74 replies to this topic

[malbear]

friends would a nuttless titanium conrod benefit from using a helicoil to prevent thread stripping or siezure ?
does anyone have some experience or wisdom to impart?

Edited by malbear, 27 May 2011 - 02:55.

[Greg Locock]

friends would a nuttless titanium conrod benefit from using a helicoil to prevent thread stripping or siezure ?
does anyone have some experience or wisdom to impart?

Depends on the heat treat and hence yield stress of the Ti. Are you getting galling of the bolts? That is common with ti.

[gbaker]

A ringnut would help,

http://www.google.co...E...p;q&f=false

or a better bolt

http://www.alcoa.com...o_page/home.asp

[bigleagueslider]

friends would a nuttless titanium conrod benefit from using a helicoil to prevent thread stripping or siezure ?
does anyone have some experience or wisdom to impart?

malbear,

Titanium galls horribly. So anything you can do to eliminate threads in titanium is probably a good thing.

From a structural standpoint, a through bolt and nut is probably a better solution than a bolt and tapped hole in the rod beam. But with most high performance rods, there is not room to do this. So if you must use a rod beam with a tapped hole in titanium, I would not use a helicoil. Even though a helicoil insert does not require much additional diameter to install, most conrods usually have very little edge margin between the bolt hole edge and bearing bore to begin with, and there would not typically be enough extra room for even a helicoil. Plus helicoils are only available in steel alloys, which would also end up galling with the titanium bolt.

Galling in the beam's titanium threads can be minimized by making sure the female threads are very accurate in pitch tolerance, form, major/minor/pitch diameter, and surface finish. Using a controlled root radius threadform (UNJF) will also help, as will using a roll tap that cold works the thread surfaces. Keeping the total engaged thread length to a minimum will also help, since that will result in less interference in the engaged threads. And applying a dry film lube (such as moly disulphide) to the bolt threads will also help.

If your rod has a high-strength steel bolt in titanium threads in the beam, the titanium threads will have adequate root shear strength as long as the thread engagement exceeds about 6 or 7 pitches.

slider

[gruntguru]

Studs and nuts?

[Magoo]

friends would a nuttless titanium conrod benefit from using a helicoil to prevent thread stripping or siezure ?

Possibly, but the thread insert would have to be incorporated in the connecting rod's original design, mainly to provide sufficient shoulder cross-section. In the end, there is no reason to do it unless frequent disassembly/reassembly are anticipated -- like with a Top Fuel engine or test mule or something.

You would never want to install a thread insert in an existing ti rod, or a steel one for that matter.

[Lee Nicolle]

Titanium is light, and strong but can go hard and breittle as it work hardens. In a short term race engine very good but for endurance use use a similar steel one and you wont get bit.
As for helicoils Mac is 100% right

[malbear]

malbear,

Titanium galls horribly. So anything you can do to eliminate threads in titanium is probably a good thing.

From a structural standpoint, a through bolt and nut is probably a better solution than a bolt and tapped hole in the rod beam. But with most high performance rods, there is not room to do this. So if you must use a rod beam with a tapped hole in titanium, I would not use a helicoil. Even though a helicoil insert does not require much additional diameter to install, most conrods usually have very little edge margin between the bolt hole edge and bearing bore to begin with, and there would not typically be enough extra room for even a helicoil. Plus helicoils are only available in steel alloys, which would also end up galling with the titanium bolt.

Galling in the beam's titanium threads can be minimized by making sure the female threads are very accurate in pitch tolerance, form, major/minor/pitch diameter, and surface finish. Using a controlled root radius threadform (UNJF) will also help, as will using a roll tap that cold works the thread surfaces. Keeping the total engaged thread length to a minimum will also help, since that will result in less interference in the engaged threads. And applying a dry film lube (such as moly disulphide) to the bolt threads will also help.

If your rod has a high-strength steel bolt in titanium threads in the beam, the titanium threads will have adequate root shear strength as long as the thread engagement exceeds about 6 or 7 pitches.

slider

I am still in the design stage so there will be enough room for a helicoil . I was anticipating using a well proven good off the shelf steel bolt . assuming a helicoil is available in say a 3/8 fine thread. (arp ) My thinking was that a helicoil would allow more frequent dissassembly and assembly without a ruined female thread in the beam section. Has anyone tried it?
would a titanium bolt be better than a steel one?

