Newby Clutch Installation Report (G15-CS)

Joined
Jul 2, 2015
Messages
272
Country flag
Hi, all-


Wanted to share my experience so far putting a Bob Newby belt drive on my G15-CS.


I chose the Newby unit because I was tired of the mess and repeated re-gasketing of the wet primary, having had it put together and needing to take it back apart a few too many times already. I also have a Newby clutch on my Enfield, and am very happy with it. I also took the opportunity to modify the inner plate a little to gain easier access to the magneto cap and the primary tensioner bolt, and to ease routing of/access to the stator wires.


I spoke with Bob and he was encouraging, but warned that some work was necessary to fit the setup into the G15’s primary case; notably, the outer cover needs to be spaced away from the inner. He directed me to a Jampot article about installation in an AJS for reference, which noted:


"Four modifications need to be made to the alternator chaincase of which only one is visible.

1. The embossed circular ridge surrounding the gearbox mainshaft seal/tin slider on the
inside of the inner chaincase needs to be ground flat, either with an angle grinder or a
rotary file. In this manner the new clutch can sit comfortably on the gearbox mainshaft without fouling the chaincase at the rear.

2. The lower section of the inner edge of the chaincase filler plug boss needs to ground
down on the inside of the chaincase. Only a small portion of the bottom of the boss needs to be removed to allow the belt to clear the outer chaincase and the removal of metal should not affect the fitting and sealing of the chaincase plug.

3. The standard inner/outer chaincase locating dowels (2) should be removed and
replaced with new dowels made/inch longer.

4. A spacer should be inserted between the two chaincase halves. I used black/inch
thick hard Vitryl rubber on the prototype and torqued each chaincase screw to 5 lbs. If the screw clearance holes in the spacer gasket are punched out on the tight side, they'll stop the screws coming loose. Latterly, I intend to fashion an alloy spacer, probably in two parts and, I've noticed now that I can probably reduce the thickness to 1/8 inch (N.B.reduce the dowel lengths accordingly). The spacer is the only visible sign of the conversion as far as the chaincase is concerned."
 
Joined
Jul 2, 2015
Messages
272
Country flag
So I ordered the kit and got to work on preparing the primary. I had a machinist mill the chaincase flat per item 1. from the article, while cutting out what would become my access port for the magneto, primary case tension adjuster, and stator wires.

I also ordered longer, hex-cap primary cover screws from British Fasteners.


IMG_20191008_120419240 by Mick Doul, on Flickr


I cut, dimpled, and re-hardened the clutch pushrod for use with a 6mm ceramic ball between the rod sections, with another at the clutch end to better engage the adjuster screw, which has a cupped shape. Newby recommends grinding the pushrod to a “bullet shape” but the ball has worked well for me on the Enfield and I stuck with it. I wanted it very close to flush with the end of the transmission shaft, as that position worked well for me on the Enfield.


IMG_20191008_120845597 by Mick Doul, on Flickr


Also did the initial grinding and smoothing on the chaincase filler boss using dremel, carbide bits, and a flap wheel. Without this grinding, the case will interfere with the belt path. As you can see, the plug itself could be a problem, but I figured I’d handle that once it was running.



IMG_20191009_160348696 by Mick Doul, on Flickr


Inner in place, with and without the access cover; later, I ended up getting some rubber edging and using a Dremel flap wheel to widen the kerf to accommodate its width. Still have some final fitting to do with that.

IMG_20190923_100145376 by Mick Doul, on Flickr



IMG_20191008_130525515 by Mick Doul, on Flickr
 
Last edited:
Joined
Jul 2, 2015
Messages
272
Country flag
I also had 1/2” longer locating dowels made; the Jampot article indicated the final spacing-out of the outer cover could be very narrow, but I figured I could cut these back down myself easily if needed.


IMG_20191011_153957000 by Mick Doul, on Flickr


When the kit arrived, it contained the pulley, clutch, belt, and spacer for the alternator rotor.


IMG_20190922_134156845 by Mick Doul, on Flickr


Unfortunately, Bob sent a splined pulley suitable for some Matchless engine, and not the Atlas tapered arrangement. He was quick with the replacement pulley and spacer, and I was able to get underway.


I found the spacer didn’t like to work with the Woorduff key, but I simply trimmed a little off and it fit nicely.


