I have been mulling over the use of titanium nuts for the locking nuts on the valve lash adjusters. In terms of benefit, this would reduce the reciprocating mass of the valve train at the most crital point. Although I have not yet measured this, I estimate a mass saving of about 2-3 grams per nut. This is close to 50% of the mass reduction achieved through titanium valve retainers., hovever, this installation would only require removal of the valve cover to gain access to the nuts.

I know that increased wear is associated with titanium parts in the valve train. However, these nuts wouldn't actually be exposed to cyclic rubbing. Does anyone have any thoughts as to the pros or cons of titanium valve lash nuts? Would this application be subject to a wear mechanism for titanium?

 

It shouldn't have any wear issues at all, in fact this is a pretty good idea. They shouldn't cost hardly anything to make either. It's a simple upgrade that can be done in less than an hour, plus everyone will have an excuse to readjust their valves.

 

good idea. What about aluminum? cheaper? same weight?

 

I worry about the bearing stress on the threads with an aluminum nut. It would be easier to over-torque and gall an aluminum fastener. Also, aluminum has a large coefficient of thermal expansion which could lead to thread fatigue and failure. We need to get a Mech E's opinion on this.

 

I'm thinking that they will be readily available. They are used commonly on bicycles, although not necessarily in a fine thread. I'll measure the threads on the nuts tomorrow.

 

 

SOunds like a good idea, I would be interested if you could find a suplier

 

Thermal expansion coefficients...

Steels are typically in the neighborhood of 7 ppm/F but some variation among the zillions of different alloys.

Aluminum & Al-based alloys go around 13 or 14 ppm/F.

Titanium & Ti-based alloys around 5 or 6 ppm/F.

Aren't the rockers some kind of cast aluminum alloy? So the mis-match of Ti might be in the wrong direction. I don't really know much about the fatigue behavior of this stuff either.

 

On the B18C, the rockers are cast iron. They have to be as the camshaft rides directly on the rockers. I'm not sure about the K and F series with their rollerized rockers.

It looks like steel and titanium should be interchangeble in terms of the thermal expansion coefficient. I worry about aluminum due to the fatigue issues associated with the stress due to the expansion mismatch.

My initial measurements show that the valve lash lock nuts have an M7x0.75 thread. I'll do some searching for a supplier later.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dogginator &raquo;</TD></TR><TR><TD CLASS="quote">On the B18C, the rockers are cast iron...</TD></TR></TABLE>D'oh! Yeah, I should have known that. How many times I've adjusted valves on my GSR...

So many different kinds of cast iron with different CTEs, I wouldn't guess without knowing the alloy.

I agree, fatigue behavior of Al isn't usually great. But that's sorta vague knowledge on my part, & maybe some Al alloys exist that have good fatigue properties.

 

The things that people think up, even some of the smallest things, never cease to amaze me. (In all seriousness, I'm not bullshitting).

I don't see the fatigue of aluminum being that great, sure they would be easier to plastically deform if torqued to far, hence why care would have to be used when installing these. I don't know how much of a factor heat would be under the valve cover and mixing with the oil, I don't know exact temps under there.

The only issue could be verifying that the titanium of the nut and the stud material are compatible. I don't see this being an issue off hand, but more research should be done to verfiy.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dogginator &raquo;</TD></TR><TR><TD CLASS="quote">We need to get a Mech E's opinion on this.</TD></TR></TABLE>

&lt;--- Raises hand...

 

Aluminum might be a better choice then, as it would have less mass. Even if the aluminum were to fatigue and fail, the result would just be valves that are out of adjustment. This would result in a noticeable clatter. The aluminum nuts would then need to be replaced.

OK, here are some of the numbers. My sample valve lash nut (p/n 90206-590-000) and valve lash rivet (p/n 14744-PR3-003) have masses of 1.85 g and 5.09 g, respectively. The densities of carbon steel, aluminum alloy, and titanium are 7.8, 2.8, and 4.43 g/cc, respectively. (Reference) This would yield potential mass savings of 0.00, 1.19, and 0.80g, respectively. This is lower than I had hoped for, but that is why we measure things. Aluminum seems to be the realistic choice here, provided the cost is not ridiculous.

 

Remeber messing around with different rocks, metals, etc in 10th grade chemistry? Getting taught different things about their physical properties in lab. Things like the hardness tests (scratch test). I'm no Mech E, yet, But I'd say that hardness difference would be the biggest worry. If one is harder than the other it will wear it. In the adjusting nut I dont think strangth should be TOO much af an issue as the nut in question, done properly, isn't torqued that tight. Now if hardness if the same or close then I dont see there being a problem.

If I remember correctly thius was one of the problems years ago when titanium retainers started hitting the mass market. They galled and many pictures of dropped valves ended up on H-T. At that time titanium nitride coating was a popular thing to raise the surface hardness of those retainers to prevent the galling.

If im way off base, etc i'll edit my comment.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by neogenesis2004 &raquo;</TD></TR><TR><TD CLASS="quote">If I remember correctly thius was one of the problems years ago when titanium retainers started hitting the mass market. They galled and many pictures of dropped valves ended up on H-T. At that time titanium nitride coating was a popular thing to raise the surface hardness of those retainers to prevent the galling.</TD></TR></TABLE>

The application is slightly different here, as there is no rubbing except during installation. The valve springs rub quite a bit on the spring retainers.

