Straightening Bent Exhaust Flanges

Written by Randy Fox (Randysgym)   
Monday, 02 March 2009

Introduction

Yamaha roadstar exhaust flange fix bent straighten
Exhaust Header, Showing Warped Flange

I went to remove my aftermarket exhaust pipes the other day, but they wouldn't come off. At first, everything looked normal:

  • The exhaust header-studs looked fine.
  • Those four, chrome, exhaust-flange nuts weren't rusty or visibly damaged. In fact, they were new this year.
  • The flange--that part that rattles around when the pipe is off--looked good to me.

Nevertheless, after easily removing the flange nuts, I simply could not coax the flange of either pipe off the header-studs. I wiggled; I prodded; I pulled; I angled; I even pried a little. Somehow, it seemed the exhaust-studs had become wedged tightly against the outer edge of both flange bolt-holes. It actually appeared that the exhaust-studs had become bent in a direction away from the center of the exhaust-port.

Ultimately, I decided to use a hammer and cold-chisel on the end of one exhaust-stud, to bend it back toward the center of its exhaust-port. This released the flange, and the pipe fell into my hands with relative ease. Of course, I was now committed to replacing the exhaust header studs, since I had just ruined one of them.

In any case, when I examined the previously flat, quarter-inch thick, solid steel exhaust flange, I could see it had been bowed to a very large degree. Then I knew what happened.

I remembered that the nuts went onto the studs much further than with the stock pipes (which have thicker flanges). I had dutifly torqued the nuts, which was something I hadn't done on pipes before. In other words, I followed the service manual specs instead of my 'feel.'

The thinner steel (true for most aftermarket exhaust flanges for the Road Star), combined with the fact that they are made from mild steel, meant that I should have used much less torque than Yamaha specifies.

In addition, because my flanges bent so far, they bent the exhaust-studs, too. In the end, I had to replace all the studs and un-warp (re-flatten) the flanges on my new pipes.

My exhaust flanges are not removable from the pipes, and no trustworthy muffler or machine shop was handy, so I did it myself. This article describes how I straightened my own exhaust header flanges and replaced my exhaust header studs.

Note: This article assumes you know how to normally remove and install the exhaust system, including how to remove the right-side floorboard for the front pipe. If not, refer to the Road Star Service Manual and/or the manufacturer's installation instructions for your exhaust system.

 

Tools Needed

 

8mm Allen wrench -- for the exhaust header flange nuts, preferrably with long reach

Sockets, screwdriver, or other simple tools -- for the other fasteners of your pipes, depending on the make and model of your exhaust system

High-Temp silicone gasket paste -- (tube), optional, for sealing the exhaust header gaskets. Note: I have used Versa-Chem Mega Copper, high-temp silicone gasket maker from my local auto parts store

 

----- If Your Exhaust Header Studs are Bent or Damaged -----

Hammer -- for 'straightening' exhaust header studs, as needed

Cold chizel or punch -- for 'straightening' exhaust header studs, as needed

Vise-grip pliers -- for removing exhaust header studs, if needed

Regular pliers -- for removing exhaust header studs, if needed

Dremel rotary tool -- (or other) for cleaning out the exhaust header stud holes in the head(s) if needed, and/or cutting studs or flanges if necessary

Safety glasses and ear plugs -- for protection while using Dremel (rotary) tool or other power tool, as needed

Thread-lock liquid -- if exhaust header studs will be replaced

Torque wrench -- optional, for installing exhaust header studs, if needed

 

----- If Your Exhaust Heat-Shields are Removable -----

Smooth-jaw vise, large -- or two thick board pieces (like 2"x8"x16" or more), for straightening removable type exhaust header flanges, if yours are this type. as needed

 

----- If Your Exhaust Heat-Shields are NOT Removable -----

Sturdy board piece -- like a 2" x 4" wall-stud at least 12" long or more, for straightening non-removable type exhaust header flanges, if yours are this type

Small set of open-end wrenches -- (Qty: 2), for 'jacking' the flange back to its original flatness

'C'-clamps -- (Qty: 2) 4" to 6" or so, to clamp the exhaust header flange while bending it back flat. They must be large enough to spand the exhaust header, flange, and the board; and they must be small enough to fit the opening between the heat-shield and header flange. See the clamp-jaw and heat-shield clearance in the upper right area of the photo below.