IMG_20191008_141827015 by Mick Doul, on Flickr


IMG_20191008_142721057 by Mick Doul, on Flickr


IMG_20191008_142956305 by Mick Doul, on Flickr


Checked alignment of the belt path before putting the inner back on


IMG_20191004_173233733_HDR by Mick Doul, on Flickr


IMG_20191004_173223101_HDR by Mick Doul, on Flickr


Mocked up and checked tension; loose with an easy twist to 90 degrees cold


IMG_20191008_125905035 by Mick Doul, on Flickr


And got it running as a test. You can see the clutch adjust screw is waaay out; I think I had an extra ball in the pushrod at this point, as I was dealing with some disconcerting clutch slip.


IMG_20191008_153253935 by Mick Doul, on Flickr


So after all this, the clutch really had some tremendous slip. After some flailing and thinking, I realized the clutch pressure plate was lightly riding on the transmission shaft. To fix it, I ground out just a tiny bit of metal from the center of the pressure plate which freed it to apply full pressure to the clutch pack. After talking with Bob, he said that with the “norton-type extended mainshaft,” this was always an issue, and he recommended taking 2mm off the mainshaft itself or adding another steel disc to the clutch. I may consider this if the clutch slips anymore in use after heating up fully, but for now my fix is working.
 
Last edited:
Joined
Jul 2, 2015
Messages
272
Country flag
To make my spacer, I found I needed at least 5/16-3/8" to feel comfortable the belt wouldn't foul on anything. 3/8" was about the max before the footrests would interfere, as well. I tried some aluminum spacers, but they were really awkward to install individually, so I got a strip of 3/8" wide silicone rubber and a 5/16" cutting punch from McMaster and got craftsy, making a spacer that fits most of the way round the perimeter. There's a gap on the bottom/rear for now, but this got me round the block.

IMG_20191111_093506185 by Mick Doul, on Flickr

IMG_20191111_093548288 by Mick Doul, on Flickr

Once it was started, I used the punch to shape the inside to help it curve how I wanted from hole to hole. Looks rough from the inside but pretty good from the outside.

IMG_20191111_100455424 by Mick Doul, on Flickr

IMG_20191111_100459698 by Mick Doul, on Flickr

IMG_20191111_150726608 by Mick Doul, on Flickr

IMG_20191111_150737294 by Mick Doul, on Flickr

IMG_20191111_162124938 by Mick Doul, on Flickr
 
Last edited:
Joined
Jul 2, 2015
Messages
272
Country flag
Next, I have located a slightly damaged spare inner primary cover. Planning on trimming out everything but the rim and milling it to make it into a solid 3/8" spacer. We'll see how that goes, but for the meantime, the proof of concept is working as-is.
 
Joined
Aug 16, 2019
Messages
65
Country flag
superb work , all the british stock clutches were at best a compromise , they could have done better but unfortunately cost was the limiting factor

early honda clutches must made the designers hang their heads in shame
 
Joined
Jul 2, 2015
Messages
272
Country flag
Thank you, guys.

I also forgot to mention I stacked a few washers under each alternator stud to nudge it back towards the optimal location. This, however, has created my worst fear--trying to re-align the rotor and stator in this stupid, stupid arrangement. I'm pretty sure I have a very light rubbing going on. Best I can think (and after checking by PM with Grandpaul) is to slap some Prussian Blue on the stator and try to offset it based on any observed rubbing. This, of course, is a giant pain in the butt with all the assembly and disassembly going on to get at the primary cover. But it's easier without a gasket and fluid to deal with, so c'est la vie I suppose.

Anyone have any tips on getting the alignment right? Honestly, it barely moves at all, as the cover limits the stator's ability to travel even with the nuts totally loosened, even after being spaced out from the original location deeper in the cover.
 

Kelly

VIP MEMBER
Joined
Dec 18, 2018
Messages
4
Country flag
Very nicely done man. Great write up with pics too. Now I get what you were talking about on the cut out on the rear primary.
 
Joined
Jul 2, 2015
Messages
272
Country flag
I am going to take this to a machinist to skim it to 3/8" thick, which will eliminate all the remaining material aside from the rim and hopefully yield the best possible spacer.

I might echo the cut-out on the backplate once it's mounted, or maybe just take it off whole along with the cover each time. I'll see what seems best when it's in place.

spacer by Mick Doul, on Flickr
 

texasSlick

VIP MEMBER
Joined
Jan 2, 2013
Messages
2,859
Country flag
Remove all those sharp corners, notches, and cracks on that spacer plate, or vibration will make more!

Slick
 
Joined
Jul 2, 2015
Messages
272
Country flag
Yeah, those will disappear when the milling is done. It will be just the rim of the piece with the bolt bosses.
 
