Extra long screw for furnace exhaust

Rdenney

Rdenney

Well-known member
Dec 29, 2005
6,270
95
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NoVA
The stock center screw that connects the vent with the exhaust tube on the
Suburban furnace is 3-1/4” by #8. It’s designed for wall thicknesses up to
2-1/4”—about 1/4” less than the side of the coach. The new furnace requires
about that much more screw length because the threaded hole is deeper in
the tube by a bit.

I have completely struck out on finding a #8 sheet metal screw that is
longer than the special 3-1/4” screw Suburban provides. Nothing at McMaster
or any of the other usual suspects. Suburban sells exhaust vent assemblies
for thicker walls (not that anyone keeps them in stock), but the screws
don’t come with them and they don’t seem to be available separately. My
exhaust and intake tubes fully engage the furnace, so I don’t need that
item, but a screw a half-inch longer would be nice.

The furnace isn’t going anywhere and I can live without the screw, I
suppose, but I would prefer to have one in there.

Any ideas?

Rick “who wouldn’t have thought a #8x4” sheet metal screw would be that
hard to find” Denney
--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
 
Rick,

I may be a bit slow but I'm not sure what kind of screw you're looking for and the length. If it's an 8/32 screw you could use some all-thread and cut it to length.

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of Richard Denney
Sent: Monday, April 30, 2018 9:54 PM
To: gmclist
Subject: [GMCnet] Extra long screw for furnace exhaust

The stock center screw that connects the vent with the exhaust tube on the
Suburban furnace is 3-1/4” by #8. It’s designed for wall thicknesses up to
2-1/4”—about 1/4” less than the side of the coach. The new furnace requires
about that much more screw length because the threaded hole is deeper in
the tube by a bit.

I have completely struck out on finding a #8 sheet metal screw that is
longer than the special 3-1/4” screw Suburban provides. Nothing at McMaster
or any of the other usual suspects. Suburban sells exhaust vent assemblies
for thicker walls (not that anyone keeps them in stock), but the screws
don’t come with them and they don’t seem to be available separately. My
exhaust and intake tubes fully engage the furnace, so I don’t need that
item, but a screw a half-inch longer would be nice.

The furnace isn’t going anywhere and I can live without the screw, I
suppose, but I would prefer to have one in there.

Any ideas?

Rick “who wouldn’t have thought a #8x4” sheet metal screw would be that
hard to find” Denney
--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
#8 sheet metal screw

-----Original Message-----
From: Gmclist On Behalf Of Rob Mueller
Sent: Monday, April 30, 2018 10:12 PM
Subject: Re: [GMCnet] Extra long screw for furnace exhaust

Rick,

I may be a bit slow but I'm not sure what kind of screw you're looking for and the length. If it's an 8/32 screw you could use some all-thread and cut it to length.
 
Rick,

Looks to me like you're gonna have to settle for this #10 x 4" SS:

https://www.boltdepot.com/Product-Details.aspx?product=5442

Ken H.

> The stock center screw that connects the vent with the exhaust tube on the
> Suburban furnace is 3-1/4” by #8. It’s designed for wall thicknesses up to
> 2-1/4”—about 1/4” less than the side of the coach. The new furnace requires
> about that much more screw length because the threaded hole is deeper in
> the tube by a bit.
>
> I have completely struck out on finding a #8 sheet metal screw that is
> longer than the special 3-1/4” screw Suburban provides. Nothing at McMaster
> or any of the other usual suspects. Suburban sells exhaust vent assemblies
> for thicker walls (not that anyone keeps them in stock), but the screws
> don’t come with them and they don’t seem to be available separately. My
> exhaust and intake tubes fully engage the furnace, so I don’t need that
> item, but a screw a half-inch longer would be nice.
>
> The furnace isn’t going anywhere and I can live without the screw, I
> suppose, but I would prefer to have one in there.
>
> Any ideas?
>
> Rick “who wouldn’t have thought a #8x4” sheet metal screw would be that
> hard to find” Denney
> --
> Rick Denney
> 73 x-Glacier 230 "Jaws"
> Off-list email to rick at rickdenney dot com
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Rob,

Rick specified "sheet metal screw". If it were an ordinary machine screw
thread, he could easily create any length needed with, as you suggest,
all-thread; or, use a Phillips head+a barrel nut+all-thread.