 

Yamaha roadstar exhaust flange fix bent jack straighten

 

Homemade, miniature pressure jacks, as follows:

  • Bolts: 6mm to 8mm shank, (or 1/4"). (Qty: 2) -- to use as miniature 'jacks' for bending the exhaust flange flat. See 'jack bolt' in the photo above.
  • Nuts: Non-locking type. (Qty: 4)) -- to use as pressure 'jacks' for bending the exhaust flange flat. See photo above.
  • Smooth Washers: Thick, with hole to fit 'jack bolts' described above. (Qty: 2) -- to be used against the exhaust flange. See photo above.
  • Small sturdy metal scraps: Any heavy gauge (16ga or less), flat metal pieces, such as large fender washers. (Qty: 2) -- to use as base-pads for the miniature jacks for bending the exhaust flange flat. See 'scrap metal' in the photo above.

Parts Needed

Exhaust header studs -- (Qty: 0 to 4) Note: Only required if yours are damaged, corroded, or you just want to replace them. Yamaha part#: 95617-08625-00, BOLT, STUD. Or you can get stainless steel ones (like I did) from places like MMS Stainless. I got ones with hex (allen) recesses in the ends for easy replacement. Important Note: If you replace your studs with standard ends (not ones with hex recesses in the ends), you will also need two metric nuts (8mm X 1.25) for installation -- available at hardware and home-improvement stores.

Exhaust header flanges -- (only necessary if you destroy your current flanges). You must determine the make/model of your exhaust system, and contact the manufacturer. It is beyond the scope of this article to list all past, current, and possible future manufacturer possibilities. Post questions in the forum section of this website if you need help identifying your exhaust make/model. Note: Flanges are fairly standardized, so a flange from one manufacturer may well fit an exhaust pipe from another manufacturer.

Exhaust gaskets -- (Qty: 2, unless your flanges are thin compared to stock, in which case you might need 4). You can use any of the following:

  • Yamaha O.E.M. part#: 3EG-14613-00-00, GASKET, EXHAUST PIPE. (about $6 ea.)
  • From your local auto parts store: Fel-Pro 23588, These fit fine on all models, without triming. (about $1 ea.)
  • From your local auto parts store: Fel-Pro 23561. These must be trimmed a little, but are easier to find. (about $1 ea.)

Removing the Exhaust-Header Studs

First, protect all vulnerable areas against scraping or touching that may occur as you remove parts of your exhaust system. Especially, place soft rags between the engine and exhaust.

Next, you will need to remove, or at least loosen, your right-side floorboard (unless your bike has been converted to forward-type foot-pegs). See the service manual for instructions on this. You will need to be very careful not to strain the connections for the rear brake. Be careful.

Next, remove or loosen the rear sections of your exhaust system according to the manufacturer's instructions. For instance: My Bub Rinehart pipes are one continuous piece for each pipe, while the Road Star stock pipes consist of one muffler piece and two head pipes. The point is: First remove any tail pipe section(s).

Finally, be sure each head pipe section that fastens to the engine is loose and ready to come off. See photo of stock exhaust system below:

 

Yamaha roadstar exhaust flange fix bent straighten

 

Note: The photo above also shows the black bracket that connects the stock tailpipe to the frame. It is NOT necessary to remove this bracket for this project.

Next, attempt to remove one of the head pipes completely. Do not assume your flange and/or engine exhaust studs are bent just because the flange does not release from the studs easily. It can become wedged in due to intense heating/cooling cycles, uneven tightening/loosening, or uneven removal pressure. Spend at least 15 minutes trying gentle or at least non-destructive means to coax the flange off the studs. Repeat for the other head pipe.

Use destructive force only as a last resort. Do your best to do no harm to the exhaust header studs, the pipe flanges, and especially the engine. However, if it appears there is no other option, use any means necessary to separate the exhaust pipe from the head without damaging the engine-head or the pipe.

Determine if your flanges are removable from the pipes. In other words, can the flange be slid off the tail-end of its pipe-section once it's off the bike? The largest, and usually the only, determining factor is: Are the pipe's heat-shields removable? Many heat-shields are held on via clamps, screws, or springs. But a some are actually welded to the pipe, like my Rineharts.

