Piston failure

[Walt Fricke]

One way to move the pin up, thus allowing the benefits of a longer rod, is to run only two rings. Porsche did this on some of its racing pistons. Should allow a bit more room for beefier pin bosses, if that has anything to do with this kind of failure.

1) Which ring gets deleted? 2d or oil?

2) By how much does this shorten component (ring, piston, cylinder) life? Shorter ring life might be OK for 40-80 hour amateur race motors. Bit costly if the more expensive components need more frequent replacement.

3) How does having two rings save weight (beyond the weight of the missing ring)? Add back in the weight of the missing land, plus the extra weight of the longer rod.

You don't hear much about 2 vs 3 rings - what's the drawback for racing?

I don't know about 98s, but I weighed a 95mm J&E bare at 470g. While perhaps not a good comparison, a used Alusil Kolbenschmidt stock 9.3/1 95 weighed 530g. (knew there was a reason to keep those pistons).

Walt Fricke

[cnavarro]

Usually you delete the second ring, and the oil control is very small, 2mm or smaller if I remember, since JE does have a line of two ring piston rings. I'm not sure if the weight savings is that monumental. I'd be willing to bet you'd save more just doing a lighten combo on any given piston.

The majority of the flat top pistons I make run a 1.112" pin height with a 22mm pin. On the 356, it is a 1.065" pin height, again with a 22mm pin unless they use the rods I make, then I set it up with a 19mm wrist pin - lighter pin, more material around the boss, lighter pin end on the rod. Any weight savings on a 356 translates directly to longer rod bearing life.

[304065]

Walt, I found an interesting article on this, cite below:

What if no second rings are used? It is possible to delete the second rings in a performance application. Doing this, in conjunction with a file back top ring (with a fairly small gap) can reduce friction, and it can also allow the piston to be shorter in the ring belt region with consequent weight savings. However if oil consumption is to be kept under control the oil ring needs to have more load, and this negates friction benefits. However blowby can be less with only one compression ring. Formula One engines have only one compression ring.

http://www.autospeed.com/cms/A_108913/article.html

I have seen some SINGLE-ring pistons but I don't know how you would get away with that unless you are using a two-stroke. Where it says F1 engines only have a single compression ring, they MUST mean one compression and one oil ring, because oil has an octane rating of zero!

Just for fun, here's a photo from www.elevenparts.com of an old Carrera GS piston! Count those rings!

[cnavarro]

A vacuum pump would also help with the oil control on a two ring piston engine. Not exactly ideal, but that's what many do to get away with low tension rings on drag engines.

[Grady Clay]

Good discussion.

Dave, sorry for your misfortune.

Something not mentioned here are operating conditions (other than over-rev). Detonation can be an issue if the piston is already ‘fragile’ in this area. Even a slight ‘hydraulic lock’ only once can damage the pin or piston. Of course temperature is always an issue.

Another clue is finding pistons with cracks at the pin oil hole. That tells me there is some issue with the piston.

Best,
Grady

[cnavarro]

With the forced pin oilers, I'm wondering if there are stress risers introduced, pre-disposing the pistons to fail at the oilers. Same idea goes for connecting rods - when they edm the oiling hole down the middle of the rod, if you don't extrude hone the passage, the rods crack and fail, starting at the hole. Short of extrude honing the pin oilers, it may be best to leave them out and look at other solutions for pin oil retention and longevity. Calico offers coatings for wrist pins as does Anatech, Ltd with their thin film diamond like carbon coatings, typically reserved for Ti valves. Another thing I have been looking at for some time is micro dimple formation. WPC Treatment does this (www.wpctreatment.com).

[cnavarro]

I'll revive this thread to let everyone know that JE has come out with a radically different forging specifically for the 95-105mm bore sizes for Porsches, espcially beefed up around the wrist pin bosses but should not add more weight to the piston overall from what I was told. Very similar to what CP sells now. Better yet, no added price for the new forgings.

