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Question on YZ forks/triples on TT500

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I'm in the process of putting '79 YZ400 38mm forks onto my '79 TT500 vintage mx racer.

I know this is a fairly popular swap and everything I can find through searching is that it's "straightforward", but I'm stumped on something so hoping someone can help me out.

I have a set of late 70's YZ triple clamps for the 38mm forks. I'm not sure the exact year of the clamps, they still have the pinch bolt on the steering stem so know they are older than '79 (have had a '79 YZ250 and 400), but from what I can see, they look like what I need.

Sitting the YZ triples next to the TT triples, everything looks basically the same except the outer diameter of the YZ bearings is bigger and the YZ steering stem is maybe a couple of mm shorter than the TT's, but should work.

I've been running tapered roller bearings in the TT. I thought all I needed to do is get a set of roller bearings for the TT, and use them on the YZ steering stem.

The problem I've run into is that it appears that on the TT bearings/stem, there is a shoulder that raises the lower bearing about 2-3mm up off the bottom triple. On my '79 TT triple, it looks like it's a shoulder forged into the steering stem. I looked at an old set of XT triples I had laying around and the shoulder stuck up off the bottom triple clamp, but accomplished the same thing.

The YZ steering stem and triple clamp doesn't have a shoulder like that, and without it, the bearing sits too "low" and doesn't go far enough up into the TT steering tube to seat on the race.

So, unless I'm missing something, I'm wondering if others are putting some sort of spacer under the lower bearing on the YZ stem to lift it up? Or do I need to swap the steering stem out of the TT lower triple into the YZ lower triple (in which case I need to get a new model YZ triple that doesn't use the pinch bolt).

Any help is greatly appreciated!

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are the forks on the 79 yz larger than a 78? reason I'm asking is that I put a set 78 yz forks on my 79 tt and they were a bolt up,everything fit.

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I'm 99% sure the '79 YZ 250/400 forks are essentially the same as the '78's. How exactly did you bolt it all together? YZ forks, YZ upper triple, YZ lower triple, YZ steering stem with TT500 bearings and TT500 races... or some other configuration?

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I'm starting to think I need to press the TT500 steering stem into the YZ lower triple clamp.

On the '79 style lower triple clamp (no pinch bolt), which direction do you press the stem out? Up from the bottom or down from the top?

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the 79 tt 500 came with leading axle forks,shorter than the yz.mine was a pull out the old ones and slide the yz forks in place. the triple clamps are basically the same.

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That really surprises me. YZ250/400 forks are 38mm. The stock '79 TT500 forks are 36mm.

Yep, in '79, the TT500 went to leading axle forks and an aluminum swingarm.

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I think I've determined that I need to press my TT500 steering stem into the YZ triple clamps as part of the swap.

Can anyone tell me which way you press the stem out of the TT/YZ triple clamps? It's not obvious by looking but I'm sure it will only go one way.

This is the style that is only pressed in, no pinch bolt on the lower triple clamp.

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The stem needs to press out from the top. It usually takes a press to do it.

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The stem needs to press out from the top. It usually takes a press to do it.

Thanks! I have a press. Just to make sure. I will want to press stem DOWN through lower triple clamp, right?

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Yes and be sure the bottom clamp is well supported as close to the stem as possible. A little heat applied can help if the stem is hard to move. I use a Mapp gas torch to heat up cases to remove and install main bearings. Good luck

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You only need a 3/16 thick spacer between the top of the bottom triple and the bottom of the lower bearing to use the YZ triples. The TT got it's front suspension and wheel from MX YZ inventory so most Yamaha front ends will work on the TT500 with minor fettling only

Edited by jimspac

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