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BFB
Samba Member
Joined: November 03, 2014
Posts: 2774
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 Posted: Thu Aug 07, 2025 6:02 pm Post subject: Re: Wtf causes this |
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FFS this is like trying to play clue with one card.
Theres a hundred and one things that could’ve gone wrong here..
If detonation is on the table then have OP post top of pistons pictures.
How about pulling the other pistons and posting pictures of their skirts & wrist pins. Pics of cylinders in the case, base of the cylinders, case spigots.
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"how am i supposed to torque the rear wheel nut to 250 ft lbs??? " - clonebug
An interesting thing happens in forums where everyone starts parroting the same thing and "common knowledge" takes over.
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chrisflstf
Samba Member
Joined: February 10, 2004
Posts: 4112
Location: San Diego
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| Posted: Thu Aug 07, 2025 6:30 pm Post subject: Re: Wtf causes this |
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| Look at the heavy, wide groove in the first pic on the left side of the piston, from the pin. How can that be detonation? To me, its an alignment issue, but i cant explain how. |
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patricke1971
Samba Member
Joined: August 04, 2017
Posts: 140
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| Posted: Thu Aug 07, 2025 7:06 pm Post subject: Re: Wtf causes this |
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| I use 93 octane and at full advance it's like 26 degrees full advance.. |
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NJ John
Samba Member
Joined: September 21, 2007
Posts: 2934
Location: HdG, MD & NJ
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| Posted: Thu Aug 07, 2025 7:31 pm Post subject: Re: Wtf causes this |
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Who bored the case? I had one done by a non vw machinist. He left a step that the skirt hit. If a step was left, and misses during mock up, but at RPM?
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1973 standard, yellow, lowered, 3” narrowed front, 1600 blo-thru turbo w/single dell 15.4@86, so far
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patricke1971
Samba Member
Joined: August 04, 2017
Posts: 140
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| Posted: Fri Aug 08, 2025 4:32 am Post subject: Re: Wtf causes this |
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| The case was new..and aluminum bubble top .it came 94mm |
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94touring
Samba Member
Joined: October 24, 2020
Posts: 543
Location: Tulsa - OK
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| Posted: Fri Aug 08, 2025 5:09 am Post subject: Re: Wtf causes this |
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| Did you retune for the larger bore? Are you running a turbo at low boost for such retarded advance? |
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22manybugs
Samba Member
Joined: March 30, 2006
Posts: 405
Location: Yorba Linda, Calif
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| Posted: Fri Aug 08, 2025 10:50 am Post subject: Re: Wtf causes this |
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| BFB wrote: |
FFS this is like trying to play clue with one card.
Theres a hundred and one things that could’ve gone wrong here..
If detonation is on the table then have OP post top of pistons pictures.
How about pulling the other pistons and posting pictures of their skirts & wrist pins. Pics of cylinders in the case, base of the cylinders, case spigots. |
Totally agree. The reason there's so many theories is there's not a lot of detail coming back so it's difficult to rule out anything. Still haven't seen a compression ratio. The full advance is not very advanced (26 deg), why?
If the skirts were hitting something or had any interference at the bottom of the stroke, the pictures should show a lot of damage on the skirts. The skirts are not damaged that I can see.
Something else to consider: at the end of the day, this engine is a 94mm bore x 84mm stroke. That's on the ragged edge, and maybe beyond the ragged edge, of what can be built for a reliable VW engine. The key word being reliable. I've seen a rule of thumb to not use 94mm bore because the cylinders are too big, can't get enough cooling airflow around them, and that causes problems. Maybe this engine is too close to design limits - like a race engine - and will have to be rebuilt at a set interval to avoid failures. That doesn't help address this particular failure.
