Titanium Rocker Shafts

[chris_seven]

We have finally bitten the bullet and started to manufacture a trial batch of Titanium Rocker Shafts.

The idea is that the lower modulus will cause the fit between the bore and the shaft end to be improved.

We have also decided to change the design of the grooves to accommodate an O ring rather than a square section seal as it will be easier to install.

The seal does not need to have a significant pressure capability so we have decided to use a 'dynamic' fit which should make installation more straightforward.

The 'fit' of rocker shafts has also concerned me for a while and I think many of the problems that occur are due to poor installation/removal of the shafts.

The h5 fit specified means that some shafts will be an extremely tight fit and it is possible that the factory could have used an informal 'selective assembly' procedure which would mean that new engines would generally be oil tight and undamaged.

Later in the life of the engine it would be more difficult to follow this procedure and some shafts may have been 'helped' into bores causing scoring.

I could be wrong but as we have more flexibility we have eased the fit to a g5 which will make assembly a little easier.

We hope the O ring will have sufficient capability to seal slightly scored bores.



We have selected a 6AL4V Titanium alloy which will be solution treated and precipitation hardened to around 175 ksi.

After grinding the shafts will be isotropically superfinished and then PVD coated with a Titanium Carbo Nitride Layer which has a surface hardness of about 3500HV (harder than DLC).

They will be very lightly polished after coating to further reduce friction.

We should have them on test early in 2014.

[HawgRyder]

Chris...are these to go with the bronze type bushings in the rockers?
Now that you have gone to Titanium...is there a better or longer lasting bushing that could be used?
Just asking.
Bob

[tctnd]

Chris,
I'm curious to know if you have had any previous experience using titanium as a bearing surface. I once tried running a titanium shaft through an oilite bushing (in a cool, slow, very low load situation) but found it would gall if anyone breathed within half a mile. I was rather surprised but replaced it with SS (not exactly your friendliest bearing material) and had no further problems.
regards,
Phil

[chris_seven]

Galling is a substantial issue with Ti alloys in general but it can be used if the surface is treated correctly.

We used to make Ti Diaphragm Couplings for Military Helicopter Engines and this involved using the hub of the coupling as part of a 'rubbing' oil seal.

We initially plated the hub with a Chrome Oxide coating and this worked well but was costly and difficult to get a good surface finish.

Modern PVD Techniques are better and I am confident that this aspect of the shaft will be OK.

TiCN (titanium carbonitride)
TiCN is used wherever great hardness and sufficient toughness are needed in combination.
Very high wear resistance and protection against galling and fretting.


I would worry about running a 906 type rocker-without bushes- on this coating but it may be worth testing.

The rockers we have made - so far- have Glyco bushes which are a Babbit style of alloy rather than a bronze. I am not sure that the life of these bushes is a real problem.

The issue is that any harder bush that will last longer will probably wear the shaft more quickly.

I think it is a question of compromise.

We are trying the Ti shafts to overcome some of the clamping and leaking issues rather than wear.

I expect them to last reasonably well.

I guess the ultimate for wear would be DLC against DLC but the cost would be high and this issue of sealing would remain.

[65rsr]

Chis,

Would copper beryllium bushes work well?

[Trophy]

Chris,

Always love seeing you push the boundaries with exotic materials... What additional benefits are you likely to see here?

[chris_seven]

Originally Posted by 65rsr

Chis,

Would copper beryllium bushes work well?

The only time I have used any Beryllium/Copper was for the manufacture of gravity die casting moulds when we used to make brass castings.

I am aware it is used for electrical brushes, springs, non-sparking tools and wear plates but I am not sure about bushes.

In a solution treated condition its around 30HRC and when fully aged this increases to around 40HRC so much harder than the standard Glyco bush.

I think an experiment with either a Silicon or Aluminium Bronze would be an easier starting point if we move away from the standard bush.

Originally Posted by Trophy

Chris,

Always love seeing you push the boundaries with exotic materials... What additional benefits are you likely to see here?

We spent quite a time looking at two-piece shafts and other ideas to solve some of the issues with these parts.

We came to the conclusion that the easiest way to make a shaft that could clamp up without overtightening the bolt was to use a material with a lower modulus and Ti fits the bill.

