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Angry Piston Failures

Rebuilt 1968 911T motor 12 months ago in 914-6. Upgraded engine performance with Solex cams, larger carb parts ( jets, venturis, etc.) and 9.8 to 1 compression ratio Ross pistons. I have experienced two identical piston failures since the rebuild. The failures were on cylinders #1 & #4. Post failure piston examination / analysis revealed the skirt which forms the lower circumference of the exhaust valve pocket was fractured. There was no damage to cylinder head with the exception of piston debris. Discussions with piston manufacturer proved fruitless regarding root cause analysis. Mechanic and machinist are pointing fingers at piston quality / design. Ross is pointing fingers at tuning. Opinions?
Old 08-08-2002, 08:11 PM
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Did the exhaust valve and piston touch each other in an inappropriate manner?

What did the spark plugs look like (as in white, glue bubbled, etc)?

What did the tops of the pistons look like (other than hammered, looking for vaporization of aluminum)?

Were the piston skirts scored?

Were the top rings broken?

Ok, other than physical contact, looking a lean mixture and preignition (detonation) in those cylinders.
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Old 08-08-2002, 09:16 PM
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A couple of items to think about; Are the pistons you used forged or cast? If they are cast, the failure could be from high heat in the front two cylinders (I think 1 & 4 are across from each other) causing metal failure? Could also be from a lean condition in two of the cylinders and detonation which melted the pistons. You did not say what you were doing when the failure occured, but I'll bet it was racing or at least driving really hard? Was there any funny noises, missing, rough running just prior to the failure? Finally, have a valve/head expert check the valves to see it they are burned or over heated which could have been caused by air leaks, etc during driving? I am generally a 4 cylinder person, but I have been chasing valve and head troubles for a year and I did find that forged pistons and titanium valves are worth their weight in gold when it comes to taking abuse. Good luck
Old 08-09-2002, 11:03 AM
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While I have opinions, I'm a little short on facts

Using pistions "other than Mahle" is a bit risky in a 911 motor.
Since Mahle has a limited selection of bore/stroke/compression
combos, some folks (myself included) use after market brands.

My research led me to Shasta (which are made from JE forgings).
I got "good words" on them from a couple of racer guys.
I'm sure that JE would have been equally good........
Thus far, I'm happy with em'.

I have heard of Ross, but yours is the first experience that I've heard on them.

That's it on pistons for me.

Your failures on #s 1 & 4 may indicate something other than piston quaity.
These holes have a couple things in common.
Both have their own carb float bowl
They are both the most suseptable to air leakage around worn butterfly shafts/bores.

Detonation due to a lean condition may well be the problem.
9.8 : 1 compression is kinda' iffy for street gas.
My pistons are 9.7:1. I blended/smoothed out the piston top (around the valve reliefs) edges to prevent (hopefully) hot spots.
You don't mention what plugs you're running, nor their condition.
I'm running NGK BP7ES but would go to 8s for track work.
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Old 08-09-2002, 11:47 AM
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I had an email all written up telling him it was the carbs.

We burnt 3 friggin engines before we sent our carbs out to be professionally rebuilt.

Guess which cylinders ??

I decided by the tone of his email that he didnt want to hear that there was a 98% chance its the carbs and his mechanics wont/dont admit it.

Thanks JP. You opened the door for A-hole.


B
Old 08-09-2002, 01:29 PM
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Quote:
Originally posted by Ron Meier
Did the exhaust valve and piston touch each other in an inappropriate manner? No there was no contact between valves and pistons in either failure.

What did the spark plugs look like (as in white, glue bubbled, etc)? The spark plugs were sooty, as the car was set up to run intentionally rich for track events. No street driving

What did the tops of the pistons look like (other than hammered, looking for vaporization of aluminum)? no just sooty like the plugs

Were the piston skirts scored? Yes after passing the aluminum which broke off the valve pocket

