The Stovebolt Site Forums The Shop Area Engine Shop The Fenton Offenhauser clash

Over the years I've seen postings on the fit problems between the Fenton Exhaust and the Offenhauser dual intake.
If I remember correctly, there's a mismatch in flange size between the two so that the Fenton's should be thinned down to the Offenhauser flange. This would require a machine shop with a precise milling machine to maintain absolute flatness accross the flange.
Patrick of Patrick's (Antique Cars and Trucks) told me to just grind the high side of each of the manifold mounting brackets so that a step is formed to compensate for the unevenness(sp) of the flanges.
Sounds simple enough, but who thinks it will work? Who's done this and what was the outcome?
AND was there any clearance problems with the rear exhaust header and the throttle bellcrank?
Thanks ahead of time

i have both and there was a small clearance problem but it was solved with a little grinding on the fentons to clear.

Have them both myself and yes, a milling machine works great. However, many have just ground on the flanges and other components until they fit cleanly. I have documented some of this process in my webshots album under engine rebuild. Good luck!

http://community.webshots.com/user/geezer

Did the grinding myself, little by little, with a dremel. It REALLY helps to use a mock-up head so you can do it on a work bench.

I have used a mock up head to set things up and it is the greatest help of all. Even better is to use the whole engine, if your engine is on an engine stand.

To me the best of all worlds is to mill the header flanges to the same thickness as the flanges on the intake you are using. By doing this, the flanges are both on the same plane for the clamps to work correctly and apply the even pressure needed to seal the gaskets, the headers should fit correctly and the unit should be close to in line for your linkage to work correctly. If the headers didn't fit correctly, my next choice would be to grind on the headers where they pass under the intake. I think it's worth the price to have the header flanges milled to the proper thickness. Finally, let me say that if you can find a vintage set of Fenton headers, even though the price might be higher, that is the best way to go. The extra in a higher price will pay for itself.

Joe

I just finished doing mine and have a few tips for you.

You've got two problems and two options on the second problem.

The first problem is getting the hold down tabs on the fenton and offy to match up. The only solution for that is to grind the OFFY in some spots and the FENTONS in other. There is no way around this solution. I used a 4" angle grinder for this and it worked great.

The second problem is clearance between the intake and exhaust. The new Fentons tend to hit the offy on the back half.. There are two possible solutions for this. First, grind the bottom of the Offy to clear the Fentons, and maybe take a little off the Fentons too. If you go that route, you better figure out how you plan to heat the intake and put those pieces on it to make sure you take them into account for clearance.

The second possibility, and in my opinion a much better solution, is to take your fentons to a machine shop and have them mill the mounting surface at an angle so that the exhaust manifolds point a little closer to the block. That will take care of your clearance problem and I think milling the mounting surface is preferrable to grinding your offy or header tubes 'cause you won't risk making something too thin. Of course if you have the mounting surfaces of the flanges milled, you do that BEFORE you grind the mounting tabs to solve problem one.

Before you put anything together don't forget to take care of the two zinc plugs in the offy. They need to be replaced with aluminum plugs and heli-arced to properly seal it otherwise you'll either end up with a water leak or a Carbon monoxide leak, depending on how you heat the Offy.

Another good idea is to remove the studs at either end of your head, thread the holes, and use bolts.

Also, if you plan on having your fentons jet coated, get the clearance and mounting issues taken care of first before you send them out for coating or paint them.

OK,
It appears that grinding the mounting tabs (cheap way) could be a bit bush league with the creation of unequal pressure. So the best answer is to get them to a machine shop and have them ground on the face to the thickness on the Offenhausers.
I mentioned that the clearance of the throttle bellcrank was already in question. By reducing the thickness of the flanges on the Fentons, that distance moves even closer to the bellcrank. If having the machine shop put a slight angle down when planing to clear the rear underside of the Offenhauser, that clearance becomes even worse.
And then there is also having the 2 15/16 mounting holes filled then re-taped to 2 11/16 to accomadate the Carter W-1's that are going on top. And oh, those zinc plugs? I remember something about that. What's the deal again with those?
Man, do you guys thinks I should get the new recast Fentons and put these Offys on ebay for $20 bucks?

I'm not sure you can mill the mounting flanges on the fentons so that they are all of an equal thickness amongst them selves or the same thickness as any of the offy mount flanges. Plus there are tabs on the outside tubes of both the offy and the fenton that probably are different heights. On my Fentons, the mounting flanges were not all of an equal thickness.

I don't think its a problem to grind the back side of the flanges to match the flange width of the offys.

