Duramax Diesels Forum Truck of the Week
  #1  
Old 05-15-2019, 09:14 AM
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Default main cap question

aside from the fact its best to keep the main caps that came with the block together, if the set of main caps that went with a block were lost in shipping, can other main caps besides billet be used?

long story short, the mains for the block i got were lost, never shipped, or some other bs and now im on my own here. yes i can go billet caps but im coming to my limit on spending on this damn thing though it may have to happen.

my concern on using my lb7 main caps is 1. they have been aline honed once already. 2. im unsure about the difference in main cap and block seating area, theoretically they should be the same but i dont know how precise GM is here. im half tempted to take the block and my old main caps to the machine shop and see what they say as far as straightness and if they will need just a hone again or a bore (no bueno if it needs a bore unless i can just get away with the caps needing the bore).

anyone dicked with this kind of stuff before?
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Old 05-15-2019, 04:10 PM
gmc502 gmc502 is offline
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I've done it on marine bbc engines(used other caps) before,twisted them to 6800rpm and never a problem.
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Old 05-15-2019, 07:28 PM
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I don’t see why you can’t mix and match as long as they line up. The machine shop will be able to tell you if they will work.
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Old 05-15-2019, 07:38 PM
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Yeah I called and talked with them. We will be going over them pretty close to make sure everything sits flat, clearances are right and wonít take more than a hone.
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Mike L is my role model. I want to be like him when I grow up.
James

02 LB7, LLY, LBZ, LMM, LML, L5P 2500HD CC/LB dmax/alli "The Limo"

BIG THANKS TO: Mike L, Steve, Trent, Guy, Dan, Ruben, Josh H, Scott, Brian and everyone else who has put a hand in to help me.

best time to date: 12.39

motor died/bent rods = 3/11/11
back from the dead 7:04pm 4/9/2012

Limo is back in the garage, now driving a built chevy tracker
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Old 05-15-2019, 08:41 PM
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If they end up being a little large for just a hone, they should be able to skim the caps a little and re line hone it.
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Old 05-16-2019, 03:39 AM
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If we werent talking fractured caps, Id say you would be ok. Not sure if using other caps will work in this case without careful machining. Still, its worth a try. Good luck.
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Old 05-16-2019, 04:56 AM
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You're thinking about the rods Tom
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Old 05-16-2019, 05:58 AM
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We squished the lower mains and junked the caps on an engine once. Machinist tried close to a dozen random 'good' used caps and none of them would work.....

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Old 05-16-2019, 06:01 AM
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I don’t see why you couldn’t skin the register, to make them able to be honed to size again?
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Old 05-16-2019, 07:34 AM
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Quote:
Originally Posted by PureHybrid View Post
If they end up being a little large for just a hone, they should be able to skim the caps a little and re line hone it.
Quote:
Originally Posted by WolfLLY View Post
I donít see why you couldnít skin the register, to make them able to be honed to size again?
Thats what we were thinking, long as we dont have to take too much and the side bolts still go in as they should. there "should" be enough play in them.

Quote:
Originally Posted by TheBac View Post
If we werent talking fractured caps, Id say you would be ok. Not sure if using other caps will work in this case without careful machining. Still, its worth a try. Good luck.
Honestly, i wouldnt have even asked this if they were fractured caps but the mains are not fractured. just the rods are. i appreciate it though tom

Quote:
Originally Posted by ikeG View Post
We squished the lower mains and junked the caps on an engine once. Machinist tried close to a dozen random 'good' used caps and none of them would work.....

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was he not considering giving them a shave (caps only) to get them to fit or were there other reasons to it?
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Mike L is my role model. I want to be like him when I grow up.
James

02 LB7, LLY, LBZ, LMM, LML, L5P 2500HD CC/LB dmax/alli "The Limo"

BIG THANKS TO: Mike L, Steve, Trent, Guy, Dan, Ruben, Josh H, Scott, Brian and everyone else who has put a hand in to help me.

best time to date: 12.39

motor died/bent rods = 3/11/11
back from the dead 7:04pm 4/9/2012

Limo is back in the garage, now driving a built chevy tracker
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Old 05-16-2019, 07:49 AM
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Quote:
Originally Posted by Chevy1925 View Post

was he not considering giving them a shave (caps only) to get them to fit or were there other reasons to it?
Now that I chink about it, I think the entire main tunnel was shot. And there were no conglomeration of used caps that would allow him to re-align hone.


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Old 05-16-2019, 08:11 AM
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Quote:
Originally Posted by ikeG View Post
Now that I chink about it, I think the entire main tunnel was shot. And there were no conglomeration of used caps that would allow him to re-align hone.


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ah yeah i could see that doing it in!



either way, ill report back what we wind up doing. Billet main caps require an align bore to square them up but to keep crank centerline the same distance as stock, you would have to run that bore down the "caps only" far as i can figure so wouldnt be far off from what we are doing with stock main caps if we take a bit off the mating surface of the caps.
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Quote:
Originally Posted by JoshH View Post
Mike L is my role model. I want to be like him when I grow up.
James

02 LB7, LLY, LBZ, LMM, LML, L5P 2500HD CC/LB dmax/alli "The Limo"

BIG THANKS TO: Mike L, Steve, Trent, Guy, Dan, Ruben, Josh H, Scott, Brian and everyone else who has put a hand in to help me.

best time to date: 12.39

motor died/bent rods = 3/11/11
back from the dead 7:04pm 4/9/2012

Limo is back in the garage, now driving a built chevy tracker
Tailgate Crew Member #4
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  #13  
Old 05-17-2019, 06:45 AM
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I thought at one when digging around I had found a King bearing part number for a main bearing with a +.020" housing bore, I will look again than you could save the block at least.
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Old 05-17-2019, 06:50 AM
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http://www.king-catalog.com/Catalog/Engine/20045152
MB5848GPC this is for a +.040" Housing bore main bearing
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Old 05-19-2019, 12:48 AM
1FastBrick 1FastBrick is offline
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If the Duramax Block is cast and machined anything like an LS block, good luck.

Long story short, I took a gamble on a block that was in a fire. The pan was partialy melted off in the front. It distorted the bearing cap and it no longer fit correctly. They attempted to line hone it to clean it up and it didn't work. So they peened the cap in the bearing register in an attempt to stress relieve it and re honed it. When I saw the cap I was like No Bueno, Not Acceptable. I had another block that was given to me and we pulled the cap off and tried it. Nope it was slightly off to one side in comparison But It was a useable cap to Line bore and correct the issue. They made it right and Line bored it.

If you don't want to go billet caps and it needs more than a hone with the caps Let us know.
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