Rocker bushings

[quattrorunner]

Who can I send my rockers to for Rhenish? Good price and fast turnaround?
Thanks.

[rsscotty]

Steve @ Rennsport Systems is the best.

[Steve@Rennsport]

We can rebush and regrind the rocker faces to assure they are parallel with the shaft centerlines. The latter is critical for camshaft durability.

[quattrorunner]

Thanks b
I suspect that's what's making the clicking noise as its the only thing that didn't get my attention when I rebuilt my engine. I'll try and get them sent over or is there a good core system?

[Steve@Rennsport]

Originally Posted by quattrorunner

Thanks b
I suspect that's what's making the clicking noise as its the only thing that didn't get my attention when I rebuilt my engine. I'll try and get them sent over or is there a good core system?

Currently, I don't have any exchange cores. Send them and I'll try to get them turned around fast for you.

Be sure to check the shafts for wear. If you can feel any ridge, they should be either rotated 180 degrees or replaced, based on inspection.

[quattrorunner]

Thanks Steve.

[Turbo_pro]

Originally Posted by Henry Schmidt

Supertec is rebuilding rockers with an entirely new process.
First the bushing is removed.
The rocker is bead blasted and inspected.
The the whole rocker is black oxide treated.
Then the adjuster treads are cleaned and restored with a forming tap. (read rolled)
A new SDU bushing is installed and sized. (greatly reduced coefficient of friction .05vs .34 for P/bronze and improved heat transfer)
Next the rocker pad (cam follower) is surfaced.
At this point the rocker is sent out for dry film lubricant.
After that, the bushing is drilled and the entire part is cryogenic treated.

We have sets in stock ready to ship. One day turn-around for most types.
$420 exchange

I found this in a previous thread...... porsche rocker arm rebuilder
Looks like Supertec has gone the extra mile and they have an exchange program as well.

[hcoles]

It looks like SDU bushing is something like this....

DU Bushings

I don't see mentioned to send in the shafts for checking, resurfacing or size adjustment. Is this recommended or just turn the shaft 180 and go?

I like the sounds of this "HS" service, get the rockers done right and drive for 20 more years. All things considered the price seems reasonable. If I could have done this (or known better) years ago when I did the top end, I would have.

IMHO - this is a highly stressed part of the motor in terms of questionable lubrication and I think many would agree the stress between the cam and rocker is high compared to many other points in the engine.

[chris_seven]

Originally Posted by hcoles

It looks like SDU bushing is something like this....

DU Bushings

I agree that the bushes being described are a DU type bush but I am not sure that I agree that this material is the ideal soultion for a rocker arm.

I am aware that it may be good enough but I have to say that I believe there are other materials that are more suitable.

DU is a material that, according to the original manufacturer GBB, has excellent characteristics when used dry and 'good' characteristics when lubricated.

It is not in the list of materials that they recommend for a 'lubricated' applications.

In the last few years generic versions of this product have appeared on the market from other manufacturers and the data provided is not always as detailed as that suppled by GBB.

Its performance rating in the presence of engine oils is said to be acceptable rather than satisfactory which means 'some corrosion damage may occur but this may not be sufficient to impair either the structural integrity or the tribological performance of the material.

The issue with engine oil is that is will dissolve the lead in the outer layers of the bearing material.

I would prefer to use a material that had a rating of 'excellent' when lubricated and 'satisfactory' when used with engine oil.


I would also worry about 'sizing' a DU Bush.

The GBB data sheet for DU material states very clearly that The burnishing or fine boring of the bore of an assembled DU bush is only permissible if a substantial reduction in performance is acceptable.

It is custom an practice to ensure that the bore of the component that accepts the bush is correctly sized so that when the bush is installed it has the correct ID to obtain the correct clearance between the bush and the mating part.

I realise that not everone will agree but I am confident that there are better solutions available at similar cost. I have used DU, DX and many of the other GBB materials in rotating machinery for many years and do have some experience in this area.

[burgermeister]

I can state from personal experience that a DU bushing will not need resizing for installation purposes after it's been pressed into the rocker. I can also state that if no other changes are made, it won't last all that long. I got about 12,000 miles out of mine (lots of track time in there) and had wear >0.01" on one of the bushings.

I know that other folks have gotten DU bishings to work quite well, even on race engines, but these folks cut additional oil grooves, they enlarge the bore slightly by honing (DU expands a lot when hot, so it needs more clearance so it doesn't cut off its own oil supply), and they polish the rocker shafts to a very smooth finish so the teflon coating is not abraded. If you are disinclined to do this, then DU is probably not the right stuff for you.