I also don't think milling just the mounting surface of the fentons so that they will mount with a slight downward angle will cause a problem with your throttle bellcrank or the linkage to the dual carbs.

The deal with the zinc plugs in the bottom of the offy is that you should remove them, replace them with aluminum plugs and have the aluminum plugs welded into place. The Stovebolt engine company ships their Offys with the plugs welded, I don't think Patrick's does.

If you got the Offy from Patricks and havn't touched it, I bet you can return it and apply the credit towards the purchase of other merchandise from him, like one of the new Fenton intakes.

If you decide you want to get rid of your Offy intake, I'll take it off your hands for $20!

NM51,
I got this Offy From Langdon. It does appear that some grinding work took place in the plug area and that a roset welding bead is in place. If zinc is the exact same color as aluminum then I'll call Langdon and ask.
By the way, what are the two 1/2 inch taped holes in the Fentons? For heat to the carbs?
So you took a 4" hand grinder and made the changes? What was the disk made of? Can this be had at Home Depot or Loews?
I should take a picture of the bellcrank clearance.
I've put myself on the list for Patrick's SS exhaust system. Living close to the salt air coast sounds like a good idea. But I've never heard their sound. Has anyone here?
The waiting list is 30-90 days. I waited over 3 months just for the new spring set from Patrick's.

I have that setup, too. I ground mine with a angle die grinder with a 3" 80 grit sanding disk.
I also did away with the factory clamps, I couln't get them to work well with the manifolds. What I did was install studs in place of the bolts, and put bolts in place of the dowells at the ends. Then I made new clamps from 1/4" stainless bar stock. I have no leakage problems at the head. By the way, my Offy came from Patrick's, it's not welded, but so far there's no leaks at the plugs.
Semi-related topic-have any of you had problems with the head pipe flange leaking? Iv'e tried several types of exhaust gaskets, but they blow out after about 3 months. Any ideas?

To heat the offenhauser you've got two choices, water and exhaust.

Both involve bolting a flat plate with two holes threaded into it over the 3"x4" divided opening in the center bottom of the offy manifold. The divided box leads to passages inside the intake that go to the plugs. If you run heated gas or water in one side of the divided box it'll come out of the other side after having circulated through the passages in the bottom of the manifold. Heating the manifold, as many other posts have noted, is critical to atomization of fuel during the colder months.

If you use water, tee off the thermostat housing to heater outlet and the inlet to the water pump and run both lines to the offy.

If you use exhuast gas, use the two holes in the fentons. If not, put some threaded plugs in there-stainless or brass are better 'cause they won't bond with the cast iron.

I went with water and my offy leaked til I welded up the plugs. Now it still leaks 'cause I ground it a little to much off the bottom of the offy and I think I made it too thin in the water jacket area. (that's why I'd buy yours if you decide you don't want it).

To grind the hold down tabs I just bought a 4" grinder from Harbor Freight and it came with a cut off wheel and a grinding wheel for metal. I used the grinding wheel and it worked fine. The trick to grinding the fentons and offys is to start by lying both of them on their mating surfaces on a bench and start with the mount flanges. Then put it up to the head, tighten it down (no gasket) and mark the outer tube mount points and then grind them. It'll take several rounds of this to get that part just right, and it'll make a huge mess of metal particles and dust from the grinding wheel so don't forget to wear a respirator/mask, eye protection and gloves.

If the plugs on yours are heli-arced, the plugs are aluminum (you can't weld steel to aluminum). Some people get lucky and their plugs never leak.

As far as removing the studs in your head and replacing them, another thing you could do is put threaded studs in. That would give you the benefit of having something to rest the manifold on while you line up the compression bars and you'd have something you could tighten down on the ends!

I havn't had any problems with my head pipe leaking and I used the flanges and gaskets that came with the fentons.

Soon you'll come to the question of what to do with your exhaust. I suggest y-ing into one pipe with a y that comes together right at the crossmember the engine mounts are on and then running 2 1/2" pipe from there to a single muffler. Of course theres lots of debate on that topic and opinions and theories vary.

Good luck!

My Fentons came from Patrick's, I did not get any flanges or gaskets, I made my own. Also, I think I misunderstood about the plugs in the bottom of the Offy, Is there a passage/jacket in the manifold? I'm not running any heat to it, so that might eplain no leakage.

