Rebuilding a 12v

mitchdog7

mitchdog7

Newb
Need a few pointers on this rebuild.
I've never rebuilt a motor before, but I figured I'd try this out, as I'm decently mechanically inclined, and this is just for a play truck.
I bought a used motor that they said ran. Maybe down a hill, as cylinder 6 had a melted piston and one other was almost melted.
So I tore it apart, had the head/ block machined, one cylinder needed sleeved, the rest just bored .020 over. As far as I know everything checked out on the block.
I just ordered a rebuild kit a couple days ago, so I started looking at the parts I've already got.
I had this all done a little over a year ago, so I can't remember what my buddy at the machine shop said, but 2 of the connecting rods have discoloration towards the small end. Does this automatically mean they're bad? Or could they still be good if I had a shop check them out again? They're Brazil rods.
Going to put in a new 24v oil pump as well.
Got a tool to oring the block, did it on my other 12v a few years ago.
Anything else I should be replacing while I'm in there? Tappets, push rods, oil cooler, etc.?

Motor is going into a 1500 single cab short bed 2wd, only looking for 600-700hp

Thanks for any help

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Throw some wide bowl pistons in it and send it. Rods will just need to be checked for size. Usually they can take a little off the bolt surface area to resize them
 
Are you talking about 1st gen pistons that have wider bowls but still keep the compression up or marine bowls with lower compression.
I'm running 1st gen pistons, wouldn't want as set of marine pistons in a DD.

OP if the rods haven't been checked by a machine shop they need to be, the discoloration doesn't bother me much but they could need bushings replaced or have other issues.
Any time I do a rebuild I have the rods checked.
 
Destroked 450 said:
Are you talking about 1st gen pistons that have wider bowls but still keep the compression up or marine bowls with lower compression.
I'm running 1st gen pistons, wouldn't want as set of marine pistons in a DD.

OP if the rods haven't been checked by a machine shop they need to be, the discoloration doesn't bother me much but they could need bushings replaced or have other issues.
Any time I do a rebuild I have the rods checked.
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Do you remember the piston number you are running? Im getting ready to rebuild a shortblock I have and I want to keep my compression up too.
 
The Mahle 286210 is the factory non-I/c piston with wider bowls, lower top ring lands and stock like compression. I had them in my engine but just took them out to go back to a 2nd gen factory style bowl.
 
Tons of different ways to achieve that power goal. How efficient do you want it? How many rpm are you planning on cranking out of it?
 
jstaylor954 said:
Why did you go back to stock bowls?
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Supposedly for a 5-600hp truck they are better suited. I think it mostly depends on how much timing you want to run, back when I put the engine together with the 286210’s I was going to turn it into a hot rod with high hp and timing. Now I just want a farm truck with 400rwhp that can tow anything lol.
 
Muddin_dude06 said:
Supposedly for a 5-600hp truck they are better suited. I think it mostly depends on how much timing you want to run, back when I put the engine together with the 286210’s I was going to turn it into a hot rod with high hp and timing. Now I just want a farm truck with 400rwhp that can tow anything lol.
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But what did you actually personally notice? Any difference?
 
Redrider2911 said:
But what did you actually personally notice? Any difference?
Click to expand...

I will say, I never felt like my mpg was as good after the rebuild with those 286210 pistons compared to the factory pistons. But it would be really hard to say for sure. I had small fly cuts in them for valve clearance and it started and ran great though. I felt like the torque wasn’t quite as good but again it would be hard to say for sure, I changed a lot at the same time.

After this rebuild I’ll have a better idea.
 
Muddin_dude06 said:
I will say, I never felt like my mpg was as good after the rebuild with those 286210 pistons compared to the factory pistons. But it would be really hard to say for sure. I had small fly cuts in them for valve clearance and it started and ran great though. I felt like the torque wasn’t quite as good but again it would be hard to say for sure, I changed a lot at the same time.

After this rebuild I’ll have a better idea.
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Just noticed you are running 155 degree injectors though? What kind of timing? How clean did it run/idle? What prompted this rebuild?
 
Muddin_dude06 said:
Supposedly for a 5-600hp truck they are better suited. I think it mostly depends on how much timing you want to run, back when I put the engine together with the 286210’s I was going to turn it into a hot rod with high hp and timing. Now I just want a farm truck with 400rwhp that can tow anything lol.
Click to expand...

I put 1st gen non ic pistons in mine to build a tow rig but only running 15 1/2 degrees timing.
 
Appreciate the info.
I have the mahle 286210, If I remember right, pistons that'll be going in.

So, I looked at the rods and saw at least 2 need new wrist pin bushings. I asked a couple shops around town who can balance rotating assemblies, and they said no one does cummins wrist pin bushings here in Sarasota. Closest place was Orlando.

Anyone have recommendations about where to send them out for new bushings/ checked out? And if im doing that, I may as well have them shotpeened/ hardened/ cryo treated right? Which I have no idea what any of that means, but I've read it before lol.

I have a feeling that this build is going to snowball into something north of 600hp after I run it for a while, so I figure I may as well start preparing for that.

The more research I do, the more I realize I'm in over my head with all this internal engine components. Everything outside the motor I've got a rough idea as to what I'll be running. Initially caused I've got some parts laying around: 5x13's, 5k gsk, haisley valve springs/ retainers/ keepers, Hamilton 188/220 cam, s363 at first, then later add a s475 or 80, and go to 5x18's or 20's.

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And, rpm wise, I have no idea what I should be shooting for..?
I hear my current 12v hit above 3200, and it just sounds wild to me. 4k I'd probably crap myself. But I have no idea what a rebuilt engine would be able to handle, or what's needed to make it handle that.
I'd assume 4k would be more than enough for a street driven truck right?

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The 286210 pistons are a good choice. The small bowls help keep the compression up for better low end torque and less smoke. I normally run 5x20s @145* at either 18 or 26-28 degrees of timing. But the bowls are wide enough for 155 degree injectors if you want.

Keep in mind the 188/220 peak powerband is ~2600-3600 rpm as compared to 2000-3000 for the stock cam. Just make sure the the rest of your build works with the cam you use.
 
A stock rod will be fine in your application. If I didn't have a local machine shop that could do rods, I'd just replace them with new rods from Cummins or post a Wanted ad for stock 12v rods; you may find some for just the price of shipping.
 
I had my crank balanced after it was reground and the fella who did it told me Cummins cranks are usually so close that they aren’t worth messing with, and mine after being ground was only 6-7 grams off. You can probably skip on the rods, but if you want to check the balance there are videos on YouTube that show how pretty easily.
 
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