Hey everyone, I'm in the middle of installing the heads on my XJR and the factory service manual says to use a new bolt when installing the cam sprockets. For the life of me I can't see any reason why you couldn't just reuse the bolt. What am I missing? Is it ok to reuse the bolt, or do I really need to get a new one?

 

I reused the bolts on my SC engine (Super V8) as they are not torqued to yield. The bolts are Grade 12.9 so the Jaguar specified torque of 115-125 Nm is well below their yield (stretch) limit and even below the standard torque specified for such bolts - 140 Nm. Accordingly, their stretch point is at torques higher than 140 Nm; with some safety margin, this could be at some 150-160 Nm.

The hollow bolts used on VVT engines are another matter. First, they are weaker because they are hollow and second, they are made of lower steel grade (10.9) which, if not hollow, allows torquing to 115 Nm. The originally specified torque for the hollow bolts was wrongly stated as 115-125 Nm (same as for the full section bolts of Grade 12.9) and were later revised to 85-90 Nm, probably after some cases of broken bolts during torquing to 115-125. It appears that the advice to use new bolts applies to the hollow bolts (as they would have been stretched during original torquing to 115-125) but Jaguar couldn't be bothered to provide separate info for the two different types of bolts.

 

So it's only the NA cars that have the hollow bolts? The SC engines don't have the VVT so they have the stronger solid bolts?

 

Yes

 

Here are some TSBs (that no one reads).

bob