On the bottom of the Offy spread about 16 inches apart are two quarter sized areas where the zinc plugs were, and, if you got them from Langdon, they have been heliarched with aluminum.
Also on the bottom, in the center is a 3 X 4 inch opening that mates with a water kit (also from Langdon; about $65) which includes the plate, two right angle hose barbs and an adapter plate w/ hose barb that is sandwiched between the head and the thermostat housing to provide the water source for heating the intake.
One of the two hose bars on the Offy then goes to a T in the heater hose. Langdon also has a gasket set for $12. I don't know yet if they leak.
Hey NM51, should the plugs for the Fentons be as short as possible to prevent or minimize flow disruption or does it not make a tinkers dink of difference? And are those outside dowels on the head threaded? (lefty loosey)
One last thing...exhaust header coating. Ceramic (pricey) vs. high temp paint???

For the Fenton Plugs I used the set screws the machine shop put in the oil line holes in the block of my 261. If I hadn't had those I would have gotten some from the machine shop. I agree with Rattletrap that short is better.

I'm not sure if the dowels on the head are threaded, they might be?

I used high temp paint on my headers. If you do that too, you'll need to read the instructions on the high temp paint can- I believe it says that after painting you need to bake on the paint at 600 degrees for x amount of time. I used my oven and have heard of other people using pottery kilns or wood burning fireplaces.

Ceramic or Jet Coating runs around $100 I think.

The cheap and "bush league" way of grinding the flanges on my headers have seemed to work out just fine. I'm not an expert mechanic, but the guy who showed me the way is. I have about 2k miles on the truck since and everything works great. As NM51 said, the flanges are of different thickness on these new fentons and so a mill would not work. As far as not creating unequal pressure - the key is to grind little by little so that it doesn't get overdone. That's why the bench helps so much. I took each header on and off about 20 times to make sure it was just right. The hold down bolts are level and parallel to the block. The fit is good. But don't let me stop you from going out and spending your money to have some else do the work for you. If I had to do it again, I would be patient and find a set of original fentons that actually fit. For the 261 that I'm building, I'm going to do that or I'm going to split the orinal exhaust manifold. Still riding the fence.

Bigmacdaddy,
The "bush league" I was refering to was that Patrick told me to grind the clamps only. Put a step in the high side.
Today, I spent most of it grinding the flanges.
The grinding wasn't too bad. But I've got to tell ya. Whoever made the casting must have taken the dimensions from something other than a 216,235 or 261. Had to cut back the inside flanges on each header 1/2 inch + to clear the bolt holes. What's with that? And the outside flanges do not allow a striaght in bolt for those original tear drop clamps. Somemore heavy grinding to gain clearance and hoping I wouldn't grind through to the other side.
The workmanship on the headers is just plain a** poor. Had to grind every ridge to get the cheeseyness out of it. Not very impressed. Patrick should be a bit ashamed to be turning out such a crude piece. Although I haven't seen them, and even though the clearance / flange problem is supposably solved, I wounldn't go near the recast Fenton intakes.
I've got my name on the SS exhaust (30-90)days out. I'm worried about the quality on those now.
Anyone get a set of those? Quality? Fit? Sound?
Anywise, just venting.
:mad: :mad:

I completely understand your frustration about the crappy remakes. And I made the mistake of having them ceramic coated before I found out that they didn't fit at all. How hard could it be to fix the castings? And Patrick seemed apathetic and acted like I should have expected to do all that grinding. Or what he said "a little grinding". After I bought them of course. I have discovered that both a McGurk and an Edelbrock 2X1 fit the original exhaust manifold just right, no grinding involved. That and the added bonus of the most effective heating system. I think this conversation has caused me jump to the split the original exhaust manifold side of the fence for my next build.
On a better note, I also have Patrick's s/s dual muffler and it sounds great. I bought just the muffler and had a local shop run 2" pipes for $300. I plan on replacing those with s/s next year when my 261 is complete.

I have Patrick's SS exhaust and one thing you need not worry about is quality on these. I haven't started my truck yet so I don't know how they sound. Mounting everything took me about 1/2 hour by myself.

I too am a victim of the crappy Fenton / Offy fit. I spent about 6 hours filing and grinding to get them to fit. I thought I had it all set and had my exhaust ceramic coated. When it returned I found that my hold down tabs needed to be ground some more. There has to be a better way!

chev235,do you have any pictures of how the exaust looks from the rear of the truck ? can you post some pictures ?

Bigmacdaddy and 235,

How was the match from the header flanges to the exhaust flanges?
Did you guys have go on a waiting list for these?
And do these take the same line to the rear as the stock pipe did? Meaning, there is a half circle bracket about 2/3 of the way towards the rear with a thin metal strap that ties it together.

