Duramax Diesels Forum Truck of the Week
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Old 05-06-2020, 08:20 AM
Doms Doms is offline
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Default Stock Rebuild

I cracked a piston on my LBZ and I am looking to do a fairly stock rebuild. The truck is used mainly as a daily driver and does a little bit of towing from time to time. For discussion sake I'll say reliable power goal of 450HP. I am tuned for more than that now with EFI live and a DSP5 but I stay out of it. If anything I would do away with the "race" tune.

I plan on rebuilding the oil cooler, replacing the water pump, replacing most fasteners with new OEM (heads, mains, rods, cam, crank, converter), sending the block and heads out for inspection and machining and then using Mahle cast pistons and gaskets and Clevite P series bearings for re-assembly.

Is the oil pump serviceable or is it just a replace it type of part? This motor had low miles (80,000) so everything is looking pretty good (aside from piston #6 haha).

At what power level should one start to seriously consider going to performance cast pistons and head studs? Would either of these be much of a benefit now?

What else should I be looking at upgrading while I have this thing torn apart? My priorities are: reliability, cost, performance - in that order. I do not want to cut corners anywhere, I'm just not looking for a high dollar build.

I know that I have a lot of questions, and I have a ton more but Ill leave it at that for now and appreciate any help/advice I can get. Thanks.
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Old 05-06-2020, 08:33 AM
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you're on a good track.

i would buy the mahle race cast pistons though. then you gain the benefit of having a better piston than you had before (stock replacement mahles are just that).

oil pump is not servicable so pick up a new one. oil cooler, i would look into a 17-19 trucks cooler as its direct bolt on with a few longer bolts and has more capacity for oil cooling. 2020 one will fit but requires different gaskets, longer bolts, different elbow and must run 2020 style oil filters but it is even better than the 17-19.

key the crank and cam, the pins like to bend or fail and it can take the vavles/pistons out.

you will probably get guys saying to do headstuds but imho, at that power level, stock is just fine. run a good mahle/victor reinz head gasket (you will need to decide A, B, C, or D). if the block is getting decked, you would need to measure piston protrusion on reassembly to figure out the right HG thickeness for you.

as for what power level you need head studs, well that depends on how you achieve your power. boost doesnt kill HG, high drive pressure does. so if you try driving the hell out of the stock charger with lots of fuel, probably going to lift a head. if you put twins on or bigger single and have tuning correct, they can hold some power. If you want a number to go by since you have this thing apart, if you plan to push over 550hp at any point down the road, do the head studs now. if you actually plan to stay at 450hp, its not needed

who is assembling it?
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Old 05-06-2020, 08:49 AM
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That's exactly the kind of advice I am after. Thank you.

I was kind of at a toss up between the cast and performance cast. Seeing as that is what I broke, it makes sense to upgrade.

For measuring piston protrusion, I was planning on using a dial indicator to reference the block and then measure the piston above the wrist pin. Is this typically how it is done?

I plan on doing the assembly.
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Old 05-06-2020, 08:59 AM
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Quote:
Originally Posted by Doms View Post
That's exactly the kind of advice I am after. Thank you.

I was kind of at a toss up between the cast and performance cast. Seeing as that is what I broke, it makes sense to upgrade.

For measuring piston protrusion, I was planning on using a dial indicator to reference the block and then measure the piston above the wrist pin. Is this typically how it is done?

I plan on doing the assembly.
yes, then rock it and use the highest measurement. measure both sides of the piston as one side can be higher than the other.

not sure what experience you have with building engines but never assume the machine shop got it all right. double check it all. even the best can miss something, we are all human.
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Old 05-06-2020, 09:06 AM
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If you do not use oe replacement pistons, it will need balanced.

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Old 05-06-2020, 09:09 AM
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Honestly it has been a while since I've been in an engine but I think it should go okay. I have some pretty nice measuring tools (do some hobby machining) so I will triple check everything. I really just plan on taking my sweet ass time, being super methodical, taking lots of pictures and probably asking a ton of questions. I have been doing a lot of reading over the last few weeks. There is a ton of good information on this forum.
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Old 05-06-2020, 09:10 AM
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If you do not use oe replacement pistons, it will need balanced.

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Thank you for pointing that out. I intend to get everything weight matched as best as I can at home and then hand it over to the machine shop for balancing.
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Old 05-06-2020, 11:31 AM
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Doms what is done to the trans ,since you are already 200 hp over stock ?
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Old 05-06-2020, 03:04 PM
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Quote:
Originally Posted by ikeG View Post
If you do not use oe replacement pistons, it will need balanced.

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No matter what pistons you use if you plan to keep the truck awhile you should balance it anyways.

Myself I’d add an lml crank and balancer and an AF cam to the build but neither are super essential.
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Old 05-06-2020, 03:15 PM
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Quote:
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No matter what pistons you use if you plan to keep the truck awhile you should balance it anyways.
I.E. -If you use a stock lbz crank with stock lbz pistons(stock rods obviously), you do not need to rebalance. That is exactly how it came off the showroom floor.
However, if you did rebalance using all stock parts, there will be room for improvement. Stock duramax engines are off several percent when new.

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Old 05-06-2020, 07:30 PM
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Did you eat piston chunks with the oil pump? Because they don't really wear out, especially at 80k miles. I'm running my original oil pump on my built motor, up around 340k miles on the oil pump now. No issues at all.

If you took some metal through it (or think you did), then yeah, just replace it. But if the piston simply cracked and didn't shed metal, I'd run the original pump.
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Old 05-06-2020, 08:01 PM
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Quote:
Originally Posted by torqued2dmax View Post
Doms what is done to the trans ,since you are already 200 hp over stock ?
Trans is a built unit. NAPC “Heavy Hauler”.
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Old 05-06-2020, 08:06 PM
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Did you eat piston chunks with the oil pump? Because they don't really wear out, especially at 80k miles. I'm running my original oil pump on my built motor, up around 340k miles on the oil pump now. No issues at all.

If you took some metal through it (or think you did), then yeah, just replace it. But if the piston simply cracked and didn't shed metal, I'd run the original pump.
No I don’t suspect so. Crack looks pretty clean. One tiny little piece missing. I think the pump is probably fine, it’s more a peace of mind thing. A new pump will only run a few hundred dollars.

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Old 05-22-2020, 01:07 PM
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So I have been slowly plugging away at this. Work and yard work has gotten in the way a little bit. Block is at the machine shop. I had a little bit of scoring on cylinder #1 so he will see how much he needs to take before I order pistons but it shouldn't be much.

I started cleaning some bits and pieces which leads me to a question. Is the front timing cover magnesium? I was under the assumption that it was going to be aluminum but the way that it oxidized with the de-greaser I was using tells me other wise. I can shave a little piece off and take a match to it but I figured someone here probably knows.
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Old 05-23-2020, 04:33 AM
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Front cover is aluminum. Only areas I know of magnesium use were transfer case housings and corvette seat frame
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