Need some help on Piston Protrusion

TonOfDalt

More is better!!!!
Aug 9, 2012
153
1
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42
Spoke Valley, WA.
Hey all, been awhile since I have posted anything constructive but the truck has been down for a year now and I am just getting ready to put it all back together.
My question as the title suggests concerns piston protrusion. This is the 1st DMAX that I have built but have built probably 50-60 other gassers so the only thing new to me here is piston protrusion.
A little history...
I sold my engine running (298,000 miles) in favor for something a bit more fresh (98,000). It was a good deal because I ended up selling mine more than what I bought the new one for. The engine came from a fire salvage and other than some very minor pitting towards the top of #5 that honed out nicely the engine was in near flawless condition as far as the long block is concerned.

The problem...
I used a complete rebuild kit including new pistons as well as rod bushings and grade C gaskets. After assembly I have the following protrusions as well as height variations... The protrusion # is a highest point and the variation is the difference between the high side and low side. All measurments where taken on either end of the pin and I verified that this has not been because of the pin bushing being honed higher than center. All figures are with ARP rod bolts being torqued to 90% of total stretch and ARP main studs tightened to spec with STD bearings.

#1 .021 / .0035 high on the front
#3 .020 / .005 high on the rear
#5 .020 / .0048 high on the rear
#7 .023 / .0045 high on the rear

#2 .019 / .005 high on the front
#4 .026 / .004 high on the front
#6 .022 / .014 high on the rear (yes this one concerns me & im pulling the rod to check for straightness.
#8 .021 / .005 high on the front

Now to me other than #6 everything is pretty well in-line so I was wondering if the pistons need to be milled. They are stockers and came direct from MAHL with rings pre-installed so I can not see them needing machining however I have not checked the height of each piston (from bottom of skirt to top of piston). One other thing to mention, I shot myself in the foot because I knew I would be using new pistons and pins so I did not bother checking all of what I listed prior to disasembly.

I know its a long post but I had to get all the info I could to you guys so we dont go back and forth.
Thanks everyone.
 

TonOfDalt

More is better!!!!
Aug 9, 2012
153
1
0
42
Spoke Valley, WA.
No sir. Everything on the block is within factory tolerance. Reight in the middle or tight for most of it.
Like I said, this beats the shit out of me. Compressed thickness of "C" is 1.05mm or .0413. This would leave .0153 final clearance. Seems a bit close.
 

TonOfDalt

More is better!!!!
Aug 9, 2012
153
1
0
42
Spoke Valley, WA.
At this point I plan on taking everything back out and re-checking. No sense in destroying a build on start-up due to lack of patience or scrutiny. I was just hoping that maybe someone had seen this before and could point the way so to speak.
 

TonOfDalt

More is better!!!!
Aug 9, 2012
153
1
0
42
Spoke Valley, WA.
I use all Shars calipers/micrometers/bore/dials accurate to .0005. Standard Proform magnetic base deck measurment tool. Shars magnetic base adjustable arm dial holder. Snap-On feelr set.
As I said, I've built plenty of engines with most being above the 400 mark and never having one blow on me. I am more than sure of myself on builds but I am not too good/dumb to ask for help with something that isn't within spec thay I have never seen before.
Again, juat wanted to ask because there is a lot of performance build experience on here and I was hoping someone would have a magic "I've seen that before" answer.
Thanks all, I will pull her back apart to recheck everything and repost with the results.
 

Chevy1925

don't know sh!t about IFS
Staff member
Oct 21, 2009
21,702
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Phoenix Az
so the numbers you have in the first post like #3 that is .020 / .005, one of those numbers are the front of the piston and one of those are the rear of the piston?
 

x MadMAX DIESEL

<<<< No Horsepower
Dec 30, 2008
7,535
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Lexington, Ky
so the numbers you have in the first post like #3 that is .020 / .005, one of those numbers are the front of the piston and one of those are the rear of the piston?



No .020 would be the high point, whether it's front or rear of pin. And the .005 is the difference of front to rear.
You should put a precision straight edge on the deck surface.
 

PureHybrid

Isuzu Shakes IT
Feb 15, 2012
3,501
484
83
Central OH
Where did you buy pistons from? I'd throw an old piston back in a hole and recheck protrusion. At worst, you could have .010 taken off the top of the pistons.
 

TonOfDalt

More is better!!!!
Aug 9, 2012
153
1
0
42
Spoke Valley, WA.
Did you ever get it figured out? I've got a piston showing .014-.015 difference also front to back


Sorry for the late response.
We found that the machine shop not only honed the pin bushings too high but also not straight. I decided to go with a set of Brian Crower rods. Got a super deal!
Hope this helps
 

x MadMAX DIESEL

<<<< No Horsepower
Dec 30, 2008
7,535
1
38
34
Lexington, Ky
Sorry for the late response.

We found that the machine shop not only honed the pin bushings too high but also not straight. I decided to go with a set of Brian Crower rods. Got a super deal!

Hope this helps



That's fine I got mine figured out. I also got Brian crower rod's with a super deal! I was not impressed with the quality assurance on these, but so far they are holding up to abuse