Rod bolts: Factory method in any way better for torque?

Mountainman · **Posted:** Wed Sep 09, 2015 5:20 pm

I'm no mechanical engineer, or metallurgist, so I'm just wondering if anyone has any reason to believe that the factory 'degrees' method for torquing bolts has any advantage to torquing to a set value?
I was told that the degrees method was developed because machines were applying the torque. But, that doesn't make much sense because in the same procedure it starts with a set value of 22 ft/lbs...

LMWatBullRun · **Posted:** Wed Sep 09, 2015 5:55 pm

Mountainman wrote:

I'm no mechanical engineer, or metallurgist, so I'm just wondering if anyone has any reason to believe that the factory 'degrees' method for torquing bolts has any advantage to torquing to a set value?
I was told that the degrees method was developed because machines were applying the torque. But, that doesn't make much sense because in the same procedure it starts with a set value of 22 ft/lbs...

The turn of nut or bolt method was devised to deal with the wide variance in clamping force experienced when torquing a bolt to a supposed final
torque value that provided a calculated clamping force. The problem is that slight stochastic variations in different bolt characteristics (thread diameter, pitch, thread profile, steel hardness and yield strength, thread roughness, etc. etc.) while all within spec, resulted in wide variation in actual clamping force.

The school solution for those custom building engines, before the advent of commercial high strength high accuracy bolts (ARP and others) was to lap each of the nuts and/or bolts together in matched pairs to custom fit each bolt and/or nut together, by repeatedly torquing and loosening the bolt to a value just below the yield point, then to do a final torque to the calculated value. The problem with this approach from a manufacturing standpoint, of course, is that this takes a LOT of time, and time is expense. The solution adopted is to rotate the bolt to a point guaranteed to stress the bolt past the yield point, so that it stretches, and stays at the yield point. For applications involving a single installation of a production grade fastener, this is more reliable than torquing. PROVIDED that the steel is within spec, and that the bolt does in fact yield. In the case of steel connecting rods in the VMM CRd engine, as opposed to aluminum heads, I'd be reasonably confident that the design of the TTY rod bolts was correctly done, especially since we have not heard of significant numbers of rod bolt failures.

BTW, it is worth noting that ARP and others sell high strength precision ground rod bolts, too, not just studs.

Mike92104 · **Posted:** Wed Sep 09, 2015 6:08 pm

Excellent explaination. Thanks.

Mountainman · **Posted:** Wed Sep 09, 2015 6:20 pm

LMWatBullRun wrote:

Mountainman wrote:

I'm no mechanical engineer, or metallurgist, so I'm just wondering if anyone has any reason to believe that the factory 'degrees' method for torquing bolts has any advantage to torquing to a set value?
I was told that the degrees method was developed because machines were applying the torque. But, that doesn't make much sense because in the same procedure it starts with a set value of 22 ft/lbs...

The turn of nut or bolt method was devised to deal with the wide variance in clamping force experienced when torquing a bolt to a supposed final
torque value that provided a calculated clamping force. The problem is that slight stochastic variations in different bolt characteristics (thread diameter, pitch, thread profile, steel hardness and yield strength, thread roughness, etc. etc.) while all within spec, resulted in wide variation in actual clamping force.

The school solution for those custom building engines, before the advent of commercial high strength high accuracy bolts (ARP and others) was to lap each of the nuts and/or bolts together in matched pairs to custom fit each bolt and/or nut together, by repeatedly torquing and loosening the bolt to a value just below the yield point, then to do a final torque to the calculated value. The problem with this approach from a manufacturing standpoint, of course, is that this takes a LOT of time, and time is expense. The solution adopted is to rotate the bolt to a point guaranteed to stress the bolt past the yield point, so that it stretches, and stays at the yield point. For applications involving a single installation of a production grade fastener, this is more reliable than torquing. PROVIDED that the steel is within spec, and that the bolt does in fact yield. In the case of steel connecting rods in the VMM CRd engine, as opposed to aluminum heads, I'd be reasonably confident that the design of the TTY rod bolts was correctly done, especially since we have not heard of significant numbers of rod bolt failures.

BTW, it is worth noting that ARP and others sell high strength precision ground rod bolts, too, not just studs.

