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Old 03-15-2004, 10:49 PM   #1
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The exhaust manifolds are off! Now what?

I must have been due for a little luck. After a week of pounding, pulling and pressing four u-joints and two carrier bearings, replacing a rear trans seal and parking brake parts and well...if you own an AS MH you know what I mean. It was time for the dreaded task that strikes fear in the hearts of the owners of old P30 motorhomes with tired 454's everywhere; REMOVING THE EXHAUST MANIFOLDS. (insert Psycho sound track here)

I had discovered, while repairing another exhaust problem, that two air injectors on the driver's side and one on the passenger's side had developed some severe cracks at the manifold fittings. These cracks were the cause of a very loud exhaust leak at speed and a lot of exhaust fumes in the cockpit at stop lights. Given the upcoming trip back east with the kids in two weeks and the spring camping season upon us, I figured it was time to deal with the last major mechanical issue on my to do list. Besides, I'm tired of guessing if the people in the car next to me are wondering if I'm restoring it...or it's all I can afford - the exhaust sounds, squeaks and rattles don't help.

So the original plan was to remove the air pumps and hoses, cutoff the injector pipes remove the 7/8" flared fittings and replace them with plug fittings. Removing the pumps and hoses...no problem, cutting off the pipes...no problem, hitting the fittings with the impact wrench...big problem. Rounded off two in a row and didn't even budge the rest. Needless to say this was not a good moment. Packed up the tools and went home to drown my sorrows and search the forum for anything related to exhaust manifolds.

So, this afternoon, after a little meditation ("visualize the manifold bolts coming out"), I decided that the only way out of this was to remove the manifolds themselves. That way I could remove the rest of the fittings, or have them machined out.

I had soaked everything with penetrating oil for the last 48 hours so I tried my trusty 9/16" on a breaker bar on the first bolt. No go...didn't even budge. BTW - those are pretty big fender wells when your working on the brakes but they sure to get cramped when you really need to wrench on something. So I took out the impact wrench again....I know, I know this is a REALLY bad idea. But I had been told that my motor was rebuilt about 3000 miles before I bought the coach. I also noticed that the manifolds were sporting new gaskets and reasonably new bolts. There were other clues as well like the drilled out manifold to downtube pipe flange and new bolts. I figured - what the heck...I'll hit it with 1/4 power and see what happens. (gulp)

2 hours and 16 bolts later the manifolds are off. The bolts all came out clean and with their threads using a "gentle" impact wrench and a lot of loosening…spraying with oil, re-tightening, loosening again, etc. Other than removing the master cylinder to get to access to the left front bolt it all went pretty quickly.

After looking at the other side of the air pipes I can understand why the 454's have manifold over-temp issues. They extend all the way into the exhaust port, right above each exhaust valve, inject air into the exhaust port to re-ignite any unburned fuel as it exits the head. This additional heat and turbulence, not to mention that these tubes are the equivalent of gluing a piece of 1/2 pipe inside each of your exhaust ports, certainly doesn't seem to follow the "ported and polished" school of engine performance. I now see why the installation of headers improves flow, heat reduction, power & mileage in a single bolt on.

So...now I'm thinking headers. Something quick and easy and on a budget. Brett had a combo that I liked on another post. I'm currently thinking about Hedmann's (for a Class A 454) into 3" collectors. Then use a kit into DynoMax RV mufflers. Possibly an H kit. Oh...and chrome tips. I think I can get everything from Jegs for about $600.

As always...suggestions would be appreciated.

Oh yes...special thanks should be given to the mechanic who dealt with these bolts before me. Thank you, thank you, thank you! I'll be replacing them with new bolts, smothered in anti-seize so I can pass the favor onto the next guy. After all, the next guy could be me!
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Old 03-16-2004, 08:14 AM   #2
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I got Doug Thorley headers and had the dual exhaust pipes come out the driver side in front of the rear tires. Peter has his like this too. It gives access to anyone who will replace the rear shocks in the future as well. The chrome tips can be permanently welded on for a price, or you can buy them as a screw on add on, as I did. One cannot tell the difference unless scrutinizing them at close range. It's a $60.00 difference.

BTW, if you don't have one, leave room for a future installation of a gear vendor...one never knows. You would have to move the H kit crossover back if you or a subsequent owner decides to install one. (I didn't though). The Thorleys are street legal even in California.
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Old 03-16-2004, 08:58 AM   #3
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WOW you did good. You'll love your new headers, the power, gas milage, quite, looks (chrome tips and you engine will be cooler, and happier too.

That's one problem I don't think I'll have again, the Banks stuff fixed it all for me.

Keep us posted on your choices and results.

Don
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Old 03-16-2004, 01:30 PM   #4
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Headers

Thorley and Flowmaster Series 70.
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Old 03-16-2004, 02:07 PM   #5
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Ordered the parts

I just ordered a complete exhaust from Jeg's. Turns out the tech guy I was talking to was a racer and has a MH on a P30 so he knew a lot about this setup. As nice as the Banks or ceramic coated Thorleys would have been...I elected to keep my project dollars for the interior work in progress but still take this opportunity to replace the entire exhaust system from front to back.

Here is the parts list:

Item# = 500-69120
Description = Hedman Hedders Headers Motorhomes Class-A 1968-91 396-454 ci, 1-3/4'' Tubes/3'' Collector

Item# = 555-30651
Description = Jeg's Universal H-Pipe Kits H-Pipe Kit, 2.5'' Dia. Tubing

Item# = 555-30561
Description = Jeg's Universal Dual Exhaust Kit w/o Mufflers 3'' Collector to 2-1/2'' Pipe

Item# = 289-17749
Description = Dynomax Hemi Super Turbo Mufflers 2-1/2'' In, 2-1/2'' Out, Offset/Offset

Item# = 720-7158
Description = Mr. Gasket CopperSEAL Exhaust Gasket BB-Chevy Square Port

I plan to buy two 2 1/2" pipes from NAPA to make the long straight run between the muffler and the turn out. So all in all everything will go on for about $450 and shipping was free.