Were the top rings broken? no broken rings

Ok, other than physical contact, looking a lean mixture and preignition (detonation) in those cylinders.
Timing was retarded slightly.
Old 08-09-2002, 02:00 PM
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Quote:
Originally posted by john rogers
A couple of items to think about; Are the pistons you used forged or cast? If they are cast, the failure could be from high heat in the front two cylinders (I think 1 & 4 are across from each other) causing metal failure? Could also be from a lean condition in two of the cylinders and detonation which melted the pistons. You did not say what you were doing when the failure occured, but I'll bet it was racing or at least driving really hard? Was there any funny noises, missing, rough running just prior to the failure? Finally, have a valve/head expert check the valves to see it they are burned or over heated which could have been caused by air leaks, etc during driving? I am generally a 4 cylinder person, but I have been chasing valve and head troubles for a year and I did find that forged pistons and titanium valves are worth their weight in gold when it comes to taking abuse. Good luck
The pistons are Ross forged, yes I was racing. The carburetors were setup rich. Car ran smoothly during previous run.
Old 08-09-2002, 02:04 PM
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Quote:
Originally posted by J P Stein
While I have opinions, I'm a little short on facts

Using pistions "other than Mahle" is a bit risky in a 911 motor.
Since Mahle has a limited selection of bore/stroke/compression
combos, some folks (myself included) use after market brands.

My research led me to Shasta (which are made from JE forgings).
I got "good words" on them from a couple of racer guys.
I'm sure that JE would have been equally good........
Thus far, I'm happy with em'.

I have heard of Ross, but yours is the first experience that I've heard on them.

That's it on pistons for me.

Your failures on #s 1 & 4 may indicate something other than piston quaity.
These holes have a couple things in common.
Both have their own carb float bowl
They are both the most suseptable to air leakage around worn butterfly shafts/bores.

Detonation due to a lean condition may well be the problem.
9.8 : 1 compression is kinda' iffy for street gas.
My pistons are 9.7:1. I blended/smoothed out the piston top (around the valve reliefs) edges to prevent (hopefully) hot spots.
You don't mention what plugs you're running, nor their condition.
I'm running NGK BP7ES but would go to 8s for track work.
Thanks for the detailed response you hit on some very key points. Obviously with two failures months apart I have had the opportunity to ponder and discuss this issue with many people. Here is the direction my interviews have led me. The edges arround the valve pockets on these pistons is very sharp in comparison to other products I have seen (i.e Mahle and JE). Obviously, during compression and combustion great thermo-dynamic forces are present in the combustion chamber. I feel quite simply what is happening is these sharp edges are heating past the design limitations of alloy becoming brittle and finally after many cycles they are breaking or chipping off. There is no other damage to the piston dome other than broken valve pocket skirt. Thus supporting your hot spot theory.

In addressing you questions regarding fuel. I was and always run a misture of 93 octane pump gas and 100 octane racing fuel. The Porsche 911 Performance Handbook recommends 97 to 98 octane to support proper combustion in performance applications for this motor which is basically a 2.0 liter "S" knockoff. No pun intended. I to run BP7ES or Bosch "7" equivalent. Regarding ignition the timing was not advanced in fact slightly retarded off the spec.

Finally, my mechanic (30 year Porsche guy), my machinist (performance engine builder) and I are going to be hard to convince that the root cause is other than the "sharp edge" valve pocket / hot spot. Of course Ross does not want to concur. The remaining pistons will be out of the motor by sundown tomorrow and into the trash where they belong.

Fooled me once and fooled me twice
Benefits; I have learned alot during this ordeal, which I can share with others. Primarily don't buy Ross Pistons for your Porsche leave them for the water cooled big block guys.
Old 08-09-2002, 02:38 PM
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Man this sounds bad:

"Finally, my mechanic (30 year Porsche guy), my machinist (performance engine builder) and I are going to be hard to convince that the root cause is other than the "sharp edge" valve pocket / hot spot. Of course Ross does not want to concur. The remaining pistons will be out of the motor by sundown tomorrow and into the trash where they belong."

I think if your builders thought there was a problem with the pistons they would have "deburred' them before installing them. I regulary hand sand all the sharp edges off all the J+E's we use.

And I havent done anything for 30 years except breath (about 15 years building engines) I'm 31.

Can I ask who suggested Ross ??

B
Old 08-09-2002, 04:01 PM
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not to defend any manufacturer, but in my experience anything sharp in the combustion chamber or piston tops was a no-no.

After maching the custom made pistons, I would always use a "green wheel" to debur and radius any fly cut pocket, domes, etc.....,. Same treatment to the combustion chamber. Ostensibly for flow and flame travel, it had many other benefits.

The block (interior), crank, rods received a "polishing and deburring". No sharp edges please - crap breaks off under vibration and flows thru the oiling system - no bueno.

