rocker arm and cam lobe failure

[trond]

opened engine and all look perfect, including main bearings, con rod bearings and ims bearing. Not one spec of debris in sight. I will look closer at pump, but as oil pressures are as they should I expect it be fine. After weekend

[Henry Schmidt]

We just got a set of rockers from a prominent So. Cal. Porsche shop. Apparently they encountered some strange cam wear on a recently "rebuilt" engine. The rockers looked rebuilt and cosmetically stellar. When we received these rockers, I called the shop to ask why we were rebuilding these rockers. That's when we heard about the strange cam wear.
We skipped our usual process and went straight to the grinder to help evaluate the rockers. Half of the rockers had pads that were not ground correctly.
Obviously, not all rebuilt rockers are rebuilt correctly.

[Classic 911]

So then there’s the $1000 dollar question:

Which vendor / vendor’s to use for camshafts and rockers ?

[mikedsilva]

Originally Posted by trond

Hadn't seen this pic till now.
Hoping someone knows the reason for this as I have experienced it too.. an engine I pulled apart to rebuild a few months ago, had very similar looking rocker shafts. From cylinder 6. Last one in the bank to receive oil??

This engine was sitting for ages and had all sorts of muck inside it. I suspected insufficient oil to the rockers, maybe a blocked spray tube, but when I pulled them all apart it was clear. The engine had not been rebuilt before.

It's a weird shape for it to wear like that.. almost as if the metals had different hardnesses or maybe the valve springs were not keeping sufficient pressure? I don't understand enough about metal wear to explain why it would erode away in those wave-like forms.

One of the theories I have is if a rocker had insufficient clearance, then perhaps a sufficient oil film between the cam lobe and rocker pad was not maintained. ie, if the rocker pad was in near constant contact all the time, then it would be wiping away the oil film?

Or perhaps the rockers are just duds to begin with?

[MoreGAS]

"Question on rocker arms; is the pad surface hardened or not ?"

The stock cast rockers(69-93) are not heat treated as one cannot heat treat cast iron materials. The 993 rockers are a different cast iron material that I believe are stronger.... The early rockers 65-to mid 68 were steel I believe and the faces were Hard chrome plated, they ran without a bushing(though some rare ones may have come with one and we have converted them to run a bushing) and there were problems with them sticking on the shafts...

The race rockers like an RSR , 934, 935 were also a steel rocker (no adjuster screw or elephants foot-PITA to service and adjust even with a pile of lash caps on hand ) with a chromed face. We had some tested years ago and learned the Chrome plating was .004" thick ...By this time mid 70's Porsche started coating the shafts as they have a Black color to alleviate that galling issue(cannot recall the process-Parkerizing?) . Another novelty , these race engines also had steel billet cams .

We recently saw new rockers from The Dealer be off by as much as .003" on the pad surface. (That is the heaviest one in the pictures above with all that mass around the bushing -yes not as bad for moment of inertia but still not likely necessary) Sometimes they touch in the center, sometimes just the 2 sides...this will be an issue no matter what rocker you start with if your's are ground improperly.

The cams on cast billet blanks today are likely made from a very similar hardness cast iron material as the cast rockers, so we avoid the issues of the much harder welded material I assume one ends up with after hard welding the cams to change the profile. We simply had way less issues once we switched to the Billet Blanks when they became widely available for fair (Thanks China) 10 years ago or so, and we've never looked back.

BeST

Kevin
GAS Motorsport

[Henry Schmidt]

A few thing we've discovered over the years. The forged rockers with chrome faces offered the most strength and longest service life at a much lighter overall weight.
Porsche abandoned them early on because they were quite expensive and caused catastrophic failure with that all too common "money shift".
Cams and rocker used in the later engines 66-83 or so, were both fairly generic cold castings, similar material running in contact with each other lubricated by a spray of oil.
In or about 84 the rockers were redesigned to a heavier configuration and I believe a lower quality metallurgy.
Before 84, we rarely saw rocker wear without an oiling issue. This is also the time we started seeing the "Green Idiots" removing lubricating compounds from engine oil.
Cam lobe failures were relatively rare until people started chasing huge horse power. Higher lift meant increased friction and from higher load rates.
Although welded cams have been a common modification on high performance cams, this process started having undeserved negative reputation.
Moving to more modern times, we start seeing billet cams flood the market. Although China would seem to be the likely culprit, most new billets are actually cold cast in Turkey.
Given the great collector value of the older cars, more and more are being restored.
That means more and more companies are looking to cash in on after market parts.
Some very good and some just plain horrible. Poorly designed with low quality metallurgy.
That is what we are seeing in the rocker market.
While other are experimenting with "new " rockers we are rebuilding our cast rockers to a higher standard than even the Porsche factory specs.