I justified this in my head by thinking I could do this replacement three or four more times before it equals the cost of a Banks system.

Should get everything by Friday. I'll keep everyone posted. On my last trip I got about 8.5 MPG. I'm anxious to see if there is a big "bolt on" difference on my upcoming trip.
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Old 03-16-2004, 02:41 PM   #6
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Questions -

Was the manifold you removed the "factory header" (first two and last two cylinder ports separated by an expansion joint - fabricated (welded) construction), or the solid cast maniifold?

and,

Exactly where did your manifold failure(s) occur?
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Old 03-16-2004, 02:45 PM   #7
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Dennis,
Yes..."factory" headers with the expansion joint. And...the headers didn't fail at all. The A.I.R. system tubes failed. Three cracked at the point where they enter the fittings into the header. Two were completely seperated.

Took me a forever to find this mysterious leak.
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Old 03-16-2004, 06:18 PM   #8
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Stainless Steel bolts. No rust. Even if they cost $2.00 each, it is only $16.00 extra for the bolts to the heads. I have a bunch of Stainless bolts on my boat, have not had a problem geting them out when needed.
Terry
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Old 03-20-2004, 12:53 PM   #9
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Everything is on!

OK..the Jegs parts came the next day and as of an hour ago everything is installed. Still working on replacing plug wires (pulled three off removing them) and a fuel pump (preventative maintenance) so I haven't had a chance to fire her up yet.

I bought two 2.5" x 7' pipes and four more clamps at NAPA. So including a replacement cutoff wheel for cutting everything went on at just over $400.

It wasn't as bad as I thought it would be. I think total time including removing the old system was about 8 hours.

I'll post some pics and an overview soon for those who have the DIY itch for some headers.
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Old 08-01-2005, 09:20 AM   #10
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headstrom Headers replacement for P30 454 Chevy Exhaust Manifolds

Quote:
Originally Posted by swebster
I just ordered a complete exhaust from Jeg's. Turns out the tech guy I was talking to was a racer and has a MH on a P30 so he knew a lot about this setup. As nice as the Banks or ceramic coated Thorleys would have been...I elected to keep my project dollars for the interior work in progress but still take this opportunity to replace the entire exhaust system from front to back.
I just ordered these headers and adapters and gasket from Jeg's as well. I hope to install the system next week, and hopefully I can kiss that annoying exhaust manifiold noise goodbye forever! Please let me know whether yopu asre happy with this system, now that you have had it on your MH for almost a year.
Thanks,
Chas
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Old 08-01-2005, 02:43 PM   #11
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Just remember to retorque the bolts after you drive for a bit. They have a nasty habit of coming loose and blowing your nice new gaskets out. The Headmans are my choise for cost, coating and performance at a very low price.
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Old 08-07-2005, 12:01 PM   #12
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Replacement of factory 454 Exhaust Manifolds

Okay guys,
You convinced me. I got tired of replacing the exhaust manifuold gaskets on the Chevrolet 454 in my 1976 Argosy motor home. I took your advice and bought the Heddmans headers from Jeg's. They look realy nice and they come with the collectors, adapters to 2.5 inch pipe, gaskets and bolts. I even sprung for the copper manifold gaskets from Mr. Gasket.
The left manifold came off easy and the replacement went really smooth. The right manifold gave me some trouble, but I finally got it off. Unfortunately, the 1976 Argosy has an engine domestic water heater to provide hot water to the coach if you have been driving. It pipes the domestic water through a heat exchanger mounted on the right side frame rail DIRECTLY WHERE THE HEADER WANTS TO BE!!!!. Has anyone else run into this. Can this water heater be re-routed or mounted elsewhere without too much trouble?
I can't get the header on the right side with this thing in the way. I ended up putting the GM manifold back on the right side with a new gasket, and ity is quiet for now, but I really want to mount the header on that side as well. Please help!
Also, has anyone exchanged the cooling unit on a Norcold refrigerator. It looks pretty straightforward and simple, but I would like some advice. Finally, how about how to troubleshoot a Dometic air conditioner that cools, but not cool enough?
Thanks,
Chas
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Old 08-07-2005, 01:23 PM   #13
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Quote:
Originally Posted by chasgould
The left manifold came off easy and the replacement went really smooth. The right manifold gave me some trouble, but I finally got it off. Unfortunately, the 1976 Argosy has an engine domestic water heater to provide hot water to the coach if you have been driving. It pipes the domestic water through a heat exchanger mounted on the right side frame rail DIRECTLY WHERE THE HEADER WANTS TO BE!!!!. Has anyone else run into this. Can this water heater be re-routed or mounted elsewhere without too much trouble?
I can't get the header on the right side with this thing in the way. I ended up putting the GM manifold back on the right side with a new gasket, and ity is quiet for now, but I really want to mount the header on that side as well. Please help!Thanks,
Chas
Can you post a photo? Maybe we could come up with some ideas, if we could visualize where it is.
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Old 08-07-2005, 01:29 PM   #14
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Quote:
Originally Posted by chasgould
...the 1976 Argosy has an engine domestic water heater to provide hot water to the coach if you have been driving...
Great idea, but does it benefit you substantially? I do not own a motorhome, so I can not appreciate the benefit.

My first thought is to remove it, install the manifold, then, if the HX is useful, replumb it in.

Tom
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