24 tooth front drive sprocket

Hello all, I'm new to the forum and had a question, i recently bought a '75 mk3 and i was wondering if a 24t front drive sprocket would fit. that's the only sprocket i can change the ratio with right? thanks in advance Cj

cjandme said:

Hello all, I'm new to the forum and had a question, i recently bought a '75 mk3 and i was wondering if a 24t front drive sprocket would fit. that's the only sprocket i can change the ratio with right? thanks in advance Cj

Click to expand...

With a stock setup, yes, that is you only viable option. 24t? Phew, that's a big change. What is in place now? You'll have to add links.
Go here and scroll to the bottom of the page to see ratios. http://www.oldbritts.com/o_ring.html

Yes its a real long legged ratio but will need to add at least 2 more chain links.

Sprockets are available from 19 to 24 teeth. What kind of riding do you want to do? A 24T is highway cruising, and with a stock MKIII it'll be lame around town.

I recommend a 21 tooth, this still gives you lots of bottom end and gives you a comfortable cruising speed at about 65 mph. I rode out to Sturgis and back(3200 mi.) with it and gave me good mileage .

Thanks for all of your responses. Highway riding is what i had in mind, when i get it running. I'm currently stationed down in southern Maryland at NAS Patuxent river and found the bike online and drove up to Buffalo, NY the weekend before thanksgiving and bought it and put it on a little trailer behind my old Subaru Wagon and brought it back. The previous owner said that he'd gotten it as a basket case from a friend of his (the camshaft had a lobe come apart), he said that he'd replaced the cam and put it all back together, but just kept on riding his other Norton, a '72 750. Well, life got in the way and next summer turned into 20 years and it had just been sitting in the back of his garage, so he decided to sell it. Again thanks for the replies, I wasn't sure if there was room behind the inner primary case for a tall 24t sprocket. Cj

You should in any event - BUT ABSOLUTELY AND IMMEDIATELY if you're going to run a 24T sprocket - check and make sure you have a roller bearing or upgraded ("Mick Hemmings" style) ball bearing as the inner bearing for your gearbox layshaft.

Lots and lots of information on this problem and its fixing here and in other Commando resources.

Best of luck and congrats on the new bike - many enjoyable hours and miles to you.

My opinion is this... A 24Tth sprocket is way too high, at 70 mph you will have no power at all for any sort of small hill. we have miles and miles of open road here in Aust. and the 21Tth sprocket handles it well, or for those that like to cruise above the speed limit a 22Tth is more than adequate. The 850 is a good torquey motor, coupled with the four speed, means not having to change gears all the time.

If ya handy can always try a few but 21-22T is more realistic in Iron Butts are not your main hobby.

Unless your moving to East Montana (Flat, No daytime speed limit) where you can wind it out to 130mph.
You'll not be very happy with 24T.

cjandme said:

Hello all, I'm new to the forum and had a question, i recently bought a '75 mk3 and i was wondering if a 24t front drive sprocket would fit. that's the only sprocket i can change the ratio with right? thanks in advance Cj

Click to expand...

You won't be happy with 24 teeth. Way too tall. Go for a 21 or a 22 at most.

thanks all, duly noted ...21-22 tooth sprocket. Cj

Next thing you will be asking what kind of oil people like and whether or not they like the Tri Spark ignition! The point being that this topic is sure to have a wide range of opinions that shall never meet (these topics have been heavily debated). You can also change your ratio by going to a belt drive primary and thus changing the size of the crankshaft sprocket. Changing out the countershaft sprocket to a 24T is not a big job in the scope of Norton ownership. I would put it low in the priority list until you have had the bike on the road. You will be better equipped after putting some miles on to decide what effects on performance you would prefer.

Oh, and post some pictures! We love new projects.

Russ

On my MK 3 I went from a standard front sprocket to a 22 tooth unit. It was like a different machine. Changing the front sprocket by one or two teeth will have a dramatic effect on how the bike goes down the road. I am very happy with the 22 tooth unit (did a 1500 mile trip this summer) and I would not reccomend anything bigger. 3800 RPM produces a relaxed 65-70 mph all day long. The only down side is that you might get a little sleepy as you glide down the freeway!

East Montana sounds like a FUN place.

Commando75 said:

On my MK 3 I went from a standard front sprocket to a 22 tooth unit. It was like a different machine. Changing the front sprocket by one or two teeth will have a dramatic effect on how the bike goes down the road. I am very happy with the 22 tooth unit (did a 1500 mile trip this summer) and I would not reccomend anything bigger. 3800 RPM produces a relaxed 65-70 mph all day long. The only down side is that you might get a little sleepy as you glide down the freeway!

Click to expand...

22 tooth was standard for the MK3. 21 for the 850s pre MK3. 23 tooth is maximum practical without engine mods and 3500 revs is 70mph.

i think what we can surmise from this thread is that most people on this forum don't like having a lot of teeth........

Getting the bike running is certainly first on my list ... I was just wondering if a 24t counter sprocket would physically fit in the space or if it was too tall and would make the chain rub on the chain guard that is cast into the backside of the inner primary case. Good to know about checking the bearing on the layshaft before making a counter sprocket switch though. Also nice to hear what everybody thinks about the ratio they are using. I was going to ask about the 530 chain versus a 520 o-ring or x-ring chain, but it i think that's kind of covered in the 100 dollar chain thread, By the way Russ, what kind of oil are you using? Just kidding....anyway I'm working on getting some photos posted, but I guess my main hobby is really my 6 kids (oldest one is eight- so lots of commotion going on at my house). Thanks again to all who took the time to reply

Hm 24 might not clear primary case lip. Might call a vendor and ask for a OD measure. Old Brits Fred might know right off the bat. Commando have torque enough to pull 24T just fine in normal traffic just not leave em behind at a light as strain free, but a down shift to 2nd as 55-60 mph would be fine passing gear pull.
With 20 and 21T on responsive Combat I often found myself trying to snick 5th over drive just to stay legal speed climbing the steepest places in Ozark carrying a couple beer cases on back, because the rush by suck little throttle increases was too sensitive to stay carefree. On the lower gear in city traffic you must be relaxed on throttle not to just bark out ahead like police bait.

The main down side of 520 chain is the teeth wear rahter faster d/t being significantly thinner. I've done 520 lighter conversion on a Combat and a SV650 and worked at treat, just detectable in better response but after a few front sprockets and a couple read drums used up in a couple rear tire changes on each bike I have sworn off 520. 530 X-ring, not O-ring Obsolete Stiff chain, just does clear in some and the others it eats a clear path in a few miles w/o any real damage but cosmetic when you ever you expose the sprocket.

23T is my favourite for touring but I have to say on my most used Commando it also has a belt drive which ups the gearing a bit also, I think you'd find a 24 a bit of a PITA on anything but highways, motorways whatever you call them. Running 22 on my Fastback and my roadster, I feel the motor is a bit buzzy for sustained 75 - 80 mph cruising with the 22 but great all round apart from that on what we call A or B roads, I'm lucky to have a Commando for almost any occasion but when I only had one and it was used for everything from going to work and holidays I ran a 23.