Exhast Manifold - Driver's side - mate to pipe

R

RobertC

Member
I guess I should relate my recent experience with the driver's side exhaust manifold.

I have always had "problems" in this area over the years -- including replacing the driver's side exhaust donut twice on the side of dirt roads in the desert.

In "preparation" for last weekend's trip to death valley, I decided to be "proactive" and have the driver's side exhaust donut replaced.

Well, that lead to "more problems" -- it turned out that there was a crack in the flange of the exhaust manifold which eventually broke resulting in replacing the manifold.

As part of the attempt to "seal" the connection (before the manifold broke), the muffler guy replaced the "donut downpipe" with a "down pipe" with a flat flange - requiring a flat gasket instead of the donut. (he did not "like" the donut.)

I got a new manifold - the muffler guy said I should get a new manifold instead of used because of the long term "effect" of heat on cast iron. He also said that the pass side exhaust manifold was showing signs of such deterioration -- "light gray areas" on the manifold.

I put the new manifold on and hooked up the new down pipe "successfully" -- no noise / exhaust leaks.

I noticed a slight increase in the "torque" / "pickup" getting on the freeway as I drove my t/a back to the muffler shop for him to check out.

The inside of the old exhaust donut was slightly "eroded" from not being perfectly aligned with the exhaust manifold.

On the trip down to death valley, I was able to "pull" the north ("steep") side of tehachapi pass (CA 58 bakersfield to mojave) all the way in overdrive. In recent years, I have had to use 4th up this pass on the "steeper" parts.

So, I assume that the slightly misaligned exhaust pipe was the cause of slightly less power. I just thought the motor was just getting old (like me:gringrin: ).

Not a recommendation to replace the donut with a flange -- just need to make sure the exhaust system is "correctly aligned".

I do not know if this is an issue with scouts -- or other fullsize ihs -- just might be my vehicle.

Hth
 
What you describe is one of my "top 5" issues with any I-4/sv-powered rig running oem exhaust manifolds!

I deal with the same quite often! In fact two weeks ago I dropped mine one last time to replace donuts, I'm not using the oem crap but even the workarounds won't workaround if the head pipes are not proper fabbed.

Jeff and I replaced an exhaust manifold at his place this same week last year, but the major issue was the headpipe which I had to have fabbed three weeks later in texas. In that case, that manifold we replaced simply rotted through and cracked above the flange portion, exhaust gas erosion over many years finally did it's thing!

And the cracking of the flange is very common if everything doesn't mate cleanly to begin with.

I don't agree with your guy's "analysis" of the cast iron deal, I've used many old manifolds with no issues at all.

Most common manifold cracking cause on fullsize stuff other than poor headpipe sealing and over-tightening, is rotten engine supports! Most especially onna fresh exhaust system that is hung too rigidly. In fact, the multiple cracked manifold deal is how Jeff and I first met up years ago, he's the one who warned me about the dogbone mounts that "looked" ok, they were the root cause of five cracked manifolds, installing the rpt 'bones solved that issue and is still viable today!

I'm currently fabbing an entire new headpipe-to-manifold system for my rig. The current one was built by "mel and sons" there in oakland, I'm sure you know who they are as they are very close to where ya hang your hat! They tried to overcome the oem crap but were really never successful, I've been "patching" their original build going on eight years now and it's time to start over again! And headers are not an option for me, they have their own set of issues when used in dd service for the long term.

Once I get the details of what I'm doing worked out, I'll post pics. This will involve oem manifolds that have been in service for many years, there will be no heat riser used (I eliminated that when mel did the work), and will involve off-the-shelf parts from the local parts house, no "custom" pipe manipulation from the local exhaust guy. I'm simply no longer able to shell out $600+ for an exhaust system I can diy inna couplea days!
 
Nope, never heard of mel and sons -- though they are nearby.

I used ron's mufflers in berkeley (used to live there) for 25+ years. Then, I think the owner (ron) sold out and I did not care for the next owner and found the current shop (in el cerrito) via a friend.

I just went thru my maintenance records and "found" / read all the work done on the exhaust system over the years.

Yes, you can use an used exhaust manifold. The current pass side exhaust manifold is used (installed 2000). At this point, I think it is getting to be "too used".

