J&E Piston failure

[Walt Fricke]

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.



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.

[winders]

Walt,

Ouch! I am so sorry to see that.

One word: Mahle

Scott

[Steve@Rennsport]

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

[AlfonsoR]

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?

[s9motors]

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

[stownsen914]

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

[PFM]

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.

[BURN-BROS]

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.

[Cupcar]

Wow. How many RPM? Scary.

[TimT]

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..

[304065]

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

[Walt Fricke]

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

[Lapkritis]

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

[winders]

Walt,

One word: Mahle

Scott

[JFairman]

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.

[Steve@Rennsport]

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.

[Walt Fricke]

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?

[Walt Fricke]

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?

[BURN-BROS]

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.

[chris_seven]

Originally Posted by Walt Fricke

Closed throttles = high vacuum = more downward load on the wrist pin?

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