Phil Stewart wrote
......."For the past couple of weekends I've been trying to get the leak=
s
at my
OEM exhaust manifolds fixed but have not been successful yet."..........
.........."I've removed the manifolds, had them ground flat at their port=
flanges,
inspected the heads which look to be in good shape without pitting
around the exhaust ports, repaired one broken center port bolt by
drilling it out of the head and re-tapping the hole, installed a set of
new SCE copper gaskets from Bushkirk's (embossed side out and without
RTV sealant), and, using new bolts and thick washers with Never Seize,
carefully torqued the manifolds in place with a torque wrench set at 25
ft.lbs. Next I started the engine and after it warmed up listened for
leaks using a stethoscope. Unfortunately, both sides had leaks at the
bottom of the center ports---arrggggh!. I applied more torque (35
ft-lbs) to the three center port bolts which seemed to lessen the leaks
somewhat but did not stop them."...........
Phil
I have been watching with interest the discussions about these leaks.
Judging by the poor workmanship around the manifolds on my coach
it was obvious that the previous owner of my coach had some problems
in this regard. After purchase of my coach last year I only put a few
hundred miles on it before my drivers side manifold started to leak
above the front exhaust port.
His past repair included many extra washers under the bolt heads to make =
up
for dirty and rusty threads.
I removed the manifolds, cleaned up the old composite gaskets off all
surfaces,
and ran a tap through all the bolt holes.
Although the exhaust manifolds were not pitted, I would have sent them in=
for
resurfacing. The drivers side was not flat. It was dished lengthwise by
about 10 thou.
I checked the drivers side head and found it crowned lengthwise about the=
same
amount. Since at this time I am trying to avoid pulling the heads I thoug=
ht
there
would be little point in machining the manifolds.
Both the manifold and the head on the passengers side were flat and witho=
ut
pits
(obviously his best side)
I decided to try the copper gaskets and decided to use the high temp
silicone,
new bolts, heavy washers the heavy lock washers and the never sieze as
well.
The gaskets I got were for all the Olds engines in this series from 307 t=
o
455.
The gaskets had a divider between the center 2 exhaust ports although on =
my
engine the center exhaust ports are not divided out as far as the manifol=
d
(I suspect
the ports may have been smaller on the smaller engines?).
Since this copper was going to do nothing but interfere with exhaust flow=
I
trimmed this section out. With this section gone it became clear that the=
raised
portion of the gasket followed the path of this nonexistant center divide=
r.
Assembled without something to block this void I suspect the manifold wou=
ld
rapidly leak just where you reported your problem.
Were your gaskets for the divided center ports?
If so I suggest that when you take the manifolds off you trim away the
useless part
of the gasket and assemble again with high temp silicone on both sides of=
the
gasket.
I didn't find a torquing pattern for the manifolds so I worked the torque=
up slowly
working first with all the bolts that are in a horizontal line from the
middle out. I left
the upper center bolt for last. I felt this might prevent the manifold fr=
om
rotating
up (the drivers side on mine also had a measurable vertical crown on the
head)
I only torqued mine to 18 pounds and will let the silicone set. I don't
want the
silicone to be thick but since silicone works better in compression than
tension
I thought I would let it cure for a few days before finally tightening to=
25 ft lbs.
I wish that I could say "it worked for me" but the best I can say is
"to soon to tell" and "I hope it works"
On the subject of headers, although I will probably go there when the
budget permits,
I have never experienced a reduction in exhaust maintenance as a result o=
f
installation
of headers. I think any reduction in maintenance would come from work
completed
at the same time to create flat surfaces.
Good luck
Regards
Gary Zingle
1973 GMC 26 foot
......."For the past couple of weekends I've been trying to get the leak=
s
at my
OEM exhaust manifolds fixed but have not been successful yet."..........
.........."I've removed the manifolds, had them ground flat at their port=
flanges,
inspected the heads which look to be in good shape without pitting
around the exhaust ports, repaired one broken center port bolt by
drilling it out of the head and re-tapping the hole, installed a set of
new SCE copper gaskets from Bushkirk's (embossed side out and without
RTV sealant), and, using new bolts and thick washers with Never Seize,
carefully torqued the manifolds in place with a torque wrench set at 25
ft.lbs. Next I started the engine and after it warmed up listened for
leaks using a stethoscope. Unfortunately, both sides had leaks at the
bottom of the center ports---arrggggh!. I applied more torque (35
ft-lbs) to the three center port bolts which seemed to lessen the leaks
somewhat but did not stop them."...........
Phil
I have been watching with interest the discussions about these leaks.
Judging by the poor workmanship around the manifolds on my coach
it was obvious that the previous owner of my coach had some problems
in this regard. After purchase of my coach last year I only put a few
hundred miles on it before my drivers side manifold started to leak
above the front exhaust port.
His past repair included many extra washers under the bolt heads to make =
up
for dirty and rusty threads.
I removed the manifolds, cleaned up the old composite gaskets off all
surfaces,
and ran a tap through all the bolt holes.
Although the exhaust manifolds were not pitted, I would have sent them in=
for
resurfacing. The drivers side was not flat. It was dished lengthwise by
about 10 thou.
I checked the drivers side head and found it crowned lengthwise about the=
same
amount. Since at this time I am trying to avoid pulling the heads I thoug=
ht
there
would be little point in machining the manifolds.
Both the manifold and the head on the passengers side were flat and witho=
ut
pits
(obviously his best side)
I decided to try the copper gaskets and decided to use the high temp
silicone,
new bolts, heavy washers the heavy lock washers and the never sieze as
well.
The gaskets I got were for all the Olds engines in this series from 307 t=
o
455.
The gaskets had a divider between the center 2 exhaust ports although on =
my
engine the center exhaust ports are not divided out as far as the manifol=
d
(I suspect
the ports may have been smaller on the smaller engines?).
Since this copper was going to do nothing but interfere with exhaust flow=
I
trimmed this section out. With this section gone it became clear that the=
raised
portion of the gasket followed the path of this nonexistant center divide=
r.
Assembled without something to block this void I suspect the manifold wou=
ld
rapidly leak just where you reported your problem.
Were your gaskets for the divided center ports?
If so I suggest that when you take the manifolds off you trim away the
useless part
of the gasket and assemble again with high temp silicone on both sides of=
the
gasket.
I didn't find a torquing pattern for the manifolds so I worked the torque=
up slowly
working first with all the bolts that are in a horizontal line from the
middle out. I left
the upper center bolt for last. I felt this might prevent the manifold fr=
om
rotating
up (the drivers side on mine also had a measurable vertical crown on the
head)
I only torqued mine to 18 pounds and will let the silicone set. I don't
want the
silicone to be thick but since silicone works better in compression than
tension
I thought I would let it cure for a few days before finally tightening to=
25 ft lbs.
I wish that I could say "it worked for me" but the best I can say is
"to soon to tell" and "I hope it works"
On the subject of headers, although I will probably go there when the
budget permits,
I have never experienced a reduction in exhaust maintenance as a result o=
f
installation
of headers. I think any reduction in maintenance would come from work
completed
at the same time to create flat surfaces.
Good luck
Regards
Gary Zingle
1973 GMC 26 foot
