Moderate LML engine rebuild... - Chevy and GMC Duramax Diesel Forum
11-16 LML Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 64 (permalink) Old 09-18-2019, 07:13 AM Thread Starter
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Moderate LML engine rebuild...

So my engine is toast, I'm looking at getting the short block done at a machine shop. What are the "must haves" for this engine. Truck will be tuned, I'm not trying to make 1000hp, just something reliable.

Is a girdle necessary?
Keyed cams and crank? I read this is a must!!! True?
Head studs? I heard the LML doesn't have head gasket issues like earlier models.
All internals will be stock, I plan on replacing the crank, cam, pistons, rod, and bearings, unless you guys chime in and recommend other wise...
ARP rod bolts?
after market main caps?

2012 GMC Sierra 2500HD Denali
Stage 1 short block, ATI damper, Fass 150, CP3, upgraded trans, Up pipe, Down pipe, EZ lynk w/ 5 tunes SOTF, Magnaflow exhaust, PCV re-route, 4 inch Fabtech lift, 35in tires, HD motor mounts
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post #2 of 64 (permalink) Old 09-18-2019, 07:25 AM
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I donít have first hand experience, but if I was rebuilding one I would look into getting an alternate firing order cam. That is if you can still find a tune for it.
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post #3 of 64 (permalink) Old 09-18-2019, 07:50 AM Thread Starter
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Originally Posted by MIkey52 View Post
I donít have first hand experience, but if I was rebuilding one I would look into getting an alternate firing order cam. That is if you can still find a tune for it.
thought that's only necessary in high horse power applications?

2012 GMC Sierra 2500HD Denali
Stage 1 short block, ATI damper, Fass 150, CP3, upgraded trans, Up pipe, Down pipe, EZ lynk w/ 5 tunes SOTF, Magnaflow exhaust, PCV re-route, 4 inch Fabtech lift, 35in tires, HD motor mounts
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post #4 of 64 (permalink) Old 09-18-2019, 08:31 AM
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Moderate LML engine rebuild...

None of that stuff is necessary on a reliable daily driver, unless you plan on going high hp/high rpm. Keyed cam and crank, alt fire cam, billet main caps, girdle, connecting rods and arps for the rods arenít necessary.

Head gaskets are an issue, definitely do studs.

No point in doing new cam and crank unless oil starvation was an issue and theyíre scarred.

If I was in your place, I would do throw a set of Mahle Motorsports pistons in it, along with new bearings, head gaskets and head studs. Iím sure the shop would love to sell you the rest of that stuff, but itís overkill. If thatís your thing, go for it.


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post #5 of 64 (permalink) Old 09-18-2019, 10:15 AM Thread Starter
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Originally Posted by M.A.M. View Post
None of that stuff is necessary on a reliable daily driver, unless you plan on going high hp/high rpm. Keyed cam and crank, alt fire cam, billet main caps, girdle, connecting rods and arps for the rods arenít necessary.

Head gaskets are an issue, definitely do studs.

No point in doing new cam and crank unless oil starvation was an issue and theyíre scarred.

If I was in your place, I would do throw a set of Mahle Motorsports pistons in it, along with new bearings, head gaskets and head studs. Iím sure the shop would love to sell you the rest of that stuff, but itís overkill. If thatís your thing, go for it.


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Thanks for your input M.A.M. I'm just trying to get people's opinions. I figured since I'm rebuilding the motor, I should do it right!!!

2012 GMC Sierra 2500HD Denali
Stage 1 short block, ATI damper, Fass 150, CP3, upgraded trans, Up pipe, Down pipe, EZ lynk w/ 5 tunes SOTF, Magnaflow exhaust, PCV re-route, 4 inch Fabtech lift, 35in tires, HD motor mounts
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post #6 of 64 (permalink) Old 09-18-2019, 10:57 AM
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Quote:
Originally Posted by mstein86 View Post
So my engine is toast, I'm looking at getting the short block done at a machine shop. What are the "must haves" for this engine. Truck will be tuned, I'm not trying to make 1000hp, just something reliable.

Is a girdle necessary?
Keyed cams and crank? I read this is a must!!! True?
Head studs? I heard the LML doesn't have head gasket issues like earlier models.
All internals will be stock, I plan on replacing the crank, cam, pistons, rod, and bearings, unless you guys chime in and recommend other wise...
ARP rod bolts?
after market main caps?

an actual power goal would help but im assuming that your looking for something in the 500 range thats reliable day to day. If that is the case, the girdle is not needed unless your just feeling like doing it. keyed cam and crank would be good, but again depends on your power goals. I would say that if your already having the block machined, may as well have them key the cam and crank, i doubt it will be that much more. LML's do still suffer head gasket failures, though not like the LB7 did, Personally i would do the head studs for peace of mind. I would use LB7 pistons and rods if you can, they are stronger than the LML rods and pistons. I dont think the rod bolt of main caps would make a difference for you one way or the other unless your trying to make bigger power than i am assuming. If the cam and crank are not damaged, i see no reason to replace them. IF you are going to replace them, i have heard the alternate firing order cam reduces the likelihood of a crank shaft failure.

If you could focus on a HP number to shoot for that would help though, If you wanted to make 800HP, some of the things above become needed and not optional.

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post #7 of 64 (permalink) Old 09-18-2019, 02:34 PM
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Originally Posted by MIkey52 View Post
I donít have first hand experience, but if I was rebuilding one I would look into getting an alternate firing order cam. That is if you can still find a tune for it.
Can't you just move some pins around in the wiring so tuning doesnt have to be changed?

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post #8 of 64 (permalink) Old 09-18-2019, 03:38 PM
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Originally Posted by denarli6.6 View Post
Can't you just move some pins around in the wiring so tuning doesnt have to be changed?
thats my understanding of how that cam works, you just rewire the injectors to fire in the correct order for the new cam.
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post #9 of 64 (permalink) Old 09-18-2019, 04:14 PM Thread Starter
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Iím people are asking for an HP goal. Iíd say 600hp, not that I would be running that tune all the time though. I know I can run 600hp with most of the stuff already in the motor.

2012 GMC Sierra 2500HD Denali
Stage 1 short block, ATI damper, Fass 150, CP3, upgraded trans, Up pipe, Down pipe, EZ lynk w/ 5 tunes SOTF, Magnaflow exhaust, PCV re-route, 4 inch Fabtech lift, 35in tires, HD motor mounts
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post #10 of 64 (permalink) Old 09-18-2019, 05:12 PM
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I agree with Matt, at that power level and assuming nothing is broken internally, I would rebuild the bottom end all stock with the exception of the pistons. The lml pistons are the weak link in the bottom end and are prone to cracking. The Mahles are much stronger, along with a few others.

On the top end , I would have the heads rebuilt and install them with studs and Mahle gaskets. Everything else stock, with the upgrades you have already done, will make for a dependable engine.

I would save the money from the other upgrades discussed and spend it on a turbo.
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