Lash cap questions

[tadd]

Two questions for those in the know:
1. Caps are typically hardened. I assume this is mainly for a wear resistant surface? Instead of a heat treat harden could I use DLC?

I'd like to make them to size on the lathe and then coat ($5 each).

2. Can you use a 'punch' of shim stock under the cap to tweak?

Thanks in advance,
t

[chris_seven]

Tadd,

I guess that you mean what can also be described as a 'Top Hat Shim'.

We have been using these parts for many years on the Ford BDA , Lotus Twin Cam and Coventry Climax engines.

There are two techniques commonly used to make these parts:

Some suppliers sell batches of shims of a standard length with a 1.5-2.0 mm grinding allowance so that they can be selectively ground to suit a specific valve/tappet combinations.

Other suppliers sell them at varying lengths - typically in 0.001" increments between 60 thou to 0.25".

Both types are available in varying length combinations to suit different cam/carrier arrangements.
The recess to sit them over the valve is typically between 2.5 and 3.0mm.

The cost of these parts here in the UK is around $5.00 each for either style and there are many different ID and OD components available.

They are generally through hardened.

I thought, but may be wrong, that for DLC to successful the surface being coated had to polished - or certainly diamond lapped as a minimum.

I have just ordered a forging die as we are going to re-manufacture the early forged rocker but to work with an Elephant's foot adjuster (FIA regs for Period F cars do not allow Solid Rockers) and I discussed DLC finishing with Balinite but the cost of lapping on the rocker heel was prohibitive and we have decided to gas nitride instead.

I would also think that if you apply DLC then they will never wear but the rocker - which is much more expensive will wear and I would rather replace a lash cap than a 906 style rocker.

I would, however, like to know more about DLC if you have any good data.

[tadd]

Chris:
I haven't done a ton of searching yet, but I've had a hard time finding any for 9 mm stems. Lots of non metric stuff for GM iron though.

I guessed they (or the stems) could be ground to size... I just got to wondering if the top hat shim needed to be hardened all the way through. With a machinable collet, they would be easy to make (even in steel at Rockwell 32-36). Not fun, but doable.

As for the DLC I've been told it's mandatory for a top end motor due to frictional losses by folks who instrument everything, but I personally don't have access to that data. DLC is pretty common nowdays, reasonably cheap, and will coat most metals.

After actually holding a 906 rocker and a cast rocker together it was a real surprise. I had read that they are lighter, but wow, what a difference. It's a crying shame that the darn things are so hard to find (or so expensive as a repop).

I hope you'll post pics of your rockers when you get them. Did you lighten them any or are they a direct copy?

t

[chris_seven]

Tadd,

Couple of points I forgot - I don't think it is realistic to put shims under the lash cap you really need to make them the correct size.

As regard 9mm bore Top Hats I can buy the following off the shelf:

Internal Diameter: 9mm
External Diameter: 13mm
Internal Depth: 3mm
Workable Depth: 1.5mm-5mm

They are a bit pricey at about $10 each but manufactured by a very reputable supplier and of excellent quality.

The thing that frustrates me about the 906/RSR Rocker is just the price.

I can buy them in the UK but at about $450 + Sales Tax each - which is crazy.

They are new parts and are reasonable quality.

For less than the cost of one set I could buy the forging tool and 250 heat treated 4340 forgings

Maching, grinding and finishing the rocker in batches would also be very cost effective. I have contarcted this work to a local camshaft manufacturer that has been making 'billet' rockers for racing motocycles for 20 years.

I have the entire process lined up for the adjustable rocker so doing the 'solid'rocker would be quite easy.

I understand your comments about frictional losses and developed a firction test system at Cosworth in the 3.0 litre V10 days and at 19000 rpm when the spark turned out the friction was around 100 Nm measured at the crank.

When you consider that the peak torque of this motor was only 300Nm chasing friction was more beneficial than thermodynamics at that time.

I am not sure, however, if it is very cost effective at 8000rpm unless you are chasing every fraction of a horsepower on a Nascar motor or similar.

I will try to find out cam friction levels in current F1 engines as I don't have any individual component data. ( I witnessed the first stage of the test programme but was kicked out as they started dismantling and making component by component measurements)

Certainly friction at the nose of the cam can be relatively high as velocity is low and tends to zero and asperities can tend to lock (sticking friction?)

I am sure DLC will help this but I think this is a reult of the high level of surface finish used before the coating.

I think a process such as Isotropic Superfinishing would also work very well and may be easier.

I would think you will need the same standard of finish on the rocker as well.

[tadd]

Chris:
If the price is right, they will come. There are a few 'better than 906/RSR' rockers out there but nothing less than $3k. Hell, the 906 rockers I bought are all needing reground and rechroming at $42 each plus 15% hazmat fee. Hexavalent chromium anyone?

As for friction, your analysis agrees with what ive been told and other than really hard materials, oiling can provide a significant improvement, hence the decent life of the chromed feet being porous and holding oil (as well as hard). Given the aliphatic nature of a carbonaceous surface, I should think DLC would be excellent for holding a film. I've often wondered if coating the inside of the pistons would see a significant temp drop due to better wetting of the metal.

Please post as you progress.

t

[Grady Clay]

Who made the rocker arms for Porsche originally?
With a ‘manufacturer-like’ quantity, the cost should be reasonable.
They were in the US$20 range ('retail') in the late ‘60s.
The current ‘market’ is because Porsche chooses to not support their ‘old’ products.


