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Post by Kick start on Jun 5, 2018 19:10:36 GMT -5
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Post by tiny on Jun 5, 2018 19:26:57 GMT -5
What the hell is up with that piston?
Is it separating the head from the skirt?
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Post by benji on Jun 5, 2018 22:56:38 GMT -5
New one to me haha.
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Post by scooterted on Jun 6, 2018 7:58:36 GMT -5
Wow. Overheat?
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Post by 90GTVert on Jun 6, 2018 8:44:38 GMT -5
Pretty odd. Only contact marks I see are right at the peak on the underside of the damage. There are a couple of scratches on the crown, but I'm assuming not related and they don't look like any major contact. What's really strange to me is the damage there, but I don't see any witness marks or damage on the piston elsewhere and the rings look fine. Are the rings good all the way around?
Do you have a scored cylinder wall in that area? Could the piston have been machined wrong or not cleaned up and something caught in that spot or a blemish in a cylinder wall? Doesn't look like it's been ran for long at all. Any details about what was going on when it occurred? No other damage? Usually if something hits it ends up smacking into other things.
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Post by snaker on Jun 6, 2018 10:38:14 GMT -5
I noticed a couple other things in the photo's.
Curious that the damage seems to line up with the valve clearance divit.
The top of the piston has two area's that look like some hack job metal removal. For valve clearance on a bad fitting piston maybe?
Also on the lower valve divit it looks like the little ridge of metal between the divit and the piston edge is missing? My old eyes cant tell but the piston edge at the damaged area appears to be there.
Seems unlikely but could the valve angle be such that it hit the piston edge and rolled it up?
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Post by FrankenMech on Jun 6, 2018 11:24:19 GMT -5
Is this an OEM engine or has the piston and jug been replaced? The metal removal may have been some lame attempt to reduce compression. I am thinking snaker may be on to something about the valve hitting. Maybe a little valve float? Whatever it is the piston, cylinder, and head are trash. |
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Post by 90GTVert on Jun 6, 2018 11:45:51 GMT -5
Possibly related note; lately there have been reports of some cheap kits coming with pistons without valve reliefs or reliefs that don't match up or domes too tall and other issues that make it seem like some manufacturer/distributor is pushing them out the door with no concern of bolt-on compatibility.
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Post by Kick start on Jun 6, 2018 13:32:57 GMT -5
 The red is for valve clearance I did that and less compression. I was using 69mm valve with stroker crankshaft and now going with 64mm valves. Yellow is what happen and I almost think it's from the cylinder being torqued to much and had the piston go passed the cylinder and when it came back down that's what it did.. I did a compression test befor I took it apart and it was the same and not leaking air. |
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Post by snaker on Jun 6, 2018 17:17:32 GMT -5
The red is for valve clearance I did that and less compression. I was using 69mm valve with stroker crankshaft and now going with 64mm valves. Yellow is what happen and I almost think it's from the cylinder being torqued to much and had the piston go passed the cylinder and when it came back down that's what it did.. I did a compression test befor I took it apart and it was the same and not leaking air. You would be stripping out threads long before you could crank down the studs enough to alter the position of the jug. Should be easy enough to reassemble the cylinder but leave the head off to see whats up. Rotate the crankshaft and see where the piston is positioned at TDC. Post a picture please.
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