Many thanks for the lesson! That makes me think that it's not worth the risk to deviate from the factory procedure.
About ARP's. I think you came up with the torque values by seeing what it took to crush a head. I guess we would have to do a similar test on rods to come up with an appropriate value? Maybe since the manual has a final check value of 65 ft/lbs, we could just slap ARP's in there at 70-75 ft/lbs and call it good? If they make a bolt of the right size I guess. I wonder if we couldn't just cut some ARP's if they have them, but in a greater length? Probably have a machinist cut them with some fancy diamond apparatus that has cooling fluid? hmm
Then again, sounds like the factory ones are ok... Geordi is the one with the rod bolt nightmares :dead:

flash7210 · **Posted:** Wed Sep 09, 2015 6:39 pm

If you plan on installing new rod bolts, have a machine shop press the old ones out and new ones in.
Its waaay too easy to screw this up without a proper press.

And BTW, the best method for torquing rod bolts is by using a rod bolt stretch gauge.

LMWatBullRun · **Posted:** Thu Sep 10, 2015 11:18 pm

Mountainman wrote:

Many thanks for the lesson! That makes me think that it's not worth the risk to deviate from the factory procedure.
About ARP's. I think you came up with the torque values by seeing what it took to crush a head. I guess we would have to do a similar test on rods to come up with an appropriate value? Maybe since the manual has a final check value of 65 ft/lbs, we could just slap ARP's in there at 70-75 ft/lbs and call it good? If they make a bolt of the right size I guess. I wonder if we couldn't just cut some ARP's if they have them, but in a greater length? Probably have a machinist cut them with some fancy diamond apparatus that has cooling fluid? hmm
Then again, sounds like the factory ones are ok... Geordi is the one with the rod bolt nightmares :dead:

ARP catalog has rod bolts in various sizes with recommended torque values; I'd check with them for recommended size and install torque.

WRT the torque values for the head studs, I calculated that the torque required to match the yield point of the factory TTY bolts was 140 FPT. RacerTracer got the factory drawing of the head bolt assembly from VMM, and that had the information I needed to do those calcs. In the event, I found that torquing the studs that high crushed the head; I had a lot of work lapping out one of the lifter recesses and more trouble getting glow plugs out. See the ARP stud thread for the gory details.

Mountainman · **Posted:** Thu Sep 10, 2015 11:41 pm

There you go Geordi. If you're really worried about them, maybe try and see if ARP has some that fit, and hopefully they don't have a suggested torque too much greater than 70ish? I think I'll stick with the factory bolts, but I'd be glad to try and track down the ARP's if someone gives me the bolt size? Probably be weeks before I have one out since my engine stand is tied up...

Mike92104 · **Posted:** Fri Sep 11, 2015 12:25 am

I'll try to remember to dig one out and measure it. I have my old rods to if we need some measurements from them. They're still good though, so no experimenting.

Mike

Mountainman · **Posted:** Fri Sep 11, 2015 12:39 am

cool, thanks Mike. I wonder if after 400k miles if we won't all wish we installed ARP's? Sure would be easy to slap them in while I'm in there, if they sell one that fits.

jws84_02 · **Posted:** Fri Sep 11, 2015 6:49 am

I would imagine just like the head bolts, arp has them for the rods. Heck, they make a bolt for almost anything.

lacabrera · **Posted:** Fri Sep 11, 2015 7:20 am

flash7210 wrote:

If you plan on installing new rod bolts, have a machine shop press the old ones out and new ones in.
Its waaay too easy to screw this up without a proper press.

And BTW, the best method for torquing rod bolts is by using a rod bolt stretch gauge.

Press ?? press for removing a bolt. Maybe I am missing something.

flash7210 · **Posted:** Fri Sep 11, 2015 8:29 am

lacabrera wrote:

flash7210 wrote:

If you plan on installing new rod bolts, have a machine shop press the old ones out and new ones in.
Its waaay too easy to screw this up without a proper press.

And BTW, the best method for torquing rod bolts is by using a rod bolt stretch gauge.

Press ?? press for removing a bolt. Maybe I am missing something.

Sorry, you are correct.
I was thinking of more traditional rod bolts where the bolts are pressed into the rod and the cap is tightened on with nuts.
I have since realized that the CRD rods use actual bolts, no nuts.

