Chris...must pass on the set for experimenting...tks anyway.
Andrew...had not thought of the wiper action....I was going by the grooves in a set of Clevite bearings we used to use in drag engines (and some circle track ones) they had a pattern to the grooves that looked like the viens in a tree leaf...a central radial groove with smaller ones radiating out in a diagonal pattern.
I just realised the those were for a rotating bearing...whereas the rockers do not rotate...they just move a slight bit in comparison.
Oh well.
Bob

I am very familiar with KS Bearings as I used to inspect their quality and environmental management systems. They put out a good product and stand behind it well.

OK so i have the engine apart For the EFI swap. I learned several things. First of all i had for a short time after market rocker shafts that walked and showed premature wear with these bushings. Those were replaced by genuine Porsche rocker shafts and run for about 30k miles in my turbo. Attached are some photos showing the coating mostly worn through which probably happened with the crappy rocker shafts. However the factory rocker shafts showed almost ZERO wear after 30 k miles. I couldn't measure any difference only a difference in the burnishing on the machined finish. So if C gar is still redoing rockers I will be sending these to him for a redo for the rebuild. I did them myself last time was less than happy with my own installation. I would definitely recommend these bushings and will use them again.


http://forums.pelicanparts.com/uploa...1378498750.jpg
http://forums.pelicanparts.com/uploa...1378498785.jpg
http://forums.pelicanparts.com/uploa...1378498824.jpg

If the bore of the housing is within specification and the shaft bolt correctly tightened there are two reasons why a shaft could walk out the carrier.

The first is that the shaft has been made too small and that there is insufficient expansion to make it grip correctly in the housing.

The second is that the wall thickness at the end of the shaft is too large so that the expansion is too low to allow the shaft too grip.

The small shaft would increase the clearance in the bush and this may affect lubrication but as these bushes tend to operate in a 'mixed-mode' this seems an unlikely reason for accelerated wear of the type shown.

If the shaft is the correct size then the clearance in a Permaglide/DU type bush may be too low and this would certainly accelerate wear of the PFTE/bronze layer and would result in a more general wear.

Ken,
I'm about to do a top end on my 3.0 with 80K miles on it due to a broken stud, and will likely need to have shafts polished and rockers rebuilt/rebushed. Who is C gar? Does he have a company name?

Chris, if I was in the UK, I'd definitely use you!

Thanks, Tom

Tom,

Cgarr is user cgarr on Pelican. He's located in Michigan. Just PM him (search for a post & click on his name to send a PM).

What he said

Guys: Interesting reading. I've got a 69 911E that I've recently (finally) got all apart. 6 of my 12 arms and their respective shafts are badly scored. Is it possible to bore out the arms and put bushings in them? One shop I talked to said that nobody around here (south bay area) does it.

http://forums.pelicanparts.com/uploa...1379628656.jpg

I'd be nervous boring that out. You will be reducing the thickness of the rocker arm by 1mm right around the bushing, which may or may not be sufficient for infinite fatigue life. Just eyecrometering, it would appear the later bushed arms kept the same thickness of material as your arm has, which suggests Porsche had similar worries.

How badly marked is the bore of the rocker arm?

The 906/RSR/935 Rocker Arms didn't have bushes and ran on a specially treated rocker shaft that had a coating applied.

We have re-manufactured this type of shaft with a hard layer (1000 HV). The technique we have used also produces and oleophilic surface so holds an oil film.

http://i197.photobucket.com/albums/a...ps557932b1.jpg


If you can lightly hone the bore of the arm and keep the diameter within spec these shafts may help.

Thanks guys. I tried turning down a couple of the shafts and realized the amount I'd have to do would create way to much clearance. Not to mention the hardening that chris_seven mentions. Didn't even try the rockers. So, I'm now looking for some good used (i.e., inexpensive) replacements.

These look like they'll fit a 3.6l 964 after being honed to size?

******** Parts Catalog

They will also need the oil feed hole machining as they are delivered as a plain bush without this hole.

A couple weeks after placing the order with ********, I was informed that the Glyco bushings were unavailable, but not discontinued. All calls to Federal Mogul Europe, the distributor of the these bearings, went unanswered. Anyone know of another source for these bearings, preferably in North America?

We have just ordered 250 and they are due to be delivered from Belgium in around 10 days but we are in the UK so maybe of no help.




New adjustable forged rocker just back from superfinishing.

http://i197.photobucket.com/albums/a...psc4aba264.jpg

http://i197.photobucket.com/albums/a...ps1b724743.jpg

The above Rocker arm after surface treatment.

Hardness is just below 1000HV (measured using a MicroVickers Hardness Tester.

This is equivalent to around 70 RockwellC and should be relatively wear resistant.

Hard Chrome would be similar in the 'As Plated' condition but if the chrome were ground after plating hardness would reduce to around 850HV.

Looks most excellent! What did you come up with surface hardness of a stock factory mid 80's rocker? Best I could tell was 62 to 65?

Craig,

I haven't tested the stock Cast Steel Rocker but next time I visit my Heat Treatment Company I will take one with me as they have a high quality and calibrated Mirco Vickers machine.

If you can access a Superficial Rockwell machine with a 30N force you may have some success but 62 to 65 sounds about right.

We tested some hard chrome rockers and had values between 850 and 900HV.

The hard chroming company that we spoke to does produce coatings with a hardness of around 1000 to 1100HV but these are very thin layers used on Ducati Rockers.

These engines are desmodromic so have very low spring forces and we didn't think that this type of coating would be adequate for 911 engines using 906 style cam profiles and valve springs.

By increasing the plating thickness the pad on the rocker would need to be ground and this process would reduce the hardness of the chrome to the level we measured.

The coating we have used is also 'oleophilic' and will help with boundary conditions and should generally improve the wear behaviour of both the rocker and the cam.