Ken H.

On Mon, Apr 30, 2018 at 11:12 PM Rob Mueller
wrote:

> Rick,
>
> I may be a bit slow but I'm not sure what kind of screw you're looking for
> and the length. If it's an 8/32 screw you could use some all-thread and cut
> it to length.
>
> Regards,
> Rob M.
> The Pedantic Mechanic
> Sydney, Australia
> AUS '75 Avion - The Blue Streak TZE365V100428
> USA '75 Avion - Double Trouble TZE365V100426
> USA '77 Kingsley - TZE 267V100808
>
>
>
> -----Original Message-----
> From: Gmclist [mailto:gmclist-bounces] On Behalf Of
> Richard Denney
> Sent: Monday, April 30, 2018 9:54 PM
> To: gmclist
> Subject: [GMCnet] Extra long screw for furnace exhaust
>
> The stock center screw that connects the vent with the exhaust tube on the
> Suburban furnace is 3-1/4” by #8. It’s designed for wall thicknesses up to
> 2-1/4”—about 1/4” less than the side of the coach. The new furnace requires
> about that much more screw length because the threaded hole is deeper in
> the tube by a bit.
>
> I have completely struck out on finding a #8 sheet metal screw that is
> longer than the special 3-1/4” screw Suburban provides. Nothing at McMaster
> or any of the other usual suspects. Suburban sells exhaust vent assemblies
> for thicker walls (not that anyone keeps them in stock), but the screws
> don’t come with them and they don’t seem to be available separately. My
> exhaust and intake tubes fully engage the furnace, so I don’t need that
> item, but a screw a half-inch longer would be nice.
>
> The furnace isn’t going anywhere and I can live without the screw, I
> suppose, but I would prefer to have one in there.
>
> Any ideas?
>
> Rick “who wouldn’t have thought a #8x4” sheet metal screw would be that
> hard to find” Denney
> --
> Rick Denney
> 73 x-Glacier 230 "Jaws"
> Off-list email to rick at rickdenney dot com
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
This is the screw that goes through the middle of the exhaust port and
screws through a flat piece of sheet metal welded across the diameter of
the exhaust tube on the furnace. The original is a Number 8 Sheet Metal
Screw, by 3-1/4" long. I suspect Suburban had those made--it's a
non-standard size. It's not threaded for 8-32 machine screw threads, and I
suspect those would not be strong enough in this material. The Suburban is
a 75%-efficient forced-combustion-air heat exchanger and the air that comes
out of that exhaust will be quite warm with a lot of propane byproducts,
particularly rather acidic moisture. That screw will need deep, strong
threads to work even when the stuff starts to corrode a bit.

The screw has a standard Phillips pan head.

Ken, I could use a #10 screw, but then I'm committed to it. That appears to
be my only option if nobody can think of an alternative. The through hole
on the vent will probably be too small, and the head may need to be ground
to fit in the recess. I was hoping to avoid all that. My scratch-n-dent
furnace didn't come with a vent and I'm using the old one that is probably
original to the coach (though it's not in the original location). A larger
screw would not have worked on the old furnace--the screw threaded into a
vane with hole made by forming a tube along its width. A bigger screw
wouldn't work there. The new one turns the vane on its side (more
restrictive, surprisingly) and has a hole drilled in it for the screw.

Rick "McM has those 18-8 4" #10 screws, too" Denney

> Rick,
>
> What sort of head is on it?
> Could you use #8 all-thread?
>
> Richard
> --
> '77 Birchaven TZE...777
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
 
Rick,

Wait until you get to Bean Station and you'll have LOTS of suggestions on how to fix the problem! ;-)

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of Richard Denney
Sent: Tuesday, May 1, 2018 1:39 AM
To: gmclist
Subject: Re: [GMCnet] Extra long screw for furnace exhaust

This is the screw that goes through the middle of the exhaust port and
screws through a flat piece of sheet metal welded across the diameter of
the exhaust tube on the furnace. The original is a Number 8 Sheet Metal
Screw, by 3-1/4" long. I suspect Suburban had those made--it's a
non-standard size. It's not threaded for 8-32 machine screw threads, and I
suspect those would not be strong enough in this material. The Suburban is
a 75%-efficient forced-combustion-air heat exchanger and the air that comes
out of that exhaust will be quite warm with a lot of propane byproducts,
particularly rather acidic moisture. That screw will need deep, strong
threads to work even when the stuff starts to corrode a bit.