I've also spent the last two months researching the modes of failure for 2618 forgings and have come up with some ways to improve the high temperature/high stress micro-fracturing of pistons under extreme loads. Weight reduction, i.e. JE's "lighten combo" can help save some weight. Also, a thermal barrier coating can reduce the crown temperature about 100F, which is pretty substantial considering the temperature at the top ring lands do not typically exceed 200C.

Additionally, one could always have the rods bushed for smaller wrist pins (or made up to use smaller ones), which would increase the cross sectional strength of the wrist pin bosses. That's what I have been doing as of late, making rods with 19 and 20mm wrist pins.

[Fishey]

Just to add some information to this thread.

J&E 3.4L Pistons have gone through 3 revisions and the new design is not bad but pretty much anything pre-2009 is going to fail. The originals will fail in short order and usually at high RPM meaning catastrophic engine damage. If I had these in my car I would spend the money now to tear it apart and remove them. If you do not know what you have in your car then tear it apart and replace the pistons. The fail rate of the early pistons is 100% I have seen atleast 10 failures. All of them have caused serious block damage as a result. I know they attempted to fix the problem on the piston by moving the oil galley machining on the original forging away from the thin spot at the wrist pin. It did not work so even the 2nd generation pistons fail that being said they might be alright for normal street use. The 3rd generation of this piston is an entirely different forging and they are strong as hell completely redesigned and if they fail it is the result of a poor build/tuning.

[cnavarro]

Originally Posted by Fishey

Just to add some information to this thread.

J&E 3.4L Pistons have gone through 3 revisions and the new design is not bad but pretty much anything pre-2009 is going to fail. The originals will fail in short order and usually at high RPM meaning catastrophic engine damage. If I had these in my car I would spend the money now to tear it apart and remove them. If you do not know what you have in your car then tear it apart and replace the pistons. The fail rate of the early pistons is 100% I have seen atleast 10 failures. All of them have caused serious block damage as a result. I know they attempted to fix the problem on the piston by moving the oil galley machining on the original forging away from the thin spot at the wrist pin. It did not work so even the 2nd generation pistons fail that being said they might be alright for normal street use. The 3rd generation of this piston is an entirely different forging and they are strong as hell completely redesigned and if they fail it is the result of a poor build/tuning.

I'm sorry, but this is just not true. You're statement that all of them are going to fail is just ludicrous. I can't even begin to imagine how many thousands of JE pistons we've sold and I can only recall one failure of the wrist pin boss reported back to us when fitted to our cylinders. It was on a 105mm bore, 12.5:1, with a piston over 600 grams in a full race engine and had 235 hours on it when it failed. They should have been houred out long before that.

I have fielded plenty of phone calls with piston failures from other brands including Mahle Motorsports, Wossner (I think at least 3 with failures in our cylinders), and others, so this problem isn't something isolated to one brand and certainly it's not epidemic. One reason you see less of the Mahle ones fail is that those tend to be houred out earlier. I know of several builders who hour them out at 100 hours. Technically most pistons should be houred out no later than that in race use, but no one does. They wait until their engines go boom instead.

[dbanazek]

Charles, is the part where they made a 3rd generation forging accurate to your knowledge? It seems to me the main problem was the thickness of the material below the wrist pin.

[Tompickett]

I have an '88 Carerra in which I used 98mm JE pistons and Nickies cylinders supplied by Charles Navarro; the car is driven mostly on track around 200 miles a day. I have 26,000 miles on the engine and 201,000 miles on the chassis.

I have had no problems at all, installed them myself in my garage...

I think maybe considering the number of JE pistons out there a few failures would be logical, wouldn't it?

[Henry Schmidt]

Originally Posted by dbanazek

Charles, is the part where they made a 3rd generation forging accurate to your knowledge? It seems to me the main problem was the thickness of the material below the wrist pin.