Edited by malbear, 27 May 2011 - 11:42.

[Greg Locock]

My thinking was that a helicoil would allow more frequent dissassembly and assembly without a ruined female thread in the beam section. Has anyone tried it?

I agree with that logic. You certainly can (I have) run steel bolts into tiALV4T6 or whatever it is called, but given the choice I'd rather helicoil it if disassembly is likely.

[gbaker]

If you go with an insert, stay away from the Helicoil line for any critical application. A better selection of inserts is here.

[MatsNorway]

Whats the issue here? whats this galling stuff?

Enlighten me please.

[Magoo]

Personally, I wouldn't use a ti rod in a mule or development engine unless it were essential to the project objectives. I think steel is very nice. True, ti doesn't like steel bolts. Well, it doesn't much care for bearing inserts, wrist pins, or even other stuff made of titanium, either. Also, it has high notch sensitivity even in 6AL4V. The rod will need a coating of moly or chromium nitride for starters, especially on the thrust faces. Would I buy a used ti connecting rod from a stranger? No. Would I buy a used ti connecting rod from myself? Hmm. I wouldn't want to hurt my feelings but probably not.

[cheapracer]

Mal, why the problematic route?

[J. Edlund]

I am still in the design stage so there will be enough room for a helicoil . I was anticipating using a well proven good off the shelf steel bolt . assuming a helicoil is available in say a 3/8 fine thread. (arp ) My thinking was that a helicoil would allow more frequent dissassembly and assembly without a ruined female thread in the beam section. Has anyone tried it?
would a titanium bolt be better than a steel one?

Use a nut and stud for the conrod instead and there should be less wear on the thread in the conrod. A number of titanium conrods use that solution. You still need a moly coating or similar though, as the thread isn't the only problem area with a titanium rod.

[Victor_RO]

In a short term race engine very good but for endurance use use a similar steel one and you wont get bit.

As Peugeot found out at Le Mans last year. Titanium conrods => three detonated engines at 17, 22 and 23 hours into the race.

[malbear]

As Peugeot found out at Le Mans last year. Titanium conrods => three detonated engines at 17, 22 and 23 hours into the race.

thanks , maybe I should stick with EN25 steel and have it nitrited and later a pollish.

[malbear]

Mal, why the problematic route?

I am naturally adventurous and like to toss ideas about here.

[nodrift4me]

Personally, I wouldn't use a ti rod in a mule or development engine unless it were essential to the project objectives. I think steel is very nice. True, ti doesn't like steel bolts. Well, it doesn't much care for bearing inserts, wrist pins, or even other stuff made of titanium, either. Also, it has high notch sensitivity even in 6AL4V. The rod will need a coating of moly or chromium nitride for starters, especially on the thrust faces. Would I buy a used ti connecting rod from a stranger? No. Would I buy a used ti connecting rod from myself? Hmm. I wouldn't want to hurt my feelings but probably not.

I too did a bit of research into titanium rods for an engine I was going to build, and for those reasons I decided it wasn't worth the risk and will be going with conventional steel rods.
That being said, the Honda NSX uses Ti rods and whatever they did with them seems to work.

[Greg Locock]

Mats- galling is where a thread picks up material from the nut, typically. You get a long thin triangular scar and a bump of welded metal at the end. Stainless steel does it but Ti has the worst rep of the obvious materials. Ways round it are geometric accuracy in the threads and lots of appropriate lube.

[Lee Nicolle]

As Peugeot found out at Le Mans last year. Titanium conrods => three detonated engines at 17, 22 and 23 hours into the race.

If that is the case they got what they deserved. Commonsense and basic knowledge would have told them that. And since their diesels are not turning that many RPM any advantage is negligible.
A 18000 rpm F1 engine is a different story, and I believe some of those use steel rods for reliability. Though I bet very trick steel of very fancy design. So probably only marginally heavier to start with.
Do drag racers still use alloy rods? Those things were so bulky they were scarcely any weight advantage in them either, but they sure broke easily.

