Lml piston install

[whitegmc06]

I have an 2012 lml that has cracked #1 piston and it didn't mess with the cylinder wall. So I am wanting to put new pistons in it with some better pistons from factory. My question is do I need to get it balanced or can I check old vs new and see how close they match and replace bearings and rings and put the pistons in? Also I was told when I talked to a company about ordering bearings I told them I have 5 a rods and 3 b rods and they said that doesn't matter they should all be the same, and the marked them wrong from the factory. So I'm just curious if that is right or wrong it kinda has me confused. Thank you any input can help

 

[PureHybrid]

Measure piston weights, if close I'd run it. Although it would benefit from being balanced. Are you pulling the engine or trying to do this in frame?

GM did have different grade bearings based on diameters. Not sure who claimed they were marked wrong? Anyway that's where the H / HX bearings come in to dial your clearances to spec

 

[whitegmc06]

I've pulled the engine to do it on the stand, and I just wasn't wanting to pull the crank out. What is the technical difference, H is an A bearing and HX is a B bearing or opposite?

 

[TheBac]

I would balance the new assy if at all possible.

 

[PureHybrid]

I've pulled the engine to do it on the stand, and I just wasn't wanting to pull the crank out. What is the technical difference, H is an A bearing and HX is a B bearing or opposite?

That I am not sure of the correlation. H is a std size and HX is +.001"

 

[whitegmc06]

What would possibly happen if it is out of balance? Would it shake really bad? I'm want to go with a mahle cast performance pistons, they said they are matched as a set when you buy them at least that's what it says on the website. That is weird to me how the bearings are different on the same crank? Is it different on the thickness on the crank side or the rod side? And when you check bearing clearance do you use plasti gauge? Or a different method?

 

[PureHybrid]

What would possibly happen if it is out of balance? Would it shake really bad? I'm want to go with a mahle cast performance pistons, they said they are matched as a set when you buy them at least that's what it says on the website. That is weird to me how the bearings are different on the same crank? Is it different on the thickness on the crank side or the rod side? And when you check bearing clearance do you use plasti gauge? Or a different method?

Depends on how far out the balance is, far enough and it'll have a vibration.

Bearing grades are based on bearing housing size, there's not going to be a ton of difference. I have a set of both ID and OD mics, so I can measure theoretical clearance. Double check the assembly with Plastigage if you have it, no issues doing that

 

[whitegmc06]

Ok what would the acceptable tolerances usually be for that?

 

[PureHybrid]

For the bearing? Usually .001" for every inch of journal diameter is a good place to start

 

[whitegmc06]

Yea

 

[Bdsankey]

I personally would NOT make a piston change without balancing the engine. If I recall, the LML piston is quite a bit lighter than a Mahle motorsport piston. If my memory is correct, it doesn't matter how close each piston is in the set, it matters what the old vs new bob weight would be.


You, in my opinion, will be doing yourself a disservice by not balancing the rotating assembly. Most machine shops are $300-$500 in my local area to balance a rotating assembly. That's worth every penny for longevity and simply a smoother running engine since GM doesn't do a great job from the factory.

 

[1FastBrick]

I had to pay the diesel Tax to have my Rotating assembly balanced. I used a Balance only shop in my area as they were the only ones that had enough bob weight to do it. MY normal shop didn't have enough weight. It was $500 but if was say an LS it would have been $250....
I did get a balance card. Also, In the unfortunate event that should say I snap a crank, They could balance a new crank or other part of the rotating assembly.

 

[TheBac]

My go-to engine shop was the same way when mine was done back in 2010.. Told me they had to use every bobweight they could find.
I laughed and said to him, "Well, it isnt a small block Chevy."

 

[1FastBrick]

My go-to engine shop was the same way when mine was done back in 2010.. Told me they had to use every bobweight they could find.
I laughed and said to him, "Well, it isnt a small block Chevy."

I almost offered to pay for them until I found out what a newer set of bob weight's cost....

 

[whitegmc06]

Ok sorry for the pause lol. I've not gotten back on here I got busy at work, thank you for all of the great advice and inputs I very much appreciate it. I have more now and everything you guys say makes a lot of sense and I have checked around and I don't have any local machine shops in Muncie Indiana anymore apparently lol I had to call around and try to figure something out because I discovered some issues it sheered the dowel pin on the crank for the oil pump gear which I was able to remove it and it also had some decent wear on the main bearing on the second one before the rear main, but it did really do any marks on the crank, but that being said I tried to call around to see if they could check it and key it and balance it and no one around me apparently wants to do anything for me so I am actually kinda lost now, other people are telling me to throw it together it will be fine and I'm not really a throw it together kinda guy I want to make it right and have no issues kinda guy lol I also need to order the external side main cap bolts and the dealership said they are discontinued but I was able to get the internal ones no problem. Like I said sorry for the pause I really appreciate this site and all of your guys great knowledge and advice I am very thankful ps I attached the bearing lol

 

[TheBac]

Send a PM to Mark Broviak on here. He used to be in Danville, and will probably have connections to any machine shops in mid-Indiana.

 

[ikeG]

Wagler is 2.5 hrs away from you...

Sent from my SM-G990U2 using Tapatalk

 

[whitegmc06]

Ok thank you

 

[whitegmc06]

Ok I went and just got everything back from the machine shop from getting balanced I am installing pistons now and the mahle cast performance pistons are marked a little different for top and bottom so now I am wondering if the arrow is at the top or bottom?

 

[1FastBrick]

The mark is up.