solid rocker shafts

tadd · 03-08-2021, 05:12 AM

I am getting ready to install solid rockers.

Factory chose nitrited shafts to run with solids since the solids do not have a softer material as a bushing.

The rockers are the unicorn piece, so having the shaft wear seems the smart move so no DLC for stock every day shafts.

Yes, the correct shafts are available, just pricey as with anything Porsche and I am getting to the point that I want get on the road and drive rather than saving to collect more parts. Its coming up on a decade in pieces and I want to drive.

My question is how big of a deal is wear if I used a set of stock every day shafts for bushed rockers?

Is this a 10 hour problem or a 5000 hour problem?

My gut says with an excellent modern lube used with spray bar and center lube cams, that stock rockers will not be an issue for a good long while in a well cared for hot rod.

What says the pelican hive mind.

gled49 · 03-08-2021, 05:17 PM

You run the risk of a rocker seizing on the stock shaft, ask me how I know. The racing shafts are parkerized not nitrated. I take stock rockers, chamfer the groves if the edges are sharp, give them a light polish and have them parkerized. Cam companies have tanks for treating cam shafts, see if u can get it done there. The shafts will turn a light black gray. Cams are parkerized for oil retention when new, it slowly wears smooth, same with treated shafts.

Walt Fricke · 03-10-2021, 06:23 PM

What engine do you have in this '67 912?

tadd · 03-11-2021, 04:22 AM

Walt:
It is a Frankenstein of parts.

Early 2L aluminum case, typical machining mods including an MFI mount, RSR crank (thanks to BMEP years ago), crower Ti rods, Mahle 2.8 pistons (I measured 11.7:1 with 'regular' heads), LN cylinders, Steve Weiner ported heads (he also put a cut down intake from the 3.0 for more), set of GE100 center lube cams reground to 3.8RSR lobes but on 102* LC, solid rockers, and tilton 5.5" twin plate clutch/flywheel.

I have an inline 6 MFI pump from a benz that will eventually get used if all works out. Short term will be EFI using DFI injectors in the stock 'in the head' location.

Object was to run on premium pump gas with the crazy CR, so hence the crazy cam. Idea was to make sure that at lower running speeds the dynamic CR falls off, so detonation is avoided, then once 'on cam' there is enough turbulence to stave off detonation.

If I end up needing to mix toluene in (or race gas) all the time, the plan B is to go liquid propane injection using DFI hardware and EFI. Most systems I have seen use a special pump that has super hard internals due to propane having zero lubricity, but my current thinking is to use a hydraulic accumulator and just pressurize the system with air on the back side of the bladder.

We shall see.

Been at at this a long time as life keeps getting in the way of getting done. But my hope is to be on the road 2022. Currently at the short block stage. Been stuck at a way to check valve/piston clearance without doing a full build. Think I finally have a process for that, just need to execute.

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally Posted by tadd

I am getting ready to install solid rockers.

Factory chose nitrited shafts to run with solids since the solids do not have a softer material as a bushing.

The rockers are the unicorn piece, so having the shaft wear seems the smart move so no DLC for stock every day shafts.

Yes, the correct shafts are available, just pricey as with anything Porsche and I am getting to the point that I want get on the road and drive rather than saving to collect more parts. Its coming up on a decade in pieces and I want to drive.

My question is how big of a deal is wear if I used a set of stock every day shafts for bushed rockers?

Is this a 10 hour problem or a 5000 hour problem?

My gut says with an excellent modern lube used with spray bar and center lube cams, that stock rockers will not be an issue for a good long while in a well cared for hot rod.

What says the pelican hive mind.

Another possible solution to your problem might be to install a bushing in your rocker.
We had a special bushing (DP-4) made for early forged rockers that could fit your needs. DP-4 is a metal-polymer, composite bushing material. They are steel backed, sintered bronze, PTFE with a wicking Kevlar filler.
The fiction reduction from this bushing material versus the standard bronze bushing is phenomenal.

tadd · 03-11-2021, 10:36 AM

Henry:
So you think there is enough meat in the rocker to fit a bushing?

I don't have one in front of me, but bushings were discussed with Chris many moons ago.

I don't know if he went that route.

The solids have very little material around the shaft.

Walt Fricke · 03-11-2021, 11:32 AM

I also wondered why you weren't using bushed rockers, or having yours bushed. Weren't the 2.8 RSR rockers with lash caps bushed?

But that wasn't your question, whose answer I hadn't a clue.

tadd · 03-11-2021, 01:01 PM

Walt:
The solids with lash caps are not bushed. The run on pins that have a surface treatment.

faapgar · 03-11-2021, 03:47 PM

Henry is correct with his bushings.There is plenty of material there.Since you add a bit of Tolunene why not add an equal mixture of Electronic Grade Acetone.I used to use that with a bit of Nitro -Methane for qualifying.This was late 70,s and I think our limit was .74g.The Nitro will make your eyes tear a bit so do not start the car until the tech inspectors walk through the grid.Add some dizzy advance as well.Ciao Fred

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally Posted by tadd

Henry:
So you think there is enough meat in the rocker to fit a bushing?

....edit.....

I don't know if a bushing will work or not. That's why I posted "Another possible solution to your problem might be to install a bushing in your rocker."

dannobee · 03-11-2021, 04:50 PM

It was common in nascar to soak the air filters in propylene oxide for qualifying. ;-)

Nitromethane in any amount that actually added power tended to burn the eyes and throats of the tech officials and competitors behind you. Don't ask me how I know.

gled49 · 03-13-2021, 04:12 AM

One of the sets recently used. Back to original question.

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally Posted by gled49

One of the sets recently used. Back to original question.

To answer you original question, if you don't want to buy nitrited shafts, your best bet is installing a bushing. We can do that for you or perhaps you can source them for yourself.
The new bushing install will require that you strip, surface and re-chrome the contact pad and at that point, your costs are through the roof.
Cost aside: DP-4 bushing will reduce friction and in theory, increase hp and reduce operating temperatures.

Walt Fricke · 03-14-2021, 11:20 AM

Looks like post #2 is your answer? Treat the regular shafts? I take it you don't have the original shafts? Looks like your idea of the shaft as the sacrificial part hasn't really been explored? But post #2 suggests it was, and didn't work.

If I have it right, the 911s started with unbushed rockers, but soon went to bushings. Makes one wonder why the 2.8, in 1972, went back to unbushed. Or had the preceding race motors, 2.3, 2.5, all used the forged/lash cap/unbushed system?

gled49 · 03-14-2021, 06:56 PM

Basically all race engines had lash cap non bushed solid rockers. 906/910/911R/RSR/934/etc. Starting around RSR, 2 oiling groves were cut into the load side of the rocker going from oil holes, 30% around the bottom of the rocker.