The current guy mentioned removing the heat riser.
 
Hey guys my 74 ,304 is in the same shape it blew the right ne last trip out and I need to relace the donuts my flanges are ok and mnifolds are also good. I was reading a previous post that michael refered to some replacement donuts he purchased. Can I get a part number for these. It would be great to do this maybe once a year instead of every few weeks thanks brad
 
Tow,
I have always had good luck going in to a muffler shop with an id requirement and they go to there peg board rack and pick one. They May have 10 different ones.

I had my exhaust system built new when the new engine went in. The guy was going to weld on a 2 bolt flange and just us a flat gasket. I was not to keen on a gasket so I told him to flair the dump and use a crushable ring and the cast iron flange. I had to re tighten the bolts a couple of times as the gasket crushed but I have not had to touch it for a few years. I figured the joint would allow more misalignment. I did try the metal oem cone but I could not get it to stop leaking.

After having the system built I removed the 2-bit crap bolts the shop installed and went to my an bolt stash and installed an high temp self locking nuts and an cad plated bolts. They will never come loose and have good corrosion resistance. A bolt shop will have high temp lock nuts (usually have a couple of threads coined to create a thread interference). The an nuts have a narrowed top that is slit 2-3 ways and closed up. They are will last better and not damage the bolt.


Robert, would like to know why the manifold change or gasketing method had anything to do with a power increase unless the donut was the wrong size or crushed down and in causing a restriction. Is the down pipe any better/straighter?
I do know that some engines respond well to a slight increase in back pressure.

Just thinking about your power improvement not questioning it. If you experienced an improvement in performance it would be good to put a finger on the root cause so others could do it.
.......tim?

Rk
 
I'm with Robert on this deal, anything is superior to the oem headpipe-to-manifold connection!

Ihon has the "workaround" crushable donut substitutes that I used. A year ago, one of those failed again but that was because the headpipe flange (formed as Robert described) was rotted beyond use when Jeff helped me out and we didn't have time to deal with it at that point as we were traveling under a deadline. So I had another replacement pigtail fabbed in texas and replaced the "crushable" donut with a new one off the rack in tha dude's shop. He kinda wanted to argue...but I told him that I was paying him, if it didn't work he'd never see me again anyway since I was "on the road".

I've had two of the pressed metal oem-style donuts literally shatter while in service. Chunks fell into the headpipe and rattled for days until they moved on and are now clogging the muffler on one side. So I can fully support robertc's position regarding an exhaust restriction!

Plus...just not having a major exhaust leak seems to mentally add at least thirty ft./lbs. More torque!

I use anti-sieze on anthing exhaust system-related. Shitcan those scruuee oem manifold bolt "lockers", use the hardware Robert describes with hardened flat washers. The manifolds will come off and on with no problems even after years of service. And I use plain old oem fel-pro steel shim manifold-to-head gaskets, new ones any time the manifold has to be removed for whatever reason.

And...just last week when servicing the hubs, I finally discovered why the head pipe on the passenger side has never sealed properly onna regular basis. With the trailer connected, and the equalizer spring bars set, the headpipe hits the pumpkin continuously now when the front suspension compresses! So the new headpipes I'm fabbing will dam sure be re-routed away from that area and also allow complete underbody service without removal!
 
Let's see if I can describe this adequately:

I knew I should have taken a picture of the old donut, but it hit the trash pickup two weeks ago.

My "theory" is that the "old" head pipe was slightly "mis-aligned" with the outlet hole of the exhaust manifold.

The old donut was "pitted" / "eroded" on one inside edge. I assume this edge was "hanging out" into the exhaust flow

when I replaced one donut in the desert, I had a hard time getting the "head /down pipe" to align with the manifold and completely seal (much pulling on exhaust system by my part with help from a friend).

My assumption / conjecture is that the prior slight power loss (maybe 5 - 10%?) was due to the inside lip of the donut "causing turbulence in the exhaust" at the outlet of the exhaust manifold.

But, you are much more knowledgable about performance than I am.

I assume that the previous down / head pipe was just a tad "short".