LMWatBullRun · **Posted:** Fri Sep 11, 2015 10:53 am

Mountainman wrote:

LMWatBullRun wrote:

Mountainman wrote:

I'm no mechanical engineer, or metallurgist, so I'm just wondering if anyone has any reason to believe that the factory 'degrees' method for torquing bolts has any advantage to torquing to a set value?
I was told that the degrees method was developed because machines were applying the torque. But, that doesn't make much sense because in the same procedure it starts with a set value of 22 ft/lbs...

The turn of nut or bolt method was devised to deal with the wide variance in clamping force experienced when torquing a bolt to a supposed final
torque value that provided a calculated clamping force. The problem is that slight stochastic variations in different bolt characteristics (thread diameter, pitch, thread profile, steel hardness and yield strength, thread roughness, etc. etc.) while all within spec, resulted in wide variation in actual clamping force.

The school solution for those custom building engines, before the advent of commercial high strength high accuracy bolts (ARP and others) was to lap each of the nuts and/or bolts together in matched pairs to custom fit each bolt and/or nut together, by repeatedly torquing and loosening the bolt to a value just below the yield point, then to do a final torque to the calculated value. The problem with this approach from a manufacturing standpoint, of course, is that this takes a LOT of time, and time is expense. The solution adopted is to rotate the bolt to a point guaranteed to stress the bolt past the yield point, so that it stretches, and stays at the yield point. For applications involving a single installation of a production grade fastener, this is more reliable than torquing. PROVIDED that the steel is within spec, and that the bolt does in fact yield. In the case of steel connecting rods in the VMM CRd engine, as opposed to aluminum heads, I'd be reasonably confident that the design of the TTY rod bolts was correctly done, especially since we have not heard of significant numbers of rod bolt failures.

BTW, it is worth noting that ARP and others sell high strength precision ground rod bolts, too, not just studs.

Many thanks for the lesson! That makes me think that it's not worth the risk to deviate from the factory procedure.
About ARP's. I think you came up with the torque values by seeing what it took to crush a head. I guess we would have to do a similar test on rods to come up with an appropriate value? Maybe since the manual has a final check value of 65 ft/lbs, we could just slap ARP's in there at 70-75 ft/lbs and call it good? If they make a bolt of the right size I guess. I wonder if we couldn't just cut some ARP's if they have them, but in a greater length? Probably have a machinist cut them with some fancy diamond apparatus that has cooling fluid? hmm
Then again, sounds like the factory ones are ok... Geordi is the one with the rod bolt nightmares :dead:

Given that we have not seen many rod bolt failures to date, I'd question what value aftermarket bolts add, unless you are prone to overpressurizing or overspeeding the motor. :SOMBRERO:

Those who plan to extract more performance from this engine might want to consider them. Probably more bang for the buck would be weight balancing the rods themselves and their matched pistons, etc.....

geordi · **Posted:** Fri Sep 11, 2015 12:15 pm

According to the book, the pistons and rods are already weight-balanced and stamped as such on the rod. This is a bit of an annoyance, b/c I have an engine that doesn't want to rotate, so it is in need of at least one piston / rod combination. It would be a lot cheaper if it didn't need all 4 to get a matched set.

Thinking about this thread's discussion though, I'm leaning toward the idea that these aren't TTY bolts, and just reusing them when I get the block torn down. On the engine that is banging (and still rotates) I'm expecting to find that the bearings are the leading cause, and hopefully I don't need a micrometer and a degree in engineering to rebuild the bottom end. It does seem that the block will need to come out no matter what though, which kinda blows.

LMWatBullRun · **Posted:** Fri Sep 11, 2015 3:33 pm

geordi wrote:

According to the book, the pistons and rods are already weight-balanced and stamped as such on the rod. This is a bit of an annoyance, b/c I have an engine that doesn't want to rotate, so it is in need of at least one piston / rod combination. It would be a lot cheaper if it didn't need all 4 to get a matched set.

Thinking about this thread's discussion though, I'm leaning toward the idea that these aren't TTY bolts, and just reusing them when I get the block torn down. On the engine that is banging (and still rotates) I'm expecting to find that the bearings are the leading cause, and hopefully I don't need a micrometer and a degree in engineering to rebuild the bottom end. It does seem that the block will need to come out no matter what though, which kinda blows.

Weight balanced, but to what tolerance? I do not recall; +/- 5 grams, 10? I do know that performance engines are balanced a lot closer tolerance than production motors..... If you have a lighter replacement rod, then you could in theory trim a bit off the heavier ones and rebalance. WRT TTY rod bolts, I expect that these bolts are in fact TTY as they are steel on steel, and I would not reuse them unless I had a chance to study the specs for the bolt steel that was used, as I did for the head bolts, Geordi. The head bolts I would reuse, if I wanted to use them in the first place.