[cheapracer]

If that is the case they got what they deserved.

I have no doubt a computer told them otherwise even though the practical information is out there.

[Grumbles]

Do drag racers still use alloy rods? Those things were so bulky they were scarcely any weight advantage in them either, but they sure broke easily.

They sure do, especially in blown fuel or alcohol applications. Their advantage is in their ability to absorb and dampen shocks to some degree. Rod breakage is relatively rare provided they are changed out before they become fatigued.

[Victor_RO]

I have no doubt a computer told them otherwise even though the practical information is out there.

And dyno testing told them otherwise as well, it was the eventual pace of the race (which ended with a record distance) and the conditions that caught them off-guard. I think the reason they gave out in the end was the fact that the engines ran cleanly at the absolute limit for a very long time, producing more power than expected due to air temperatures. Two engines gave out with less than 2 hours to go.

[Grumbles]

...That being said, the Honda NSX uses Ti rods and whatever they did with them seems to work.

Likewise for GM with their LS7 engines.

[MatsNorway]

Mats- galling is where a thread picks up material from the nut, typically. You get a long thin triangular scar and a bump of welded metal at the end. Stainless steel does it but Ti has the worst rep of the obvious materials. Ways round it are geometric accuracy in the threads and lots of appropriate lube.

how does that happen?

pure friction and vibration? or is it some wierd electricity stuff going on?

Or is it just to much force on the given surface area?

would inserting the bolt with copper paste improve things?

Would it be less critical on bigger threads?

What about hardcoated threads on the bolt?

termal spraying and so on gets cheaper and cheaper. We use it at trainparts at my job. And have been doing it for years.

Here is the NSX vs the GT-R rods.
http://speedhunters....mparison-a.aspx
I love the fact that despite my knowledge about it they opted for a grove in the rod for the head to lock it in place. Just like i imagined would be a good solution.

Only thing i do find odd. is how quickly it gets narrow going up to the piston.

Edited by MatsNorway, 28 May 2011 - 11:36.

[bigleagueslider]

My thinking was that a helicoil would allow more frequent dissassembly and assembly without a ruined female thread in the beam section.

As someone else suggested, stay away from helicoils, they are the worst type of thread insert. While they are cheap and compact, they have a bad habit of coming out when you remove the bolt. Also, if you look at the thread length of your conrod bolt and compare it to the length of a helicoil, you'll note that the helicoil is much shorter.

Your best option would be a steel stud in the beam and a nut. You can make the stud with a slightly larger diameter, coarse pitch thread on the end that threads into the rod beam to help equalize the stud's tensile strength versus the root shear strength of the titanium threads. The stud threads that go into the rod beam can also be made very slightly oversize, so that this thread is self-locking and will prevent the stud from backing out.

Good luck,
slider

[gruntguru]

how does that happen?

pure friction and vibration? or is it some wierd electricity stuff going on?

Think of it as a kind of welding. It is most common with two components made of the same material eg stainless steel or titanium. It is also more likely if there is no foreign coating or oxide layer - making aluminium and normal steel less susceptible as these form oxide layers very quickly.

So even though the two components are cold, the extreme contact pressure between asperities creates weak bonds. Movement in the contact area generates heat and high local temperature (at the microscopic level) which initiates further bonding and the cycle accelerates.

[MatsNorway]

So termal spraying/coating is in teory a viable option then.

Not sure about how you could coat the internal threads tho.. if both needs a layer..

Regarding ti rods and development..

you ask the old man with the experience to make something reliable..

you ask the new kid with the ideas to push the boundaries..

pair them up and let the new kid absorb the info and then develop a teory, let him bounce ideas on the old guy and something new might arise.

Edited by MatsNorway, 29 May 2011 - 08:26.

[gruntguru]

In most cases coating one mating surface only should be enough.

[Canuck]

We use a copper plating on the male threads of an assembly made entirely of 17-4 stainless that must be routinely assembled and disassembled that operates in some of the most severe environments (downhole oil tools). Works beautifully.

[cheapracer]

So termal spraying/coating is in teory a viable option then.

It is for an Irishman I'm sure .....

[Tony Matthews]

It is for an Irishman I'm sure .....

