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XT TT 500 - minus 5 deg. rake / caster

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So I've been flattracking my XT500 for a number of years it's always worked pretty well but I've always known the Rake angle / Caster angle wasn't optimal.  The way I had things set up it was pretty close to 30 degrees great as a drag bike or desert racer not so good for short track. 

Lots of people have done this mod to the 500 Yamahas  and most people just cut the lower part of the frame and heat the tank with a torch and pull the wheels together to bend the tank.

I'll start by saying I didn't have a torch handy but I did have a TIG welder handy.

Wanting 5 degrees I looked at a draft angle chart and did some simple calculations and they worked out pretty well.  From the bottom of the frame to the top of the tank is almost exactly 6".   So 5 degrees over one inch of height  is .087" Multiply that by the 6" of height =.522"

So the cut at the bottom of the frame worked out to .522"  at the top it should be zero .

 

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all marked up

 

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the first cut is the most painful

 

 

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cut goes from .522" to .348" give or take a few thow :)

 

 

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at this point be gentle there isn't much holding it together any more.

 

 

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Strap and ratchet it together.

 

 

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The fit's not too bad.

 

 

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I clamped a parallel to the side of the frame to keep everything in line.  It worked pretty well.

 

 

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Welded the bottom first

 

 

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Then the side

 

 

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and the other side

 

 

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Check the angle.

 

 

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? 24.75 ? ish . 

 

 

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Now to weld the oil tank. I've run another Argon line to the tank to back purge the oxygen out of the tank this makes the welds nicer on the inside. 

 

 

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and done.

 

 

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Just for insurance I made some simple fish plates out of .060" 4130 sheet and welded them on wrapping them slightly around the bottom also.

 

 

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And that's it .   Now for rear shocks and mounts. 

Edited by BruceD_500
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Commendable. Very commendable. Nice work on the frame and the pix, Bruce.

Is the fork angle measured off perpendiular? Or frame at the seat or engine cradle?

Edited by Jimmy Pascol

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Commendable. Very commendable. Nice work on the frame and the pix, Bruce.

Is the fork angle measured off perpendicular? Or frame at the seat or engine cradle?

 

Thanks Jimmy,

 

I measured the fork angle with the bike sitting on it's wheels.  stock is apparently more like 28ish from what I've read. So I figured -5 would be about right.  I took a reference measurement before I cut it and that was showing 30deg. ended up just under 25.

Once I get the ice tires on I'll need to adjust shocks and forks again to get it where I want it.   

Edited by BruceD_500

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IMG_4391_zpsgoyeh2ab.jpg

 

 

 

I'm pretty sure this area on the frame is plenty sturdy for flat track but I probably would not use this spot for MX   IMG_4348_zpspitrtntw.jpg

Edited by BruceD_500

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You do good work, Bruce.  You may be the first I've heard of to cut the oil tank too.  Glory belongs to the bold.  

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You do good work, Bruce.  You may be the first I've heard of to cut the oil tank too.  Glory belongs to the bold.  

 

 

 

I probably should have mentioned how I got the metal shavings out of the tank after the cut. The saw blade was covered in grease for the cut.  I then flushed the oil tank with lots of mineral spirits and lastly I always run a magnet epoxied to the top of the screen at the bottom of the front down tube. I've yet to find any shavings on that magnet.  But if anyone plans to go this route take care to clean the oil tank well.   

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Bruce, how did you determine your shock angle and new upper mount location?  Some lay 'em down and some leave them more upright.  

 

Man, if I could weld or hit a curve ball, my life wld hv bn been completely different.   

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That upper mount location is the stock location of what I think was the seat strap ??  It's an M8 thread if I recall correctly . So really it's already there I just beefed it up a bit.   The small spacer is also threaded inside then screwed down to touch the frame so the threads match the factory threads then welded in place .         IMG_4248_2_zpsb4henjwc.jpg

Then I went about making the shocks the correct length.  Which happens to be the stock length shocks and honestly I'd like them a 1/2 longer I think.  Only because the swing arm seems a bit flat. Idealy  I think raising the swing arm pivot up 1/4" - 1/2" would be better but that's not easy and hard to put back if you don't like it.  In the end the fork angle ended up right at 25 deg. The forks are Kawasaki EX500 forks with emulators that were set up for road racing. I got them cheap on e-bay they were a bit stiff but with oil level I managed to soften them a bit to where I like them ok.  But they are fully down in the stock triples so I can't raise the front I can only lower it. But I haven't needed to do either yet.  I keep waiting for it to do something wrong but it's very stable and just seems to work.   

