I may need to replace the studs which bolt the exhaust manifold to the header pipe on a 1993 volvo 240 exhaust and am looking for advice. I am going to try to case the threads first but think I may need to replace the studs and have a few questions:

0.5. What is the thread on the studs?

1. Would I need to remove the manifold to replace the studs?

2. How much risk is there of damaging the engine or studs that the exhaust manifold bolts to the engine if I try to remove the manifold?

3. Should I plan to replace the exhaust manifold gasket up by the engine if I need to remove the manifold?

4. How do you replace the exhaust manifold studs that bolt the exhaust manifold to the header pipe?

5. Does anyone know if the torque is critical when replacing the O2 sensor on the cat converter?

Any general tips for this job.

thank you

 

I have a 1993 240 wagon and I haven't had to replace the studs but have replaced the downpipe and just took off the manifold for a head gasket/cylinder head job.

Are you sure you need the studs? and not just a gasket leaking?

0.5 = I believe the thread is an 8 X 1.25, FCP Euro carries them Volvo Exhaust Stud (Manifold to Header Pipe) Bosal 258-953 | FCP Euro

1 = could probably get away without taking the manifold off, but always easier if you do.

2 = no real risk, just use lots of PB Blaster and let it soak, should come off with no issues

3 = yes, always replace a gasket seal you break

4 = they are just like the studs on the engine for the manifold (see the FCP link), basically screw one end into the flange with some thread locker and then bolt the other side up

5 = the Bentley book lists the torque for "oxygen sensor to exhaust manifold" as 40 ft-lb, I am assuming they assume exhaust manifold continues until the cat. Without the special oxygen sensor socket (can get one at Harbor Freight for $6) it would be tough to get exact torque.

I had to replace a couple studs on the engine for the exhaust manifold on the new cylinder head I bought, pretty easy. For the old ones, lots of PB Blaster and let it soak and they should come out with no problem, a little heat can't hurt either.

Make sure you use a new gasket for the manifold/downpipe flange connection too.

Hope that helps.

 

Thanks thats really helpful info. Makes the job sound doable.

I have never installed/removed a stud before. How do you apply torque to it where as it has no flange to put a wrench on and threads down the whole length? I soaked it with PB blaster and have a oxyacetylene torch for heat if need be.

thank you

found a utude vodeo on this

 

I had no trouble with the manifold ones on the engine, I haven't done the ones you're talking about. Getting them out is easy since you're not saving them, vise grips turned them right out.

I tightened them by hand first, turned them best I could with vise grips without hurting the thread, and as you tighten the nut down, since the threads all go the same way, once the bolt hits the flange it will pretty much auto tighten it until it stops, just don't over torque it.

It's hard to see on the picture of the stud but there is almost a little stop mark or small area with no threads so it will stop going into the flange at some point.

Make sure you compare it to the old stud, one side is "shorter" than the other, the shorter thread part goes into the flange and the side with the longer threaded section goes with the nut.

 

Thank you for the tips. I was able to chase the threads using a thread die. The threads were 10 1.5 on the manifold studs that fixed the header pipe to the manifold. The exhaust is now on and the car is quite. If I were to ever do this job again I'd plan on chasing the threads.

I ran into a new problem. The bosch O2 sensor I bought is the California emission variety and has a different plug on it than the one that was on the car. The sensor appears the same but the California sensor has the same female connector that the car has. I could splice the wires together to connect the California emission sensor to the other 49 state car but I am hesitant to do this. Does anyone know if the California emissions O2 sensors is truly different from the other 49 state sensor beyond the connectors. My guess is yes otherwise why would there be two different plugs but figured I'd check. Will driving 100 miles without the o2 sensor damage my new cat converter?

 

The sensors should be the same, but these days with all the varieties, who knows... I use Ford O2 sensors so I always splice them into the Volvo plugs. You shouldn't drive w/out the sensor: bad for the car, and it will make a helluva racket. And don't worry about torquing it, just tighten it well, it's not going anywhere.