If you know your flanges are removable from the pipes -- and therefore replaceable -- you may chose to destroy the flanges rather than the engine exhaust studs. In this case, or if you just feel more comfortable preserving your engine exhaust studs, the flange(s) can be carefully cut away. But if you do this, you will be required to do at least one of the following:

  • Replace the flange, which is only possible if your heat shields are removable, and the flange can be slid off the pipe. Also, be sure the manufacturer still makes flanges for your pipes.
  • Replace the pipe.
  • Fabricate a new flange. Note: This is not easy unless you have access to advanced machine tools. Note: If your heat shields are not removable, you could make a two-piece flange that could be welded together over (but not to) the pipe section forward of the heat shield(s) but just rearward of the actual pipe head-collar. This demands great skill to do without damaging the pipe, and is not recommended.

Because my pipes were nearly new, I chose to destroy the engine exhaust header studs instead of the flanges. It turned out to be a good choice, as the damaged studs were easily removed and replaced. Tip: Maybe I was lucky. I know that sometimes exhaust parts, including studs, can become seized, due to the intense heating/cooling cycles of the engine.

If you decide to damage your studs in order to get your pipes off, you must do so carefully, so as to leave the engine head, and if possible, the pipe flange, undamaged. To accomplish this, I suggest any of the following:

  • A cold chisel or large punch, and a hammer -- carefully striking the side of the end of the stud to straighten it.
  • A sacrificial nut, 8mm x 1.25, screwed loosely onto the end of the stud, then carefully struck with a cold chisel/punch and a hammer. This method might save a bent stud. See photo below.
  • A small cut-off wheel on a saw/grinder such as a Dremel or Roto-Zip with flex-shaft attachment. Note: Extreme caution must be exercised so as not to damage the engine head, the flange, or the pipe. The cut must be made between the flange and the engine head, leaving enough stud remaining in the engine to allow you to clamp vise-grip pliers, or to thread on two nuts to unscrew the stud from the engine head.

 

Image

 

Once the pipes are off, if your exhaust-header studs look straight, true, and in good condition, they probably don't need replacing. In this case you can skip to the section of this article entitled: Straightening the Exhaust-Flange(s). However, if any of them look bent, badly rusted, or otherwise beyond help, replace them. If in doubt, try threading a nut (8mm x 1.25) onto the stud. You should be able to screw it on with your fingers; if you can't, I'd recommend replacing it.

My studs weren't held into the cylinder head very tightly, so it wasn't hard to get them out, but I believe they were held in with a bit of thread-lock. This means, you've got to get a firm grip to get yours out without damaging the head(s). This is critical; if you damage a head, you must take it to a reliable Yamaha repair shop or automotive machine shop for repair or replacement -- and that won’t be cheap.

You could get two, 8mm x 1.25, standard nuts from your local hardware store. You could thread them both onto the end of the stud and then jam them hard together. Finally, you could unscrew the stud by using a wrench on the inner nut.

I say, "You could," because in my case, that wasn't an option. My studs had been bent and thread-damaged to the point that a nut couldn't be threaded on far enough.

Instead, I used locking pliers to firmly grip the stud. I had no trouble getting the studs free of the head. Then I cleaned out the stud holes in the heads with a little brush attachment on my Dremel rotary tool, and then blew any debris away with compressed air.

Important Tip 1: If you use power tools around the engine's exhaust port(s), be sure you stuff a rag or something into the port-hole(s) to prevent any chance of debris finding its way into a cylinder, and possibly damaging your engine.

Important Tip 2: If you use any power tools on the heads, be very careful and work slowly. Heads are made of aluminum (soft), and new heads are well over $1,000... Work slowly and cautiously.

 

 

Installing New Exhaust-Header Studs

You can replace your damaged or rusted exhaust-studs with Yamaha O.E.M. replacements, but I opted to go with aftermarket, stainless ones. See the Parts Needed section above for details.

My supplier offered stainless replacement studs with two different options:

  • With hex (allen) recessed facets cut into the ends. Note: This is what I got.
  • With plain (blank, solid) ends, like stock studs.

The stainless won't rust, of course, but it also doesn't expand/contract as much as steel. In my opinion, this MIGHT help a little by creating less variable stress on the nuts, the gaskets, and the head -- which, in turn, MIGHT lead to less potential for seizing or loosening over time. Note: I have no proof one way or another. It's just a theory.

Examine your replacement exhaust header studs. They usually come with a short, non-threaded section near-ish the middle. If so, sure to orient the shorter thread-sections into the heads when you install them. See photo below.

 

Image

 

If your studs have no non-threaded section, but do have a recess-hole in one end (for an allen wrench), the hole ends go out away from the heads.

