camshaft binding with re-torque / broken stud

[burgermeister]

I torqued up my heads yesterday, and had a camshaft bind. After re-torque sequence #4, it spins freely. I'm reusing the pots & heads in their original locations, and nothing was machined. It follows that the 911 cam tower is a very finicky thing.

This leads me to think that having a broken head stud might cause the camshaft to bind? It's not one of the consequences typically discussed.

It further leads me to think that re-torqueing the heads after 1000 miles as suggested in Wayne's book is at least somewhat perilous (not castle Anthrax perilous unfortunately). The lubricant will have burned off the studs & nuts, making the torque / clamp load relationship much more random. And since the initial torque sequence made the difference between a binding cam and a freely rotating one, how can I verify that the re-torque sequence won't make the camshaft bind?

Were the 911 heads originally re-torqued? I don't recall it being listed in my service booklet.
Any experience with not re-torqueing the heads?

[matt demaria]

Normally you don't retorque. I think the engines were made with a "set it and forget it' philosophy. If you have a broken stud you won't be able to torque. If the stud is pulling you will be able to feel it in final torque.
By the way try using an electronic torque wrench you can feel the change in torque on the other studs as one is tightened. It opens a new world on torquing.

[cgarr]

most times after a broken stud, if the head has been working against the cylinder it can change the dimensions and will need to be surfaced.

[Flat6pac]

Im a Carrera, the torque for the heads is 15ft# + 90 degrees where in earlier cars it was 25ft#. with a need to retorque.
Bruce

[Eagledriver]

Re-torquing is not a factory requirement. That being said I've found loose nuts on my race car after a short time. So to me a re-torque is a good idea. Since you have already torqued the nuts up to spec and the cams don't bind, when you re-torque you are really basically checking that they haven't come loose. This should not cause a bind.

-Andy

[burgermeister]

cgarr, I was just thinking iof driving a car with a broken stud - seems like it could be driving a car with a binding camshaft, which may cause damage beyond the head and cylinder interface. All my Dilavars were pristine looking and intact, though they still got replaced with steel.

Flat6pac, that is what the Bentley says (I remember 11 ft*lb, but memory is fuzzy & bentley in the garage), but given some of their other torque values (ie, wrong torque values), I ignored them and went with Waynes book (25 ft*lb)... the 90 degrees would add a LOT of torque to some of the studs.

Eagledriver, I suppose if some of them are quite loose the camshaft would likely already be binding anyway, so no harm tightening them back up.... I can follow that logic. Though the pattern of torqueing the nuts up to spec made the difference between binding and free cams ... I sort of remember what I did ... but only sort of.