Straightening Bent Exhaust Flanges

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

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.

 

 

 
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