To install the studs, just paint some blue thread-lock on four or five threads of the engine-head end of the stud. Then screw the stud in with your fingers.

If your new studs have a hex hole in the end, finish screwing in the stud using a hex (allen) wrench. If however, the stud ends do not have a hole, like stock ones, just thread two 8mm X 1.25 nuts onto the stud and jam them together. Then finish screwing in the stud using a wrench on the outer nut. Use 7.2 ft-lbs of torque for stock or other plain steel studs. Use 6 ft-lbs of torque for stainless steel studs--not very tight at all. Then, of course, if you used jammed nuts, un-jam and remove them.

Straightening the Exhaust-Flange(s)

If your pipes have removable heat shields, and you can slide the flanges off the exhaust pipe, straightening the flanges should be easy. Once you get the flanges off the pipes, if you have a large, smooth-jaw vise, you can just clamp them flat (after protecting the chrome, of course). If you don't have such a vise, you could just sandwich each flange between two thick boards, and drive a car over it. Or better yet, take your flanges to an auto body shop or muffler shop and have them flatten your flanges.

If you've been able to straighten your flanges by the above means, great; you can skip the rest of this section. If not, read on.

Now comes the hard part: getting the flanges flattened out by yourself.

The idea is, to hold the flange sides down against the header neck while applying back-pressure at the hole-ends. Note: While it would be less complicated to simply brace the flange's hole-ends while using clamps to screw down the flange sides, I dismissed this option, as the clamps would have wedged against the heat shields and thereby bent or scratched my new pipes.

To create this setup, assemble the miniature jacks (described in the Tools Needed section above) into both mounting holes of the flange, as follows:

  • Thread a nut onto each of the two bolts, nearly all the way to the bolt-heads.
  • Slide a flat washer onto each bolt.
  • Insert a bolt through each flange hole. Tip: The bolt head goes toward the pipe's head.
  • Slide another flat washer onto each bolt -- optional.
  • Thread another nut onto each bolt -- optional, but recommended.

The result should look like the following photo.

 

Image

 

Next, find a scrap of sturdy wood; a piece of 2" x 4" wall-stud will do nicely. Hold the wood flat against the pipe's head while you simultaneously secure two C-clamps to hold the pipe-head and wood together. To do this, place the C-clamp's fixed jaw at a point on the flange 90° from the flange-bolt-holes. Of course, the other clamp goes to the opposite side of the flange. The screw-jaws of the clamps are set against the back side of the wood. See photos below.

 

Image

 

 

Yamaha roadstar exhaust flange fix bent jack straighten

 

Tip: A helper can ease the frustration of getting the C-clamps snugged up tight, as there are many awkward pieces to control at once.

Once you have the board firmly clamped onto the pipe's head, tighten the C-clamps further. As you do this, be sure to alternate between both clamps -- little by little -- until the clamps are very tight. It is important that the clamps be tight. Just be sure you don't make them so tight as to bend the flange or break a clamp.

Now you're ready to straighten the flange.

Next, slip a large fender washer or other piece of thick sheet metal (roughly 1/16" or so thick) between one of your jack-bolts (in the flange holes) and the board. Then slip another washer (or whatever) likewise under the other jack-bolt.

Now, put an open-end wrench on one of the little jack bolt-heads. Then put another open-end wrench on the jack’s nut. See photo below.

 

Yamaha roadstar exhaust flange fix bent jack

 

Next, begin to screw the jack-nut up against the flange while holding the bolt-head from turning. Once the nut begins forcing the jack against the washer (or whatever), switch over to the other side, and do likewise.

Now, it's simply a matter of alternating between the two jacks; keep tightening the nuts, little by little. As you do this you should begin to see the flange straightening out. Note: I find it amazing how tightly the nuts must 'jacked up' to straighten the flange, compared to how little force was used to accidentally bend it. I guess that demonstrates to power of heating and cooling.

Finishing Up

 

Image

 

 

Image

 

Now it's just a matter of putting everything back together. If your flanges have been removed from the pipes, slide them back onto the pipes before re-attaching the heat shields.

Next, follow the manufacturer's instructions for loosely mounting the pipes. If you do not have access to decent instructions, then I would recommend you begin with the header section of the front pipe. Work it into place, being careful around the place where it passes between the floor-board and the engine cases. Use soft rags to protect scratching or touching. After positioning a new exhaust gasket into the exhaust port of the engine head, slide the flange onto the engine header studs. Hand thread the flange nuts, but do not tighten. Then do likewise with the header pipe section for the rear cylinder.

