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Whitley
Samba Member
Joined: January 04, 2010
Posts: 158
Location: Smiths Grove, KY
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 Posted: Sun Mar 21, 2010 7:00 pm Post subject: 76 Preheat Question |
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I have an early 76 Bay 2.0 with the 6 pin AFM. I'm running stock heat exchangers with an extractor muffler. This leaves me with no preheat and while I understand what the preheated air does, I don't really understand how the stock preheat pipe worked with the two holes in the rear sheet metal. Was air drawn from the engine bay through the left port via hose down into the preheat pipe and then from the right side of the preheat pipe up to the air intake duct?
Since the bus is nearing the end of extensive repair and restoration, and I've spent tons of time trying to replace everything the POs removed, I could use some advice on the importance of the preheat system and how I could fab one to do the job. Otherwise I will simply seal the holes.
Thanks for the input-
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Third and Sixth owner of a 76 Westy
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busdaddy
Samba Member
Joined: February 12, 2004
Posts: 51144
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Sun Mar 21, 2010 7:50 pm Post subject: |
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Welcome, indeed the 75-76 preheat was a second tube piggybacked on the crossover pipe, but FI really doesn't need preheated air as there is no venturi in the system to ice up. Unless you are willing to fabricate a tube that can heat the air to a temperature that will open the preheat thermostat in a few minutes you're best option is to block the holes and disable the thermostat in the airfilter, it's another potential vacuum leak that L-jet doesn't like much. You can put a dummy hose on if you want it to look stock.
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Whitley
Samba Member
Joined: January 04, 2010
Posts: 158
Location: Smiths Grove, KY
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| Posted: Mon Mar 22, 2010 6:07 am Post subject: |
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Thanks Busdaddy- I'll seal it up and disable the thermostat flap.
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Third and Sixth owner of a 76 Westy
What I do- www.mwhitley.com
Dig Americana Music? www.markwhitleyband.com |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21518
Location: Oklahoma City
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| Posted: Mon Mar 22, 2010 9:59 am Post subject: Re: 76 Preheat Question |
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| Whitley wrote: |
I have an early 76 Bay 2.0 with the 6 pin AFM. I'm running stock heat exchangers with an extractor muffler. This leaves me with no preheat and while I understand what the preheated air does, I don't really understand how the stock preheat pipe worked with the two holes in the rear sheet metal. Was air drawn from the engine bay through the left port via hose down into the preheat pipe and then from the right side of the preheat pipe up to the air intake duct?
Since the bus is nearing the end of extensive repair and restoration, and I've spent tons of time trying to replace everything the POs removed, I could use some advice on the importance of the preheat system and how I could fab one to do the job. Otherwise I will simply seal the holes.
Thanks for the input- |
Are you talking about the vertical metal chimneys coming from the heat exhangers....one on each side.....about 2 inches or so from the joint where the heat exchangers connect to the muffler? If so...those are generally not heat risers for intake. They are to connect to the auxiliary fan that pushes air into the heat exchangers on models with gas furnace. Ray |
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busdaddy
Samba Member
Joined: February 12, 2004
Posts: 51144
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Mon Mar 22, 2010 10:36 am Post subject: |
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I'm pretty sure he's referring to the 75-76 only preheat system, the tube is #24 here:
And the holes in the tin for it are these:
BTW all type 4 powered busses have the booster fan tubes, gas heater or not.
_________________
Rust NEVER sleeps and stock never goes out of style.
Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
Stop dead photo links! Post your photos to The Samba Gallery!
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Whitley
Samba Member
Joined: January 04, 2010
Posts: 158
Location: Smiths Grove, KY
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| Posted: Mon Mar 22, 2010 10:51 am Post subject: |
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I'm talking about Part #24 on the diagram- which does not exist when you use the aftermarket muffler/tailpipe combo Bus Depot and others offer. I have the chimney tubes from the heat exchangers to the heater booster fan no problem. I was just concerned that with the 6 pin AFM and no intake air temp sensor, how vital the preheated intake air was for good operation. I'm assuming its not an issue as long as the ambient air temp is above 68 degrees F, and even when its cold outside, the engine bay warms up relatively fast, so the the intake air is warm anyway. It will just require disabling the flap on the air intake duct that was specific to the 75-mid 76 buses. After all my searching, I've never found any info about this issue, so I wanted to throw it out there for those of us who have this specific, overly complicated exhaust/intake set-up.
