I have a 96 XJS with the AJ16, but this question applies to any model year or engine, I believe.

I ended up reinastalling the new exhaust manifolds. I torqued the manifold nuts back up to 50Nm, which is a lot more than my standard torque wrench could handle, so I had to borrow one, without any drama.

The downpipe nuts, not so much. I was able to torque the front manifold to the required 30Nm, but I ended up stripping the copper locknuts on the rear manifold downpipe.

Problem is, I don't know if the problem is bad access, or a bad donut. One slid on with a lot of effort. I checked to make sure it fit in the manifold flange and everything.

I did not do the same with the second donut, but it slid on the downpipe without much effort at all. Don't ask me why I did not test it the same way. The rear manifold downpipe is the one that had the easy-to-install donut, which is the one that has the stripped new lockbolts.

The front downpipe assembly is tight. There is no gap between the manifold and the downpipe. The rear manifold has a gap where you can see the donut. Not much, but it's not tight.

So far, no exhaust is leaking from the assembly.

The question is, if I pull the assembly apart, will I need two new donuts?

 

Vee,

50Nm is only 37ft lb. Even most basic 1/2" torque wrenches can handle 100+ ft lb. Are you sure you're reading the scales correctly?

Sometimes you can reuse the sealing rings. It depends if they deformed on installation. Unfortunately, you won't know until you take it apart.

Paul

 

I own a 3/8" torque wrench.

Never thought I'd need a 1/2" model.

That being said, the one I borrowed was also a 3/8" model. It was a SnapOn, I own a Craftsman.

I have to assume to front ones deformed already. Looks like I may be ordering two more.

I do want to add, that I believe an 02 Sensor Orientation is in order after this work. (I did remove each 02 sensor to apply some nickel antiseize once I found out the shop that initially installed them didn't use any)

 

Vee,

If you do use Copperease, or similar on the O2 boss in the downpipe, be very careful when you fit the sensors that NO compound gets on the nose of the sensor as it can really mess it up. Take them out and make sure the nose of the sensor is perfectly clean.

Unless your sensors are less than 2 years old, I would take the opportunity to replace them.

Good luck

Paul

 

I wanted to share something I learned when reassembling my exhaust manifolds.

The service manual directs you to install the downpipes once the manifolds have been tightened up. I found that the best way it make sure the downpipes can be alighted with the manifolds is to leave the manifolds loose on the studs, without any nuts.

That's the time to attach the Downpipe nuts and torque them to the specified 30Nm.

Once tightened then secure the manifolds to the block, tightening them to 50Nm.

The loose manifolds allow the downpipes to force the manifolds to perfectly align with each other.

I hope this helps someone in the future.