Edited by BruceD_500

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My 1979 TT500 specs at 30° rake stock setup. For my intentions of creating a better handling package I will be bring the rake in to 27° or 28° and replace the stock swingarm with one from a PE400. I have had this mocked up for a few years and only thing left is the derake.

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So 3 deg.      .087 x 3 = .261"  cut at the bottom (don't forget to factor in the blade width) for that small change I would probably just heat the tank rather than cut the tank and since I assume you'll be doing some jumping I'd definitely do the gussets on the bottom over the cut area.  

Just make sure it doesn't shift side to side when you're pulling it in other than that it's pretty hard to go wrong.  Take photos when you do it ;)

Edited by BruceD_500

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Thank you. I already know how to do layouts as I have been an engineer , programmer, and fabricator since the mid 70's when these bikes were new. Even though I will only be pulling in 3°, I am trying your method because myself and a few others frown on heating and bulging the oiltank. I know it works but does not mean I have to like it:)

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Agreed on the torch and bulge  ;)    Mine now has a full year on it with ice last season and dirt track this season. No issues at all and it handles more the way I wanted it to.  I have an XT that I street and trail ride with, I'd like to do a mild rake on that similar to what you're doing.  Maybe when I get time. 

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Same process but without cutting oil tank....

 

Deraking Frame pic One.jpg

 

Universal Truth in Flat Track:  Your shock length will determine your swingarm angle.

 

I was shooting for 7-8 degrees but can only get 4 degrees out of it using a 13" Redwing shock off Ebay.  The bike squats and runs wide coming out of a turn because of that.  I'll be dropping the fork tubes in the triples or going to Plan B with a longer shock to get the 7-8 degree s/arm angle.  I welded my shock mounts 1" too far back on a Radian swingarm and life hasn't been the same since.  Maybe relocating the upper mounts like yours is the answer.  My measuring tape must be off.

 

Let's hope somebody out there is learning from our work.  My Flat Track Notebook is still available for the asking if anybody wants it. 

Edited by Jimmy Pascol
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Trying the top location I'm using is easy , it's already there you just need a bushing for the top eye on the shock.  If that works for you then you can do the fab work to make it permanent. 

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Same process but without cutting oil tank....

 

📎Deraking Frame pic One.jpg

 

Universal Truth in Flat Track:  Your shock length will determine your swingarm angle.

 

I was shooting for 7-8 degrees but can only get 4 degrees out of it using a 13" Redwing shock off Ebay.  The bike squats and runs wide coming out of a turn because of that.  I'll be dropping the fork tubes in the triples or going to Plan B with a longer shock to get the 7-8 degree s/arm angle.  I welded my shock mounts 1" too far back on a Radian swingarm and life hasn't been the same since.  Maybe relocating the upper mounts like yours is the answer.  My measuring tape must be off.

 

Let's hope somebody out there is learning from our work.  My Flat Track Notebook is still available for the asking if anybody wants it. 

 

 

Is that an SR500 frame ? 

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BruceD, I must say you do nice work! Please come back with a ride report when you finally get it rolling.

 I bet very few people know it was a fad for a while to pull the rake in by cutting and re-welding the frame the early Yamaha DT series, like the DT-1 - even for MX.  

A friend had one that was modded.  I think it was an attempt to get the DT's to corner like the European bikes.

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Thanks motovet as for a ride report, this thread is a bit old now that work was done about a year ago so I rode the bike Jan-Mar 2016 on the ice. It was much better on the ice than previous. It didn't tend to drift out on the corner exits. You could steer it through the corners properly. I ended up tied for second place in the D14 (Michigan) vintage ice races last season one point behind first . hahaha.  It was a fun season.  That was so much fun that come flat track season we hit that pretty hard did the Flattrack Canada series across Ontario. It was a big season and busy summer so chasing the points was never my plan I just went out to the races I could. The bike worked much better than it had in previous years. I had fresh tires on it and a fresh motor in it so that helped but as for handling the bike was very stable and I didn't crash it all year, that's always a good thing. The steering again was much better than previous. I kept waiting for the bike to do something bad or strange but it never did. It was just a pleasure to ride every time out.   I would like to try lifting the rear a tiny bit with longer and better shocks but that will cost some $'s to get some good shocks. That will happen eventually but for now it seems to be working just fine ;)

 

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Edited by BruceD_500
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