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Old 04-03-2012, 01:19 PM   #49
FJ_Kevin OP
Gnarly Adventurer
Joined: Dec 2010
Location: Maryland ==> originally from Long Island
Oddometer: 365
wfopete: It seems some OW's had a steel brake stay (OW40 above) and some had aluminum like the Rick Burgett OW41. I like the look of the alloy one better

So now onto the exhaust pipe/silencer system!

Some time ago I picked up a nice (and cheap) DG pipe intended for a 1982 YZ490. I figured the motors are so closely related that it should work fine on the 465 too (displacement wise, the bore on mine will be 1mm oversize and that gives 476cc's, not too far off the 487cc's of the 490).

In comparing the 490 pipe to the original, I found the connection to the silencer is made at a different point along the stinger. In essence, the portion of the stinger attached to the pipe is shorter on the 490 version. The overall length of the stinger (pipe + silencer) is about the same. This wasn't such a problem as I was replacing the silencer anyway and would be redoing this connection.

I wound up using the same universal FMF turbo core silencer / spark arrestor as used on my it490. This is a good quality part (~$100) and comes as a kit with an extension pipe, a weldable mounting tab and a hanger bracket. The outside is aluminum so it's not too heavy either.

The spark arrestor part of it may be a bit restrictive for motocross although I have to say this didn't seem to hurt the output of the IT490 . In any case, the restrictive arrestor section can be removed for the most part by drilling out the internal cone as I did for the 465. This can be done from the end, using a 3/4 - 1in drill bit mounted in a drill press.

Below is a pretty good photo of the IT490 exhaust I did last year. You can see how the stinger extention has been welded to the end of a new DG pipe. The silencer is clamped on to the other end of the extension. The mounting tab is welded to the extension at a point where it can be bolt to the original rubber mount. Again, this setup has been working well and so I decided to something similar on the 465.

Now for the 465,

Here is the pipe and silencer test fitted with the motor in the bike. Yamaha normally uses a rubber coupling/clamp arrangement to attach the silencer the the end of the pipe (the point above the airbox in photo). I never liked this as the joint often leaks hot exhaust gas onto the plastic number plate, sometimes melting it. My plan was to weld this joint to avoid leaks and side plate damage.

Before welding, some care was taken to ensure the stinger section was well tucked in. I did not want any possibility of melting my new side panels nor did I want the pipe to rest or vibrate against frame tubing.

This next photo shows how tight the routing area really is between the side plate and frame.

After tack welding and some clearance checking I welded everything up for the final time. BTW, I should say the front of the pipe is in much better shape than it looks in the photo for some reason. Also, most of the exhaust is isolated using the (new) OEM rubber mounts. The silencer mounting point is partially isolated from the frame with a rubber bushing.

With the exhaust taken care of it was time to move the motor back onto the bench for some freshing up. And there was plenty of surprises to be found there (to put it mildly!).

But until then...

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