Flipped Sprag,,,,,,,, again !

This is what happened when I tried to start my bike the other day.


I heard an unusual noise when I kicked it over. Too much drag too. Then I tried the push button and only a click from the solenoid. Pull the primary cover off and the sprag was locked in place. I had a hard time removing the big gear but finally wiggled it off. I pried the sprag out in one piece luckily. But I think it's junk now from the way it looks as the dogs are locked in place? This sprag was replaced last year at the tune of $182.00.

I suppose the big gear needs replacing too because it has thin tiny nicks on the flange surface. Whada think?

Tim_S

I think it's wierd how mine (and many others) works perfectly, at the same time many others have nothing but troubles.

It also seems that once a particular Mark III has sprague issues, they tend to repeat themselves on that bike.

I would assume that replacing the gear and the srague as a pair is the best advice.

grandpaul said:

I think it's wierd how mine (and many others) works perfectly, at the same time many others have nothing but troubles.

It also seems that once a particular Mark III has sprague issues, they tend to repeat themselves on that bike.

I would assume that replacing the gear and the srague as a pair is the best advice.

Click to expand...

I would replace the gear and sprocket along with the sprag. I know my wifes MK3 has around 20,000 miles on it now with the original sprag. I doubt that it has ever been kickstarted.
The longest lasting ones seem to be the original sprags [not the heavy duty replacement] used with the 2 brush starter , a good AGM battery and a 3 phase alternator. Jim

I don't know if this will be of ANY use but let me post it just in case.

On my Ducati 900SS, the sprag clutch weights are held inboard by a spring that is basically a long coil spring, one end of which coils into the other. You can repair it,when it goes, by uncoiling the ends, cutting off the LARGER - not the smaller - end and reinserting/coiling the smaller end into the larger. Google it, it's out there. IT WORKS A TREAT! I can usually do this a couple to a few times before the coil spring gives out and you need another (another story altogether, but there is a cheaper KTM spring that works...).

Again, NO idea if the Mk III sprag works this way, as I'm a kickstart only Mk I guy, but I thought I'd mention.

Best of luck. Brian K

I flipped mine back last year and it still works. Try it youv got nothing to lose.

Phil

Your right Phil,,,, what do I have to lose? If I can free it up I'll report back.

Now back to my regular programing ,,,,,,,, 8)

Tim_S

It's wear in the bore of the sprocket and on the dia of the gear stub allowing the sprag paddles to tip over.

Cash

My first "new to me" sprag lasted about 3 years, hardly ever kickstarting the engine. This is with a Dyno dave starter on.

My replacement sprag bought last July has just failed last week, (although I haven't yet dismantled it all to check what state it's in). This is after replacing the gear assembly and sprocket as well last July, "just to be sure." My Commando is 920cc with a C:R of 9.8:1. I'm a bit disappointed :cry:

Do I understand correctly that the Steiber P/N DC 4127 (3C) is the one to go for? Does anybody know if this is the one Andover Norton sells?

I'm thinking of taking up the ancient art of kickstarting, and using the electric starter for stalls at traffic lights etc. It may last a few years then?

I learned a lot today about this sprag creature. Believe it or not but Borg-Warner right here in the good Ol' US of A holds the patent to the Norton OWC. We have a retired Borg-Warner engineer in our group that was one of the young pioneers back in the day who was involved in the Norton E-Start project. We heard several stories on quality control at the Norton factory and how individual work groups made their parts "to fit" as they worked they way down the line.
After awhile some parts were made in Germany because the Germans couldn't stand for the Brits quality control. And since it a proprietary part we're stuck with what we get.
Our friend is also going to check the hardness of the drive gear surface that has the marks on it from the sprag. The Rockwell hardness of the part was the biggest issue back during that time. That gear should have never been marred by the sprag. Another thing that was mentioned was the type of oil used in the primary. Since a lot of the oils today have been stripped of important additives. You should use an oil with zinc still in it. I don't know the oil ratings that still have zinc? A good 10/30w or 10/40w should work? No synthetic's !

That's my story and I'm sticking to it....... Parts now on order. :?