Block oil passages, crank oil passages were cleaned with gun brushes.

It goes on and on - many hours and then a close to hospital sanitary wash & dry before any attempted assembly (Sorry, didn't have a clean room.

I agree with BRM

Oh! If you really wanted to blow bucks you could take it to a metallurgist and have it analyzed - they can tell you the root cause.
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Old 08-09-2002, 05:35 PM
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Quote:
Originally posted by Ron Meier
not to defend any manufacturer, but in my experience anything sharp in the combustion chamber or piston tops was a no-no.

After maching the custom made pistons, I would always use a "green wheel" to debur and radius any fly cut pocket, domes, etc.....,. Same treatment to the combustion chamber. Ostensibly for flow and flame travel, it had many other benefits.

The block (interior), crank, rods received a "polishing and deburring". No sharp edges please - crap breaks off under vibration and flows thru the oiling system - no bueno.

Block oil passages, crank oil passages were cleaned with gun brushes.

It goes on and on - many hours and then a close to hospital sanitary wash & dry before any attempted assembly (Sorry, didn't have a clean room.

I agree with BRM

Oh! If you really wanted to blow bucks you could take it to a metallurgist and have it analyzed - they can tell you the root cause.
So it seems we have a pattern developing in the responses. The sharp edges are winning over the BS tuning excuses I'm getting from a manufacturer who does not want to stand behind his product.
Old 08-09-2002, 06:35 PM
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Quote:
Originally posted by BRM9148
Man this sounds bad:

"Finally, my mechanic (30 year Porsche guy), my machinist (performance engine builder) and I are going to be hard to convince that the root cause is other than the "sharp edge" valve pocket / hot spot. Of course Ross does not want to concur. The remaining pistons will be out of the motor by sundown tomorrow and into the trash where they belong."

I think if your builders thought there was a problem with the pistons they would have "deburred' them before installing them. I regulary hand sand all the sharp edges off all the J+E's we use.

And I havent done anything for 30 years except breath (about 15 years building engines) I'm 31.

Can I ask who suggested Ross ??

B
Ross was suggested and purchased through MotorMeister. I was considering JE from EBS but they were out of stock and I was anxious to get the car on the track. So I went with MotorMeister's suggestion. As it turned out the Ross pistons were not instock as MotorMeister had led me to believe so I ended up waiting on them. Big $xpensive mistake. Regarding your comments on the engine builder in his defense he was concerned about the sharp edges on the valve pockets, but we got no guidance from MotorMeister or Ross on this issue. Last week in a conversation with Ross they were in denial with regard to the need to massage the parts. Saying that many of their big bl0ock pistons were even finned. Just typical I'm looking for the easy way out of this BS, which is of course to hide behind technology and blame the user and mechanic.
Old 08-09-2002, 06:46 PM
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Quote:
Originally posted by BRM9148
I had an email all written up telling him it was the carbs.

We burnt 3 friggin engines before we sent our carbs out to be professionally rebuilt.

Guess which cylinders ??

I decided by the tone of his email that he didnt want to hear that there was a 98% chance its the carbs and his mechanics wont/dont admit it.

Thanks JP. You opened the door for A-hole.


B
You are right I don't want to hear the carburetor line. The carbs were recently professionally rebuilt and we have been if anything working to get leaner, plugs were nice and sooty as were the pipes. Weber 40s, 32 venturis, 130 mains, 180 ACs, 60 idles, f26 tubes and Solex cams. 3.5 lbs of fuel pressure. Compression ratio slightly derated with additional deck spacing. Now you know the rest of the story.
Old 08-09-2002, 06:54 PM
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Motor Meister?......Ross?...........I've heard enuff......gots nuthin more to say.
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Old 08-09-2002, 07:20 PM
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This is the last of what I'm going to post.

If fault finding is the purpose, I will lay it on inexperience. I've been in and out of racing since I was 19 and I'm now a salty 57 year old with a bad attitude.

Before I wrenched on racing engines, I talked to people like me that had blown engines learning and trying new things. I spent hours in the library researching. I bought everybody's book and studied them. I talked to the winners and loosers alike. I begged for information (winners don't like to give information up).

My last go round was building SCCA Datusn (not Nissan) G Prod motors. 2 drivers, 2 cars. My learning curve was adequately displayed on one of the cars - a license plate with the number of the engine in the car written on it. When it blew, I crossed the number out and added the new one. Went home and studied more. I took the plate off at #11 - it didn't blow.