Its coefficient of expansion is almost identical to steel so there will be no expansion issues.

The RSR Seals appear problematic and the design is at best unconventional.

The seal design we have chosen is standard practice and is in basic agreement with the Parker Hannefin O Ring Manual.

I was told -yesterday- that the Wrightwood Racing Seal with a bevelled edge is much better than the stock Porsche seal. We looked a making a bevelled seal a few months ago - $600 for tooling - but came to the conclusion that the seal design was still flawed and if we were addressing clamping issues we may as well modify seals at the same time.

As the shaft end - if unconstrained- would expand more for a given force than the steel shaft - we have been able to reduce the fit to a g5, which should make assembly easier and it should also be less likely to cause further damage.

In general the major benefit should be ease of installation and simplicity.

They should work just as the standard parts, with standard hardware and appearance and solve the problems of walking and leaking without the risks associated with overtightening the clamping bolt.

The risk is, as have been stated, to do with galling. If left untreated I would agree that Ti would be a real issue in this respect.

The use of a TiCN coating should eliminate this problem and we are having the coating applied by a market leading PVD specialist.

One of the worst applications for galling is the pressing of stainless steel where it is common for press tools to pick up and be significantly damaged.

TiCN is used as a coating for stainless steel press tools an it will withstand the pressures and shocks associated with this activity so a simple rotating shaft should be OK but it does need testing.

[HawgRyder]

Chris...since you have now designed the pins with a good sealing groove...would something like an X-ring or Quattro seal be the seal of choice?
They are available in Viton@ flouroelastimer for -15 to +400F and I looked at McMaster-Carr .. they seem to be in lots of sizes.
Bob

[chris_seven]

Originally Posted by HawgRyder

Chris...since you have now designed the pins with a good sealing groove...would something like an X-ring or Quattro seal be the seal of choice?
They are available in Viton@ flouroelastimer for -15 to +400F and I looked at McMaster-Carr .. they seem to be in lots of sizes.
Bob

Probably a good idea - McMaster - Carr don't ship to the UK any longer so I can't buy them from this source but I will see if I can find them.

[KTL]

Let me know if you happen to need anything shipped from McMaster. Not just in this case but any time going forward. I have a distribution center a stone's throw away from me so I can get items quickly & minimize multiple ship costs.

[HawgRyder]

I love this site...no matter what the problem... Like Chris not having access to McMaster...there is someone who can help.
Way to go Kevin.
Bob

[chris_seven]

Originally Posted by KTL

Let me know if you happen to need anything shipped from McMaster. Not just in this case but any time going forward. I have a distribution center a stone's throw away from me so I can get items quickly & minimize multiple ship costs.

Kevin,

Thank you, I will let you know.

[Walt Fricke]

If a better O ring could solve the oil leakage issues, what would the problems be if a guy just recut the slots in the stock shafts to be a bit wider or deeper or whatever is needed?

I know you can solve side to side movement with various bolt-on gizmos, so if a different slot reduced the shaft's ability to wander there might be bolt-on ways to deal with that also.

But if the shaft isn't securely enough locked into place, would it not have a tendency to rotate? Or is the torque transferred through an oiled surface from a bushing so low that shaft rotation isn't an issue?

[chris_seven]

Walt,

I am, not quite sure of your point, if you want to bolt parts onto standard shafts then the solutions are available.

The Turbokraft Locks will stop the shaft from wandering but uses RSR Sealing Methods.

The Autofarm system uses external O rings and new hardware which doesn't have the means the hold the nut to either tighten or loosen the bolt.

The 935 Shaft Locks will also stop wander but the cost is high and again they still use the RSR Seal.
Both are reasonably expensive and neither seem to improve the clamping.

I am not sure how expensive it would be to recut existing shafts but the existing grooves are far too deep and don't back up the seal correctly to provide radial compression.

If you cut the groove wider it wouldn't help much as the O ring would still not seat correctly and so it still wouldn't be backed up.

I am not sure re-cutting the groove would help improve clamping.

I think that if the shaft isn't correctly clamped and it does wander axially bit rotation is not much of an issue.

