Final drive modification - Disk to Drum.

[dogshome]

Not one to give up, I should soon have in my possession another FD with a more relaxing ratio. IF she passes the 'spin with a gun drill' test then operations will commence   

This one is from a through-axle swingarm, but disk-braked. Hence blanks in the casting. I'd love to have a disk on the back of my R65 though.

Option 1. Fit FD with an 18" alloy from a disk equipped bike. Make a carrier, torque rod and obtain various other bits to get a disk on the back. Depends on cost and availability of a wheel - if it will fit due to offset and width on the short R65 swing arm?
Option 2. Drill the new FD, tap for the shoes pivot and straight through with a brass bush for the drum lever. Doesn't sound too hard and I have a spare case if it all goes pear shaped.
Option 3. Gut the noisy FD I have and fit the new internals into its case. Will require a complete re-shim. Something I am confident doing now.

Thoughts?

[Barry]

I'd be inclined to do option 3. That way you would get a good look at the condition of the new final drive and end up being sure it was correctly shimmed.  Are you going to change the speedo or will the new ratio just take all the optimism out of the old speedo so that it ends up being accurate.

[dogshome]

Option 3 is most sensible. The lid has to come off for drilling and you are right, a good look at.

I also have a 70% set of new bearings cunningly matched with a scrap set of gears 

The only issue I might have is getting the right thickness belville washer to set the gap. The other side can use a mixture of standard shims for free play. If I am lucky, the cases might be similar. The nose shim is no trouble as they are also trapped and can be stacked. The belville is a live one and multiple thin shims liable to tear or get spat out. I used flat ones to see how blue patterns changed (static) before, but can't use that type to run.

The Speedo reliably indicates at least 10mph optimistically at 60. I have a GPS speed stuck inside the canopy and compare with that, my phone and those handy roadside displays. Moving from 3.56 to 3.0 should be about right. Approx 15% change.

If it passes the gundrill test, expect lots of annoying updates. Pain, glory, disappointment or euphoria as applicable 

[Tony Smith]

I would say option 3 is your best bet as it doesn't place any difficult to replace parts at risk.

I once considered making my R860 a three disc machine, but then I needed crucial components for my RS.

If the final drive you are thinking of using is a 31/11 "moonshot" ratieo from m an RS I can tell you it will not be happy in an 860.

That ratio demands lots of low end torque, something a short stroke engine will never have.

[dogshome]

This one is 33:11.No, the 860 isn't a chugger and this isn't ideal. A 6th gear would be!

On the other hand, 70MPH is 4,600RPM, quite buzzy and lively for acceleration. Much quieter at 60 in top and still pulls for overtaking. I never use 4th for driving, even in 50 limit. Always changing up.

I tend to change gear at 4,000 on the open road, which will be 70 on the new ratio. I will have to use 4th to drive in 50 I expect and that is what I want.The bike is quite flexible in town, but no, don't expect to pull any stumps out at 2000 in third. Keep it spinning, don't lug it.

I'm always solo, minimal luggage apart from local shopping for my mum. Flat landscape with the odd hill. I can easily switch back.

[Tony Smith]

I have the FD from an R75/6 in my 860. I also would like a 6th gear but nowhere near as badly as I wanted one when the R65 FD was still fitted.

[dogshome]

YAY!

https://youtube.com/shorts/45EfpMxQLTs?feature=share

[Justin B.]

The splines look practically new!

[dogshome]

It makes up for the dodgy one my friend sold me   

We sorted it out commercially. No body bags       Actually, he was gutted that he'd sold me a pup    Won't stop me from reminding him when it suits me though 


"Who's round is it?" "Well, you remember that FD you sold me?"   

[dogshome]

Hm.... 95% drilled already...........   

[dogshome]

16mm OD brass tube. 13.88 ID, which is a good tight fit on the brake shaft O rings. Successive drills, 13, 14, 15, then 5/8" (15.875mm) which gives a nice fit for the tube.
JB Welded in. I am short of a 10.2mm bit and a decent M12 taper tap for the brake pivot. So there will be a delay in proceedings.

[dogshome]

Well it looks square. JB weld curing on the second bush now. We'll see how accurate when I put the brakes shoes on and try it in the drum 

[dogshome]

This side also looks unnervingly OK 

I have noticed that this early casting has several holes and blemishes that the later one doesn't. Also, the machining of the brake pivot hole and its counterpart 180 degrees away on the other case doesn't match the casting. A few degrees rotated. This one locates square to the cast.

If this doesn't work and I have to use the other case (designed for the later straight through bush) I will pull the bit of stainless tube that I cut to fit and make it a 2-part like this. As long as the O rings are sized it doesn't leak. The through bush doesn't make sense when trying to seal and line up two different parts - especially if you ever want to take it apart again.

[dogshome]

Drilled and tapped. All square. Waiting for poxy O rings for the brake shaft (again!). 9mm x 14mm is a really good fit, but somehow I don't have any and the 50 I ordered 2 weeks ago (before going on hols) haven't turned up. 10x14 fit (unless you get rubbish ones that measure 1.8mm not 2mm diameter), but the 9s are preferred and squeeky tight.

[dogshome]

 

Fitted. Brake works fine. No diff noise at all (quieter than my 65,000 mile original). First gear seems no different, second and third much more useful. Second does 30MPH in town without sounding 'over-revved' and third for 40 equally relaxed. I'm not switching gears as much now. No issues in 4th or 5th and much nicer to ride and suits my laid-back riding style. 650 wouldn't pull it, well tuned 860 with crank sensing ignition, all good. As I get more roads and miles (hills and headwinds) on it, I'll feed back.

The speedo now reads correctly 


Note on brake shaft O rings - 9x14 (2.5mm dia) are the best fit. 10x14 (2mm dia) are technically correct and don't leak, but the thicker 9s are squeaky tight.