Piston rock and deck height (Mahle forged)
10-23-2005, 10:30 PM
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Piston rock and deck height (Mahle forged) How much piston rock and deck height is acceptable?
My brand new TSP forged motor died on the way home.
I popped the heads off and noticed what looks like piston contact on the heads. Ring lands broke on mirror opposite sides, cylinder four and cylinder five.
The block is a new 2nd gen LS1/6, the crank is used, the pistons are Mahle forged pistons. TSP told me the deck height should be -0.001 to 0.000 deck height, but measuring deck height between cylinders I measure .007". There's significant piston rock, and on the high side deck height is .023" (opposite of where I push down on the piston). I'm using stock GM MLS .045" gaskets.
My brand new TSP forged motor died on the way home.
I popped the heads off and noticed what looks like piston contact on the heads. Ring lands broke on mirror opposite sides, cylinder four and cylinder five.
The block is a new 2nd gen LS1/6, the crank is used, the pistons are Mahle forged pistons. TSP told me the deck height should be -0.001 to 0.000 deck height, but measuring deck height between cylinders I measure .007". There's significant piston rock, and on the high side deck height is .023" (opposite of where I push down on the piston). I'm using stock GM MLS .045" gaskets.
10-23-2005, 10:40 PM
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Originally Posted by xssive
Sounds like maybe an issue with the crank being as those pistons ride on the same throw
10-23-2005, 11:14 PM
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Oil pressure is good, 40psi at idle and otherwise higher.
Right before it started it's 'running rough' act, I put a half throttle into it on the freeway, enough for a downshift. It wasn't at max boost, and I never heard it ping.
Right before it started it's 'running rough' act, I put a half throttle into it on the freeway, enough for a downshift. It wasn't at max boost, and I never heard it ping.
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10-24-2005, 10:20 AM
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Originally Posted by oange ss
rock piston to one side measure highest deck height, divide by two..measure from other side do the same thing
OK - I get .0236" total on valley side, .0157" on header side. So deck height is .012"/.008". Gasket is GM MLS - .045". Leaves .033" squish, the distance of a sparkplug gauge. So no accounting for piston rock? .045" - .024" rock (rounding up) leaves .021" squish.
Last edited by blu00rdstr; 10-24-2005 at 10:42 AM.
10-24-2005, 09:18 PM
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From the pix I can't see signs of contact on the head. I'm 99% sure that's detonation, dude! See how the #4 piston is eaten away at the exhaust side? Also, even forged pistons wouldn't rock nearly that much with normal clearances, but once the pistons collapsed they might rock enough to hit...
10-25-2005, 01:45 AM
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Originally Posted by oange ss
MLS should be .054, unless you're using the graphite which would come out to .040
Originally Posted by MadBill
From the pix I can't see signs of contact on the head. I'm 99% sure that's detonation, dude! See how the #4 piston is eaten away at the exhaust side? Also, even forged pistons wouldn't rock nearly that much with normal clearances, but once the pistons collapsed they might rock enough to hit...
I can't quite get a good pic of the sandpaper effect in the quench area, this is the best I can get of the piston, and another close up of the quench area in the head. See the grainy surface? Having a sandpaper like texture in a squish area just ain't right. Maybe it's micro detonation, but could it be caused by running at 6,000+rpm with rock and rod stretch and squeezing out what's left of .021" of static squish?
Last edited by blu00rdstr; 10-25-2005 at 02:11 AM.
10-25-2005, 07:47 AM
#15
I just measured mine and it came out to .053, I measured my new one and it came out to .057, measurements were taken with a dial caliper, which is not gonna be dead nuts on but close enough for comparison. Is this the first time you've done your heads ?
10-25-2005, 10:29 AM
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Here's .053" around the cylinder without squeezing, but I have a metal metric caliper which I can squeeze harder and will measure .047" around the cylinder. Having to translate just doesn't work as well in photos.
The flycut area for the intake valve appears to be both a weak spot and a high spot. Here's the matching area on the cylinder head (good cylinder) followed by a pic of a failed piston.
The flycut area for the intake valve appears to be both a weak spot and a high spot. Here's the matching area on the cylinder head (good cylinder) followed by a pic of a failed piston.
Last edited by blu00rdstr; 10-25-2005 at 10:54 AM.
10-25-2005, 10:54 AM
#17
Bill - As we discussed via e-mail, we will have to send the pistons to Mahle Motorsports for inspection. As you can see in John Goodwin's excerpt below from Mahle Motorsports, he feels it is a detonation issue as well. But, that's why we will send the pistons to them for detailed inspection.
"The pictures indicate detonation . I would like to have all 8 pistons returned here for evaluation . Due to design , our pistons do have more rock than is usual for full round piston in a static , cold engine . Under operation , due to pressure and expansion that rock goes away .I do not think that this failure is related to piston to head contact . A quick look under the microscope will tell the story."
If there was a crankshaft problem with the piston hitting the head, this is something you should have definitely been able to hear on initial start-up. I will let you know when we receive the short-block.
Trevor
Texas Speed & Performance
"The pictures indicate detonation . I would like to have all 8 pistons returned here for evaluation . Due to design , our pistons do have more rock than is usual for full round piston in a static , cold engine . Under operation , due to pressure and expansion that rock goes away .I do not think that this failure is related to piston to head contact . A quick look under the microscope will tell the story."
If there was a crankshaft problem with the piston hitting the head, this is something you should have definitely been able to hear on initial start-up. I will let you know when we receive the short-block.
Trevor
Texas Speed & Performance
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Last edited by Trevor @ Texas Speed & Perf.; 10-25-2005 at 11:02 AM.
10-25-2005, 11:00 AM
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Just to let everyone know, Trevor has been more than helpful. I'm facinated by the failure, trying to analyze the parts and what went wrong, completely separate from the who.
TSP provided only the shortblock, they didn't provide gaskets, heads, tune, boost, assembly, etc.
TSP provided only the shortblock, they didn't provide gaskets, heads, tune, boost, assembly, etc.
10-27-2005, 01:49 AM
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Bottom end looks fine, the big ends have a little side play but that's normal.
The Mahle pistons have no quench surface at all, they're all dish. Here's a pic of the piston rocked to the left.
The Mahle pistons have no quench surface at all, they're all dish. Here's a pic of the piston rocked to the left.
