forged rockers - friend or foe?

[66S]

Are the early adjustable forged rocker arms good for racing? Im assuming the racing rockers are also forged. Ive been told cast rockers will work for racing but X-ray them first. What do 911 racers use?

[tom1394racing]

Many racers use them because of the added strength.

The problem with them is that they are too strong. In the case of an over-rev situation, where the pistons and valves come in contact, the cast rocker will break and limit the engine damage while the forged will not and something else gets damaged like a valve or a piston.

I recent parted out an early Al case motor that had been over-reved. Every piston had a deep impression from the valve and one piston pin was broken from the impact ruining that piston and cylinder. All the rockers were in tact with no impact damage.

[a911s]

Grady Clay told me the same thing. Nice and strong, but they are a b**ch to adjust and will not break before the valve damages the piston. They are nice but not necessary for an 8500 rpm motor that has all the other good stuff, so I went with polished forged that were inspected.

[kenikh]

The forged have a (minimally) better rocker ratio than cast.

[Steve@Rennsport]

Forged rockers are slightly lighter and do raise the threshold of valve float (much like RSR ones do) but like Grady said, they will not snap off if the valves collide with the pistons.

That said, I've seen PLENTY of bent valves using the cast rockers so its no guarantee they will break off to save the valves & pistons,...

I have no qualms about using them provided they are in excellent condition and good aftermarket valve springs & retainers are installed.

[304065]

Steve, what did we ever conclude about the rocker face? How could that be renewed? I think you said it was hard chromed?

I have a set from the '66 resting in eternal slumber in cosmoline, along with the shortie rocker shafts with the 5mm pinch bolts.

Did we ever validate the rocker arm ratio by an objective measurement? I've heard they are a fraction better, but wonder 1) where on the rocker face that calculation is performed, or is it an average and 2) what is the methodology for that test. Seems to me that the geometry of the stock cam tower is the limiting factor but what do I know, I just read a lot.

[Steve@Rennsport]

Hi John,

I been referred to a place that can renew the hard chrome facing on these rockers and I'm going to send them a few sets to redo for me.

LIke you, I've been unable to validate the claim about a ratio difference as the lats few times I made quick measurements, they were identical to the iron ones. I thought I read that Henry wrote something about a ratio difference, but I'd like to confirm the precise numbers to allow me to optimize a cam profile, if possible.

When and if I get time, I'll make a jig using a cam tower and see if this is true or not and to what degree.

Your servant, I am,

[chris_seven]

I realise that this is an old thread but possibly still relevant.

The FIA have specifically banned the 906 Rocker from use in Period F and it is becoming increasingly difficult to find original forged rockers in a serviceable condition.

There are some CNC Billet machine rockers available but these are also frowned on by the FIA.

We have recently re-manufactured the forged rocker arm for use in FIA Race Engines which rev to 8000+ rpm.

The arms are forged from 4340 VAR heat treated, machined, isotropically superfinished and surface treated to 1000HV using a carbonitriding process applied in a PVD chamber.

The pad length has also been increased to be the same as the 906 Rocker so it works correctly with high lift cams. Glyco bushes are also fitted and honed.

The increase in pad length is an improvement over the original rocker and does provide some advantage in terms of wear.



I would agree that they don't break when an engine loses its timing but neither will they fail due to metal fatigue when used in high revving engines.

We also make a surface treated rocker shaft and we are working on a lightened version of the 'Elephant's Foot' Adjuster.

[ajwans]

Chris, are you able to share where you are sourcing the glyco bushings from? I'm coming up short lately.

Regarding the adjusters, I saw some neato racing adjusters which were internally wrenched. Seems a much nicer solution than the factory slotted adjusters.

andy

[chris_seven]

Andy,

I bought 250 from Federal Mogul in Belgium. When they have stock it isn't an issue but when they run out they don't re-manufacture until they have a backlog of 1000 pieces. There is a company in Germany sells them in small volumes but at silly prices (10 Euros) and Rock Auto in the USA usually have stock at around $3.00.

I have been looking at the adjusters and have drawn a part with a hexagon socket for adjustment.

Looking at the design of the Elephant's Foot although it seems good from the point of view that is doesn't mushroom the end of the valve any scrub does translate directly to a lateral force which may account for the oval wear pattern found commonly in the guides.

It may be interesting to try to reproduce the 906 style by using a lash cap on the valve and a ball ended stud for adjustment.

We are trying to model the relevant parts and look at weights.

Where did you find the socket adjusters I would be interested.