Yamaha TRX850 Enthusiasts Forum

The R1 front on a TRX is a great march and pretty easy to get hold of, but there's just one problem; As many would be aware, the R1 speedo doesn't run from the front wheel (rather it has sensor pickup on the output shaft I think? doesn't matter..) so to keep the original TRX speedo whizzing about, you'll want to use the TRX front wheel, but then you find that the R1 axle is too fat and won't go through the TRX hub which can't be machined to take a larger bearing. Bummer.

So, TRX axle diameter... too skinny for R1 axle bores. End of story? Not necessarily. What I needed was an axle that was fat on the ends but skinny in the middle, that could still be poked through the wheel hub. Solution; a composite axle. It sounds radical, and was a little bit of a muck-around for sure, but in my opinion well worth the effort.

To explain the attached design diagrams below; red bits are original R1 (2000) - green bits are TRX - blue bits are custom fabricated.
Basic run-down of the task was as follows;

1. Threaded end of R1 axle is cut off at 54.5mm long and threaded internally to accept M12 HT bolt* at the outer end. The end facing inward may need to be bored to 17mm to accept the TRX axle. This part will effectively sleeve the R1 left fork axle-bore to accept the smaller diameter TRX axle.

2. The TRX axle is cut down to an inside length of 218.5 mm, and also threaded to M12 and fitted with a M12 x 50mm HT bolt (with head cut off), permanently fixed in place with thread-locking compound (after test fitting of course). Even though the bolt is HT, wheel forces are transferred directly from axle to fork ...any load on the bolt is negligible.

3. A steel or aluminium bush (ED 28mm, ID 17mm, Length 28.5 mm) needs to be turned up and fitted to the Right-hand end of the TRX axle. IMPORTANT!;[/b] the axle must be completely unable to rotate inside this bush, otherwise the axle could unwind itself during riding, despite the clamp bolts in the fork axle-bore being done up tight.

4. Because the R1 doesn't have a front-wheel mounted speedo drive, it doesn't allow for placement of such between the wheel hub and the left fork on the axle. A few mm of material (forgot how many exactly) will need to be machined off the inner face of the left fork to allow room for the TRX speedo drive and keep the wheel centred in the forks.

5. To prevent the free rotation of the speedo drive, I made a small L-shaped locator lug from 3mm aluminium and fitted it to the inner face of the left fork by drilling and tapping a shallow hole and fixing with a small thread-locked bolt. *M12 bolt; diagram originally had 13mm 14mm threads specified, but axles were found to have sufficient thickness to allow 12mm thread which made fabrication much simpler.

NOTE: As stated on the diagram, it should be noted that this drawing represents a modification that is yet to receive engineers approval. Laws regarding road use may apply to it's application in various jurisdictions. No warranty expressed or implied.

Excellent stuff. Thanks for posting, I am am sure many will find this helpful

Possibly a sticky?

Agreed. Very good. Love the disclaimer, a sign of the times


Mark.

Yep, I hereby take ZERO responsibility for anothers piss-poor engineering skills!

you make me laugh mince

Is the TRX thread M16x1.0 ?

@previous poster: the TRX axle thread is 16x1,5mm.

Very glad to have found this topic. Just recently bought an R1 fork and after transferring the TRX steering stem with some handmade bushings was able to fit it to the TRX frame.

The front wheel is indeed a difficult one. There isn't an comparable rear wheel to be found which fits the TRX rear swingarm, so I too want to adapt the front fork to accept the TRX axle.

Some nice, perhaps recognizable thoughts here, from the start (easiest solutions first!) of this thought process towards my current plan including a drawing
- R1 axle is 20mm. TRX bearing is 17mm inside diameter and 40mm outside. Let's see if there's a bearing with 40x20mm spec --> non existent and if so, perhaps not up to the load, deemed too unsafe
- Mill the TRX bearing notch to a larger diameter which will accept the R1 bearing --> impossible to do safely and reliably
- Insert a helicoil in the M18 thread of the R1 leg --> helicoils are a temporary solution, deemed to unsafe
- Use the solution of our topic starter -> not all cutting/tapping equipment is available to me, also it seems to me that creating an axle out of 2 parts and drilling the inside of the TRX axle is not reliable enough for track use
- Create a complete bushing inside of the R1 leg --> M18 bushing leaves to little space around the M17 thread of the TRX axle when inserted, even though not inserted fully.
- CURRENT PLAN!
Drill the M18 thread
Tap an M20 thread
Insert an M20 bushing
Tap an M17 thread
Presto!


I reckon that with 1,5mm 'wall' on either side of the bushing, it will provide sufficient support for the axle.
Small thing here is that to create a safe bushing in the RIGHT leg, the 'nut' part of the TRX axle needs to stick out of the leg, as shown in the topic starters picture.
This will require the thread to be on a different spot in the LEFT leg.

Measure, think, remeasure, think, measure, measure, drill!

Any remarks before I fire up the lathe?

I did mine differently.
I used a longer 17mm swing arm pivot pin from a DT.
Welded a 17/22mm spacer in place at the bolt head end that took care of the 22mm fork axle hole on 1 side. 2 x 17mm ID wheel spacers to fit either side of the trx wheel. And then slipped a 17/22mm spacer inside the other fork leg. Cut and re thread the axle to take a nut and not screw into the fork. ( just like the rear axle set up.
But your R1 forks need to be early model that took a 298mm disc.
320mm disc on a trx is a big overkill and more weight and rotating mass so only slows down your handling...