23t gearbox sprocket. Problems or not. (2013)

Reggie · Apr 16, 2013

I have a friend who is considering fitting a 23t gearbox sprocket on his Commando 850 , and was asking me if I thought it was a flawed idea because of the extra torque, and based on the advice in the Norton service notes which suggests that:

J.H.: I believe layshaft bail bearing failures arc more frequent when:-
1. The 22T gearbox sprocket is used as on 850s and
2. Every failure I have seen has been a Portuguese SKF bearing.

.......and

with a larger engine sprocket and retaining say, a 19T on the gearbox (as was
standard on all Norton Nortons from Model 50 to Atlas and Manx) the speed of the box would be
increased without such a heavy journal load on -the bearings and tooth loading on the pinions
themselves.

Also I spoke to Norman White about this a while ago and he also thought it was not a good idea because of this.

I know that there are people on the forum running 23t g/box sprockets, but wondered if they can give any feedback as to if there have been problems that are likely to be as a result of running a 23t g/b sprocket and if high milages have been achieved without problems?

pete.v · Apr 16, 2013

Nowadays it really is a matter of personal preference. Highway riding over city riding, rpm vs vibration and feel, where you live(some cities are much slower than others), etc, etc. Belt drive, chain drive? As far as the gearbox goes, it is what it is. Sorry for the expression.

I have a 20 with a RGM belt drive. I have run a 19 and a 21 and for how I ride and the 20 just give me the best all around performance.
Don't get me wrong, I am not comparing. It s just an example of my personal preference and the equipment and riding environment in my part of the world.

comnoz · Apr 16, 2013

I have seen no problems as long as a roller layshaft bearing is fitted.

Better gearbox life will be achieved however by gearing up the primary rather than the secondary. Jim

concours · Apr 16, 2013

LOVE my 22! Long cruising legs... 80 feels so effortless

Torontonian · Apr 16, 2013

That's really tall ,highway speed stuff.

Reggie · Apr 16, 2013

Comnoz wrote;

I have seen no problems as long as a roller layshaft bearing is fitted.

Jim, would the "Mick Hemmings" layshaft ball bearing be suitable/unsuitable as I think that is what is fitted. I would assume it's OK if it goes in Mick Hemmings racers?

Reggie · Apr 16, 2013

Comnoz wrote;

Better gearbox life will be achieved however by gearing up the primary rather than the secondary. Jim

My friend has had 2 x belt failures whilst using a Norvil system, and so has gone back to chain drive as he can't take another breakdown. I believe that the belt drive had dropped his revs (by speeding up the primary) and he notices and is unhappy with his bike which now feels and sounds like it needs another gear.

jaydee75 · Apr 16, 2013

I had a 24t on mine back when I was young. Got almost 60mpg, seemed to pull it ok. Cruised nicely.
When I restored my bike I took it off, still have it if anyone needs.
Jaydee

1up3down · Apr 16, 2013

just my opinion but I feel a 23 is too big if for no other reason than just getting off the line without increased revs and clutch slipping to prevent the bogginess that large a sprocket involved

Hobot · Apr 16, 2013

I'm in acetrel's racer camp that the higher ya gear up the more pleasant and surprising the pull becomes as can stay in lower gears longer. Its well know the faster tranny can be turned the longer it lasts and more power it can handle but that's mainly for racers application not lolly gagging along within safe thrilling Cdo handling zone. The best ratio I had on Peel, which did have like 70 hp was 21-ish ratio - 2:1 Haywood drive and 20T sprocket. On my factory power Combat 20T feels better to for pull and ease to cruise 70-90. Above 20T the clutch engagement in 1st was a bit of commitent on loose rough surface to take off w/o some slippage on purpose. If rpms above 3000 then engine is protected even if tranny straining its life away, they do that any way with not in top gear.

comnoz · Apr 16, 2013

Reggie said:
Comnoz wrote;

I have seen no problems as long as a roller layshaft bearing is fitted.

Click to expand...

Jim, would the "Mick Hemmings" layshaft ball bearing be suitable/unsuitable as I think that is what is fitted. I would assume it's OK if it goes in Mick Hemmings racers?

The Mick Hemmings bearing is a good bearing. It will last a long time. I prefer the roller as it will just about last about forever. Jim

comnoz · Apr 16, 2013

Reggie said:
Comnoz wrote;

Better gearbox life will be achieved however by gearing up the primary rather than the secondary. Jim

Click to expand...

My friend has had 2 x belt failures whilst using a Norvil system, and so has gone back to chain drive as he can't take another breakdown. I believe that the belt drive had dropped his revs (by speeding up the primary) and he notices and is unhappy with his bike which now feels and sounds like it needs another gear.

If you install the tall ratio belt drive then you will need to go to a smaller chain sprocket on the gearbox or you will end up geared for the moon.

The only time I ever see a belt failure is when they have been adjusted too tight or the gearbox has adjusted itself because the adjuster was not set to hold the trans forward. Just about everybody -including me -starts out adjusting the belt too tight and failure happens quickly.