Are replacement caps of same or better quality than original?
The hardness issue is due to the very high pressures at the rocker contact.

I need to supplement my set.
These were all from Frau Baer, decades ago.



Best,
Grady

[tadd]

Grady:
Twenty dollars seems like such a 'cheap' number!

However when you go here (Inflation Calculator | Find US Dollar's Value from 1913-2011) and use 1965 it spits out $139 .

Way better than just under $200 each plus rework (if you can find them).

t

[tadd]

Ok, so what is the 'modern' choice to replace the original nitrited rocker shafts?

Once again I was thinking of getting new OEM shafts from our host and having them DLC coated.

Is there another (better) option?

Finally, one of my set I got is not like the others. It doesnt have the bottom rib and no grooves in the ID. Any guesses to what it is from?

Sorry for the crappy cell phone photos below...

Thanks again... you guys are invaluable.

t

[jcge]

Originally Posted by Grady Clay

I need to supplement my set.
These were all from Frau Baer, decades ago.
Best,
Grady

Grady - could you please post dimensions or closeups of the OE caps ?
ID, OD and pocket depth and any taper/chamfers or fenestration?

I'll never need a set as comprehensive as you have shown, but can machine, harden grind and lap silver steel (AISI O1, DIN 1.2510 100 MnCrW4) to meet my personal needs.

Thanks
John

[chris_seven]

Tadd,

The bore looks larger diameter on the rocker without the spiral grooves and it could be that this is a later roker that used to have a bronze bush, which is now missing.

Have you weighed the two rockers to see if there is much difference?

I would guess that the rocker with the strengthening web is an early rocker - 906 maybe as it looks quite like the early forged adjustable rocker in terms of this detail.

With regard to the shafts - the Tuftrided Motorsport Shaft isn't a great advance on a standard shaft but would be reasonable on rockers that didn't have a bronze bush.

If you apply DLC to a standard rocker shaft I am sure the friction will decrease and again the shaft will never wear but I would question the surface finish of the shaft and the fact it may wear the rocker.

If DLC is applied to a surface that is to rough I have been told, by a cam grider we know quite well, that it has a tendecy to flake and cause serious wear.

I have the impression that the DLC coating specialists are looking for surface finishes in the order of Ra between 20-30 nanometres but I don't know if this is true. I will try to learn more.

Can you measure the surface roughness of a rocker shaft? I have a Talysurf tucked away somewhere but it may not be accurate enough as like me it is getting a bit old and hasn't been calibrated for years

[KTL]

Why coat the shafts when you can change the bushing material instead? A teflon-like bushing has been found to be a significant improvement over the original bronze material

[tadd]

KTL:
There is no bushing on the lash cap rockers. I'm not sure why not other than to save weight. There isn't room to bore larger for a bushing either.

Chris:
As for DLC, the only failure mode I've been told about (second hand) is bending of the item causing delamination. That said I have not yet called to chat tech with the coating company.

My Ti wrist pins are DLC coated so I assumed rocker shafts would be an appropriate use as well.

Do you have any other suggestions above the ringing endorsement for the motorsports shafts?

[chris_seven]

The info about DLC that I have - so far at least- is that if you have a surface roughness greater than Ra ~ 0.93 microns you can get aggressive wear due to flaking of the coating on the peaks - I have been promised some SEM phots to demonstrate but so far I have had no reply.

I have been considering finishing my new forged rockers with DLC but my cam grinder, who will machine thr rockers is worried about the finish. If the finish is good enough DLC would be great but again would preferentially wear the rocker.

F1 engines run DLC against DLC but long term durability isn't a major goal.

If ' tuftriding' on the Motorsport shafts is good then why not simply tuftride some standard shafts? It will only cost a few dollars and is a relatively simple process.

If you could fit a bush I would agree with the comment above that using a modern PTFE impregnated materisl would seem the way to go and someting I would prefer.

[KTL]

tadd,

I was referring to the rocker cross-shafts with respect to teflon bushings vs. DLC, not the lash cap cup. I know the thread is about lash caps, but in one of your posts above, you mentioned you consider buying new shafts and having them DLC coated. My point was, if you're reconditioning the rockers, just have the bushings replaced with Permaglide type bushings and that should be a significant improvement alone, w/out the need to DLC coat the shafts?

Sorry to stray the topic from the lash caps, but I thought i'd share my two cents about the tangent on the rocker shafts.

[tadd]

KTL:
Correct. I was speaking of the cross shafts for DLC too. This was another question I posted further down. The 906 rockers (like the 65-66) forged rockers have chromed pads. When the chrome pits, grind it off and rechrome.

That said there is no bushing inside the rocker ID like the early forged ones with adjusters. There is nowhere near enough meat to enlarge the hole to add a bushing as that would be the KISS option. They are really minimal material.

When I get them back from the chrome shop I'll post a side by side pic. It's pretty self-evident then.

Unless of course I am totally misunderstanding .

t

[cgarr]

How are the rocker bores? are they pretty good yet? I guess if they were out of spec is this something you could have plated like they do cylinders to bring them back to spec?

[cgarr]

BTW I like the spiral cut to help oiling in the one rocker. If you look at the exhaust rockers and the way they are tilted outward the oil hole position really does not help oil to flow to the underside of the rocker where all the pressure is. I am tempted to mod a set and add an extra oil hole on the underside just for the exhaust rockers rather than try to spiral cut the bushings.