Thanks-
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Third and Sixth owner of a 76 Westy
What I do- www.mwhitley.com
Dig Americana Music? www.markwhitleyband.com |
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 12722
Location: on a bike ride somewhere
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| Posted: Thu Mar 03, 2016 12:18 am Post subject: Re: 76 Preheat Question |
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Hi folks,
| busdaddy wrote: |
| …your best option is to block the holes and disable the thermostat in the airfilter, it's another potential vacuum leak that L-jet doesn't like much. You can put a dummy hose on if you want it to look stock. |
So there's a thermostat in the air cleaner AND a vacuum-actuated flap? Where is the vacuum takeoff point? (Manifold? Ported?) Any pictures of the system other than generic engine shots?
Thanks!
Robbie
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Wildthings
Samba Member
Joined: March 13, 2005
Posts: 50348
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| Posted: Thu Mar 03, 2016 12:43 am Post subject: Re: 76 Preheat Question |
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| I have the early '76 Bus FI system system transplanted onto my 411, it has always worked fine without having the preheat. |
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busdaddy
Samba Member
Joined: February 12, 2004
Posts: 51144
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Thu Mar 03, 2016 8:26 am Post subject: Re: 76 Preheat Question |
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| asiab3 wrote: |
Hi folks,
| busdaddy wrote: |
| …your best option is to block the holes and disable the thermostat in the airfilter, it's another potential vacuum leak that L-jet doesn't like much. You can put a dummy hose on if you want it to look stock. |
So there's a thermostat in the air cleaner AND a vacuum-actuated flap? Where is the vacuum takeoff point? (Manifold? Ported?) Any pictures of the system other than generic engine shots?
Thanks!
Robbie |
I've seen both vacuum operated preheat flaps and wax thermostat ones, could have been a mashup of later beetle airfilter parts adapted to the bus, can't say for sure. The vacuum would likely Tee into the supply line for the electric EGR.
_________________
Rust NEVER sleeps and stock never goes out of style.
Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
Stop dead photo links! Post your photos to The Samba Gallery!
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 12722
Location: on a bike ride somewhere
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| Posted: Thu Mar 03, 2016 2:25 pm Post subject: Re: 76 Preheat Question |
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Ok that makes sense. Does the same air filter also have an EEC valve? Wouldn't it be nice to have two vacuum leaks in the same spot.... 
Robbie
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busdaddy
Samba Member
Joined: February 12, 2004
Posts: 51144
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Thu Mar 03, 2016 2:28 pm Post subject: Re: 76 Preheat Question |
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| asiab3 wrote: |
Ok that makes sense. Does the same air filter also have an EEC valve? Wouldn't it be nice to have two vacuum leaks in the same spot....
Robbie |
Why yes, yes it does, the more the merrier. 
_________________
Rust NEVER sleeps and stock never goes out of style.
Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
Stop dead photo links! Post your photos to The Samba Gallery!
Слава Україні! |
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airschooled
Air-Schooled
Joined: April 04, 2012
Posts: 12722
Location: on a bike ride somewhere
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| Posted: Thu Mar 03, 2016 3:17 pm Post subject: Re: 76 Preheat Question |
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| busdaddy wrote: |
| asiab3 wrote: |
Ok that makes sense. Does the same air filter also have an EEC valve? Wouldn't it be nice to have two vacuum leaks in the same spot....
Robbie |
Why yes, yes it does, the more the merrier. |
I remember there being one 3.5mm hose connected, but I didn't remove the air cleaner to check for others. I'll report back when I'm stumped Saturday night when I pick it up...
Thanks 
Robbie
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BennyynneB
Samba Member
Joined: November 16, 2010
Posts: 10
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| Posted: Thu May 24, 2018 3:09 am Post subject: Re: 76 Preheat Question |
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| I just recently re finished and reinstalled a transverse crossover pipe for a 75 FI. |
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BennyynneB
Samba Member
Joined: November 16, 2010
Posts: 10
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| Posted: Thu May 24, 2018 3:10 am Post subject: Re: 76 Preheat Question |
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BennyynneB
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Joined: November 16, 2010
Posts: 10
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| Posted: Thu May 24, 2018 3:11 am Post subject: Re: 76 Preheat Question |
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BennyynneB
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Joined: November 16, 2010
Posts: 10
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| Posted: Thu May 24, 2018 3:12 am Post subject: Re: 76 Preheat Question |
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BennyynneB
Samba Member
Joined: November 16, 2010
Posts: 10
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| Posted: Thu May 24, 2018 3:12 am Post subject: Re: 76 Preheat Question |
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| I just recently re finished and reinstalled a transverse crossover pipe for a 75 FI. |
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