The screw has a standard Phillips pan head.

Ken, I could use a #10 screw, but then I'm committed to it. That appears to
be my only option if nobody can think of an alternative. The through hole
on the vent will probably be too small, and the head may need to be ground
to fit in the recess. I was hoping to avoid all that. My scratch-n-dent
furnace didn't come with a vent and I'm using the old one that is probably
original to the coach (though it's not in the original location). A larger
screw would not have worked on the old furnace--the screw threaded into a
vane with hole made by forming a tube along its width. A bigger screw
wouldn't work there. The new one turns the vane on its side (more
restrictive, surprisingly) and has a hole drilled in it for the screw.

Rick "McM has those 18-8 4" #10 screws, too" Denney

> Rick,
>
> What sort of head is on it?
> Could you use #8 all-thread?
>
> Richard
> --
> '77 Birchaven TZE...777
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
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What Rob said. I can think of several ways to end up with a #8 sheet metal end for the vent.

--johnny
--
76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
"I forgive them all, save those who hurt the dogs. They must answer to me in hell" - ol Andy, paraphrased
 
Could you put a speed clip (spring nut) over the sheet metal bracket at the hole and use a long machine screw instead of the specialty sheet metal screw?
 
Try a SS wood screw. If the hole it threads into has not been previously deformed by a screw, run a shorter sheet metal screw through the hole first to form some threads. It wouldn’t be the first time someone used a wood screw on sheet metal :)

Les Burt
Montreal
'75 Eleganza 26'

>
> Could you put a speed clip (spring nut) over the sheet metal bracket at the hole and use a long machine screw instead of the specialty sheet metal screw?
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
#8 wood screws that are 4” long are not exactly thick on the ground. And
the longest ones have flat heads, which is a detail but the hole is not
countersunk.

Johnny, I’m all ears. Try thinking out loud. But I’m not going to weld two
screws together. :) that juice doesn’t seem worth the squeeze.

I’ve ordered some 4” #10 screws to see what it would take to make it work.
That might be easier than trying to convert to an 8-32 thread using a
threaded rod.

I did also consider making a J hook out of 6-32 or 4-40 threaded rod, and
haven’t given up on that idea.

Rick “who ordered from McMaster late last night so they should be here any
minute :)” Denney

> Try a SS wood screw. If the hole it threads into has not been previously
> deformed by a screw, run a shorter sheet metal screw through the hole first
> to form some threads. It wouldn’t be the first time someone used a wood
> screw on sheet metal :)
>
>
> Les Burt
> Montreal
> '75 Eleganza 26'
>
>
> > On May 1, 2018, at 8:50 AM, Dave Stragand

> >
> > Could you put a speed clip (spring nut) over the sheet metal bracket at
> the hole and use a long machine screw instead of the specialty sheet metal
> screw?
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
 
Justin, Dave also suggested that. It would require drilling out the hole
that the screw threads into and then fitting a nut-clip. But that replaces
the hole, when there's really nothing wrong with the current hole.

The #10 screw is the right answer--I just test fitted a shorter #10 screw
in the vent cover, and the existing hole is big enough. I don't have to
drill it out (which would remove the plating on the inside of that hole).
I'll just use the 4" #10 screws I have on order. They should be here by
tomorrow morning--maybe in time before we leave for Bean Station, maybe
not. We probably won't make the whole drive in one day, though--I have a
conference call in the middle of the day--and we are planning to boondock
at the Cracker Barrel in Roanoke Wednesday night. That will give McM's
shipper at least part of the day to show up.

Rick "just checking that sufficiently long #8 screws really are not readily
available" Denney

> Rick,
> Can you put in a nutsert or a spring clip and then use all thread?
> --
> Justin Brady
> http://www.thegmcrv.com/
> 1976 Palm Beach 455
>
>
>

--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
 
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