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Do Hybrid swaps go through pistons like mad? Mine is.

D

davygravyt

New CEG'er
Joined
May 30, 2007
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8
So I have had a 3l Hybrid swap CSVT for about a year and a half now. A little over a year a go, a piston broke after about owning the car for about 8k miles, and I had a local engine rebuilding shop, Waggamon Brothers rebuild the engine. Since then the car is going through pistons like toilet paper. The shop says it is because the compression ratio is too high. Although 11.25:1 is a pretty high compression ratio, I haven't seen anything on the forums about this being a common problem. Are they right? Do these motors blow through pistons? Or is the shop just not aligning them right or something?

P.S. The shop said there doesn't appear to be any cylinder wall damage.
 
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sounds like a tuning problem, or running low octane fuel?

most hybrid guys have no problems or complaints. but most of those guys have their setups tuned for the setup. is your motor an 01+? if it's an earlier piston, they have been known to crack in the ring lands under high cylinder pressures.
 
I only run 91-93 premium unleaded, and the car ran great for about 7000 miles before the connecting rod broke the first time. Also, I'm pretty sure the car has a superchip performance chip in it, because that's what the previous owner told me.

It is an 03 Taurus engine.
 
okay. so are the pistons scoring........ rings going out (burning oil) or just breaking into pieces?

sounds like an oiling issue, or running lean somehow.
 
The pistons are all breaking at the skirt and I don't think there is any oil burning.
 
sounds like something else is up. I've got almost 50k miles on my hybrid and she runs like the day I first turned the key. Sorry thats all I have to add.
 
So would you say it's not very likely the cause of the pistons breaking is compression? Because the shop wants us to buy forged pistons for it due to the high compression ratio and I definitely don't think that's the problem.

I still think they didn't put it together right. It just doesn't seem right to me.
 
wow. i'd start asking if the block has been bored, and ask if everything is being mic'd out it sounds like something my buddy had a problem with on a saturn, the block was 10 thou bored and the pistons were stock bore. it went together fine so he set the ring end gap and put it together. with the rings on the piston it felt fine but he didnt know that it was piston slapping bad on the skirts.
 
Also, are all you hybrid guys running 11.25:1 compression like me? Or did you lower it (like by porting the heads)?
 
TRicker said:
wow. i'd start asking if the block has been bored, and ask if everything is being mic'd out it sounds like something my buddy had a problem with on a saturn, the block was 10 thou bored and the pistons were stock bore. it went together fine so he set the ring end gap and put it together. with the rings on the piston it felt fine but he didnt know that it was piston slapping bad on the skirts.
Click to expand...
The shop said that was the first thing they checked. They honed the cylinder walls but they said they aligned perfectly with the pistons.
 
Pictures

Pictures

Here are pictures of the pistons. I only have 2 of the 3 that broke, but they are all broken in the same way. One of them is only cracked and not actually broken, but in the same place.

Also, notice how thin the metal in the pistons is. Is that normal?

Pistons027.jpg


Pistons026.jpg


Pistons023.jpg


Pistons022.jpg


Pistons021.jpg


Pistons020.jpg


Pistons019.jpg


Pistons018.jpg



This is the cracked piston. Notice the vertical scoring that was also present on the other piston.

Pistons024.jpg


Pistons025.jpg
 
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FYI you need to use macro mode on your camera when the distance is under two feet. There is usually a button with a flower looking logo on it. This is why all your pics are blurry, I'd bet your camera is fine.
 
K99ja04 said:
FYI you need to use macro mode on your camera when the distance is under two feet. There is usually a button with a flower looking logo on it. This is why all your pics are blurry, I'd bet your camera is fine.
Click to expand...

Thank you. Pictures fixed.
 
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I think there is a general consensus that the stock hypereutectic pistons are brittle. Anything that ups the peak cylinder pressure seems to crack these guys. We've seen turbos do it, nitros, and it seems that your high CR may be generating enough pressure to do it. Time for forged eh?
 
Ah much better detail. I don't think the thickness is abnormally thin. Just the nature of the metal being brittle = engines eating pistons.
 
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First off, You are breaking them at the skirt. This is not a sign of high compression or detonation. This is a sign of piston slap or perhaps pistons that are not properlysized for the bore.

We run stock hypereutectic pistons on 10:1 compression motors with turbos running up to 14psi of boost. This yields an actual compression ratios much much higher than 11.25:1 of a hybrid. More accurately the turbo cars are running effective compression ratios of about 16:1 under that much boost.
That is WAY higher cylinder pressures than what you have.
When we break pistons they usually pop the ring lands at the top and sides or crack the piston in half. The skirts are never touched.

I think they built the motor wrong.
You need to PM a guy named Procyon here on the boards and ask his opinion.
Also Big Jim may know or have seen it.
From the information I've gathered about the tight piston to bore clearances we have, you've either got pistons that are too tight and oversized or too loose and they've slapped under load and cracked off the skirt.

The solution is to junk the block, spend $300-$500 on a used 3L engine form a Taurus/Sable/Escape from 1999 and later, dissassemble and clean it all first and then install it.
You'll be very happy then.
 
Third pic down looked like he cracked a chunk of ring land to me. But now that I look closer it's a ring gap. Don't his ring gaps look a bit excessive? I know they're not compressed at all, but looks a bit open to me.
 
My engine machinist has a SEALED POWER poster that has pictures of various piston failures and an explaination of what caused each one. This picture of yours is almost a perfect match for the piston on the poster that says "Incorrect Bore Clearance." (the differences between your picture and the poster is that your picture is up-side-down, yellow, and has a carpet background) In short, listen to Warmonger's advice.

Pistons026.jpg
 
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From back in my early hot rodding days it would take an extremely loose fit to cause a problem. It was not uncommon to run them as loose as possible to try to cut drag. A tight fit is another matter.

An engine machinist (or experienced engine builder) would go to great effort to fit the pistons to the bore. All pistons and all bores would be measured to match them up as close as possible before anything else. Then if additional clearance was needed, the bore would be honed gently until the desired fit was achieved. If the pistons were too loose, the skirts were knurled to expand them.

It has been so long ago that I don't remember the clearance that was sought, but it was thin enough that a long thin feeler gauge was often used for the final measurement and the feeler gauge would flex to the arc of the bore.

Some engine builders liked starting with undersized pistons and intentionally knurling them to provide a pattern to better hold oil. I don't think it really made any significant difference though.

My guess is that those pistons are too tight but without measuring things I cannot tell.
 
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