In the process of doing this now for an 81 DT175 - 1997 RT180 donor forks - with disk brake .
I'm stumped at how much fork oil to use. Have spent an hour online (Rt180 fork oil, fork oil level, fork oil amount, shop manual, fork oile specs, etc, etc, etc. Nuttin. Did find an owners manual - that indicated fork servicing shall be performed at an authorized Yama Dealer...

So. Anybody know?
I am about ready to install enough to give me around 5-6'' from oil level to top of fork with springs out - the last couple bikes with normal forks I have done were close to this.

Send a PM to MarkT. He has a lot of experience with those bikes.

Here is a downloadable factory service manual?

www.tradebit.com/filedetail.php/10022749...180-rt-180-a-g-90-98

From service manual:

Thanks gents.
I saw that download, but have had less than good results with others of that ilk "download here!". That said, this was my plan B...

Thanks for the exact #'s Mark. I guessed pretty close - I used 260cc, which resulted in 5" (125mm) clearance between top of fork and oil level, no springs, with forks fully compressed. Oddly, I have only seen these measurements using "fully compressed" - not as the shop manual for the RT180 indicates - with "tube fully rebounded".

I'll post some pics once I get a little further along.

Also oddly, while I have seen some threads mentioning this swap, have not seen any build threads or pics. I spent a fricken day trying to get the rusted in c-clips and the plugs out of the tubes. After breaking the c-clips into pieces, ended up having to drill and tap an 8mm hole in the plug (this was after the 6mm bolt stripped), insert a bolt with a couple big fender washers, and beating on a dang pickle fork with a 5 lb sledge.

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Hey. Guys. Do you release the tubes from the sliders to get the fork seal out? Is there an allen bolt to slide down the fork tubes to get release the bottom 8-mm allen bolt ? Then pull the tube up and use as a slide hammer? What size allen screw is at the bottom of those tubes? 1992 RT180...

The only thing you need to remove is the allen bolt at the bottom. The forks slide apart easily after that.

Putting the springs back in and pushing down to collapse the fork while using an air or electric impact wrench on the bottom allen zips the bolt out about 80% of the time. (Friction/pressure of the spring on the damping rod keeps it from spinning)

If that doesn't work, Yamaha makes a special tool you use with a long extension to keep the damping rod from spinning while you loosen the allen bolt. That tool might be a must without an air/electric impact wrench.

A friend told me he's used a "gator grip" socket (the ones with the spring loaded pins that fit "any" nut) to hold the damping rod. I don't have one of those sockets and have never tried it.

What I do if the spring pressure doesn't work is hold the damping rod with a tapered wooden tool handle you can buy at most hardware stores... you probably have to file/whittle/sand the taper to fit into the damping rod. Then tap the wood rod into the damping rod to wedge it in place and zip the bolt loose with the impact.

Here's a pic of the rod in the damping rod.... shown outside the fork tube for clarity.... when assembled the damping rod is down inside the fork tube.

Thanks Mark! Got it. The impact wrench worked great. These forks are kinda a weird design? At least the seals were easy to get out.

I am adapting a set of RT180 forks and triples to my wife's XT250. 

I made this tool out of scrap metal and an old socket to hold the damper rod:
 

Does anyone have the torque spec for the large 19mm allen plug in the top of the forks?  

I torqued the 8mm allen at the base of the forks to 20 N-m.  Can anyone tell me if that is close? 

Thanks in advance, 

TS