Joined
Jul 2, 2015
Messages
272
Country flag
I just had to take a little more material out of the dowel and screw holes to make everything fit easily by hand; didn't want it to become a struggle with the relatively fragile piece down the road and possibly bend something, plus I cleaned up the sharp edges left by machining.


I also opened up the hole in the backplate where the wires pass through a little more, and also flap-wheeled that to super-smooth. The way the cutout is designed, I no longer have to fish wires and connectors out through that stupid hole...it's open to the top when the cutout is removed, and trapped in place in the little cavity I left once I put everything back in place.


Drilled some little drain holes in the bottom of the spacer, too, since it's not weather-tight.


Lastly, I need to take threads off the forward chaincase plug so that they don't interfere with the belt. Gonna mark the position it's in when it's tight and just grind away what little is needed for clearance.


So I'm here now, and it's exciting!

IMG_20191205_121309081_HDR by Mick Doul, on Flickr
 
Joined
Oct 28, 2014
Messages
911
Country flag
My method for the spacer was to get a sheet of aluminum, lay the cover on it and trace closely around the cover. It is also a good time to drill the screw holes. I used a band saw to cut it out and a disc sander to shape it. A mill was used for the interior.
 
Joined
Jul 2, 2015
Messages
272
Country flag
My method for the spacer was to get a sheet of aluminum, lay the cover on it and trace closely around the cover. It is also a good time to drill the screw holes. I used a band saw to cut it out and a disc sander to shape it. A mill was used for the interior.

Much less lazy (and destructive of old parts) than my way!
 
Joined
Jul 2, 2015
Messages
272
Country flag
So it occurred to me that the clutch is running fine now, but as the plates wear, I'll have slippage again...the pressure plate will once again rest on the transmission mainshaft.

Therefore, I bit the bullet while the fork was off anyhow, and did some in-situ surgery to better meet the first half of Bob Newby's instructions when he found out about my clutch slip: remove 2mm from the mainshaft.

Avert your eyes now if you can't stand lazy, amateur hackery...I know the proper solution would be to disassemble the gearbox, put the mainshaft on a lathe, and turn it down. But since there's nothing actually touching the end of the mainshaft, I figured it only had to be roughly square. My only concern with the end shape, best I could see, was ensuring the smooth, snag-free operation of the pushrod. Next time the transmission is apart, I'll probably go ahead and get it touched up on a lathe for propriety's sake.

First, I covered the primary like a good operating room (or a Dexter kill scene...) using some foam packing sheeting pressed over the mainshaft. Then I used a combination of Dremel cutting wheels, carbide bits, and flap wheels to remove the requisite material, re-chamfer it, and smooth it all out. Going slowly and using my caliper's depth gauge helped me get it roughly even while working freehand; the flap wheel largely evened out the imperfections and made everything nice and glassy-smooth.

IMG_20191219_111212278 by Mick Doul, on Flickr

However, the shortening of the shaft led to another issue...in clutch engagement, the ceramic ball I had on the end of the pushrod arrangement would now stand fully proud of the mainshaft, pinned against the adjuster screw. Though it's held in that position against six springs, it made me uneasy. There was still a potential for it to somehow slip out. So, I went to follow the second half of Newby's instructions: grind the pushrod end to a "bullet shape."

To do this, I set my drill up on the workbench with a clamp, with the rod in the chuck, and spun it while I worked a counter-rotating dremel flap wheel to round out the end, periodically stopping to test-fit it against the pressure plate adjuster screw. It only took two or three fittings before it was perfectly shaped.

IMG_20191219_142642157 by Mick Doul, on Flickr

IMG_20191219_143642542 by Mick Doul, on Flickr

Then, I attempted to re-harden the pushrod by heating to glowing with a propane torch, quenching in oil, and re-tempering with the torch till I got a blue sheen on the outside. (Per WikiHow instructions...) I've never done that before, and do hope I got it right. I figure I'll check for wear periodically and make a new section if I have to. (Any input welcomed!)

IMG_20191219_145722341 by Mick Doul, on Flickr

Fits perfectly.

IMG_20191219_150755234 by Mick Doul, on Flickr

Looks like I will need to get a new pushrod and make attempt #2, however, as the loss of the ball at the end of the arrangement makes it too short, overall. I could put the ball back into the pushrod tunnel, as seen in this pic, but that makes the rod-ball-ball-rod arrangement slightly compressible as the balls stack up slightly on each other when engaging the clutch. It works that way, but doesn't seem optimal.

I also found that getting the short inner segment out of the pushrod tunnel could be a pain. If I do another multi-piece setup, I'll make the inner rod a little longer and the outer a little shorter.
 
Last edited:

Top