I'm not saying the part was faulty. I'm not saying it was your fault. I'm saying your information was faulty. Tag that anywhere you want.

Nuff said!!!!!

Sorry, I fogot - I would DEARLY LOVE TO SEE A FINNED PISTON.
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Last edited by Ron Meier; 08-09-2002 at 08:55 PM..
Old 08-09-2002, 08:52 PM
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Before tossing the pistons, Why not have them looked at by a Metallurgist. There must be a qualified P.E. lurking around one of the 914 or Porsche sites. Why just guess, point fingers, and speculate? If it is a result of an over heating problem caused by a sharp edge in the valve notch, the remaining pistons should display the same evidence. During disassembly don't spin the rings out of there set position. Examine the top ring for discoloration in the area of the valve notch, and the ring groove of the other pistons for evidence of collapse. Before removing the piston from the cylinder, examine the upper edge of the cylinder for heat damage. Don't just assume the Ross pistons are the cause. Be sure. If the cause lies some where else you will repete the problem no matter who's pistons you use. Don't take the word of your engine builder either. Why would he tell you he may have been the cause. I've had a very hit and miss association with machinist's. My most recent experience was with an MGB 1800 block. I purchased +.40 pistons and requested a simple over bore job. The machinist called 2 days later and asked if I could get +.60 pistons. It seems he (I've know the guy and used him off and on for 25 years) bumped the boring machine and opened up one bore to +.50! I now have a sleeve in my block for no good reason! I had a BMW head cut I instructed the machinist to do a bunch of trick work. (Big Shot drag motor builder bragged about how good he was) He cut the head like a wedge. I managed to bring it to another low buck guy and have it recut. .111 over the maximum reccommended cut to square it up. Ya it's junk...I'm using it but I had to cut notches in the pistons, make up off set sleeves for the cam bolts to shift the cam back into phase, and make a custom chain tensioner. These are just two examples of why you keep your friends close and keep your enemies closer. Use an independent source to help find the true answer. 911 rebuilds are cost prohibitive for most of us. Much less having to toss out parts based on speculation. You can put them in my trash.....
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Old 08-09-2002, 09:56 PM
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Joe,

you had the carbs dialed.

Survey says:

Sharp corners on pistons.

I feel bad...ok I'm over it. LOL

B
Old 08-09-2002, 11:17 PM
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I don't think I said that.... I think joe ross is bitter towards the piston manufacturer based on the opinion of a couple of guy's that have real cash to loss if it was there fault. Asking our opinion based on a deduction made by a mechanic and an engine builder, and with out the aid of actually seeing the parts is fine but we can only speculate and lend moral support. I just think joe should send the parts to an expert. The mistake is far too expensive to repeat. Who knows, the fix may require different engine builder, mechanic, and or carb tuner, not different pistons. Then if it's the pistons by all means give us the report. How about e-mailing a guy like John Force. He seems like a regular guy. Ask him to take pity and have his top engine builder look at a couple of your pistons for free. Those guy's look at their pistons hundreds of times a season. I think you should be resourceful. Oh ya, If you find someone willing to look at a failed piston and the balance of the other pistons, don't give them the benefit of your opinion; let them tell you what happened. I know from experience that the PE's can be influenced. It's their nature to ask questions. I'm speaking in general terms; please no flame. I am an Insurance adjuster. I hire these guy's to look at mechanical things that fail and render an opinion.
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Last edited by rich; 08-10-2002 at 07:09 AM..
Old 08-10-2002, 06:55 AM
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Tho I said I had nuthin' more to say..........I lied
This is more of a clarification.

My concern about " hot spots" was to prevent pre-ignition or detonation (it's kinda like having a "glow plug" in there). THAT is a piston killer. A rich mixture is no insurance against this.

I'm still long on opinions, short on facts. Some "piston postmortum" would be a gud plan.
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Old 08-12-2002, 08:57 AM
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Rich,

I agree 100% about having somebody look at them. I'm just blown away that mechanics with as much knowledge as they have would'nt message the pistons strait out of the box.

I even hand sand/grind all the casting flash off the blocks before they go to the machine shop for cleaning and mods.

B
Old 08-12-2002, 09:15 AM
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