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Piston to bore clearance - galling or not?

Engine Building Fundamentals

Discussion and questions related to the course Engine Building Fundamentals


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Hello.

I have some pictures of used pistons from Toyota's 3S-GTE 2.0 turbo engine.

Can somebody please confirm - is it galling or just wear during long period of operation? It's OEM cast pistons.

One interesting thing: on pics we can see significant wear on both intake and exhaust sides. But I thought that during power stroke only on side of the skirt is heavily loaded.

Also here we can see common issue for this engine: pistons are broken between ring bores. Maybe someone knows the exact reason? Only detonation or maybe something else?

Thanks.

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The pictures show wear that is not what you'd expect from normal use. This sort of damage can be the result of insufficient PTW clearance (unlikely in a factory engine), or putting too much heat into the pistons from a lean AFR. What I would point out however is that there is an indication that a lot of debris has been making its way into the cylinders as you can see where this has been embedded into the top ring land. This debris can also be responsible for the scoring on the piston skirt.

Andre, thank you :)

I see signs of detonation, especially clear on intake side 2.2. The top edge of the piston is clearly melted, and the dull 'sandblasted' look between the upper compression ring and the edge (which is present on several of them) is absolutely indicative of detonation. I'd suspect that's what broke the ring lands too. The scoring is probably from debris causing damage to the bores and that damage transferring back into the skirts.

Thanks guys :) So it's not galling. I'm just trying to add some practical examples for my engine foundamentals course )

Good spotting John! Somehow I missed that particular picture. The pitting on the top ring land along with the broken and missing section of ring land below are signs of significant detonation.

Ok, lol! I was just about to point out that fact that there's some broken ring lands but I see that's already been discussed. Now my question is, is the detonation what caused the rings lands to break? or was it the heat that got to the rings, which then cause them to expand and butt together, thus breaking the ring lands? ( i think, im still learning so go easy on me lol).