'95 Odyssey Exhaust Leak

My '95 Odyssey suddenly began sounding like an airplane, from the front of
the engine, which I suspect is an exhaust leak. It seems to be especially
bad when the engine is cold, but improves quickly as it warms. I tried
pulling the exhaust manifold heat shield off to see if anything cracked, or
view any other evidence of the problem. Strange thing happened. One of the
two top bolts unscrewed about three turns without much trouble, then began
to really tighten up. Tighten up enough to make me worry about stripping
something or breaking the bolt head off. I said the heck with it and
decided to look at it another day. Now, the screw will only turn in about
one turn, before tightening up and bottoming against the shield! How can
that happen? I left it that way, and now the exhaust leak sounds worse than
ever. From a parts breakdown, this is just a bolt screwing into a boss on
the manifold. How can I get the bolt out?

Thanks,

- Phil

 

Heat it up before you reef on it.

And don't burn yourself....

t

 

Have you tried some penetrating oil like PB Blaster on it? Unscrew as far
as it will go without binding hard; spray some Blaster on the threads and
screw back in; unscrew again and repeat several times to get the oil worked
into the threads. Each time you unscrew, it should come out a little
further until you feel it's ready to come all the way. It sounds like that
boss is open on the inner end and the bolt is corroded where it sticks
through - see if you can get some spray on that inner end of the bolt but
it'll likely be impossible to be aim accurately.

Rgds, George Macdonald

"Just because they're paranoid doesn't mean you're not psychotic" - Who, me??

 

Not tried penetrating oil, but will. What I can't figure out is why I can't
screw it BACK in. I can understand your point on exposed corroded threads
not wanting to come through the threaded hole, but why not screw back in?
Also, I looked at the length of the boss and the bolt in the diagram, and it
looks to me that the boss is quite a bit longer than the bolt, meaning all
threads were engaged.

I'll try the oil and also see if it moves more easily when hot.

- Phil

me??

 

Well, I tried turning the bolt when the engine was warm, and it moved more
easily. But, with moderate torque, the bolt head sheared off. Another day
of never ending failures and repairs for this thing that sounds like a B-17.

- Phil

 

Hang in there. Are you aware that drilling an appropriately sized hole in a
sheared bolt and then applying a screw extractor is often successful?

I don't think those heat shield bolts are high grade, meaning they should drill
pretty easily.

You can buy a screw extractor set for under $10 at places like Autozone. I think
I paid $7 last year for one. Used it successfully again yesterday, as a matter
of fact. The extractor is a high strength steel left-hand threaded screw. One
turns it COUNTER-clockwise to advance it into the drilled hole. This CCW action
and the left-hand thread tends to unscrew the outer bolt that one is trying to
remove.

Hopefully you can get a power drill into the region where the bolt is.

If you can't, I'd bet an independent shop could for under $20.

FWIW, the Majestic online parts site says this is a 14 mm bolt.

Start soaking any other exhaust bolts you think you'll have to remove with PB
Blaster.

I removed my 91 Civic's exhaust manifold header pipe the other week. (This was
part of getting at the oil pan's bolts, because I was replacing the oil pan
gasket.) All bolts came free, but I had to use torque extension arms and PB
Blaster here and there. Also, one of the three header pipe nuts had rusted from
a 14 mm socket to a 13 mm socket (fit with a bit of pounding). That took an
afternoon to figure out right there.

When re-assembling, I replaced several exhaust system nuts and anti-seized
everything. A $3 tube of anti-seize (available at Autozone) will go a long way
and may spare a lot of misery later.

I think replacement bolts that clearly are subjected to high temperatures should
be material class 10.9 (which is the metric equivalent of SAE Grade 8). Or, to
put it another way, buy the really expensive version of the nuts/bolts. Someone
else will hopefully confirm, as I'm a bit new to nut and bolt material
requirements for automobiles.

I figured the heat shield bolts where only material class 8.8 (= approx. SAE
Grade 5). They're quite a bit cheaper than the 10.9 equivalent.