Teory Wogan? If you're lucky, you don't know who he is...

[Magoo]

Likewise for GM with their LS7 engines.

Porsche has also done a number of engines with titanium rods. Years ago they did some engines with titanium rod bolts, if you can imagine that.

[desmo]

Ti rod bolts? What were they thinking?

[Magoo]

Ti rod bolts? What were they thinking?

906, 908, 917. I wouldn't presume to know their thoughts, except to note that these are the people who brought you the aluminum roll bar. The 917 used lots of ti components and fasterners, as well as the proverbial balsa wood shift knob.

[desmo]

That long ago? That makes sense in a way, at the time there was a lot of fashionable simple substitution of steel with dimensionally identical Ti equivalents. I guess some people were reading the "strong as steel, as light as Al hype" and taking it to heart. That said, those racing Porsches were obviously mostly hugely successful in endurance competition so if they used Ti rod bolts it seems it was at least a bad idea well executed, which is usually better than the poor execution of good ideas.

[Greg Locock]

Is bolt elasticity a big deal in a conrod?

[Lee Nicolle]

Ti rod bolts? What were they thinking?

But did it work? Or did it explode! Titanium rods are ok in very big budget where they are replaced regularly but rod bolts just sounds dumb to me. Nowher near the elasticity of a proper steel bolt

[gruntguru]

But did it work? Or did it explode! Titanium rods are ok in very big budget where they are replaced regularly but rod bolts just sounds dumb to me. Nowher near the elasticity of a proper steel bolt

So bolt elasticity is a big deal in a conrod?

[Lee Nicolle]

So bolt elasticity is a big deal in a conrod?

When you stretch them they break, or gall. And yes some elasticity is needed to clamp the joint properly in place. Doweling the bolts in that situation would help. But by the time that is done any weight saving is marginal to say the least.

Edited by Lee Nicolle, 31 May 2011 - 07:45.

[MatsNorway]

It is for an Irishman I'm sure .....

didn`t get that one..

[cheapracer]

didn`t get that one..

In 2 days it will be Tursday in Ireland.

[gruntguru]

Ahh but it won't be the turd.

[Greg Locock]

When you stretch them they break, or gall. And yes some elasticity is needed to clamp the joint properly in place. Doweling the bolts in that situation would help. But by the time that is done any weight saving is marginal to say the least.

Hang on, Ti in the usual grade has a yield stress better than unbrako bolts. So the same stress would have broken an unbrako. Now, it may be that conrod bolts are better than unbrako steel, but otherwise that doesn't seem to make sense.

[gruntguru]

When you stretch them they break, or gall. And yes some elasticity is needed to clamp the joint properly in place. Doweling the bolts in that situation would help. But by the time that is done any weight saving is marginal to say the least.

Hang on, Ti in the usual grade has a yield stress better than unbrako bolts. So the same stress would have broken an unbrako. Now, it may be that conrod bolts are better than unbrako steel, but otherwise that doesn't seem to make sense.

and since Youngs modulus for Ti is about half that of steel, the Ti bolt will be considerably longer when it yields. To me that is "elasticity" or did you mean something else Lee?

[malbear]

Thank you friends ,
It seems that the best option for clamping would be a stud with say 7/16 course thread on the beam end and 10mm x1mm on the nut end and necked down to 9mm in between. cheers malbeare

[J. Edlund]

Porsche has also done a number of engines with titanium rods. Years ago they did some engines with titanium rod bolts, if you can imagine that.

There have been F1 engines with titanium rod bolts too. The Asiatech V10 (rebadged Peugeot V10) used titanium studs and nuts for the rods, so did the TWR-Hart 1030 engine.

[carlt]

There have been F1 engines with titanium rod bolts too. , the TWR-Hart 1030 engine.

Not a good example for engine longevity ! ?

[Powersteer]

dont the corvette ls7 motor use ti rods for a production car? seems to work fine althought i dont know the stud bolt configuration.

[bigleagueslider]

dont the corvette ls7 motor use ti rods for a production car? seems to work fine althought i dont know the stud bolt configuration.

Honda NSX used titanium rods w/ steel bolt and nut in production.