The other issue is fatigue. All steel has a finite limit on cycles, and used rod bolts have however many miles less life than new ones.....

I'll buy new bolts, one less thing to worry about, but I probably will not buy ARPs.

geordi · **Posted:** Fri Sep 11, 2015 6:44 pm

LMWatBullRun wrote:

The head bolts I would reuse, if I wanted to use them in the first place.

The other issue is fatigue. All steel has a finite limit on cycles, and used rod bolts have however many miles less life than new ones.....

I'll buy new bolts, one less thing to worry about, but I probably will not buy ARPs.

Well, the bolts are only like a buck and change on IDparts, so for that little... Yeah, I probably will just buy fresh too. These should reasonably only have one cycle on them anyway, being installed at the factory?

But I still am dubious about their being TTY or not. I'll have to look at the old ones to see if there is a neck or if they are threaded all the way up. If they are full thread, they aren't TTY. I also don't subscribe to the TTY because it is steel on steel. That makes no sense, there are many many examples of fasteners that are normal ductile steel clamping another type of steel... It all comes down to the function. Maybe they are figuring that the clamping will be severe enough that it will produce some galling in the threads and that will assist in locking the bolt in place? Obviously the rod cap is not going to compress or be driven to deformation by design, that would be a poor choice. So once you have contact and clamping, any further torque is just to assist in retaining the clamping in position.

Oh - the book does specify a tolerance for the weight, apparently it is 5 grams. The book said "5gr" which I am taking to be grams, but I suppose they could have meant grains? I'm not sure if that would translate to the same weight overall, I'm not one to load my own powder. If I had any bullets laying around, I'd probably put them into the side of the engine at high velocity.

For sale, one Jeep. Good condition, low miles, several bullet holes. :banghead:

LMWatBullRun · **Posted:** Fri Sep 11, 2015 7:40 pm

geordi wrote:

LMWatBullRun wrote:

The head bolts I would reuse, if I wanted to use them in the first place.

The other issue is fatigue. All steel has a finite limit on cycles, and used rod bolts have however many miles less life than new ones.....

I'll buy new bolts, one less thing to worry about, but I probably will not buy ARPs.

Well, the bolts are only like a buck and change on IDparts, so for that little... Yeah, I probably will just buy fresh too. These should reasonably only have one cycle on them anyway, being installed at the factory?

But I still am dubious about their being TTY or not. I'll have to look at the old ones to see if there is a neck or if they are threaded all the way up. If they are full thread, they aren't TTY. I also don't subscribe to the TTY because it is steel on steel. That makes no sense, there are many many examples of fasteners that are normal ductile steel clamping another type of steel... It all comes down to the function. Maybe they are figuring that the clamping will be severe enough that it will produce some galling in the threads and that will assist in locking the bolt in place? Obviously the rod cap is not going to compress or be driven to deformation by design, that would be a poor choice. So once you have contact and clamping, any further torque is just to assist in retaining the clamping in position.

Oh - the book does specify a tolerance for the weight, apparently it is 5 grams. The book said "5gr" which I am taking to be grams, but I suppose they could have meant grains? I'm not sure if that would translate to the same weight overall, I'm not one to load my own powder. If I had any bullets laying around, I'd probably put them into the side of the engine at high velocity.

For sale, one Jeep. Good condition, low miles, several bullet holes. :banghead:

Thanks, Geordi, I'll pass. I have three now including one of yours, and I don't need another!

BTW, did you definitively determine that your rattle/bang is lower end?

geordi · **Posted:** Fri Sep 11, 2015 10:28 pm

I was joking with that last line - it isn't for sale (at the moment) and I haven't determined anything about it yet. The next step will most likely be to have the block pulled so that I can work on it.

Mountainman · **Posted:** Tue Sep 15, 2015 11:02 am

geordi wrote:

I was joking with that last line - it isn't for sale (at the moment) and I haven't determined anything about it yet. The next step will most likely be to have the block pulled so that I can work on it.

A $50 chain hoist works great, even if you don't have a suitable garage, a tree would work. Just good to have two people to remove the hood.

Rod bolts: Factory method in any way better for torque?

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