If I remember this issue correctly, JE determined that they were using wrist pins that were flexing (too thin?) and that flexing and extended use fatigue caused the piston failure.
They have responded with piston updates to address the failure but I believe the "real" solution was a better wrist pin and educating customers as too the life expectancy of any racing component.

[chris_seven]

IR Telemetrics, Inc. - Wrist Pin Sensor

It seems reasoanble to assume that pins that deflect too much will significantly affect the clearance between the pin and the piston and generate high levels of stress

It seems quite difficult to model the behaviour of the pin/rod/piston interface using numerical methods and I have seen FEA solutions that predict maximum defletion at the free ends of the pin and other solutions that show maximum delection in the centre of the pin.

May be the telemetry system may help.

[EBS_Don]

It's likely a combination of using lighter(thin wall), more flexible pins and pin towers that flex with them. Newer forgings and especially the FSR version goes a long way towards solving this issue using shorter pins in conjunction with a considerably more advanced pin tower reinforcement design.

[HawgRyder]

Just to add my $.02
You can run a single compression ring and one oil ring on a piston.
I have done it several times with good results.
BUT...you need to use a Total Seal type ring for the top...and a good quality oil ring.
AND...I used Teflon buttons on the skirts of the pistons to keep it straight in the bore (to prevent piston rock).
In this way the buttons reduce the friction way down (benefit of no skirt scuffing)...and the oiling requirements are less too.
Bob

[cnavarro]

Here is the answer straight from JE:

"Six or seven years ago we received requests for a more durable Porsche piston for racing applications. We replaced to old 96P forgings with the new 32P forging. The new forgings are internally braced and gained some weight. To address the extra weight and produce a modern racing type forging we produced a Forged Side Relief forging called 932P."

The 32P forgings have been the same for six or seven years and are still used today for the majority of jobs. The FSR is an upgraded piston that is lighter.

[JohnJL]

5 years in now with at least a thousand hard miles on 12psi supercharged boost and my JE s showed no sign of problems when I did a preventative rebuild last winter. The skirts and domes are coated and all were intact.

[Walt Fricke]

Bob - do the Teflon buttons replace the piston pin clips?

If they do that reliably, as well as reducing rocking, and last at least 100 high RPM hours, they sound like a winner all the way around. I've never understood why J&E doesn't cut its pistons for a regular circlip, with ears and holes, so installing and removing the pins is easy.

I got used to the clips Mahle uses. Despite having Stomski's install tool, I still find the J&Es tough to install. And instead of just using a machinist's scribe or the like to remove them, I had to cut a notch in the end of a pin drift, which I insert in the relief and then twist so I can get a scribe in to start teasing the clip out. It all seems so much more difficult than using snap ring pliers.

[fredmeister]

Originally Posted by Walt Fricke

Bob - do the Teflon buttons replace the piston pin clips?

If they do that reliably, as well as reducing rocking, and last at least 100 high RPM hours, they sound like a winner all the way around. I've never understood why J&E doesn't cut its pistons for a regular circlip, with ears and holes, so installing and removing the pins is easy.

I got used to the clips Mahle uses. Despite having Stomski's install tool, I still find the J&Es tough to install. And instead of just using a machinist's scribe or the like to remove them, I had to cut a notch in the end of a pin drift, which I insert in the relief and then twist so I can get a scribe in to start teasing the clip out. It all seems so much more difficult than using snap ring pliers.

Great question, I just fought for what seemed hours trying to remove the clips on my JE pistons. Having a normal circlip or at least a little tail on the wire clips to aid in grabbing with a set of needle nose would help tremendously.
Why does JE go this route?

[KTL]

I rotate the clips in the groove to get a free end near the pick hole. Then I coax the clip out of the groove with a pick (of course) and then grab the end of the clip with some small needle nosers. Not saying its easy peasy japanesy. Just saying that's how I do it successfully without too much swearing.