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Main bearing studs

Twisted Steel Performance

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Where is the thread with the ARP main bearing stud part numbers?

Anyone purchased them, do the studs fit the caps like the stock bolts do or are they a generic straight stud?

The stock bolt has the bosses that locate the caps not just a straight bolt..
 

Twisted Steel Performance

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Yea I know, a customer thinks he want's them but rumor is they don't fit the cap like the tty bolts do, I also sent Kennedy a message to see if he still offers his splayed caps, I would rather go the splayed route if possible.
 

KrisML

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Since when are the stock main bolts tty? I know the stock head bolts are. But I was under the impression that the stock main bolts were a standard reusable bolt.
 

Paveltolz

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My main bearing studs were made for Bill by ARP which will make them for you. When I was stupidly thinking of rebuilding the truck's motor myself, I called them and couldn't get the info. I didn't have the original bolt to even give them the specs but, that may be an option for you to consider. I imagine they would try to source the order from existing stock first. Cheaper for you and them. Can't hurt to give them a call and tell them you need an 'X' length stud at "Y" thread pitch.
 

Twisted Steel Performance

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I'll wait to see what the customer wants to do, the splayed caps are nla, studs will require a line honing due to the distortion so we will see.
 

WarWagon

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Where is the thread with the ARP main bearing stud part numbers?

Anyone purchased them, do the studs fit the caps like the stock bolts do or are they a generic straight stud?

The stock bolt has the bosses that locate the caps not just a straight bolt..
Not sure what is in the "kit" offered, but, the ARP single stud part numbers are around here and there. One example:

ARP doesn't offer single studs on their website, just kits, and the main stud is not a kit "ARP" offers. Others do...

I am asking because I don't know and couldn't figure it out: Not sure how the main bolts locate anything because they feel sloppy to me when I just put a main bolt in a main cap hole on the 6.2 here. Perhaps this is why the DSG main stud girdle only has 6 studs total?

Sloppy quick and dirty measurement indicates the (DSG Kit) ARP Studs are thinner than the main bolt upper shoulder, but thicker than the OEM bolt the rest of the ARP length. The section below the OEM main bolt head may have a taper.


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Will L.

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I also measured the main bolts diameters, and the main cap holes from 2 different engines. 1 Gm and 1 GEP.

Same. Well, sort of...
Main caps are 0.478-0.491. The gm engine caps were closer to each other’s and the gep were closer to each other.

If someone ( @WarWagon ) has a 6.2 around they could measure the inside of the cap holes to make sure they are the same just to end future questions...
But all the holes in the maincaps are the same within 1 thou.

Note the newer gm and gep using the smaller outside bolts on caps 2,3,4 are still the larger size holes.

The main bolts: although it is obvious they tried to make them the same- there was a noticeable variance.
0.465 to 0.47 when I only measured 3 bolts and didn’t have time to invest. I went back- measured 2 full sets and a few loose ones left around from previous builds in the jic box. 0.450 to 0.475.

I have built a couple oddball engines that the mains weren’t captured like the 6.2/6.5 is, and the idea of better centering and holding main caps was solved by use of a centering washer.

But looking at how inconsistent gm and gep is with these bolts... and that they didn’t even bother with making new main caps for the smaller holes when they already had to go through the experiences of using smaller bolts on the outside of 3 caps - makes me not so panicked about bolt or stud diameter to main cap hole clearance. Even so, the more consistent clearance is achieved by the ARP main studs of the stock bolts. Because the one thing that is obvious is gm fits with a wide range of tolerances.


I am trying to find a copy of the ARP main stud instructions- as luck would have it mine is missing them. Gonna do a post on that separate shortly. But already left message at ARP and when they get back to me I will also ask about stud diameter to cap hole diameter- something I never gave a lot of thought to before.

But I never remember clearances super tight on any studded engine before. Its always been a light tap of the mallet to the cap and the slide off the studs with no issues. If they were all tight, if would be snug as heck going on or apart.
 

Rockabillyrat

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I'm also concerned about the stud to main cap clearance. I was thinking about using insert washers. Might have to machine the main caps for them to fit. But that would tighten up the gap and hold them square.
 

Will L.

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Well thats the thing about the variance of sizes from the factory bolts- the entire stud is larger than the entire bolt except the top 1/4”. And some of the bolts were slightly smaller or same size as the studs there, while most were larger. Basically the factory bolts are all over the place on sizing.

And even then- NONE of them actually fit anywhere near tight in the caps. It is all down pressure.

That’s why when you put on the center cap you check for and aft for thrust clearance- to ensure centered front to back.

All the side to side or any twist and any cap walk is held by the block\ where it is an interference fit.

I used Self centering washers before on a different engine. But that engine didn’t have registers for other caps to sit in like these engines do.

Something else- as far off as everything is for these- imagine you did sleeve the caps. You really think the threaded holes are PERFECTLY centered? Inwould
Doubt it. I think it is left wide open on purpose.

When they changed caps 2,3,4 outside to the 10mm instead of the 12- if having the fastner fit anywhere near clearance- they would have made new maincaps with smaller holes.

None of the studs that I remember for any high perf engine gas or diesel had the studs fit tight to the cap holes.
 
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