Unusual Rocker Installation Problems

[OLD901]

Hi All,

I have followed Wayne's book to the letter.

However, once I have torqued number four cylinder inlet rocker to the correct value, the rocker's shoulders bind / interfere with the shoulders on the cam tower / housing. I can rock the rocker a little way before the binding gets worse. If I loosen the bolt the rocker works properly. I have the same problem with exhaust valve on the same cylinder. I have fitted new bushes and shafts, and have used lots of lube in assembly. Each rocker's bush was correctely reamed to suit it's shaft. RSR seals were also used.

Could the cam tower / housing be somehow distorting when I tighten up the rocker bolt(s)? Should I loosen the head stud nuts on the troublesome side of the motor?

Has anyone had this problem.

Cheers,

[SP2]

Hi, are you sure the rocker shafts are in there correctly. It sounds like it might be off center. The two ends of the rocker shaft expand when the 5mm bolt is torqued down. If part of one end is in the rocker bush, then it will bind it. I hope that is your problem because it is an easy fix.

I did the factory recommendation of pushing the rocker shaft in until a feeler gauge catches the notch, then pushed it in a little more. The book says 1.5mm but I took caliper measurements and it is actually 3.5mm for my SC. But in the end, one side is pretty close to flush with the cam tower housing, if that makes sense. Good luck!

Most on this board recommended using no assembly lube. Just install them dry, and then after torqued down squirt some oil into the holes in the rockers. That way the rockers are less likely to leak oil.

[OLD901]

Thanks for your reply James.

Yes, I made sure that the shaft is centralised with one end almost flush with the thinner part of the cam tower.

In the mean time I have had another attempt and have had some success.

It seems that the condition of the cone shaped washer and nut, and bolt have an impact on the problem I am experiencing. If the cone is worn / scored on the area where it mates with the beveled part of the shaft or the bolt does not turn smoothly in the washer, then the problem I am experiencing gets worse. I will order new washers, nuts and bolts to make sure that they do not cause a problem.

Also, I have found that by moving the shaft a little to one side it also improves things. Maybe the cam tower rocker shaft bores wear due to tightening and loosening of the shaft bolts over several rebuilds. Moving the shafts a little to one side or the other finds a part of the bore that is not scored or worn.

Has anybody found this out as well?

Regards,

Norbert.

[304065]

Norbert, since your handle is OLD901, are you working on an old 901 engine? Like a 64-68? As a new user you may want to add the year and model of your car to your signature, so we can help you more easily.

Now, what rocker shafts do you have? If it's a really old car, they might be 18x48, compared to the 18x53mm of the later, post 1967- or so cars. The early version uses a 5mm bolt which was prone to being stretched beyond its elastic limit. The later version has a 6mm bolt which requires a lot more torque to stretch to failure. In any event, if you are using the old shafts, change them out for new ones, these are not expensive used.

Next: what is the bore diameter of the cam tower? If some prior owner has removed the rocker shaft without properly loosening the pinch bolt, the bore can be scored or distorted, making it impossible to tighten things down. This is ordinarily measured with a bore gage, an internal micrometer like a Holtest or Intrimik, or even a plug gage. If you don't have any of those, make absolutely certain that your rocker shaft without the bolt, nut or expander is EXACTLY 17.99mm and then check to see how loose it is in the bore.

See here for everything I know about the pinch bolts.

Rocker shaft pinch bolts

Good luck! Your problem sounds like worn out hardware, I would try that first before a new cam box.

[OLD901]

Thanks for your reply John.

I have taken your advice and ordered all new rocker shaft hardware. I will also measure the shafts and their bores.

I have an original / stock 1971 911E coupe with sunroof and S-trim.

Regards,

Norbert.

[BURN-BROS]

Norbert,

If possible please take a picture of the problem area.