It looks as though I'll have a conflict with the rear header flange and the bellcrank from the throttle.
If I hammer straighten the jog in the bellcrank so as to move throttle arm towards the block it will leagthen the arm to the carb linkage and conflict with the vertical clearance it has now passing up through the manifolds.

I had to rebend the vertical rod of my throttle linkage. Not only that, when the engine gets warm, it still touches metal at low idle and prevents the throttle from coming down the entire way. After countless rebending, I've surrendered to the idea of getting a longer rod to bend. The shop hooked the exhaust to the headers and did the entire job (pipes, muffler, bowtie tips) in less than 3 hrs. My pipes come straight out the back on either side of the hitch which is obviously different than the original single pipe with the end behind the left rear tire. The pipes to the muffler are in roughly the same position as the original pipe and muffler.

bowtietim
Sure, I'll post some pictures in the next day or so. The pipes sit on top of each other. As Patrick says they are Shot Gun Style (over/under)

Rattletrap52
1. The Match from the header flange to the exhaust flange was really good.
2. I got mine last year. I go down to see Patrick and Phillip often. It so happened that one time they had an extra set so I got it.
3. Yes, they follow the same line. Patrick is a purest at heart and he doesn't want any uneccesary cutting of these trucks. With that said you have to cut out two rivets on the frame that are right behind the cab. That is where the the half-circle brackets mount.

I haven't hooked up my vertical rod on the throttle linkage not sure how that's going to go.

I got Patrick's exhaust last winter. One of the first produced. It's beautiful. Will be going on the truck as soon as I get the engine back in. Like 235 said, they exit shotgun style out the left rear. Had my throttle rod done beautifully until I realized that I had it on the forward shaft on the block rather than the rear shaft/pin. Now back to work on it.

Is phillip his son ? If so,he has the gift of gab.Really nice people to deal with.

Yes, Phillip is his son. They are awesome people! In fact about the second time I went down there Patrick and his wife took me out for lunch. They have been great friends ever since. The only downfall is you need to make sure you have some time to spend cause they'll talk your ear off.

Copy that 235.
Hey those two rivets....my body is off right now and everything is really excessable. Could you walk me through the exact location of those rivets or pictures?

Also, does that mean that the muffler/glasspack/whatever is strapped in the exact location as the original?

Yes, the muffler is strapped in the same position as the original.

You can see the rivets in the picture. They are on the left side(drivers side). I think I said they are on the right in a previous e-mail.

Here is a link to my pictures. This is a test run so please let me know if you can or cannot get to them.

http://picasaweb.google.com/akuips

235 (Aaron),
The link worked perfect.
I see that the 2 rivets hold the original muffler bracket on the underside. Darn-it. Do you think there is any way to incorporate this old bracket with the new bracket/muffler?
Any possibility of snapping a photo from the underside to see the connection?
I'm not sure from the photos, but did you paint or powder coat the frame? It's grey isn't it?
Looks great! I powder coated my frame grey as well. Didn't want to go w/ that old black look.
Also, I see that you were able to create a web link on Picasa. I use that program for my photos but didn't realize the other potential.

Thanks for the pictures.Nice project you got going.Looks great !!

Thanks for the comments. I was actually dissapointed in the pictures, right now everything had about an inch of bondo dust on it.

Okay ...
I posted some new pictures of the underside of the bracket. I don't remember what the original mount looked like so I am not sure if it will work or not. If you choose to use Patricks SS kit it comes with absolutely everything you need.

http://picasaweb.google.com/akuips

I did have the frame powder coated. I went with heavy metallic silver. It turned out pretty good. I agree black wasn't doing it for me.

Rattletrap what color are you doing on the body?

As far as Picasa I downloaded the latest version. When you open the program up there is a tool bar at the bottom of the window. Select the Web Album icon and it will walk you through the process. I really like using the tools that Google provides.

Given the super ease of use with Picasa, this could be a real revelation for anyone in this forum with a digital camera.
When trying to read a description of or writing a description about a certain whatchamacallit, having a picture can often times bring in those of us who have an answer or comment if only we could get a visual.
Having said that, I went to the description for Picasa Web Albums. This beta test software having come out in June. It seems you have to sign-up using a cell phone to start an account in Gmail. Is that true?
Not really sure I would want to do that. Just want the software upgrade.
Any thoughts?

Ya .. Rattletrap I could understand why you wouldn't want to provide your cell phone number. I read through all of the info and I think the reason is they are trying to promote Google's celluar phone web browsing. I'll let you know if I have any problems.