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1969 Karmann Ghia convertible
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JSmith
Samba Member
Joined: August 18, 2005
Posts: 90
Location: Over There ->
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| Posted: Fri Aug 08, 2025 12:33 pm Post subject: Re: Wtf causes this |
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| I have a similar set up, 2332 turbo and I had a similar thing happen just not so catastrophic. I had a clip come out due to it being installed sharp side in, the wrist pin worked it's way out and luckily it just sounded like a rod knock instead of coming apart . Replaced the P&C with Weisco's and used Jaycee buttons no more problems. Just past experience hope it helps. |
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geeze
Samba Member
Joined: July 30, 2025
Posts: 30
Location: land before time
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| Posted: Fri Aug 08, 2025 2:02 pm Post subject: Re: Wtf causes this |
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| what cc is the chamber volume in your heads and did you recheck the cc after having them bored for 94mm ? |
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VWporscheGT3
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Joined: September 01, 2006
Posts: 2182
Location: Gardnerville, NV
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| Posted: Fri Aug 08, 2025 3:27 pm Post subject: Re: Wtf causes this |
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Patrick,
Without having things like the rods and pistons in hand all i have are theories.. if you would like to send them in i'd be happy to take a look and do a proper failure analysis. One poster mentioned the half moon wear mark on the opposite pin boss and i agree thid looms like it could be possible that the lock worked out allowing the pin to slide out. Bent rods as others are mentioning can excacerbate and cause lock failure, putting stress on a lock ring in greater forces than it was ever meant to handle. Then once the pin worked out the one side it ripped the material away once the piston cocked in the bore do to unequal loading... again theory.
Offer is on the table if you wanted to send in your parts to be looked at, i and the other techs at UEM would be happy to take a look.
-Trevor Cleveland
Icon Pistons
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BFB
Samba Member
Joined: November 03, 2014
Posts: 2774
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| Posted: Fri Aug 08, 2025 4:05 pm Post subject: Re: Wtf causes this |
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This reminds me of the Simpsons episode where the kids are in the treehouse theorizing why their not getting dinner.. “ the Rand corporation, in conjunction with the saucer people, under the supervision of the reverse vampires , are forcing our parents to go to bed early in a fiendish plot to eliminate dinner”.
“The detonation, in conjunction with the wrist pin clip, supervised by the twisted connecting rod is forcing wristpins into cylinders in an evil plot to destroy pistons and thereby force long overdue retirement of this engine thusly bringing forth a new engine build and a new era“
_________________
"how am i supposed to torque the rear wheel nut to 250 ft lbs??? " - clonebug
An interesting thing happens in forums where everyone starts parroting the same thing and "common knowledge" takes over.
Most experts aren't. |
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VWporscheGT3
Samba Member
Joined: September 01, 2006
Posts: 2182
Location: Gardnerville, NV
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| Posted: Fri Aug 08, 2025 5:58 pm Post subject: Re: Wtf causes this |
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| BFB wrote: |
This reminds me of the Simpsons episode where the kids are in the treehouse theorizing why their not getting dinner.. “ the Rand corporation, in conjunction with the saucer people, under the supervision of the reverse vampires , are forcing our parents to go to bed early in a fiendish plot to eliminate dinner”.
“The detonation, in conjunction with the wrist pin clip, supervised by the twisted connecting rod is forcing wristpins into cylinders in an evil plot to destroy pistons and thereby force long overdue retirement of this engine thusly bringing forth a new engine build and a new era“ |
Thats kinda my point , until we have more pictures, measurents , components in hands thats all we can do, theorize
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If you have any questions about Forged ICON 4032 VW pistons just shoot me a line. |
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BFB
Samba Member
Joined: November 03, 2014
Posts: 2774
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| Posted: Sat Aug 09, 2025 7:34 am Post subject: Re: Wtf causes this |
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| VWporscheGT3 wrote: |
| BFB wrote: |
This reminds me of the Simpsons episode where the kids are in the treehouse theorizing why their not getting dinner.. “ the Rand corporation, in conjunction with the saucer people, under the supervision of the reverse vampires , are forcing our parents to go to bed early in a fiendish plot to eliminate dinner”.
“The detonation, in conjunction with the wrist pin clip, supervised by the twisted connecting rod is forcing wristpins into cylinders in an evil plot to destroy pistons and thereby force long overdue retirement of this engine thusly bringing forth a new engine build and a new era“ |
Thats kinda my point , until we have more pictures, measurents , components in hands thats all we can do, theorize |
Right, but you werent the first or only person to say that yet here we are 3 pages deep and no more info from OP than his first couple posts
_________________
"how am i supposed to torque the rear wheel nut to 250 ft lbs??? " - clonebug
An interesting thing happens in forums where everyone starts parroting the same thing and "common knowledge" takes over.
