main studs, girdles, and carnage

stillsmokin

stillsmokin

all out of fuel
Joined
Jan 23, 2007
Messages
228
I have been working on a new engine for next season over the winter. I have started on the bottom end. I'm using a "navistar" 12V 14mm main block from a mid 90's F800 school bus as the basis for everything. It will be a wet block for 2.6, but will probably see more local brush pulls than anything to be realistic. The cost of a decent PPL legal 2.6 turbo is tough to justify.

My past experience with main studs in engines was to provide greater clamping force on the main caps to hold the thrust alignment. Since the cummins has doweled mains, there should be far less issue with keeping thrust alignment.

A long time ago, they used to place "bridges" of steel across the bottom of the 2 bolt main caps in old engines when boost came into the equation, this prevented the crank from pushing through the main (which was sometimes only 3/8" thick. I don't know this is an issue with the 12V, but have noticed some girdles which have the bridges. I can see the need for a block stiffener plate to box in the block to keep it from twisting so much. Girdles are nice to spread the load over several mains when the need arises.

My question is this... Who is getting away with stock 14mm main bolts and maybe a cummins block stiffener plate at 900hp or better?

Is there problem at higher engine outputs where these engines are popping the heads off the bolts, stretching bolts, or pushing crankshafts through the main caps or what? I did a search and couldn't find where anyone pushed a crank through a main or had some other sort of catastrophic failure...
 
There have been several 1000+ hp engines out there with main studs only. IMO unless you go with a true girdle that ties in all the mains and pan rails, I think you're wasting your time.
 
BluegrassDiesel said:
There have been several 1000+ hp engines out there with main studs only. IMO unless you go with a true girdle that ties in all the mains and pan rails, I think you're wasting your time.
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I think the plate will do more for me in the way of keeping the oil pan rails from spreading so much. I have solid engine mounts. I believe this may have been cummins' real intention for the stock block stiffener.

The long ARP studs are nice, but the crown on those nuts look like a problem when you torque down a cut, welded, and drilled stiffener plate on there. I would think the plate would crush into the narrow crown of the nut, a spacer would be a better situation I would think.
 
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I'm at the same point myself. Looking for my next build to be 800-900hp on fuel, with the option of spraying it. It's primarily a street truck, that will see a fair amount of track time. Thing with me though, is I'm on a tight budget for the rebuild, and a girdle with XL studs stretches the budget.

After a fair amount of research. The general opinion is that 14mm bolts with a stiffener will go 1000hp, but anymore is stretching it. I've got 2 blocks I can use. One is a 14mm main and, the other is a 12mm. I already have 14mm studs that I got cheap, but they're too short to incorporate a stiffener or a girdle.

One thing I'm researching right now, is to drill the 12mm block and use 9/16-18 bolts instead of studs. They are a little lower tensile strength than studs, but that should be offset by the larger diameter, and by that I can tap fine threads in the block. Not a problem getting a length that will work with a stiffener and spacers either. I can do the 9/16 bolts and modify a stiffener to work with them for less than $300, instead of $900 for a girdle and XL studs. Don't think that I'd go that route for a 1000hp+ build, but for 1000 and below, it might be an option. Still researching it though.
 
I'm well over 1000 and I don't have a girdel but my block is filled
 
Drothgeb said:
One thing I'm researching right now, is to drill the 12mm block and use 9/16-18 bolts instead of studs. They are a little lower tensile strength than studs, but that should be offset by the larger diameter, and by that I can tap fine threads in the block. Not a problem getting a length that will work with a stiffener and spacers either. I can do the 9/16 bolts and modify a stiffener to work with them for less than $300, instead of $900 for a girdle and XL studs. Don't think that I'd go that route for a 1000hp+ build, but for 1000 and below, it might be an option. Still researching it though.
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I have read that the 12mm blocks are stronger than the 14mm blocks because the bolts are smaller, there is more material to the block around the bolt to keep from popping a main bolt out of the webbing
 
I've come across that, but not at not less than 1000hp. And, is that due to the block or, is it due to finer threads on the fastener. The 14mm are 2mm threads, the 12mm are 1.75, the 9/16-18 would be more like 1.4. There's engagement to consider too.
 
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I am over 1,150 HP with a filled block and just a stiffener in 2.6...
 
at what hp levels is a filled block a necessity?
at what hp levels is a full girdle necessary?

what about a half filled block so one still has some cooling as in my experience every one of the filled blocks I have seen in a tear down are scored beyond use after a season - which isn't hard to fathom as hot steel expands, and with the block full - it only has one place to expand - inwards towards the piston. Even with increased bore clearances this seems to be an issue.

I have seen pics of girdles ranging in thickness from 1/2" to 1" - does the block actually twist that much or is it more a symptom of mid block mounting for the motor mounts?
 
Girdle is never necessary. One of the biggest builders in the Cummins world doesn't use them at all unless specifically ask by the customers too. They said there is no benefit
 
DISTURBED said:
Girdle is never necessary. One of the biggest builders in the Cummins world doesn't use them at all unless specifically ask by the customers too. They said there is no benefit
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What about the regular stiffener?
 
Hard to 2nd guess Cummins using them in OEM apps. Anything done to tie the rails & mains together helps. They are alot of work at best to setup & install but to say there no benefit I would be headen for the door.
 
renopker said:
Hard to 2nd guess Cummins using them in OEM apps. Anything done to tie the rails & mains together helps. They are alot of work at best to setup & install but to say there no benefit I would be headen for the door.
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Just curious how many 1000+ HP engines you have built? I would take the word of some who builds them everyday over someone who doesn't. if they aren't putting cranks on the ground or having bearing failures where is the benefit? I'm well over 1000 and have been for 7 years. Mains look brand new and I turn 5000+ every run. No girdle here. In a V engine I could see a benefit but a inline engine I can't see it. Does the OEM cr stiffener tie into the mains???
 
Im waiting on my Monster Mike setup. His ties the mains and block tegether with 14mm studs. Not saying this is the best. But what i decided on my 1000+hp cr

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We are 1250whp on fuel and 1500+ on the juice, we run a modified factory block stiffener, and 12mm main studs. Nothing to this point that would suggest the need for anything more.

Pretty sure Ashley Black was running a stock CR main bolts, and factory block stiffener into the 1200whp+ range.
 
As with any scenario you can get away with it until you don't, ounce of prevention is worth a pound of cure, a girdle weighs 22 lbs.
 
renopker said:
...ounce of prevention is worth a pound of cure...
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I fully agree with this, but until the bearings (which we check several times a season) start to tell me I need some prevention this scenario works for us. Take it for the whole obsolete Canadian penny it is worth.
 
With a few of the motors a buddy has done, that I've been able to see after tearing down and assembly and abuse threw the years. I don't feel a girdle is much necessary. Specially once filled. By the time you buy a girdle and XL main studs, your in the $1000 mark easily. Just not justifiable in my opinion.
 
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