Then attach the tail-pipe section, if your pipes have one, to the head-pipes and to the frame -- loosely. Note: If you have a three-pipe-section, you will need to loosely assemble all parts for both front and rear head-pipes before attaching the tail-pipe (if any).

Once all parts are together, you can tighten everything up. Just be sure you use two principles as you tighten:

  • Tighten each nut, bolt, and screw a little at a time -- usually starting at the header flanges, and working your way aft.
  • Slightly wiggle the pipe(s) as you go, to be sure everything is seating squarely and properly -- especially each head-pipe where it seats into the exhaust gaskets.

Of course, be especially aware to tighten the header flange nuts SPARINGLY. 3 or 4 ft-lbs of torque should be enough. Tip: The easiest way I've found to gauge this is to insert the long end of a long, 'L' shaped allen wrench into the flange nut. Use this by hand to snug the nuts down, little by little, as you continue to tighten everything up. Finally, after the flange nuts are hand-tight and all other fasteners have been tightened, use some linesman (blunt nose) pliers on the small end of the allen wrench to tighten a bit more. Tighten each flange nut about 1/2 turn more with the plier assisted allen wrench.

Carefully and thoroughly clean the pipes and engine cases of all dirt and finger prints. Sometimes the heat can permanently etch fingerprints and smudges into chromed and/or painted pipes. If your pipes are chrome, be sure to use a very soft cloth, as it scratches VERY easily.

Next, go for a ride. Pay special attention to the sound of deceleration. If, under hard deceleration, you hear popping sounds you may have one or more exhaust leaks that must be found and fixed.

If you have an exhaust leak you should carefully examine where the leak might be coming from. To do this, you can look for signs of soot around the pipe joints, flanges, and surrounding areas. You can also try holding a smoke (cigarette or incense or something) close to pipe joints -- including around the exhaust gasket area -- while the engine is running.

Tip: If your flange nuts thread onto the studs too far (due to thin flanges), or you are having trouble sealing exhaust leaks at the gasket area, you may find it useful to use two exhaust gaskets for each pipe. You may also find it helpful to use silicone exhaust sealant between the gaskets. See the Tools Needed section of this article for information on sealant, and the Parts Needed section for information on gaskets.

Once the leaks have been found, wait for the pipes to cool before fixing them. Then go for another ride and listen again.

Once you're comfortable no leaks exist, let the system cool down. Then check the flange nuts for tightness. The heating and cooling may have compressed the exhaust gaskets and worked the nuts loose, especially if you installed two gaskets per cylinder. Tighten as needed.

Ride again for at least 15 or 20 minutes, until the engine and pipes have thoroughly warmed. Then let the pipes cool, and check the flange nuts for tightness again. If you feel they have come loose, tighten them down just a little more than you originally did, and go through the ride tests again.

If all is well, check all the other nuts, bolts and screws of the exhaust system for tightness, one last time.

You're good to go.

 



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DISCLAIMER: This information and procedure is provided as a courtesy and is for informational purposes only.  Neither the publishers nor the authors accept any responsibility for the accuracy, applicability, or suitability of this procedure.  You assume all risks associated with the use of this information.  NEITHER THE PUBLISHERs NOR THE AUTHORs SHALL IN ANY EVENT BE LIABLE FOR ANY DIRECT, INDIRECT, PUNITIVE, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, OF ANY NATURE ARISING OUT OF OR IN ANY WAY CONNECTED WITH THE USE OR MISUSE OF THIS INFORMATION OR LACK OF INFORMATION.  Any type of modification or service work on your motorcycle should always be performed by a professional mechanic. If performed incorrectly, this procedure may endanger the safety of you and others on your motorcycle and possibly invalidate your manufacturer’s warranty.


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  Comments (1)
Straightening Bent Exhaust Flanges
Written by arty, on 04-16-2011 01:33
I had this problem 4-6 months ago when removing the chrome covers from my bub shorts. I still had some movement in the flange though, so rather than hit and bend stuff I was able to patiently work the flanges off. Once off I gripped one end in a bench vice and used a 12" shifter the pull it straight. 5 seconds tops. When reinstalling I tightened till the pipe didn't move when pulled/wiggled by hand then a touch more. No problems to date.

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