Most experts aren't. |
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VW_Jimbo 
Samba Member
Joined: May 22, 2016
Posts: 11246
Location: Huntington Beach, CA
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| Posted: Sat Aug 09, 2025 8:12 am Post subject: Re: Wtf causes this |
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| Rob Combs wrote: |
Curious, if detonation were the cause, is it the constant hammering on the piston and extreme thermal cycling causing the metal to fatigue and fail at the weakest point?
I recognize the piston does get a bit of force changing direction then pulling it down on the intake stroke and if it's already weakened...
Also dawned on me a few minutes ago the scenario I guessed at earlier this afternoon cannot be the cause - piston is too clean on the pin boss on the non-damaged side. |
I do not look inside engines everyday anymore but I see a ridge, pointed out by an earlier poster, “crescent shaped” on the rod side of the far wrist pin hole. It looks as if the wrist pin walked out of the hole, except for a 1/16”, where it beat on the piston until it was stuck at an angle and then POP! There goes the piston!
I will return with a doctored picture. Give me a few minutes.
From this picture. See the edge of sliced metal?
Looks like a lack of oil on the wrist pin bore. Probably the root cause!
Can you see that rectangular wear marks on the front bore? Looks as if the pin was static and loose in the bore.
Really interested in the wrist pin. Thinking it got very little oil. Over heated and got stuck in the piston on and off. As the connecting rod rocked back and forth, with no oil to use for a bearing surface, the piston stated to wear. The piston wrist pin hole opened up, it moved sideways and POP goes the piston!
Is the oil supply path free and clear of obstructions? Do the oil holes in the bearings need to be in alignment with the rod? Was there a channel for oil?
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There is never enough time to do it right the first time, but all the time necessary the second time!
| TDCTDI wrote: |
| Basically, a whole bunch of fuckery to achieve a look. |
| 67rustavenger wrote: |
GFY's Xevin and VW_Jimbo!  |
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chrisflstf
Samba Member
Joined: February 10, 2004
Posts: 4112
Location: San Diego
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| Posted: Sat Aug 09, 2025 10:00 am Post subject: Re: Wtf causes this |
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That crescent shaped wear is on both ends of the piston pin bore. I think that is poor alignment caused.
There are also 2 circular voids at the break on the left side of the 1st pic. What is that from?
Do you have any other broken piston pics? |
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VW_Jimbo
Samba Member
Joined: May 22, 2016
Posts: 11246
Location: Huntington Beach, CA
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| Posted: Sat Aug 09, 2025 10:36 am Post subject: Re: Wtf causes this |
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| chrisflstf wrote: |
That crescent shaped wear is on both ends of the piston pin bore. I think that is poor alignment caused.
There are also 2 circular voids at the break on the left side of the 1st pic. What is that from?
Do you have any other broken piston pics? |
It is like the retainer jumped ship or was missing and the pin was allowed to move all over the place!
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Jimbo
There is never enough time to do it right the first time, but all the time necessary the second time!
| TDCTDI wrote: |
| Basically, a whole bunch of fuckery to achieve a look. |
| 67rustavenger wrote: |
| GFY's Xevin and VW_Jimbo! |
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atechfab
Samba Member
Joined: July 24, 2025
Posts: 7
Location: so. cal
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| Posted: Sat Aug 09, 2025 10:53 am Post subject: Re: Wtf causes this |
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It certainly looks like a retainer failure. Examine the clip; if there is little to no damage, then the piston broke first. If the clip is heavily damaged, then the clip failed first.
Since it happened 3 times, it is not a random event, something is wrong.
If the wrist pins are too long, the clips will not get seated completely.
For reliability, I have always used buttons. But for my next build I was going to look at using Spirolox rings in order to reduce reciprocating weight. Teflon is a fairly heavy material. Even though they are harder to install, they are less likely to pop out on their own compared to C-clips. |
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