As far as refacing the rockers, I am not sure the processes used are of sufficient accuracy to make much difference. After the DU bushings wore out, I had a set of mine rebushed with bronze and refaced, and the contact area on the camshaft appears to be anything but even. This is after about 1800 miles of driving, maybe 200 of it track time. Contact is clearly not even across the pad.



Bronze bushing wear after 1800 miles is visible, but not really measurable, so it's <= 0.001".

[hcoles]

I see at least a couple of interesting subjects here:

1 - regrinding the rocker pad
I had my pads "reground" by a mystery person in San Jose. I think there is a "guy" that does this that the local or other people use. Checked later after the engine ran for a year or so and saw the same possible issue, the wear does not appear exactly even across the pad. Two general thoughts come to mind:

a - some angle difference may be OK, not ideal but OK even for long term durability, do the "high" areas get worn down a bit and all is well or gets better over time?

b - consider all the tolerances involved with getting the grinding process to align with the actual installation for a given cam lobe - the length of the list seems considerable - I'm not a machinist but to get the rocker pad to be within say 0.0002" across compared to the cam lobe surface I would guess is not trivial. If the primary reason for this is to get a "new" surface against a "new" cam then it makes sense.

2 - I would say we don't have agreement on the best possible bushing replacement part or material. I made and used some 660? bronze parts, I consider my fix to be amateurish considering the latest info. discussed (Cgarr and now DU) in the last 5 years. So far my rockers seems to not have obvious issues.


I'm staying tuned to read what the experts continue discussing on this.

[chris_seven]

Originally Posted by burgermeister

I can state from personal experience that a DU bushing will not need resizing for installation purposes after it's been pressed into the rocker. I can also state that if no other changes are made, it won't last all that long. I got about 12,000 miles out of mine (lots of track time in there) and had wear >0.01" on one of the bushings.

I know that other folks have gotten DU bishings to work quite well, even on race engines, but these folks cut additional oil grooves, they enlarge the bore slightly by honing (DU expands a lot when hot, so it needs more clearance so it doesn't cut off its own oil supply), and they polish the rocker shafts to a very smooth finish so the teflon coating is not abraded. If you are disinclined to do this, then DU is probably not the right stuff for you.

The clearance of the bush to the rocker shaft will critially affect the life of the bush and there is a chart in the technical manual for DU which allows the calculation of diametral clearance with repect to operating temperature and it is quite important to have this close to the correct value.

The other clearance issue with DU is the introduction of hydrodynamic oil films and shaft clearance needs to be increased. GBB recommend a reduction of shaft diameter of 0.1% for bearing that is either fully hydrodynamic or has mixed film lubrication.

As I said earlier remaing or burnishing DU to increase clearance will catastrophically affect the life of the bush.

There are, however, similar style bearings that can be substitued for DU and that have much better properties.

We are using a material in our new forged rockers that is designed for hydrodynamic or mixed film lubrication and its comparitive performance is:

Wear Resistance under Steady State Load - 4 x greater than DU

Fatigue Resistance - 5 x greater than DU

Cavitiation Erosion Resistance - 8 x greater than DU

It is still important to have all of the clearances and surface finishes optimised.

Looking at this problem in more detail make me think that there are two considerations that need to be investigated.

The first is that the housing to bush fit must be correct to the design standard and as we have new forgings I can easily achieve this requirement.

If it is an issue with used rockers then they can either be honed if the clearance is insufficient or perhaps the bush can be plated if the bore is too large.

Once the bush is correctly installed it may be worth centreless grinding the rocker shaft to the optimum clearance as under hydrodynamic conditions the clearance is likley to be too small rather than too large at least with new rocker shafts.

I have been considering Plasma Nitriding new shafts and then grinding to size which would not be ridiculously expensive.

[Walt Fricke]

Chris - if you can come up with a way to reface old rocker shafts, I have a largish bag full of them. They all fail the fingernail test on at least one side, and some almost all the way around (having been rotated several times already) If they could be brought back to standard for less than the cost of new ones, that would be good.

Alternatively, if the bearing used required a slightly smaller diameter, and it is possible to grind just the bearing parts, leaving the parts which support them and fix them in place at the original OD (which they all are, as no wear happens there), that too would be a good thing. As long as the bearing will allow the original OD to pass during installation, that would be trick.

For that matter, might this be a market for worn shafts? Already machined, in a sense, to a slightly smaller diameter where it counts? Not quite concentric, but would that matter? We rotate these when only one side is worn, and that seems to work reasonably well.

