INTRODUCTION
Last year I completed a mechanical restoration on my IT490 and a few things about the exhaust really bothered me. Firstly, there is no good gasket solution for where the head pipe flange meets the cylinder flange. The "Gasket" as listed in the Yamaha parts diagrams isn't really a gasket but a really thin metal washer designed to prevent the steel pipe header from wearing away the aluminum spigot on the cylinder. It also doesn't work well in the DG pipe. I really disliked the Spooge that accumulates on the front of the motor and frame and the rattle and exhaust leak from inadequate sealing drove me crazy. I also worried about sucking water during deep river crossings and also wondered if an absolute seal would improve performance.
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The second issue I really disliked is that the silencer was angled towards the rear fender and would carbon it up. The angle seems to be caused by incorrect bend in either the DG pipe stinger, the Answer silencer, or both. Also to race and ride where I live, I need a spark arrestor and this silencer lacked that. So in the post I will show how I solved these issues so others can follow suit.
DEALING WITH THE HEADPIPE FLANGE
In my research I found most just live with it or attempt to seal it by using lots of high heat RTV sealer. To me, I did not feel like that was a good solution, I did not want to deal with sealer every time I wanted to remove the pipe. Finding no adequate solutions online, I decided to figure it out on my own. I found that the metal washer pictured above cross-references to YZ250 models 1987-1994 and WR-250 models up to 1997. This implied to me that there's a good chance those models used the same exhaust cylinder spigot flange size. Looking at their parts diagrams, it showed that those models used an integrated O-ring on the exhaust header! I looked on ebay and found a seller selling a smashed FMF pipe off a 1988 YZ250. I offered him $45 to cut the header off and send me just that piece and he agreed! This is the header flange from that year. Notice the O-ring on the inside.
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Measureing the cylinder exhaust spigot revealed around 55.65mm in diameter. Measuring the inside diameter of the O-ring in the new Head pipe flange revealed just under 55mm. This seemed like it was going to work! The head pipe flange fit nice and snug on the spigot but with virtually no clearance to the frame. The motor will have to come out to clearance the frame.
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After removing the motor, I used propane torch to heat the area red hot, then a big socket and bigger hammer to create clearance for the new head pipe flange. Then A bit of sanding and a dusting of rattle can black to fend off corrosion.
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Next, with the motor refitted to the frame, I can check if the clearance worked. Looks almost factory!
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Next, I cut the Flange off the DG pipe and the Flange of the YZ250 head pipe. I found a socket that perfectly fit the inside diameter and used that to fixture the flange concentric with the DG head pipe.
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After a test fit, a bit of welding and a bit of paint, I now have a perfectly sealed head-pipe on this old girl!
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FITTING AN FMF UNIVERSAL SILENCER
Next is addressing the non-spark arresting and horrible fitting silencer. I wish I got a better picture of how misaligned the silencer was. Unfortunately I didn't but The below image shows a photo before I mechanically restored the bike, you can kind of see it. The end of the silencer was pointing under the rear fender.
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The silencer kit I used to fix this mess and get a spark arrestor is a universal FMF turbine core 2 kit with 1 1/4" stinger size. The part number is 020303 and comes with everything in the below image.
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To ge the right angles on everything I ended up cutting and shortening the Stinger on the DG pipe. I don't know about the newer pipes but this old one just had the wrong angle on the stinger. In the future if I buy another, i'll probably shorten the pipe on the silencer instead but for now, this worked best.
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To make removing the silencer easier, I spot welded the stainless steel band together once I had everything aligned on the bike. This way when removing the number plate, I don't have to deal with the clamp springing open.
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Not the best welding, but here's how I installed the rear support hanger for the silencer.
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Here's some photos of everything installed and buttoned up. Fit is now perfect!
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Conclusion:
With these exhaust mods, the bike no longer spooges all over the front of the motor, it runs much quieter and cleaner without the exhaust leak. The silencer fit is exactly how I want it and I have a legal spark arrestor so I can race and ride public lands. I will measure and make a drawing of the header flange so any interested persons can take it to their local machine shop and have them turn you the flange on a lathe. I will probably get some made up for myself so as I smash and replace pipes, I can just easily weld on a new flange to the new pipes I buy to get that sweet o-ring seal. Hope this helps! Thanks for reading!
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