularly to an inertial chassis dyno, but am open to theories. Closed throttles = high vacuum = more downward load on the wrist pin?

Checking my invoices, I see that I purchased these in 2005. I just didn't get around to building the motor until 2011. The long stroke 2.8's 10.5:1 J&E pistons were purchased in 2007. They have happily spun up to an 8,200 shift point for quite a few racing years.

Perhaps somewhere in between was when J&E changed?

J.E. changed the forging and no longer supply the tapered pins. These two changes were done at the same time, so it is hard to say which one(or both) caused the issue.

What did your pistons weigh in at? Any undercrown milling done to reduce weight. It doesn't look like it from the pic.

Some interesting information here: :http://math.mit.edu/classes/18.086/2008/final_report_dongfang_bai.pdf

Anyone know if the JE piston marking under the crown "97" means this is the improved design? I have a set of 98mm pistons that have the marking in the forging that says "97". Its in the flat area of of the piston dome between the wrist pin bosses. I took this to be in internal JE part number for the forging blanks they use.
I just had these made a year and a half or so ago. No troubles with these pistons yet in my 3.4 liter turbo engine. Its not routinely revved beyond 6600rpm though.

Thanks,
Fred

OMEGA . Went this route after three different JE wrist pin boss failures on my 3.4....

We saw a number of JE piston failures in our Norcal area several years back (mid last decade). Quite a few of them were 98 mm pistons that failed in the wrist pin area. We also saw some failures in larger displacement apps. My own 102 set suffered from cracks in several domes at about 25-30 hours of under 7500 max revs. The cracks got big enough for massive compression loss at RRIV at Laguna in the Sunday Group 7 race.

One NorCal driver/engine builder saw some big ones fail after about a half-dozen hours if I recall correctly.

My engine builder was one of the last holdouts to try various "new and improved" JE designs. But he has given up during the past few years, resorting instead to off the shelf and custom Mahle pistons for many applications.

These experiences were all with racing applications.

We have always liked Omega Pistons and have used them in 80 to 85mm diameter in early engines with good results.

http://i197.photobucket.com/albums/a...ps8d4e0afd.jpg

For 3.0 litre Engines we have used CPS Pistons with a similar design

http://i197.photobucket.com/albums/a...psfa783a8b.jpg

For the next engine we build we are going to try a Double Bridge design as we are trying to push revs a little higher.

http://i197.photobucket.com/albums/a...ps3b9c5840.jpg

JE has redesigned their shelf piston for exceptional longevity.
Most failures we see in the modern casting are because people refuse to establish a reasonable life for racing parts.

Here is a comparison of the old JE vs the new JE FSR piston. These are 100mm.

http://forums.pelicanparts.com/uploa...1363218013.jpg

Does this mean that all JE Porscge pistons now use the FSR Design and are automatically supplied is this form?

No Chris
It means that they have forgings in some sizes and you can order any piston that can be machined from those forging.

Zero pin boss failure, 100 hour rebuilds, 500 hour pistons, every shift at 8600+, high compresssion, high horsepower, 3.367 high butterfly / kugelfischer with oil temps <180°F. Possible?

Walt, with all the things that maybe going through your mind, don't forget to check the oil system to make sure you don't have any potentially damaging metal particulates in the system.

I have recently found that to be THE most troubling part of a rebuild after a failure. Is it clean enough is the question always running thru my mind. You can't leave anything to chance and have to disassemble everything down to its base parts, or sometimes dispose of things.

You never know where FOD will lurk. A good example is the timing chain. Lord only knows what debris gets lodged in there when broken parts spew debris. Those chains are FOD collectors and no way should they be reused.

Even when you get stuff back from the machine shop after reconditioning, you have to clean it. I had a reconditioned rod come back with grit in the bolt head recess (think rods with threaded caps like Carillo, Pauter, Arrow, etc.) and it munged the threads a bit. That ticked me off to say the least......

The piston on the left looks very much like the forged piston I was referring to with the "97" marking on the crown a little earlier in this post. Its is still a forged blank-not cast so I am hoping it is one of the modified designs and I am not going to have a short lived engine. Its not as nice as the one on the right (FSR) though...thats the top of the line they offer.
FWIW, I don't have a racing 3.4 (98mm) turbo but do drive 50% DE and track days.

JE is supposed to be top notch and recommended by alot of top engine suppliers in Pano and Excellence. This talk of exploding pistons is pretty disturbing.

Fred

This noise is old news. JE confronted this issue and corrected it at least 6 years ago. There are some old pistons floating around so if you're not certain of your piston design, don't use it for long life (high hour) racing. Always establish a reasonable life for all racing parts and count that in your budgetary concerns. If you have an old set and you're running it under moderate conditions, make sure you run straight/ thick wall wrist pins not tapered.

Thanks man. Looks like I am good.

Thats a load off my mind. And a load off my pistons too, ha,ha.

Fred