LBZ: 2 cylinders funny protrusion

[x MadMAX DIESEL]

Hey guys just have to ask for some second opinions here. I've got 2 pistons #2 and #4 that don't seem running up square. Standard lbz rods so I don't really want to try and swap cylinders around to see if it follows just yet to avoid getting new bolts etc.

Concerning to me is the .0133, and .0126 differences shown in my pic. Please let me know your thoughts thanks

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[x MadMAX DIESEL]

That is how they come up with out hand assistance to get them even in the bore. On this measuring session I did not center the Pistons up by hand FYI


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[Chevy1925]

cyl 8 also looks like a problem area and cyl 1 looks like a rod is a tad short.

are you measuring over the wrist pin? what do they change to when you slide the piston side to side across the wrist pin?

 

[x MadMAX DIESEL]

#1 is a brand new piston, all the others are used Pistons, cleaned but still black coated. I will redo all measurements later tonight with them centered in bore. Yes that was right over the pin for the most part. I maybe moved a 1/4 inch up or down on it to find the highest possible reading though


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[SmokeShow]

your difference on piston 8 is off by a decimal. It should be .011 rather than .0011

 

[x MadMAX DIESEL]

your difference on piston 8 is off by a decimal. It should be .011 rather than .0011

Good looking out Mitch

 

[TheBac]

IMO, if you're rocking along the pin's axis, then you've got problems.

I believe mine were all between .012-.015 protrusion when I rebuilt.

 

[x MadMAX DIESEL]

I cleaned the heck out of the piston tops. I thought they said they cleaned them off at the machine shop. But I was able to get some stuff off of them with just brake cleaner. My differneces look better after centering them in the bores. I did not have my bore gauge with me at the time of installing the Pistons. Machine shop said they did PTW to about .0045. I believe mahle calls for closer than that. Maybe that is why I am able to center them and cut the difference down. I can't say forsure. I will measure the bore as deep as I can get to check ptw but i can only get to the top of the a BDC piston, so about 2 inches higher than normal if it's tapered much at the bottom. but maybe close enough to verify the .0045 idk


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[x MadMAX DIESEL]

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[x MadMAX DIESEL]

Okay so I've got about .0025 PTW. Measuring off an old .020 over bore mahle I have laying around.


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[PureHybrid]

That much difference front to rear would not be good on the bushing and bottom end bearing.

What is the history behind the rods?

 

[x MadMAX DIESEL]

About 130k miles, running about 620 hp for the past 4k miles. came out of the same block that snapped the crank a few months ago


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[x MadMAX DIESEL]

Also, they are lb7 pins of unknown miles I had to buy to use in the mahle Motorsport piston. Though I don't see how those could be bent, and even if they were how they piston and rod would assembly on them.


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[Chevy1925]

i highly doubt the wrist pin is your issue. the bushing in the piston or rod would be more at fault than the wrist pin. since all this is used, did you check for out of round in the piston wrist pin bore or the same on the rod?

 

[x MadMAX DIESEL]

i highly doubt the wrist pin is your issue. the bushing in the piston or rod would be more at fault than the wrist pin. since all this is used, did you check for out of round in the piston wrist pin bore or the same on the rod?

No I didn't the Pistons have only like 2-3k miles max on them. I am gonna throw a different couple rods in that never saw over 530 hp in the 2 and 4 bores and see if there is a change

 

[Chevy1925]

No I didn't the Pistons have only like 2-3k miles max on them. I am gonna throw a different couple rods in that never saw over 530 hp in the 2 and 4 bores and see if there is a change

the rods would be more likely to show the wear and cause them to have one side sit low.

why are you not looking at Cyl 8 as well? you still have a big difference there.

 

[x MadMAX DIESEL]

I highly doubt a pin would cause it too that's why I said idk how those would bend lol. And I thought it was bent rods so I called the machine shop and ran that by them. Said most likely I'd have some bind spots rotating assembly around if they where bent. But I'm putting different rods back in for the test. If they are good then I will grind them down to weight the same as the ones in question to match balance and use those... or I know of a good deal on some aftermarket rods. I'd like to save my money still though lol. But yes, I would look at every one cylinder again. I kinda forgot about the 8 as I'm not in front of it now. But if 2 and 4 were fixed then I would have a good idea the problem and move on to other cylinders.


I will see about checking for out of round bushings too if I have something I can measure it with.

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[x MadMAX DIESEL]

No found issue yet. I'm a busy man with other things lol I swapped a rod, no change. I'm pulling the piston squirter now and gonna put the piston in backwards. See if it follows...


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[x MadMAX DIESEL]

Still front way high


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[SmokeShow]

I've got no ideas. Curious what IS an acceptable difference? Is that different for a street build versus performance build?