Of course if the sprockets are completely out of alignment the belt will run to the side and wear the guide plate or the side of the belt- but if the belt is loose enough the the alignment is not real critical.
[it can't be with the amount of flex in the gearbox shaft.]

Jim

Dances with Shrapnel · Apr 16, 2013

For what it is worth, I had some very bad experiences with a Jason brand belt but this is with a ultra short stroke Norton with +85RWHP. They would break and strip teeth on a very regular basis. Holmeslice put me on to a special supplier out of North Carolina and those problems are now in the past.

The point is that not all belts are the same.

I would not think the lay shaft bearing durability is a factor one way or another when choosing a sprocket. You do want a good bearing there.

comnoz · Apr 16, 2013

Dances with Shrapnel said:
For what it is worth, I had some very bad experiences with a Jason brand belt but this is with a ultra short stroke Norton with +85RWHP. They would break and strip teeth on a very regular basis. Holmeslice put me on to a special supplier out of North Carolina and those problems are now in the past.

The point is that not all belts are the same.

I would not think the lay shaft bearing durability is a factor one way or another when choosing a sprocket. You do want a good bearing there.

I have definitely heard of some poor belts but I have always stuck with name brand stuff. Anytime I had problems it was because I asked for it. Once I got my racebike over about 80 horse I switched to a Gates Polychain and found that to be indestructible.

Layshaft durability does seem to be affected by how much torque the gearbox is transmitting. A larger gearbox sprocket does mean there will be more torque across the gearbox under steady cruise conditions.

Of course the maximum torque across the gearbox is going to be how much torque the motor makes times the primary ratio. That will no doubt affect breaking things like shafts and gear teeth but I suspect the steady state torque will affect the bearing life and that is determined by the secondary ratio. Having a very tall gear ratio also means you will spend more time in the lower 3 gears where the layshaft bearing is under load. Jim

tpeever · Apr 16, 2013

I am running a 22 tooth sprocket on my 850 and I think it's a bit too tall for the majority of the riding I do. I ride a lot of secondary roads and find that I am shifting too much between 3rd and 4th to keep the bike in the powerband at 50-70 mph. I think for secondary roads a 20 or 21 tooth would be ideal on the 850. Now if you are doing a lot of motorway cruising at high speeds, that's a different story and the 22 tooth or even a 23 tooth would be ideal. All depends on how you ride.

Reggie · Apr 17, 2013

comnoz wrote;

The only time I ever see a belt failure is when they have been adjusted too tight or the gearbox has adjusted itself because the adjuster was not set to hold the trans forward. Just about everybody -including me -starts out adjusting the belt too tight and failure happens quickly.

Of course if the sprockets are completely out of alignment the belt will run to the side and wear the guide plate or the side of the belt

Both myself and my friend have had guide plate failure. This was on a Norvil MK3 belt drive. My belt was running out a bit, but my friends wasn't. The keeper plate is made from thin ? anodised alloy and isn't up to the job in my opinion. With a small amount of wear it then broke through on two of the three retaining countersunk screws and 33% of the plate fell off on mine but I caught it before total failue, but not in my friends case.

comnoz wrote;

Having a very tall gear ratio also means you will spend more time in the lower 3 gears where the layshaft bearing is under load. Jim

A good point that I hadn't thought of :idea:

Thanks for everybodys imput.

johntickle · Apr 17, 2013

In the days before belt drives 29T front primary sprockets were available, speeding up the gearbox by approx. 10%.
In order to fit one of those the alternator mounting bosses have to be "relieved" somewhat. You will also need a "custom made" triplex chanin of course.
If I run into problems with my belt drive I will use that setup.

MFB · Apr 17, 2013

Another benefit of gearing up via the primary rather than final drive is that kickstarting gets a bit easier.
I don't know what effect it has on electric starts, being unfamiliar with them newfangled inventions.

Martin

triumph2 · Apr 17, 2013

Years ago I switched to a Norvil belt drive and initially didn't pay much attention to the different ratio until I noticed everybody was driving so slow (speedo not working, using the tach) then realised I had to use a smaller gearbox sprocket. The Gates belt that came with the kit lasts a very long time. I bought the kit in person on a trip over 'ome and Les himself told me how to set it up and it has never been a problem. I do have dual adjusters to align the belt.

tricatcent · Apr 17, 2013

I have the equivalent gearing to a 22 tooth sprocket on the gearbox. I find it very pleasant for all kinds of riding, in town, country roads and 80 MPH. I usually have a passenger. Between the two of us that is a 350 lbs load. When I am in town or on slower roads I use 3rd gear. I have changed my layshaft bearing to a roller and have had no problems with the gearbox.

I think that the tall gearing is what makes a Norton 850 very pleasant. I think a 23 tooth sprocket would be too large though unless you plan on cruising at over 80 MPH frequently. With a 22 tooth sprocket when your engine is turning 4000 RPM you will be going at about 78 MPH. Cruising at 78 MPH is very comfortable. The engine will pull that ratio really easily. !st gear is still ok for pulling away from a stop

23t gearbox sprocket. Problems or not. (2013)

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