LBZ: 2 cylinders funny protrusion

[x MadMAX DIESEL]

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

That's what I've been trying to find but no luck. I wish I had a "precision straight edge" to run across the block. closest I have is a 2 foot bostitch level, with some quickie saw marks on it from using as a guideline lol.

Maybe I could throw a longer lbz wrist pin in some pistons. Flip them upside down on a flat surface. Measure and see if there is a difference between the compression heights of the front and the back...

 

[x MadMAX DIESEL]

Actually that shoulda shown when I flipped the piston over. So I guess finding a straight edge to use would be my next step. I hope it's exceptable difference. But I still would like to have less a difference and run a tighter gasket as this is a daily driver


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[Chevy1925]

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

.003-.004 is the most id want to see. basically, its the same tolerance difference as the compression height of head gaskets. i base the HG of the peak of the piston. cant say i have come across this issue though.

Actually that shoulda shown when I flipped the piston over. So I guess finding a straight edge to use would be my next step. I hope it's exceptable difference. But I still would like to have less a difference and run a tighter gasket as this is a daily driver


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was this block bored over? i wonder if the machine shop misaligned the bores.... you would have to mic the wall thickness between each cyl at its closest point to each other if that makes sense

 

[x MadMAX DIESEL]

Yes I will try that. Yes it was bored over to use .020 over mahle pitons. Torque plate honed. I also have a buddy at the ford dealer gonna let me borrow their straight edge to set on the deck surface


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[x MadMAX DIESEL]

I know I should really add the front and rear protrusion numbers and divid by 2 to get an average. That is called the protrusion. But if they come up like that why wouldn't they always come up like that and hit front of piston lol


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[Chevy1925]

I know I should really add the front and rear protrusion numbers and divid by 2 to get an average. That is called the protrusion. But if they come up like that why wouldn't they always come up like that and hit front of piston lol


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because something isnt square. you might also swap pistons to other holes but leave the rods in the same holes they are in. see if the difference follows suit. if so, you know its the head of the piston out of square if the mic doesnt show anything between cyl gap. to machine the bore that far off is a pretty big mistake so i wouldnt think they did that but stranger stuff has happened

 

[WolfLMM]

Use a height gauge on granite surface plate. Flip piston on its top, and measure each side of the wrist pin bore. (You will be using a test indicator which has been zero'd on the table surface) check for difference. It will show out of square. So if all that checks out (Pistons, pins, rods, bushings) I would think the cylinder bores aren't square with the deck, no?

 

[x MadMAX DIESEL]

Use a height gauge on granite surface plate. Flip piston on its top, and measure each side of the wrist pin bore. (You will be using a test indicator which has been zero'd on the table surface) check for difference. It will show out of square. So if all that checks out (Pistons, pins, rods, bushings) I would think the cylinder bores aren't square with the deck, no?

Yes I mentioned trying that. I thought me flipping piston upside down in bore showed that was not the case? I will go ahead a five that a try though

 

[x MadMAX DIESEL]

No time for engine tonight. I had about 5 mins and ran some straight edges though and eye ball fine.

This is an LML CRANK. The block was milled. How many ppl mill the block much or even much of the heads for that matter. Everyone is so quick to second guess a machine shop that they will get close to a service limit. So with that being said. They may not notice something as clear or feel it with a finger so they don't worry about doing a lot of measuring. Just throw a c grade on and bolt it on.... so I have to ask a stupid question that I thought of in the shower lol


Is there a possibility that the lml crank has something to do with this?

Like the counterweights or something pressing on the rods? I know that doesn't really make sense because it turns over smooth as well as some side clearance on the rods even at tdc where the problem is. Stupid but trying to think outside the box?!
I might as well check crown height front and rear while it's at bdc also while I'm at it. Maybe that could shed light. I'm about to take the dang thing to the machine shop in the next couple days. I barely have time to work on it plus I'm obviously not getting anywhere lol



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[Chevy1925]

No time for engine tonight. I had about 5 mins and ran some straight edges though and eye ball fine.

This is an LML CRANK. The block was milled. How many ppl mill the block much or even much of the heads for that matter. Everyone is so quick to second guess a machine shop that they will get close to a service limit. So with that being said. They may not notice something as clear or feel it with a finger so they don't worry about doing a lot of measuring. Just throw a c grade on and bolt it on.... so I have to ask a stupid question that I thought of in the shower lol


Is there a possibility that the lml crank has something to do with this?

Like the counterweights or something pressing on the rods? I know that doesn't really make sense because it turns over smooth as well as some side clearance on the rods even at tdc where the problem is. Stupid but trying to think outside the box?!
I might as well check crown height front and rear while it's at bdc also while I'm at it. Maybe that could shed light. I'm about to take the dang thing to the machine shop in the next couple days. I barely have time to work on it plus I'm obviously not getting anywhere lol



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Just the last build I did had a new lol crank, stock lbz rods, lbz block and cut lb7 Pistons. Protrusion was .012-.014 min/max with no more variance than .002 from one side of the piston to the other. I highly doubt it's the crank. I know what you mean about jumping to a machine issue. I'm not trying to do that but most things you check will be stuff the machine shop should have done or worked on.

 

[LBZ]

If you swapped the rod but not the piston it could be a block bearing or piston issue.

To eliminate all but the crank and block I'd swap the whole piston rod and bearings with another. If it doesn't change, you likely have a block issue.

 

[x MadMAX DIESEL]

If you swapped the rod but not the piston it could be a block bearing or piston issue.

To eliminate all but the crank and block I'd swap the whole piston rod and bearings with another. If it doesn't change, you likely have a block issue.

When you say block bearing, what's that? The main bearing or rod?

 

[x MadMAX DIESEL]

Well I've pretty much established that the connecting rods are bent. I guess the "good rod" I slung in to check a few days ago was bent too. (Out of a 530hp lbz) so that confused me. I thought that bad boy woulda been straight


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[LBZ]

I meant block OR bearing.
But sounds like your buying rods.

 

[x MadMAX DIESEL]

I meant block OR bearing.
But sounds like your buying rods.

Sounds like the all mighty lbz rods are junk to me.

 

[WVRigrat05]

If yours are bent at 530 hp, musta pulled pretty hard down low??

 

[x MadMAX DIESEL]

If yours are bent at 530 hp, musta pulled pretty hard down low??

Not more than any other truck around here at the time

 

[WVRigrat05]

Just seems odd, my LMM doesn't pull down low but it would be interesting to see if they are deviated.

 

[x MadMAX DIESEL]

Just seems odd, my LMM doesn't pull down low but it would be interesting to see if they are deviated.

What do you mean by that?

 

[WVRigrat05]

Id be curious to see if mine are slightly bent as well if yours aren't true at the same HP.