Tim_S

Tim_S said:

I learned a lot today about this sprag creature. Believe it or not but Borg-Warner right here in the good Ol' US of A holds the patent to the Norton OWC. We have a retired Borg-Warner engineer in our group that was one of the young pioneers back in the day who was involved in the Norton E-Start project. We heard several stories on quality control at the Norton factory and how individual work groups made their parts "to fit" as they worked they way down the line.
After awhile some parts were made in Germany because the Germans couldn't stand for the Brits quality control. And since it a proprietary part we're stuck with what we get.
Our friend is also going to check the hardness of the drive gear surface that has the marks on it from the sprag. The Rockwell hardness of the part was the biggest issue back during that time. That gear should have never been marred by the sprag. Another thing that was mentioned was the type of oil used in the primary. Since a lot of the oils today have been stripped of important additives. You should use an oil with zinc still in it. I don't know the oil ratings that still have zinc? A good 10/30w or 10/40w should work? No synthetic's !

That's my story and I'm sticking to it....... Parts now on order. :?

Tim_S

Click to expand...

Truck oils and motorcycle oils still contain zinc. 10-30 or 10-40 car oils do not because it fouls catalytic convertors. Same story whether it is conventional or synthetic oil.
I agree that hardness could be the issue. Jim

Ugh what a dilemma you thumb commensor guys face. The metal additives must reach their operating temperature to react to the surfaces they are supposed to protect. Don't know it those conditions ever exist in this poor sprag-thorpe design. Here's more on oil as applied to cog works and the additive importance you can't read off their label specs.
http://www.macysgarage.com/myweb6/gear_lube.htm

EP additives are mostly made up of Chlorine, Sulfur, Phosphorous, Zinc and Lead compounds. Due to environmental concerns, Lead is for the most part gone and Chlorine is only used in limited applications. These compounds become active at different temperatures, and therefore, if balanced properly, provide protection at all operating temperatures. The problem in the past with some Sulfur EP additive packages in gear oils and yellow metals is not how much is in the oil, but that the additive breaks down and forms an acid. This acid, if formed, would eat up yellow metals and steel alike.

The problem is the difference between what is called active and inactive Sulfur in the EP additive package. "Active" Sulfur compounds chemically react and form these protective films at much lower temperatures than "inactive" Sulfur EP additives. In some cases these "active" Sulfur additives may even stain the yellow metals in the gear sets.

Whether a particular manufacturer uses active or inactive Sulfur EP agents is really only known by them.

Click to expand...

As eye previously mentioned our engineer friend was going to test the hardness of the drive gear and the sprag dogs. Here are his findings:


Curiosity got the best of me so I checked out your starter gear this morning. Unfortunately the hub where the OWC sprags operated was short and shrouded by the gear making it impossible to get my machine to read directly on the hub outside diameter. So I had to take measurements on the end of the hub and surrounding gear. Then deduce the hub hardness.

The gear and hub are one piece so is all made of the same steel alloy. Also the entire gear has been hardened then finish ground to size the hub dimensions. By the looking at the condition of the gear surface it has no residual scale on it so appears to have been carbon nitride hardened. I'm not positive about that. But, it appears so. The carbon nitride process calls for heating the part up to around 1200 degrees F and immersing it in a carbon rich gas. The process gives a hard case on the exterior surface. But the case is rather thin, usually being .010" to .015" deep. A part used for a OWC should have a minimum of .040" case depth, .050" .060" being better.

Anyway, here is what I found:

My hardness machine calibration piece is 62.7 Rockwell "C" scale. I ran three checks on the standard and got 62.0, 62.5, and 62.0. So my reading should be fairly accurate. The usual allowable variance is + or - 2.

I took 2 reading on the gear near the teeth that appeared not to have been ground after hardening. I measured R "C" 60 for both readings.

I then measured the hub at its' end and got readings 54.0, 54.0, and 53.0.

I have a calibrated file that when used on a piece of steel cuts anything softer than the file. My file is R "C" 62. When the file is pressed and moved on the OWC hub sprag diameter it cut the hub.

I inspected the OWC sprags with a magnafying glass and could not find any flats where the sprags rode on either the inner or outer races.

Withe the above limited data I have concluded that the mode of failure of the OWC assembly was a soft inner race. My recollection what the hub hardness should be was R "C" 62 +/- 3. I think when the hub was finished ground the thin R "C" 60 case was removed leaving a R "C" 54 core.