Uneven Wear Pattern on Reground Rocker Arm Pads

[burgermeister]

Rocker arms were rebushed and resurfaced by a very reputable upper west coast shop 18,000 miles and 20-30 trackdays ago. Pulled the engine for what turned out to be a loose valve guide, and found cams and rockers in the shape shown in the pictures.

Notice the one-sided wear on the rockers. Cams are factory originals, never reground (though they will be now). Rather disappointed in the value I got for the $500+ I spent on the rocker reconditioning...

Point being, check everything, and if something looks not quite like it should, do not assume a good reputation or large sums of money spent are a guarantee of sufficient workmanship. I probably should have checked a few of the arms with blueing before install, and I could have avoided getting the cams & rockers reground.

[RedCoupe]

You're right about how important is to check everything when you have work done. However, the rocker arms may not have been improperly ground. The cams and rocker arms wear into a particular pattern over the miles and years. When you introduce new flat, perpendicular rocker arms to used cams that are no longer completely flat you can get extraordinary wear. The opposite of that is when you install new cams but don't regrind the rockers. Still can get bad wear patterns. Anyway, with both reground cams and rockers, all should be well.

[Steve@Rennsport]

Sadly, its common to find improperly reconditioned rocker arms and we fought that problem with a vendor for a long time until we finally decided to do this in-house. There was simply no other way to control QC and the health of our engines.

We built a proper fixture to do these and now that issue is no longer a concern.

Call me during business hours if I can help.

[cgarr]

If they are checked before they leave the shop this would never be a problem, its so easy to check!. I don't care how good your fixture is, you still have to check every rocker leaving your hands!! Period

These are way too far off for the cams to be a problem, You can see the high pressure point and pitting! If your not 90% surface contact you will have pitting due to high pressure points. I could grind one by hand and get it closer than that

[camgrinder]

Originally Posted by RedCoupe

The opposite of that is when you install new cams but don't regrind the rockers. Still can get bad wear patterns.

This is a good point. Each profile uses up a different area on the rocker face. If you compare the rubbing pad on an intake and exhaust rocker you will see this.
An upgrade profile like the 964 uses up more of the pad vs. the SC profile. The 964 will ride on both worn and unworn sections of the pad. not good.

And if anyone is wondering, burgermeisters rockers did not come from our "west coast" shop

[burgermeister]

Got the reground cams & rockers back from DRC.

I did check all of them on a cheesy HF "surface plate" using a couple of v-blocks & sliding an indicator across the pad noting max excursion - all rockers pads were parallel to the bore within 1.5 thousandths, which is probably the accuracy limit of my setup to begin with.

They look to be wearing very evenly. Lobes appear to be contacting across the full width, and base circles near the middle. Base circles are not fully worn in yet - not surprising, as there is zero contact pressure due to valve lash. Pics are after 20 minute 2000 RPM break-in and 100 miles of driving.

FWIW, DRC charged me less (and took less time) to grind the cams & rockers than the original outfit charged to poorly grind and rebush just the rocker arms.

[mikedsilva]

Gents, I am in the midst of re-assembling my 964.. I got to the point of setting cam timing, and then installed all my rockers.
However, I then bought some new tension tools, so I removed my rockers to re-do the camshaft timing.
As you know, when you set timing, you turn the motor over by hand a few times.
However, a couple of rockers were showing slightly uneven wear... as in the pic.
The cam and rockers were re-ground by the same place at the same time.
My question is, is this OK to continue and will the slight unevenness "wear in" as the engine is run in, or should I pull the bloody thing apart again??

[burgermeister]

I assume that wear pattern is after running it for a while?? I can't imagine getting it from assembly.

One of my cam lobes got some pitting on slightly less than 1/2 contact (you appear to have just a wee more than 1/2 contact). Took 15,000-ish miles and maybe 15-20 days on track to do it. I run high-ZDDP oil. All the other pitted ones had maybe 1/3 contact.

So, if you got that wear pattern from running it, I'd say it is likely you will pit a cam lobe within maybe 30,000 miles if you track the car, probably more if you don't. But, that is a total SWAG simply based on my experience.

The rockers don't "wear in" much (mine never changed), neither do the cam lobes. The partial contact causes higher contact pressure, and while ZDDP oils keep everything from wearing, the increased pressure fatigues the metal until little chips break off.

[mikedsilva]

Thanks for the reply. This is actually from just turning the motor over while it is still on the engine stand. I have turned it over quite a few times. The surface of the cam lobes is not nice and shiny like a used cam.. it is quite dull and to my fingertips "rough"..
I wonder how many people, re-assemble a motor and don't know if they have even wear or not?

If I had not pulled my rocker out, I would never have known.

[burgermeister]

If it's just from the motor turning over, it may wear in better than that once it is in actual operation. But - weird that it would do that! I've never seen wear on anything from turning the motor over by hand!!