MK3 STS starter system upgrade

John Snead at STS sent me their newly developed MK3 starter upgrade kit. He asked me to test it and I jumped at the opportunity. This Mk3 starter gear upgrade will be offered through cNw and its listed in their parts catalog at this time (even though they wont be available until mid June). I have many cNw and other upgrades on my MK3 and on my 750. It's mainly about reliability.

After doing a lot of research, STS decided that the factory starter motor gears and sprag gear are hardened, but its only on the outside shell. The metals are soft on the inside. This causes ridges and the sprag cannot engage properly causing starting problems. On top of that they found that the 18 tooth sprag was not as reliable as the 14.

John has been testing the setup and every time he walks past his bike he presses the starter. 2000 times now, without issue.

As usual the STS machine work is incredible. It looked and felt a little heavier than the standard gears, but it was not. I weighed the original and the new.



I am very happy I went in to do this project. I found out my alternator was about to explode. A crack in the insulation and broken wire insulation. On top of that my Barnett clutch plates had worn. The ally had worn where they engage with the clutch hub. I probably could have carried on with the old plates, but not planning to go back in the primary for a while.



I am particularly anal when it comes to the MK3 primary and starter mechanism as its weak. To begin with I have 2 lithium batteries in parallel along with larger starter wires. Then I am using the cNw 4 pole starter motor, which is a piece of work in itself.

I have meticulously and very carefully fitted everything.





I now have 1300+ miles on my MK3 since I rebuilt it (2013) with minimal issues. I have been in the primary side 3 or 4 times. Every time I have had to go in there, it was to replace the sprag system. I think I have replaced 3 in this time. Once it was my own fault. I accidentally pressed the starter button when it was idling and it destroyed itself.

Also done during this upgrade:

• Fitted lower bars (cNw) and I love them.
• Repaired electronic speedo sender.
• Torqued it all down and did valve clearances.
• Changed head bolts to stainless and added other stainless stuff.

Here is a video of me starting the bike a few times since the upgrade (plugs are in). I can't wait to get out on it again today. Love my MK3!

What is the typical lifespan of the stock parts like the sprag? 100 starts? 1000? Random?

swooshdave said:

What is the typical lifespan of the stock parts like the sprag? 100 starts? 1000? Random?

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Its hard to know. The first one lasted approx 1000 miles if I remember right. When I took it out the sprag was broken in one place. I am not sure why that happened. I torque my backfire device to 55lbs. There were ridges in the starter gear, but not too bad. I replaced the sprag only. That didnt last for long, the 18 sprag broke, so then I replaced the standard 18 sprag and related parts. That lasted for a long time. The bike would never start from cold by starter, but would start flawlessly when warmed up. Not too much of a bother. I think i got through 3 of them, I cant remember. I have no idea how many starts they last. I think its a good idea to use harder metals there.

Nice work. A little bit of JB slathered around the wires where they exit the stator helps to prevent fatigue and cracking.

When I got my Mark III 6 years ago, the starter motor didn't work. I took it to a local auto electrical shop for repair. The tech called a while later and said there was nothing but an armature inside, no brush plate or brushes. I asked if he could fix it and he assured me he could but would need to get the parts as this is an outboard motor starter (who knew). I don't know what he did to it but it starts first time every time ever since. When I was inside the primary to replace a leaky seal, one of the sprag teeth fell out so I replaced it. I measured the sprag contact surfaces and they were right on the edge so I'm sure I will need to replace all 3 pieces next time. Sometimes I wonder if stalling the bike doesn't damage the sprags? When I shut it off with the key, it just stops. When it stops because of a stall, I hear a clank out of the primary and wonder if with stall the crank doesn't roll backwards enough to engage the sprag. Any other Mark III owners experience this?

swooshdave said:

What is the typical lifespan of the stock parts like the sprag? 100 starts? 1000? Random?

Click to expand...

According to an Australian friend who commutes year round on his MK3 , 1700 starts is the average life of a stock sprag.
My 14 tooth Norvil lasted for about 20 starts.
The 18 tooth Ali-express model has done 250 or so to date.
When it lets go I'll install these CNW drive items.

Glen

worntorn said:

According to an Australian friend who commutes year round on his MK3 , 1700 starts is the average life of a stock sprag.
My 14 tooth Norvil lasted for about 20 starts.
The 18 tooth Ali-express model has done 250 or so to date.
When it lets go I'll install these CNW drive items.

Glen

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Im surprised the Norvil one lasted that long.

I’m sure they got a full refund for the defective sprag...

I guess I'm just lucky! I've owned my MKIII since 1978, converted the starter to 4 pole years ago, and always use the starter. The bike has over 60K miles and still has all the original starter components intact. Just now replaced the original primary chain.

milfordite said:

I guess I'm just lucky! I've owned my MKIII since 1978, converted the starter to 4 pole years ago, and always use the starter. The bike has over 60K miles and still has all the original starter components intact. Just now replaced the original primary chain.

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The trick may be to not open up the primary and touch anything.

You kinda have to open it when the sprag goes crunch and locks up the works. Roadside sprag removal for me.
Luckily I had tools that day.

At present My MK 111 uses the awesome DD starter and a stock sprag. Bigger cables too. Big Odyssey battery. It won't engage cold below 15 C. , Just spins. Don't know why but no cold morning startup drives here in cold Canada. Above that temp it's instant starting.

Always pull in the clutch first. I've told Matt to send me this improved system as soon as it's tested and ready for sale. Tested could include the word Cool morning.

Jerry Doe said:

I am particularly anal when it comes to the MK3 primary and starter mechanism as its weak. To begin with I have 2 lithium batteries in parallel along with larger starter wires. Then I am using the cNw 4 pole starter motor, which is a piece of work in itself.

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Hi Jerry,

I'm impressed with the dual Shorais. What size are they? I've been using the LFX21 for quite a while (I'm on my third one), but I like the idea of even more capacity.

Ken

Hi Ken,

I give credit to Fred at Old Britts for that idea: https://www.oldbritts.com/70_shorai.html

I am cannot remember what the batteries are. They are option E at Freds page. 28 Amp hour. Works very well. I just replaced them after 7 years. Unfortunately they are pretty securely bolted in the bike with the labels on the inside. If you really need me to I can take it to bits to find the model number.