The plan is to stop it wandering and to try to improve sealing all in one and without the need for any additional parts.

[HawgRyder]

With the stock material of the pin...wouldn't the cutting (of the hardened shaft) be a problem?
I guess you could grind it...but then have to reharden it.
Also...perhaps the original material needs to be as thick as it is so that the end of the shaft does not break as the bolt is tightened.
Chris is using Titanium...which is probably stronger or at least more malleable to solve the groove problem.
Bob

[Walt Fricke]

Looks like no quick and dirty for using a seal other than the RSR for stock shafts. I'd wondered about the problems Bob notes. And some of what Chris points to. I'll have to look up the Autofarm system.

I've not had problems keeping the shaft in place (leaving aside one I forgot to tighten), and generally the oil leakage hasn't been a practical problem. That is, it hasn't leaked enough that I was losing oil, or being black flagged on the track. Or even "excessive" oil dripping. But it sure accumulates dirt in there, which increases the chances of some of it getting where you don't want it, like with valve covers off, or messing with the spark plugs.

So for a "nice to fix" problem, economy seems to be one criterion. Titanium shafts with small but useful design changes and being made for seal rings and so on sounds nice, but I suspect these will cost rather more than new stock shafts.

Other ideas sound like they would have significant costs also. Bore out the carrier, shrink in tubes, and ream them to size to deal with wear and scoring on those bores?

Spot facing the ends of the shaft holes in the cam carrier, so something external would do the sealing? Fine if you have your own mill I suppose.

Though making those faces true and normal to the shaft opens up lots of design alternatives, I think. A cap with crush ring seal on the short end, and an oversize bore part way down the long end, creating a lip against which a similar cap could rest? Along with a longer bolt. Maybe this could do away with even using the conical pieces, yet still clamp the shaft adequately.

[HawgRyder]

It also occurs to me that we are all thinking of putting the seal on the shaft.
What about grooving the pin bore?
Then installing an O-ring in it (so that it would crush outwards when the pin is pushed in) and then use the stock shafts with the original method of retainment?
Just a thought.
Bob

[Walt Fricke]

Bob - I like the concept. How would a machinist go about cutting an internal groove? Is there a cutter which can be expanded while it is cutting? Or between cuts without retracting it from the bore?

Looking at Chris' second diagram, where would you make the cut? Where the shaft is thinnest - the part which expands when the through bolt is tightened?

[HawgRyder]

Walt...when working for Panavision...I used a retractable mill head for cutting inside bore grooves.
It was there when I started ...so I figure it was either one that was commercially available or perhaps one that the previous machinist had built (I think a standard tool).
It looked like a piece of round stock with two small tool bits that extended when a hex srcrew was tightened from the bottom of the tool (spring loaded to get them to retract).
Easy to use....the hex screw extended the small tool bits about .010 per flat of the hex.
So I guess the back end of the small bits was tapered to match the taper of the hex screw.
We were only cutting aluminum and I never had to sharpen the small bits in over 9 years...but didn't use it very often.
The small bits were slightly bigger than the o-rings that went into them...so 1/8" I think.
Just remembered...we also had a tool that was off-set to cut grooves too....it was also adjustable for depth and by changing the bit (one bit only) you could make it much deeper (the groove)...and by changing the depth in the bore...you changed the width of the groove.
Bob

[chris_seven]

There really isn't any difference in sealing capability between O Ring - or Quad Ring as either a bore seal or a shaft seal.

There are good reasons to use a shaft seal.

The first and most compelling is that it is simple.

Setting up to machine to bore 6 x grooves into each of a pair of carriers is complex and hence costly. (If you set out to do this with all new carriers it wouldn't be too bad) as finding the centre of the bore and then lining up the carrier would be tricky.

I can see the cost of machining being more that the cost of new shafts.

If you bore the carrier near to the thinned section of the shaft the seal will probably be effective but again quite difficult to install.

With a shaft seal you can select an Ring that has a round 2% stretch and this will keep it located in the groove and make installation easier. It is much easier to control the OD of the O Ring on a shaft than ID of a bore seal.

Caliper pistons work quite well but they have much higher levels of bore/piston clearance than rocker shafts so pinching the seal on installation is less likely.