Rocker arm binding
 

Just finishing up the rebuild of my 3.3 Turbo engine. I have built many 911 engines, but I have a weird issue I haven't seen before.

Exhaust rocker shaft of #3 cylinder slides in nice, but when tightened to spec, it causes the rocker arm to be very stiff to move.

- new shaft
-RSR seals
- Rocker arm are Supertec's rebuilt ones with their fancy coating on the bushing.
- Rocker arm turns freely on the shaft when removed from cam tower.

Clearly, it's the cam tower, but oddly it is this one valve in the whole engine!

Was thinking about letting it self clearance. IDEAS?

Shaft not centered correctly in the carrier. Some are flush and some are recessed into the bore.


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I've embarrassed myself this way.

3 & 6 are the easiest to do. Just nudge it? Maybe use the feeler gauge check (after doing that once on my first top end I just eyeball)?

Will retry the positioning for sure, but I feel like that isn't it. I've done this job 1000 times. Never had this issue, but I'll give it a shot.

If its not a position issue, try this.

Remove the rocker arm, refit the shaft and torque the bolt. Then measure the distance between the casting faces, and the shaft diameter. The casting distance between faces wants to be larger than the Rocker width and the shaft diameter smaller than the rocker bore.

Is it possible one of the RSR seals tore when you inserted the shaft into the carrier bore? Maybe there's a bit of rubber between the rocker arm and the carrier.

It was something I have never, ever seen before when building a 911 engine, and I have built many.

Turns out that regardless of the shaft position, when the bolt was tightened to 20ftlb, it caused the rocker to bind.

Out came the feeler gauge and I noticed that the clearance between the rocker and the aluminum casting was very tight on the right side of the rocker; it was the only rocker to exhibit this scenario.

I removed the rocker and shaft and touched up the casting with a jeweler's file, smoothing it down taking just a tiny bit off.

Reassembled; no binding whatsoever, everything is perfect.

The cam tower is used but in good shape. Just needed a hair filed off.

Huh.

that is a new one...I've never seen that happen. good post regarding the problem, find & fix.
regards,
al

Like others said, position is my first thought. Setting that aside, here is what *I* would do. (Your basic scientific method. I imagine you've already done this.)

1. Swap the "bad" pair with a good pair and see if problem moves with rocker/shaft or stays with the bore.

2. Take out a "good" shaft/rocker pair and compare it with the "bad" pair (measure with a micrometer, etc)

3. Compare "good" cam carrier bore with "bad" one.

4. Torque up the "good" shaft and "bad" shafts and mic them.