Broken pistons, not sure the cause?

turbo_g13
Fresh Fish
Joined: October 6th, 2011, 1:17 am

September 13th, 2018, 6:00 pm #1

These pistons were found in a G13BB engine, pieces are broken off the intake side of the piston. Never seen this before and not sure the cause, thinking maybe just cheap pistons fatigued over time on a thin edge and broke out. Problem became very apparent when a piece broke out between 1st and 2nd ring and a loss of compression became obvious. It is worth noting I recently turbo'd (low boost) this engine and I think that's when piece between rings broke. But I'm guessing the other pieces were gone already as nothing seem to have gone thorough my turbo. Has anyone seen this before or know's the cause?

IMG_20180912_160102.jpg IMG_20180912_160051.jpg IMG_20180912_160039.jpg IMG_20180912_160027.jpg
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Johnny Mullet
Elite Member
Joined: September 8th, 2008, 1:49 am

September 13th, 2018, 6:26 pm #2

I seen broken pistons before, but not there. Usually at the skirt. Maybe cheap pistons?
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wizard93
Elite Member
Joined: September 28th, 2010, 12:40 am

September 14th, 2018, 2:37 am #3

They don't look so much broken as they do burned.  Perhaps they got too hot and melted off there?
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Murf 59
Elite Member
Joined: July 2nd, 2009, 9:49 am

September 14th, 2018, 3:04 pm #4

They are broke off in the same place. What do the valves look like above the broken parts?  Maybe the valve and piston barely touched?  
A 13.5 to 1 G10. With GTi twin cam pistons. Performance head package work sponsored by our friends at 3Tech.
A set of 4.38s set up as a 4 spd. MSD ignition, and a Weber card on top. It has a SRD header on the bottom side.
I run a Glow shift tach, and a HF vacuum gauge.
This engine is still in the works. I have all the pieces, but am not able to get the energy to assemble it.

This is what it looks like running at Bonneville from the front seat of a Geo Metro
http://www.youtube.com/watch?v=rOcWzyzyjPw
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turbo_g13
Fresh Fish
Joined: October 6th, 2011, 1:17 am

September 14th, 2018, 3:29 pm #5

I sent the head away yesterday to get worked on, can't look at it now but I didn't notice any damage to the valves/head when I looked at it before. Should get a call back on it Monday as to what work the head needs. I know for sure I need exhaust valve guides and all stem seals.

Pieces are defiantly broken out though and not burned, one piston has a piece that's cracked half way off and just barely hanging on. It's a little hard to see in the pictures, camera is cheap :(.
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turbo_g13
Fresh Fish
Joined: October 6th, 2011, 1:17 am

September 14th, 2018, 4:58 pm #6

Here is a decent side picture of one of the pistons, noticed there is some pitting on the intake side, could be related or the cause or a result of? and you can see how the crown is cracking/breaking off.

IMG_20180914_115056.jpg
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Scoobs
Elite Member
Joined: June 7th, 2011, 3:39 am

September 14th, 2018, 5:18 pm #7

That looks like it got hot, very hot.
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Metromightymouse
Elite Member
Joined: February 19th, 2013, 9:09 am

September 14th, 2018, 6:04 pm #8

Scoobs wrote: That looks like it got hot, very hot.
Maybe from a turbo in a system not designed for a turbo causing the engine to run lean?
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91 ragtop
Elite Member
Joined: February 27th, 2009, 12:46 am

September 14th, 2018, 11:45 pm #9

How much boost ? What  octane fuel were you using ? What was your air/fuel ratio
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turbo_g13
Fresh Fish
Joined: October 6th, 2011, 1:17 am

September 15th, 2018, 5:41 am #10

7 psi, AEM F/IC to add fuel. Fuel map set to increase injector pulse width 65% at 7 psi. 87 octane gas. Not sure of AFR, no gauge on this car but I do have AFR on my metro running the same setup x2. runs between 12-13 AFR if memory serves. Never had this issue (that I know of) with far more full throttle runs in that car. Only bent a connecting rod by accident when the waste gate failed spiking pressures to roughly 22 PSI!

I agree the side of the piston crown between the breaks looks like it got hot, but nothing else does. spark plugs look good. piston tops look good. head looks good, valves look good. no other signs of running lean/hot. and wouldn't it usually melt the exhaust side first? Just looked at the least damaged pistons, they also have some minor pitting on the intake side but again only on the side between the intake valves. Could running lean really cause that? In Just that spot?

IMG_20180823_204941.jpg
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