I don't believe the cast rockers are hardened as we do rebuild these here in-house and have not found this to be the case. We do regrind each rocker pad to get a fresh, parallel and properly curved surface as SOP.

I will say that hardwelded cams are much harder than the rocker surfaces and its imperative that the cams are coated with a moly lube made for camshaft break-in, not general assembly lube. Further, the engine MUST be run at 2000 RPM for the first 15 minutes to break in newly refinished cams and rockers. In some cases, we hard-chrome the cast rockers for improved durability with welded and reground cams.

Naturally, one assumes the spray bars are all clean and not obstructed in any way. I do not use nor recommend the cam restrictors as the use of those are counterintuitive to me. These are highly loaded areas of the engine and require lots of lubrication as well as cooling.

Hi Steve,
you may remember I've been to your shop years ago now. The rockers are 3.2 89 vintage. I may be guilty of taking over this old thread that had another type of rocker discussed initially.
I'm fairly quickly coming to the conclusion that lack of lube is the most likely root cause and I'm considering going back to original restrictors or "split the difference" restrictors. Yes I'm going to check my spray bar, looks like I need learn the pulling the bar out insitu process. It makes sense that the cam ramp line contact hit on the rocker pad heal could be one of the highest stressed points in the engine. That's the exact area of the wear pattern. We need roller rockers :-)

Here is a rocker I ground out .040 and took off .030 and it still maintained its original hardness, however I would not use one that had that much taken off, they get a bit thin.

http://i30.photobucket.com/albums/c3...1/100_8534.jpg
http://i30.photobucket.com/albums/c3...1/100_8536.jpg
http://i30.photobucket.com/albums/c3...1/100_8537.jpg

Craig,

you took 0.040" off to start with and then an additional 0.030" per the pictures you posted and the material was still hard.... curious how you measured the hardness, do you have one of those Rockwell diamond stylus machines? I haven't run one of those since college days. There are likely many other ways to get hardness that I'm not familiar with. I think you can even use a file and get a good idea. Excellent work, this means there is a lot of meat to work with.

Even if you confirmed there was only 0.030" that would be a good amount to work with for a couple of 0.005" passes.

Thanks,
-Henry

Hi Henry,

Indeed, I do remember,...:) :)

I would recommend the original "restrictors" (lack thereof) as these are highly stressed parts even with the modest valve spring rates.

Roller rockers would be ideal but unfortunately, there is not sufficient room. Several good people have tried to do this, but unless the cam towers are totally redesigned, its not feasible.

I am assuming that hard chrome has an extra step added to avoid potential problems due to plating such as hydrogen embrittlement from the acids used. Could you please provide a little education for me on the subject? Thanks :)

I don't know the details of the process since the gent who does this regards this as proprietary, however its been VERY durable for me.

I believe its a similiar process that Porsche used with the early forged steel rockers. :) I still have several sets running in several cars and those have been in service since they were made. :)

Max,
The acid used in hard chrome plating is sulfuric acid in the 0.13-0.23 oz/gal (1-1.73 g/l) range, part of the bath containing the chromic acid or chromium trioxide (CrO3) to create the hexavalent chromium, a carcinogen but not really an acid (referred to as a hypothetical acid). This is a very weak acidic solution. For comparison, battery acid is about 33% strength in the 1.25 Kg/L range (or 1000 times stronger). I would not be too concerned about hydrogen embriddlement when acid in this concentration range is used also because the entire part is not plated as is the case for fasteners.

I imagine the hard chrome is used for the same reason that it is used in the barrels of many firearms, the .45 ACP and the M-14/M1-A come to mind. In the weapons, it is not practical to lubricate the barrel between shots and the hard chrome reduces pitting and fretting as the bullets pass through the barrel at high temperature and high speed.

The hard chrome is just that - a very hard surface that will resist the fretting caused by the impact vibration of the cam lobe against the rocker. Quality lubrication will just about prevent the fretting seen in the pictures elsewhere in this thread. However, a combination of high temperatures (thin oil), high RPM (increased surface speeds), and tight clearances, high lifts, or heavy valve springs will contribute to the problem of fretting (the hard particles that break away and then are immediately crushed into the softer surface, the rocker face).

Mark

I would imagine that the early forged rockers would be hardened and tempered to a reasonable level to ensure that they are tough and have good resistance to fatigue. The section of the rocker is reasonably cosnsistent and I would expect that the hardness would be consistent throughout the section.

The only real way to be sure would be to cut across the section and use a Vickers Hardness tester and measure every 0.5mm. A Rockwell machine is not really suitable for this type of work.

The hard chrome plated onto the wear surface does have microsopic 'pits' in the surface which help it to retain an oil film which when combined with the basic hardness of the chrome give a good wear resistant coating.

I can see no reason why this layer cannot be removed by grinding and then have the part re-chromed. Modern Hard Chroming techniques are much better than those used in the ealry Sixties and should give excellent results.

Companies such as Poeton can now Hard Chrome in a well controlled manner and hard chrome many components so accurately that tthey don't need to final grind.

The hydrogen embrittlement that occure during hard chroming is a result of a 'Hydrogen Overvoltage' in the electrolytic cell causing 'atomic' hydrogen to be generated at the materials surface.

It is conventional to oven bake susceptible parts at around 250degC immmediately on removal from the cell.

If I were to recondition forged rockers I would grind of all the chromium, shot peen the wear face and the re-chrome.

Whether or not this is worth the expense is another arguement.

The investment cast rockers are unlikely to be surface hardened. I am sure that they will be made from a stell that can be hardened and tempered which is why they will have a consistent through hardness. I would imagine it is possible to reclaim this type of rocker by hard chroming but the expense is unlikely to be justifiable.

I think if I were to remanufacture rockers now I would use a good quality steel forging such as 4340AQ and then finish the wear pad with a modern material such as DLC.

Excellent information. :)

What is the mechanism which causes atomic hydrogen to make the metal more brittle? Is it due to its greater electronegativity (along the lines of carbon) causing it to steal electrons from the metal without forming a covalent crystal lattice to strengthen/stiffen it in the way carbon does?

How does the baking get rid of it? Just by making the hydrogen more energetic so it goes quicker to a gas phase and forms H2 molecules?

I guess I could have wiki'd first. :rolleyes:

Hydrogen embrittlement - Wikipedia, the free encyclopedia