My exhaust system is a little "cobbled" together -- I replaced the original driver's side pipe to the muffler shortly after I bought the t/a. The original pipe had all these "bends" in it (to clear a tf 727, I assume) and the pipe kept coming loose.

So, I had a muffler guy replace it with a "straight" pipe running inside the frame rail (in aug 1974).

He "cut / spliced into" the original down pipe.

And, the down / head pipe is the piece that has been replaced (last time before now was 2005) over the years. The original "straight" section added in 1974 is still in place.

When the guy fabricated the new down pipe with the flange, I assume that it is perfectly aligned with the exhaust outlet.

No slight exhaust "restriction" -- a slight bit more power...

On townes pass (going west into death valley), I was last in line of "our parade" (3 other vehicles), but I dropped back and tried a "short run" to see if I could pull townes pass in 4th. Last few years, I have had to use 3rd on the two "really steep" sections. I think I might be able to pull townes pass in 4th -- I will get to find out if we go down to dv for wild flowers in mar / apr.

I do not think the flange has anything to do with it.

I do think that the head pipe / donut / exhaust outlet (or head pipe / flange / exhaust outlet) have to / should be "perfectly aligned".

Probably way too many words, but I hope I have answered your questions....

Btw -- michael, I have had two IH donuts "shatter" into pieces and "disappear" into the exhaust system -- in the desert.
 
Re: Exhaust Manifold - Driver's side - mate to pipe

Wow a lot of reading and not one picture:nono: are you guys talking rear dump manifolds or center dump? I built my own exhaust system last year. I used parts from napa and summit. Napa had the premade head pipe and 2 1/4" exhaust tubing. I got a dynamax muffler and j pipe from summit. I did a two into one using a flowmaster y pipe. Sound is nice and quiet, which is what I wanted. But you can still tell it's a v8:gringrin:

my solution to the nuts coming loose is to chase the nut with an all metal lock nut.

I will look for that napa part number

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923d1193867575-engine-motor-mount-moved-back-2-5-exhaust-hanger-2.jpg


927d1193867575-engine-motor-mount-moved-back-2-5-exhaust-under-shot.jpg
 
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We are talking only center dump, two-ear exhaust manifolds here Craig.

The problem with the oem stuff is not the head pipe bolts/nuts loosening. The primary problem is the original IH design for the head pipe-to-manifold connection. It simply is not conducive to a permanent seal, once even a minute amount of exhaust gas leakage develops due to component deterioration, the process is rapidly accelerated.

The passenger side issue is compounded through the use of a heat riser valve which requires maintenance which nobody ever did/does! And the sealing design of that application suks! Other manufacturers managed to do the same thing inna much more permanent manner. I remember that was a common complaint in the dealership shop when I worked on these pos (fullsize stuff only, not Scout) in 1969, we found head pipe leakage during pdi on new vehicles right off the transporter.

The oem pressed metal donut is flat on one surface and tapered on the other. No way that will seal properly over time. The oem manifold flange is flat and requires a gasket between the heat riser and the manifold flange. So ya have a gasket and a donut on one side.

If the manifold flange had a tapered opening, and a tapered crush-type donut with a pilot was used, these systems would never leak!

Your pic shows that you used the off-the-shelf aftermarket pigtail with the crush donut (most likely with the pilot?). That is the same setup I've bought in bulk here to make up headpipes for all my IH junk. That one won't "explode" and fall into the system to create rattling blockage. But it can be easily destroyed if overtightened, ya can crush it down to just bits of aluminum foil.
 
Lol thanks mm I did find the part# 41725. I did not over tighen mine, but found after just a bit of driving it was a tad loose, thats why I added the chaser lock nuts. I've since re tighen it up one more time and it been holding fine. But now I have this nagging feeling that I need to go check them. :icon_eek: do you like the welded bolt on top:gringrin: I hated having to stick a wrench up there to hold things still so I could tighen or lossen the exhasut nuts. The only thing is you have to drop the bolt setup in before you bolt the manifold to the head for the inside position.

I been using these
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napa link

I bought some of those ss clamps to make removing the exhaust easier, but never did install them. I figured when I need to pull it I would used them then. I did not over tighen the clamp to the muffler to make seperation later easier. Humm have I taken and put things together one to many time on the this thing:icon_eh:
 
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