 

Yet there are still active forces present. Perhaps not on the scale you are thinking, but whenever the cam lobe roles over the rocker the rocker is "trying" to change the valve lash. Your torque of that nut is what keeps those forces in check. My worry would be that the thin threads of bare aluminum would give much sooner. This is why I speak of hardness. Steel would most likely wear those threads quickly. No idea how fast, quickly is only based on how fast the stock ones would wear. If that happened it would likely only thin the threading through compression and your lash would change. Worst case scenario a lash nut takes a roller coaster ride in your head.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by neogenesis2004 &raquo;</TD></TR><TR><TD CLASS="quote">Worst case scenario a lash nut takes a roller coaster ride in your head.</TD></TR></TABLE>

That would indeed be bad.

I wonder how well aluminum lug nuts hold up? I'm not recommending those, but they could serve as a good reference point in a similar application. Does the anodization lessen the surface wear and fatigue?

 

anodizing increases surface hardness im almost positive.

 

This is from anodizing.org,

"ANODIZING, WHAT IS IT?

Anodizing successfully combines science with nature to create one of the world's best metal finishes.

It is an electrochemical process that thickens and toughens the naturally occurring protective oxide. The resulting finish, depending on the process, is the second hardest substance known to man, second only to the diamond. The anodic coating is part of the metal, but has a porous structure which allows secondary infusions, (i.e. organic and inorganic coloring, lubricity aids, etc.)"

By the way, I think the lighter valve lash nuts are a great idea.

 

I've used anodized aluminum parts for (believe it or not) where they needed to be electrically insulating. The coating is Al2O3 (ceramic), so it's really hard, maybe Rockwell C-90. Problem is, the coating is so thin that it's not easy to measure the hardness of the coating without fracturing it, then you're just measuring the soft underlying aluminum.

My simple thinking would be that it's more important to go for material strength by choosing the Al alloy & heat treatment. Anodizing might just make the surface a little smoother (more 'slippery'?) & then they'd come loose easier.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">Problem is, the coating is so thin that it's not easy to measure the hardness of the coating without fracturing it, then you're just measuring the soft underlying aluminum.</TD></TR></TABLE>

Nanoindentation would work.

Aluminum is plenty strong enough for most applications. The problem is that is fatigues well below its yield point, thus limiting is usefulness in cyclic applications. (If I recall correctly, aluminum has no fatigue limit, which means that any cold working weakens it.) A great example of this is to repeatedly bend the tab on a soda can. Compare that with the old steel cans.

After the discussion here, I think that aluminum nuts would work. However, they would need to be anodized to ensure their durability. We can't forget about the bling factor as well. The real problem is that the M7x0.75 (fine thread) is not too common.

 

Glad we could all be of use so far. I wish all thread discussions were this informative and just plain nice. I'm sure that it will be hard to impossible to find the nut you need in exactly the the right threading you need that is also aluminum, anodized, and the correct hardness. So most likely it will need to be custom made, meaning that maybe it won't be so hard to make after all. Problem is that getting it custom made oft requires a minimum order. I also think you should get the hardness of the screw measured to see how hard you need the anodized coating. From the definition posted it sounds like anodizing hardness can be controlled in manufacturing ("depending on the process"). Were you only considering replacing the nut or also the screw?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by neogenesis2004 &raquo;</TD></TR><TR><TD CLASS="quote">Glad we could all be of use so far. I wish all thread discussions were this informative and just plain nice. </TD></TR></TABLE>



I have also considered replacing the tappet screw (rivet) in the past, but that isn't quite as feasible. In that case, there is a definite wear mechanism between the valve stem and the screw. It may be possible with a titanium screw with a steel sheath on the end, where the steel would sustain the rubbing wear.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by neogenesis2004 &raquo;</TD></TR><TR><TD CLASS="quote">Worst case scenario a lash nut takes a roller coaster ride in your head.</TD></TR></TABLE>

And this could be a potentially serious situation. Things could get REALLY ugly if a lash nut got in a valve spring and made it bind up.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dogginator &raquo;</TD></TR><TR><TD CLASS="quote">The problem is that is fatigues well below its yield point...</TD></TR></TABLE>Isn't that what fatigue is all about? If you strain the material beyond yield that's plastic strain (cold-work) which is ALWAYS damaging. Fatigue is known as a separate phenomonon simply because it happens within elastic limits where you'd THINK you can flex a part indefinitely without damage.

The rockers themselves see high-cycle loading, so fatigue is important. I'm not so sure about the nuts. Seems like there's several orders of magnitude difference in number of cycles.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">Isn't that what fatigue is all about? If you strain the material beyond yield that's plastic strain (cold-work) which is ALWAYS damaging. Fatigue is known as a separate phenomonon simply because it happens within elastic limits where you'd THINK you can flex a part indefinitely without damage.</TD></TR></TABLE>

This isn't my area of expertise (PhD Chem E), so I'm not doing a very good job of explaining. Plus, someone borrowed my strength of materials book, so I cannot consult that to better my explanation. My base understanding is that ferrous metals have a fatigue limit close to the yield point and aluminum has a fatigue limit well below the yield point. Cold working was a poor choice of words on my part.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JimBlake &raquo;</TD></TR><TR><TD CLASS="quote">The rockers themselves see high-cycle loading, so fatigue is important. I'm not so sure about the nuts. Seems like there's several orders of magnitude difference in number of cycles.
</TD></TR></TABLE>

I think that the fatigue endured by the nut would be mainly due to the thermal expansion during heat cycling. In terms of dynamic forces from the valve operation, those should be minimal, as the nut would only need to accelerate the mass of the nut and the tappet screw (rivet). That is a leberal estimate, because the rocker arm should sustain most of the dynamic forces from the tappet screw and the nut would only need to accelerate it's own mass. So, I think we agree with each other.