GM LS steel main caps and line honing

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GM LS steel main caps and line honing

Post by PackardV8 » Wed Jun 13, 2018 11:06 pm

In a bunch of random cores we bought was a set of LS steel main caps. The #4 shows signs of having spun a bearing, so probably why they were in the core pile.

The question is how much wiggle room for honing and/or line boring an LS main cap before the cross bolts get cross?

Also, are oversize/thicker shell main bearings available?
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Re: GM LS steel main caps and line honing

Post by modok » Wed Jun 13, 2018 11:35 pm

I think you need to put the caps on the block and see, how far off they are. I don't know.

You can probably cut them .010, maybe at ,015 you will need to oval the holes, but still no big deal.
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Re: GM LS steel main caps and line honing

Post by bone6145 » Thu Jun 14, 2018 7:25 pm

King has some over sized bearings

MB5766SI STD/001/010/020/030
Optional to MB5293SI (housing bore +.010")

MB5398SI
Optional to MB5293SI (housing bore +.020")
crank flange length mm
STD 26.08/26.03
010 26.11/26.06
020 26.11/26.06
030 26.11/26.06

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Re: GM LS steel main caps and line honing

Post by PackardV8 » Thu Jun 14, 2018 9:55 pm

I think we've got a junk block in the boneyard, so maybe see what the #4 will take to clean up. The spun bearing must have been shut down quickly, so cap is smudged, not scarred.

Addendum: How much stock removal is usually required when aftermarket steel caps are installed on an LS block?
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Re: GM LS steel main caps and line honing

Post by modok » Thu Jun 14, 2018 10:03 pm

I found getting the cap to fit the block again was too much of a puzzle, so I heat straightened the cap.

Think about it, if it's loose in the register you can't just braze or weld one side, so you would have to do both sides. And if the cap is bent as usual, then cutting the block side flat will put the side bolts .005+ down before you even hit the middle.

it was easy to heat straighten it, since the top of the cap is flat.
i don't know if that is true of your aftermarket caps.
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Re: GM LS steel main caps and line honing

Post by modok » Fri Jun 15, 2018 12:34 am

Straightening main caps sounds like a fools errand eh?
Somebody is going to give me flack for it.
Uncharted territory, nobody really knows. So far, it's safer than straightening cranks.
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Re: GM LS steel main caps and line honing

Post by PackardV8 » Fri Jun 15, 2018 12:05 pm

This cap is hardly marked up at all; certainly not bent or spread. Back in the bad old days, before line honing was common, we'd just have polished the inside, hand-milled a couple thou off the mating face with emery paper on a drill press table, checked with Plastigage, said "loose is fast" and gone racing.
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Re: GM LS steel main caps and line honing

Post by modok » Fri Jun 15, 2018 9:32 pm

You should be smarter than to spend time on pointless speculation.

Is it warped? Put a straight edge on it,
Is it shrunk? Measure the with a micrometer.
How far is it off? put it on the block.
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Re: GM LS steel main caps and line honing

Post by PackardV8 » Fri Jun 15, 2018 9:41 pm

modok wrote:
Fri Jun 15, 2018 9:32 pm
You should be smarter than to spend time on pointless speculation.
Is it warped? Put a straight edge on it,
Is it shrunk? Measure the with a micrometer.
How far is it off? put it on the block.
For true, Glen. Yes, we already checked. No, it's not warped. No, it's not shrunk. As I said, it's an easy cleanup; just was asking about options to re-use it, what limitations do the cross bolts put on line honing?
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Re: GM LS steel main caps and line honing

Post by modok » Fri Jun 15, 2018 9:47 pm

If the side bolts hit the edge of the hole, oval the hole so they don't. They have tons of clearance in the hole, maybe .040.
Line honing, ideally you are only taking off average .005 at a time. More than that, I bore it
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Re: GM LS steel main caps and line honing

Post by jed » Sat Jun 23, 2018 1:59 pm

modok wrote:
Thu Jun 14, 2018 10:03 pm
I found getting the cap to fit the block again was too much of a puzzle, so I heat straightened the cap.

Think about it, if it's loose in the register you can't just braze or weld one side, so you would have to do both sides. And if the cap is bent as usual, then cutting the block side flat will put the side bolts .005+ down before you even hit the middle.

it was easy to heat straighten it, since the top of the cap is flat.
i don't know if that is true of your aftermarket caps.
Could you explain how you heat straighten the main cap. Please.
And I suppose you can use this process on any main cap that is loose in the register.
Very cleaver if I can get it to work. Been on plenty of fools errands but not this one.

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Re: GM LS steel main caps and line honing

Post by modok » Sat Jun 23, 2018 5:50 pm

MOST of the time I braze one or both sides of the cap, if it is loose. Most safe way to go IMO. But, have you ever tried to braze or weld powered metal? Usually it works terrible.

Like straitening a head, I realized I could use the flat side and shims to control how far I "over-bent" it. I don't recall what shim I used, maybe .010 or .015? set right in the middle, sitting on a flat arbor plate so when I pressed on it, it would only bend that much and not go too far.
So I had it in the press, with a shim under the middle. Heated the middle area of the cap gradually to a gentle glow with a torch. Then put another plate across the parting surfaces and smooshed it flat, didn't take a lot, less than a ton, and let it cool slowly still locked in the press. Came out perfect first try.

Being powdered metal, I really didn't have any idea what would happen. I magnafluxed it before and after, and roughly checked the hardness with a file, and it seemed to be OK.
Highly experimental, but I think it's worth trying. I've heat straightened a lot of things successfully, and ruined quite a few too, but in most cases there was nothing to lose.
I even figured out how to un-sag my milling machine table with just a torch and patience.
My boss used to say....."you can go to hell for bending cold iron" :D
Machinists say, "the surest way to warp the hell out of anything is weld on it"
It's true! But, can be used for good as well as evil

Now that I think about it, the cap did light on fire when I was heating it. Full of oil since it is porous. I showed it to the other guys in the shop to freak them out. :lol:
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