Head bolt length specs reference? - Dodge Cummins Diesel Forum
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post #1 of 7 (permalink) Old 07-13-2019, 09:21 PM Thread Starter
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Head bolt length specs reference?

Can anyone point me to the max length specifications for the factory head bolts for the 12 valve?

I didn't get a stretch gauge with my Mahle head gasket set, i' looked through the "FSM" and can't find it there, though I read it was in it but can't find it.

Thx,

Paul


1995 3500 2WD NV4500 105k Mods: stock plate full fwd + 0.060", AFC full fwd, stock gov springs +3 clicks, BD exh. brake, 60lb springs, EGT/Boost gages, rear axle air bags, 20psi boost (max) Towing: Alpenlite Avalon 36' ~14k, Reese 18K dual pivot hitch
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post #2 of 7 (permalink) Old 07-14-2019, 03:16 AM Thread Starter
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Ok - the trustynwdb crawler comes thru:

Cummins+Head+Bolt+Stretch+Gauge+3823921&oq=Cummins +Head+Bolt+Stretch+Gauge+3823921&aqs=chrome..69i57 j69i60.3443j0j7&client=ms-android-samsung&sourceid=chrome-mobile&ie=UTF-8#imgrc=uvAeibCQ6nD_mM:

1995 3500 2WD NV4500 105k Mods: stock plate full fwd + 0.060", AFC full fwd, stock gov springs +3 clicks, BD exh. brake, 60lb springs, EGT/Boost gages, rear axle air bags, 20psi boost (max) Towing: Alpenlite Avalon 36' ~14k, Reese 18K dual pivot hitch
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post #3 of 7 (permalink) Old 07-14-2019, 09:14 AM
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The B series bolts are maximum shank lengths 71.5 mm (2.815 in.). 122.1 mm (4.807 in.) and 182.9 mm (7.201 in.)

97 3500, 2 WD, G56, slightly bombed, 1.3 million miles. Started the second million on 8/24/13
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post #4 of 7 (permalink) Old 07-21-2019, 11:58 AM Thread Starter
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Thank you Games! Mine all check out with minimum 2mm margin to spec - will reuse.

So one more question wrt FSM bolt torque sequence. Seems odd that it specifies torque from zero to 66 lft-lbs for the first step ( i.e not 25, 50, etc). Just want to make sure I'm not missing something here but I tend to follow the spec exactly.

Maybe the idea is they want an effective clamp starting at the middle and move outward to prevent trapped material ( gasket, head) and if there was an lower initial bolt torque it may not clamp the center enough, but potentially clamp the ends of the head creating the issue ? Maybe this explains it.
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1995 3500 2WD NV4500 105k Mods: stock plate full fwd + 0.060", AFC full fwd, stock gov springs +3 clicks, BD exh. brake, 60lb springs, EGT/Boost gages, rear axle air bags, 20psi boost (max) Towing: Alpenlite Avalon 36' ~14k, Reese 18K dual pivot hitch
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post #5 of 7 (permalink) Old 07-21-2019, 12:22 PM
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The pattern is just like every other head bolt pattern that it starts in the middle and works outward. Your theory about spreading the stretch of the gasket outward is correct. There wouldn't be any harm in graduating from 25 or 50, as long as you tighten them in the correct sequence. Don't forget though that they all get torqued to 66, then the long bolts to 89, then all of them get an additional 90 degrees using the sequence.

97 3500, 2 WD, G56, slightly bombed, 1.3 million miles. Started the second million on 8/24/13
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post #6 of 7 (permalink) Old 08-14-2019, 11:49 PM Thread Starter
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Ok so I followed the process and sequence perfectly ( by the FSM instructions), including the 1/4 turn at the end. Prior to 1/4 turn I marked each bolt with a line in the same direction to be sure they are all turned 90 at the end ( let's not get confused!).

It was apparent that the short bolts (exhaust side) end at a torque that is greater than the medium bolts, by feel at the end of that 1/4 turn rotation. A few of the short bolts torqued up quicker than the other short bolts and I went only 75-80 deg turn on those (used a square to accurately ge to 90).

Given the short bolts get torqued to 66ft-lbs same as the medium length bolts to 66ft-lbs, and then both get 1/4 turn, it makes sense that the short bolts go to a higher torque and correspondingly higher clamp force on the head. ( I believe the long bolts get torqued to 89 ft-lbs vs 66 (prior to 1/4 turn) to account for lower torque increase when for a 1/4 turn applied to a bolt with a longer stretch length (distance between the thread engagement at the block deck and the bolt head bearing surface) to achieve the same torque as a shorter bolt.

I AM concerned as I always thought head design is same torque on all fasteners so the clamp force is the same and gasket loading is even.

Can anyone shed light on this. IT JUST DOESN'T SEEM RIGHT but that is the Factory manual and is well documented.

I don't really feel good about this method or the result, but I don't know the mind of the engineers behind it and if other folks experience the same result ( and more importantly the effect on the head warpage or gasket failure).

1995 3500 2WD NV4500 105k Mods: stock plate full fwd + 0.060", AFC full fwd, stock gov springs +3 clicks, BD exh. brake, 60lb springs, EGT/Boost gages, rear axle air bags, 20psi boost (max) Towing: Alpenlite Avalon 36' ~14k, Reese 18K dual pivot hitch
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post #7 of 7 (permalink) Old 08-15-2019, 10:23 AM
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You're setting preload (stretch), not torque. Torque is simply used because it's the only thing you can measure in the field. "In the field" meaning outside the lab.

I've done extensive research and testing on automotive fasteners at work. The factory torque values are a little goofy but understand it's uncommon to have so many different lengths of fasteners, and such a large range from shortest to longest, on one cylinder head. Long bolts need more torque to reach the same clamping load and a consistent clamping load is what the mating interface needs.

The torque + angle method always yields the most consistent clamping load even though the ending torque on individual fasteners may be all over the place. A recent, relevant post of mine:

Quote:
Originally Posted by dauntless89 View Post
Stock Cummins bolts, when torqued using the stock torque+angle method, will deliver between 13,000 and 15,900 lbs.

When using straight torque, 125-145 ft-lbs will provide the same range of clamping load. All bolts were brought to yield between 145 and 155 ft-lbs at an average of ~16,250 lbs.

The McMaster bolts torqued to 135 ft-lbs delivered, on average, between 16,400 and 20,200 lbs, or 24% more clamp load than stock bolts with the T+A method, however the min-max deviation spread was 30% greater than the stock bolts (T+A). I want to draw attention here to the T vs. T+A part. This 30% wider deviation spread, based on my observations, is very likely entirely due to the difference in torque method. Using regression, I calculated (not measured) that if the stock T+A method was used, predictable average clamp load would be just shy of 18,000 lbs and predictable deviation spread would be slightly more than 2300 lbs instead of the 3790 lbs seen with straight torque.

The ARP2000 studs I tested averaged 18900 lbs at ARP's torque specs, with a min-max deviation of 1350 lbs.

Synopsis: Of these three, the studs have the narrowest spread and the highest clamp load. McMaster bolts torqued to factory T+A specs would have a competitive clamp load, but with nearly double the deviation spread of the studs.

'95 2500 ECLB 4x4, 334k and paused due to epic transformation in progress.
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