For those of you who like the early forged rockers (money shift and all) we have taken them to the next level. We bore them for out proprietary DP4 bushing, regrind them to the proper radius, re-chrome them and finish with a dry film coating on the pad.

Thousands in use and no complaints "YET". 3-2-1

[rs-vic]

trond, could you please post pictures of the sides of the rocker showing the casting numbers or insignia?

[trond]

picture of failed rocker

Originally Posted by rs-vic

trond, could you please post pictures of the sides of the rocker showing the casting numbers or insignia?

[trond]

latest update is I should have used hardwelded rockers with hardwelded cam. Clearly advised on cam vendors webside but I missed it. Cost me two years off the road and enough money to launch the space shuttle

[stownsen914]

I've not heard that special rockers are needed for hardwelded cams. Why would that be the case?

[mikedsilva]

Originally Posted by trond

latest update is I should have used hardwelded rockers with hardwelded cam. Clearly advised on cam vendors webside but I missed it. Cost me two years off the road and enough money to launch the space shuttle

Still cannot understand why only 1 rocker arm was affected...

[trond]

I don't understand either why it is only one out of 12. Or how it is possible that that one could be completely destroyed so fast. Or why rockers would need to be hardwelded if the cam is hardwelded ? I understand there is a big hardness difference on a hardwelded cam and a cast iron rocker, but why that would be a problem I don't understand. It would make more sense if it was a lubrication issue but I have not been able to find any flaw with oil supply through the splash tube. Good oil pressure and no obstructions in splash tubes. I have been recommended to send in cams and rockers for assessment.

Meanwhile to get the car on the road before snow I consider using the second hand DC GT2-108 cams I got from you, 9.5CR and stock valve springs. I had 14 rockers refurbished so detracting the eaten up one I have a full set of used cams & rockers that have seen 1 hour only. No cost as I have all the parts already. And do a visual check too of how oil is moving.

Originally Posted by mikedsilva

Still cannot understand why only 1 rocker arm was affected...

[dannobee]

Would you happen to know what valve springs are in it? And the seat and open pressures?

[trond]

Asco springs set to 34 mm. Don't know spring pressure but more than stock

Originally Posted by dannobee

Would you happen to know what valve springs are in it? And the seat and open pressures?

[Henry Schmidt]

My thinking is that failure of this magnitude would suggest a metallurgical failure.
Not all cast iron is the same compound. It can have different levels of carbon (1.7% to 4.5%) and a variety of silicon, manganese, sulfur and phosphorus ect.
This iron mixture is perhaps effecting the ability to take and hold a surface hardening
with any consistency.
It's also possible that these rockers are not chill cast. The chill casting creates a surface hardness that reduces friction, increases durability and at the same time maintaining a softer interior that enhances compressive and tensile strength.
I've heard people talking about heat treating rockers but I believe that process is counter-productive. That is why we Cryo treat our rockers
These "new" rocker appear to function to the point of failure and at that point, the collapse accelerates. Simply put, given more time they will all fail.
We are doing a large number of rocker rebuilds and this specific rocker has not come into the shop yet.
I am surprised at the number of companies attempting to manufacture Porsche two valve rocker arms.

[Henry Schmidt]

Originally Posted by dannobee

Would you happen to know what valve springs are in it? And the seat and open pressures?

Originally Posted by trond

Asco springs set to 34 mm. Don't know spring pressure but more than stock

Aasco valve springs set at 34mm have a target seat pressure of 70 lbs.
Set at 34mm we are seeing over the nose pressures of around 240 lbs @ .500" of lift.
At 34mm we have a target coil bind clearance of .070" with .050" being the minimum.

[trond]

I checked all rockers again today and it only the one marked with DP1120 that has failed

[stownsen914]

Would be interesting to know the source of the bad rocker.

[trond]

unfortunately I don't know where that DP1120 came from but it was used in my engine previously, with stock cams, and survived in that application

Originally Posted by stownsen914

Would be interesting to know the source of the bad rocker.

[Henry Schmidt]

The first rockers you posted are early (pre-84) and generally considered to be of better quality. Perhaps a better mix of compounds or simply chill cast where others may not be.
As a side note: they are actually quite a bit lighter.




The others your posted with the H are the same as the dealers in the US sell as OE.
They are crudely made, heavy and prone to failure.

I have never encountered the DP 1120.