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Romans 2005 Toyota Echo


Roman

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For sure its beaten up pretty bad, but is there any sign of fatigue in there evident that a fracture started at the oil holes?

Hard to tell from the photos but appears to be a transition in cross section so holes just happen to be in the likely failure region?

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16 minutes ago, NickJ said:

For sure its beaten up pretty bad, but is there any sign of fatigue in there evident that a fracture started at the oil holes?

Hard to tell from the photos but appears to be a transition in cross section so holes just happen to be in the likely failure region?

Sorry will take a better picture. But on the other side, it's a break through all of the holes. Yeah it's pretty hard to know cause or effect though. If I can't find the wrist pin in the sump I might go for a walk near where it blew up and see if I can find it haha.

But I just wonder, if it was the rod that broke first, how do you end up with damage like that? Like the pin has been pulled out downwards rather than smashed up by a broken rod.

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1 hour ago, Roman said:

If I can't find the wrist pin in the sump I might go for a walk near where it blew up and see if I can find it haha.

if it's in a paddock near by, be sure to flatten the grass in a circular fashion while working the metal detector, this will ensure maximum chance of finding the lost bits.. 

Jb134RS.jpg

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I'm going to throw out a wild conspiracy theory that your stock pistons could do 9275 rpm before the top comes off, because of the exhaust backpressure pushing down on the top of the piston

 

Once you have a free flowing exhaust your piston lids will come off at 9021 rpms  

 

Might be time for some stronger piston return springs  

 

 

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How's the ring gap? I have heard of ring gap closing up when pistons get hotter than intended from the factory setup then wedging in the cylinder. Maybe it happened at tdc and the rod yanked the bottom of the piston off. Probably unlikely but another thing you could check on the other pistons. Maybe do some maths with thermal expansion coefficients and see if it would be likely to close the gap in the temperature ranges it could be experiencing.

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1 hour ago, Roman said:

I think you could be right about that.

If the piston is trying to fly apart, where the top of the piston is trying to carry on upwards, and the pin is pulling it back down.
So the material strength around the pin is the weakness.
Then on the exhaust stroke this force is lessened, and when the cylinder is full, on the compression stroke this force is lessened too. 

The engine didnt fail when it was approaching max rpm, it failed just after a gear shift where throttle got cut to zero. 

So the worst case scenario would be zero throttle, high vacuum, high rpm on the compression stroke.
I'm not sure if these forces are on the same magnitude as each other though. 

However, I can indeed increase my piston return spring value. :lol:
I can use e-throttle to set a minimum high rpm throttle value to something like 10% or 20%, and then use a fuel cut and/or pull zillions of ignition timing out to cut power instead.
This might bring a host of its own issues, but might be a bodgey solution I guess haha. 
Flat shifting, interestingly enough, would also help haha.

The incredibly clever @Lith made a calculator ages ago that works out forces on pistons/rods. 
Entering 1NZ stuff.  Peak accelleration on the piston at 9000rpm is 4991G!
I'm not sure what sort of numbers I was expecting, but thats bloody lots. 
Then the PEAK piston speed is 41.7 meters per second. Which is 8200 feet per minute.
Which is zillions high when 3500fpm is the reccomended mean value. 

image.thumb.png.ea7ae636a32a7cfeda97542e1e937e69.png

interesting. That could be around 1500kg yanking on the rod, which would have a yield of like 15x that, but I have absolutely no idea what im taking about. 

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2 hours ago, Roman said:

However, I can indeed increase my piston return spring value. :lol:

Some kind of air spring could work. Perhaps using a compressor driven by otherwise wasted exhaust energy?

No don't do that....yet.

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@Romanmaybe you could look into forging your own pistons like Burt Munro?

"They were hand-cast using sand from local beaches in a variety of receptacles, including tin cans. They were then painstakingly finished with file and lathe,”

Pretty sure you could improve on that with some 3dprints etc for molds

Break up some broken pistons to melt down etc

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