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replacing rod and main bearings...do's and dont's?

This is a discussion on replacing rod and main bearings...do's and dont's? within the Internal Engine forums, part of the LSx Technical Help Section category; finally got my engine out to fix that pesky lower end knock. Ive read something about resizing rods, changing rod ...

  1. #1
    its short but its skinny. jiveass's Avatar
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    replacing rod and main bearings...do's and dont's?

    finally got my engine out to fix that pesky lower end knock. Ive read something about resizing rods, changing rod bolts yada yada yada...can i get by with re-using the stock bolts if im not building a race engine and dont take it over 6500rpm? what else do i need to know before i proceed? whats the best assembly lube? timing chain? oil pump? keep in mind that im pretty much keeping the engine stock so i dont need all that high performance jazz....just want the basics.

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    Moderator Firebirdjones's Avatar
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    What would concern me most is the knock, where it's coming from and why....

    Generally speaking if it's knocking (rod or main bearing) even a very short amount of time and there is probably some damage to the bearing journal surface minimum.

    Usually when a bearing spins it also causes extreme heat in that rod or main cap. Machine work is generally required not only on the crank shaft, but the main cap and/or rod.
    On a block with a spun main, align honing is usually a good bet to make sure they are all straight and to make the offending main cap perfectly round again so you get proper bearing crush.

    Same issue with rods. Spun rod bearings generally requires resizing the rods, making sure they are round, again to obtain proper bearing crush. So this isn't going to be a simple "bearing slap and go" scenario, or you'll be taking it back apart very shortly.

    You didn't mention what was knocking. If it's a rod, it' really going to dictate the rest of the questions you are asking.....
    Don't worry about stock rod bolts, if you spun a rod bearing you'll need to resize the rod, new bolts are part of that equation at a minimum, possibly a rebalance. Another issue with the stock rods is that I believe they are snap cap rods. That means they don't have a perfectly flat cap mating surface, in which case resizing may be out of the question. Resizing involves cutting the mating surface down and then reboring the big end to proper size again to create a nice round hole for the bearing along with a certain amount of bearing crush. I'm a little out of the loop on snap cap rods simply because on our rebuilds 9 out of 10 times we use aftermarket rods. The cost to benefit ratio of rebuilding stock rods verses buying new stronger pieces is somewhat redundant.

    You'll also have to consider the amount of trash that has passed through the engine and possibly scored up other bearing surfaces.....

    Try not to skimp on this part of the build as it's some of the more critical stuff, even on a stockish build.
    Last edited by Firebirdjones; 11-07-2011 at 06:31 PM.

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    ^^ This. FBJ knows his stuff and nailed it. What's the crank look like?

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    its short but its skinny. jiveass's Avatar
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    well i havnt gotten it apart yet...just got it out of the car...will be taking it apart this weekend....if what you guys are saying is true, looks like ill be taking an ass chewing from the ol lady when i tell her that its gonna cost more ...oh well..

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    I had the same problem

    They nailed it, buy a crate engine I am at 2400 in parts and only changed one connecting rod. No guarantee iand I.am halfway to a crate engine which is about 6000 with 425 HP

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    Moderator Firebirdjones's Avatar
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    Crate engines are a great way to go for quick swaps (usually down a weekend) to get you up and running, and most times they come with a warranty. Hard to beat.
    I only build anymore for specific reasons like, numbers matching, certain power goals that aren't available in crate form, unique engines that don't come in crate form, etc....

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    its short but its skinny. jiveass's Avatar
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    so how does one go about resizing rods...is it something i can do myself? i found a complete ls1 rebuild for a ls1 for $600 on summit...but its for a 98 so i know some of the gaskets wont work on my engine....

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    Moderator Firebirdjones's Avatar
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    Resizing rods is a machine shop process. They'll remove the caps and machine the flat mating surface. This makes the hole smaller. Then the rod caps are torqued to spec and the big end is honed back to a certain size (what ever manufacture recommends) to create bearing crush and make perfectly round. This is usually done with a new set of rod bolts too. It's common to magnaflux the rods first to make sure you have a solid set to start with. This adds to the cost.

    Costs can vary up to maybe $200 or more. Depends on other things.

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    its short but its skinny. jiveass's Avatar
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    99 trans am

    i read somewhere that you cant resize ls1 rods due to the cracked cap design...



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    You may be right on that. The cracked caps are nice as they hold their alignment better -- only fit in one exact spot. You'll know more once you get things torn down. Do you have access to a dial bore gauge as you can easily check for out-of-round, taper and all sorts of stuff on both the rods and cylinder walls.

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    its short but its skinny. jiveass's Avatar
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    i do have access to all types of gauges, micrometers, all the stuff that is required for dimensional inspection....the thing is, i was hoping to be able to replace the bearings and perhaps the crank without removing the rods and pistons...

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by jiveass View Post
    i read somewhere that you cant resize ls1 rods due to the cracked cap design...

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    Yes, and I mentioned that in one of my previous posts. Basically, you spin a bearing in one of them, and they are done. Throw aways as far as I'm concerned.

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    its short but its skinny. jiveass's Avatar
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    i am thinking about buying this rebuild. i know there are a few gaskets i wont be able to use since its for a 98 but it comes with pistons and such...and ill have the rods inspected while i have it apart.
    Sealed Power ZBK6081000 - Sealed Power Engine Kits & Rotating Assemblies - Overview - SummitRacing.com

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    Moderator Firebirdjones's Avatar
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    Take it apart and see what damage is done before buying anything, because you aren't sure what exactly you are getting into until you see the damage.
    Like I mentioned, if you spun a rod bearing or two, more than likely a new set of rods are in order. Resizing those snap caps aren't doable as far as I know. You might be getting into more money than you anticipate.

    In some cases like this, by the time you figure in machine work, a new set of rods, it might make more sense to buy a rotating assembly ready to go.

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    Senior Member redbird555's Avatar
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    Yes you can resize the the rods even if they are cracked however I would have a good competent machine shop do it. Clevite makes bearings that are .002 bigger on the outside for such an application the larger bearing jacket ensures that you will get the correct amount of crush and torque on the rods. If you are going to get them line honed then I'd suggest using arp rod bolts they are about 80 bucks a set and are pretty cheap insurance with a new motor imo.

    I dont think the summit kit is worth it personally. The only things you could use are maybe the mains (if you didnt spin one in yours), the rings, valve seals, pistons and some gaskets. I would get the motor torn down and at least have the bores checked for straightness if they arent egg shaped then I'd just get a re-ring kit and valve seals, reuse the stock pistons and get some quality bearings for the mains and rods according to what you need. Depending on the mileage of the engine a set of stock ls6 valve springs from sdpc are about 60 bucks so I'd look into that also. Theyre a little stiffer than stock ls1 springs but still mild enough for the stock cam.

    As has been said here though if your engine if completely destroyed and is going to need a lot of money to repair, I would look into a long block. hen you could just swap you accessories and intake over to it and still have a warranty. There are still some ls6 longblocks floating around for around 3500 iirc
    Last edited by redbird555; 11-14-2011 at 09:29 AM.

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    its short but its skinny. jiveass's Avatar
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    i have decided to just freshen up the whole engine, and perhaps some performance heads and cam swap. i got the top end apart yesterday and the cylinders look good...still got cross hatch....sometime this week i will separate the trans from the engine and get it on the stand so i can get to the bottom end...im just gonna spend the money and do it one time and be done.

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