Problems with exhaust system in Volvo 740!

Hello!
I must repair exhaust system in my own Volvo 740.

I think that exhaust system is original ( the year 1988 , 400 000km). The
car noisily works and at times
, has a small power (the probably back silencer can be blocked up remainders
of the central silencer and may be to choke the engine, is the truth??).

The exhaust manifold is all conoded, on
exterior and screws holding of him to the cap, are all damage
(conoded)...gasket is conoded.

I think that when I will touch these screws then they will fall off. Is some
possibility, that to screw on afterwards again the exhaust manifold, without
taking out of the engine or openings of the cap??

 

I don't think I understand. It doesn't sound like you need to remove the
exhaust manifold from the engine, and if you can stay away from that you
will be happier. Disconnect the exhaust pipe from the manifold; the screws
may break but you will want to use new ones anyway. Get a new "collector"
gasket for that place, too.

If the exhaust is blocked up, it will show up on the manifold pressure. If
you connect a manifold pressure guage and rev the engine to about 2000 rpm
for a few seconds then release it, the pressure should return to the idle
pressure within two seconds. If it stays high for a couple seconds or
doesn't return to idle pressure for several seconds the exhaust is probably
blocked.

Mike

 

But problem is with screws, because the remainders of collector's screws
will be in engin's cap and I can't put the new screws on this!

I don't understand. What pressure? How can I check that the exhaust is
blocked up??


--

 

I see - you do have to get the manifold off. I've never done it, but maybe
somebody here who has can help you. Normally they heat the nuts red hot with
a torch before trying to turn them, and even then it's not good. The broken
studs can be removed from the cylinder head, but the manifold has to be off
first. I'm sorry this has happened to you. It will be a lot of work.

The vacuum or air pressure in the intake manifold comes from the engine
pumping air through the exhaust. If the exhaust is not blocked, the vacuum
returns quickly because the air is being pumped from the intake to the
exhaust. If the exhaust is blocked the air gets stuck in the exhaust and
when the engine goes back to idle it can't suck the air from the intake
manifold and push it to the exhaust right away.

So if you hook a guage up to the vacuum part of the intake manifold and rev
the engine up then let it go back to idle, the guage will drop quickly if
the exhaust is okay but will try to stay high if the exhaust is blocked.

Mike

 

The leak may not be at the manifold gasket (where the manifold joins the
cylinder head) but rather lower down, where the manifold joins the
exhaust (the flange gasket). These leaks sound very similar. The flange
gasket is much easier to repair.

If it is the manifold gasket and you do break a stud when attempting to
remove the nut, then you must drill out the remaining piece of the
broken stud, and tap the hole for a new stud. If you have never used a
tap and die set, this would not be the place to start learning; take it
to a mechanic.

--
Cheers

Andrew

<--- Remove The NO and SPAM When Replying --->

 

Uzytkownik "Andrew McKenna" :

Yeah,...You've right,...I don't know when the leak is,...maybe I haven't
leak,..but this gasket and the a stud is very old,..and in very bed
condition,..and I'm afraid that it will be damaged in moment when I'll be
for example 500 km from my house or mechanics, so I want to repair it and
put the new gasket and new studs.

I know for 100% that the stud will be broken,..because it's very old and
it's very thin. So in 100% I must put the new studs and drill and tap the
new hole.

Yes, I know it,...but the mechanic have to put out the engine or engine's
head?? or he can do it (drill and tap the new hole for new stud) without put
out the engine's head??

Thanks for all....

 

You can drive a very long way with an exhaust leak. In fact, you can
drive thousands of kilometres with the exhaust completely removed (not
recommended but you can). If it isn't broken, then don't fix it.

The rule is that the only stud that will break is the one that is
hardest to reach. Theoretically if you have a hoist and you remove the
manifold completely, you can replace all of the studs without removing
the head or the motor. In reality in a work shop with a sling it might
be easier to remove the motor complete. Only in a home garage with no
sling or hoist would you need to remove the cylinder head. That would be
a big job.

 

Uzytkownik "Andrew McKenna" :

I think,that all studs will be broken in my car,..they're very old and
conoded, they're very thin.

Yes,..but the problem is, that there will be reminders on studs in the
engine's head, because they will be broken,....I will have to make new hole
and drill it.

I don't know if the mechnics have got special equipment, which can make a
hole and drill it in the head, without put out the engine or head.

Thanks a lot...