Chevy and GMC Duramax Diesel Forum banner

Moderate LML engine rebuild...

20K views 63 replies 13 participants last post by  poosniffer 
#1 ·
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?
 
#3 ·
thought that's only necessary in high horse power applications? 'dunno;
 
#4 ·
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 aren’t necessary.

Head gaskets are an issue, definitely do studs.

No point in doing new cam and crank unless oil starvation was an issue and they’re 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. I’m sure the shop would love to sell you the rest of that stuff, but it’s overkill. If that’s your thing, go for it.


Sent from my iPhone using Tapatalk
 
#5 ·
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!!!
 
#6 ·
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.
 
#9 ·
I’m people are asking for an HP goal. I’d 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.
 
#11 · (Edited)
600 is at the top end of what you can get on stock air and fuel if im not mistaken, but i still think the only thing you need from the list would be head studs. Your still not making enough power for the girdle or billet caps, but if they would make you sleep better at night, dont let me stop you from getting them. To be totally honest i would probably do the girdle even if i didnt need it. I would swap out the LML pistons though, be it for LB7 pistons or the Mahles others have recommended. The pistons seem to be the weak link in the LML engine followed by the rods.
 
#10 ·
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.
 
  • Like
Reactions: burred and mstein86
#12 ·
Started tearing into it tonight, I don't have a factory repair manual so I'm playing it by ear. Does anyone have the HELM factory repair manual? I want to know if it's worth the money.
 

Attachments

#13 · (Edited)
I agree with matt 100%. For what you're doing I would skip 90% of your list. Victor Reinz grade cs or get lml golds, arp 425s and some mahle race cast or even delipped lb7 lly pistons would be fine. Theres been plenty of lmls bend rods also but most were running compounds where the torque is instant in the lower rpm range and that's what bends rods. Good tuning plays a huge roll also. It doesn't matter what you do with the crank. Guys buy 5k dollar ones and they still snap. Stock cam will be fine also. The alt fire ones havent proved to be the fix all like people hoped.You can still get delete tunes from very good and highly reputable tuners its who you know.
 
#14 ·
#18 ·
Quick update, cut open the oil filter and this was at the bottom, filter paper element also has lots of metal... Motor is coming out Tuesday.
 

Attachments

#19 ·
Not sure what engine failure I had until I take it a part. I will update after I get it out and taken a part. I was on a tow tune so the transmission would learn, then the truck started knocking. Not sure if it was a tune problem or a mechanical problem...
 
#20 ·
Sorry too many post to keep track of LOL so the crank shaft broke and most of the push rods are bent. Piston and rods look ok. Trans, heads and driveshafts are out for rebuilding.
 

Attachments

#22 ·
did you miss the crank? :teehee
 
#32 ·
A good friend had a 20k dollar engine trashed cause of crank failure with less than 5k miles on it. Now his truck is sitting until he can afford to put a stock short block in it cause he cant afford to build it twice. That's actually part of the reason I decided to build a cummins. I have bad luck and didnt want to stick the rods and pistons in my botton end to have the crank snap sometime later.
 
This post has been deleted
#36 ·
i would really not worry about it. its going to happen, or its not, and theres really nothing that can be done about it besides MASSIVE investments in the engine. The failure rate of cranks is significantly lower than the already low failure rate of CP4 pumps. Perhaps i should have been more careful in what i said, so let me try it again.

The crank shaft cracking at that location has been a historically documented failure mode of the duramax engine since 01 when the block was first put into use in GM vehicles. While this failure does not happen often by large, there are enough occurrences of this failure that is shows a history of this failure being possible on every duramax engine built to date, with the possible exception of the L5P because i do not know if it uses the same crank. Your chances of this failure are very low on a stock or even mildly tuned truck, and i do mean very low. You have significantly higher chances of most other things breaking before the crank does based on the number of reported failures and the number of trucks on the road. This problem becomes more common though as the load on the pistons increases, so when your making a ton of power with your twin turbo kit your chances of failure go up a good bit, but even then, are still not that high. Please do not loose sleep over this, or build a 30K engine, it is not necessary. the 5 failures a year or whatever shows up on this forum is not worth it.
 
#34 · (Edited)
Wow... the poor op's thread. Hijacked by this^

Silvergorilla is one of the most knowledgeable, no b.s. members on here. He offered relevant advice to the thread. This is ridiculous.

Could we all be trolled on an epic level lol
 
#35 ·
He is the only person in my ignore list. I just couldn’t take it anymore.
There was another guy that was really close, but he got banned recently.
 
#39 ·
Cody it would probabaly take some machining of various items in the bottom. I haven't followed the l5p too closely but I'd give it a while and see how they continue to hold up. Budget build would be cut lb7 lly pistons and some carrillos or lbz rods if you want to go real cheap. Also just read/talked about 2 of the callies billet narrow rod journal cranks that broke.
Just drive the truck. If it cracks a piston, bends a rod, breaks the crank, injectors fail, lifts the heads, whatever, just fix it and go on with life. Shit happens, everything breaks nothing is perfect. Every engine ever created has some type of weakness or small flaw.
 
#43 ·
Got my engine but they didn't install the crankshaft gear, the one that drives the cam. They are shipping me one out ASAP, what the best way to install this? Should I bake the gear to 400 degrees for 30min so it slides on easier? Any help or suggestions would be appreciated.
 

Attachments

  • Like
Reactions: poosniffer
#50 ·
M.A.M. so I'm following ALLDATAdiy.com for the rebuild procedure and I'm worried about installing the cam wrong. The website just says to line up the timing marks on the crankshaft gear and camshaft gear. Can it be that easy?
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top