As to grinding rocker pads to true, but seeing wear: the experts all assert we should keep careful track of which rocker came from where, and put them back that way. Because if the cam grind is a bit off, or wore that way, then the rocker wore to accommodate that. Which does suggest you could have issues if you get rockers reground nicely - or use brand new rockers, for that matter.

At first I tried religiously to do this, even stamping the rockers with a number and letter. Then I gave up and just put them back in any old way, sometimes replacing one or two which had gotten pitted or seemed off. That, too, didn't seem to hurt anything. But now that I can remember the rationale for keeping things as they are, I'm going to try to do that.

Nothing like understanding at least a reason for a rule to make you decide perhaps you ought to follow it. (Though there is that rule about the sequence of bleeding brakes, which makes no sense at all - certainly there is zero reason to do the rears before the fronts, as they are separate circuits and air from one won't contaminate the other. Makes one suspicious of received truths.)

[hcoles]

A general rookie question re. rocker shaft diameter, no attempt to derail.
Is the major force on the shaft absorbed in the tower by the expanded "ring" or the general diameter pushing on the tower. Likely, except for an extreme case this is both. The shaft diameter range is constrained by how it fits in the tower, too much grinding or turning down puts you toward the low end of this range. Any feeling on how much diameter clearance is allowed on the tower side? I don't have the book in front of me, but thought to mention before people grind shafts thinking only of the rocker bushing clearance. Since the diameter of the bores in the tower are likely considered as found, this seems like the place to start when thinking of the shaft diameter, the bushing clearance and then the diameter of the hole in the rocker.

[AlfonsoR]

Chris, do you have a link for your website? Do you also refinish/ rebush rockers?

[Walt Fricke]

HC - you have a good picture of things. The expanding ends of the shafts are not a good place to transmit forces. I've had a couple break off after many R&Rs. Not much meat there at the groove. They don't break at the groove, but outboard of it. Could be worse, as I think I've noticed this on removal, which means the break didn't affect operation - the shaft stayed in place. So it is the full diameter part which transmits the force to the cam carrier housing. Which means it has to be a pretty tight fit - which it is.

Which also means you can't grind these shafts. At least not without first somehow building them up - plasma spray maybe? And then regrinding back to stock. Something like that, I suspect, would cost more than just buying new ones.

My long term dream is to acquire a pair of 993 cam carriers and shafts and rockers. With a little plumbing, I believe these can be made to work on the 911. No more leaks, and much faster R&Ring the rockers. Perhaps with oil force fed to the shafts, the shafts and rocker bushings might last longer as well.

[quattrorunner]

What an idiot!!! (ME)
So last time I was in there, I wanted to ensure the rocker shafts didn't leak. So I finished off my rsr seal instal with some rtv sealant on the ends of the shafts including basicly filling the whole recess!!! I thought it was a dumb idea when I did it, I even commented that in a thread about the subject here Rocker shaft walking
So, last night I had the engine out for new clutch and to remove the rockers for resurface and was swearing at myself the whole time. Sucks to remove in an already tough location even with the engine out! RTV does do some sealing but not really in this situation, it will eventually loosten it's hold/seal and weep if it's in contact with oil and not under pressure like onder a gasket or something.
Not a good idea to use RTV. OK, now I'll go and hide.

[Ken911]

yeah so when you put it back together get thos locks from turbokraft

[Walt Fricke]

Well, the locks from turbokraft will prevent the shafts from sliding side to side. But they don't do anything to stop the weeps/leaks, do they?

I've only once had one shaft move on me, and that was because of my installation error pure and simple. Otherwise, despite reusing shafts over and over, and not being too careful in how I tap them out (I leave the hardware in so each tap on the end of a cone is going to push the shaft end out at least a little bit), I've not had a movement problem.

Now some oil getting out and making that compartment area a grungy mess when rebuild time comes around, that's another story.

[quattrorunner]

My shaft movement was because of the specified torque number advised by tech books and guides. I personally believe that the value of 13 lb ft is for a new engine. After some time and perhaps retorquing of the bolts, I believe the tower becomes stretched or pushed out from the force the shafts exert on them. I'm positive the bolts inside the shafts stretch. A combination of stretched bolts, too low a torque value and larger housing make for a loose shaft and therefore the desire for them to go in a stroll. When they walk, it's very stressful to you and the engine. There is high possibility of damage when the cams turn and rockers bounce about uncontrolled. I got lucky(twice) when mine did this. I have since used the tighten it as much as your hands can with a standard Allen wrench method. Not very clinical but tighter than 13 lb ft. Is needed. If say more like 18-20lb ft.
Sad thing is that too many of these tightenings will lead to throwaway can towers.
Comments?