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T120 With a 42 Tooth QD rear hub from a BSA? #761095
01/01/19 2:40 am
01/01/19 2:40 am
Joined: Nov 2012
Posts: 306
Sacramento, CA
Denis J Offline OP

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Denis J  Offline OP

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Joined: Nov 2012
Posts: 306
Sacramento, CA
Has anyone tried this?

I have a very early BSA A65 that has long legs...so long it lump along as if it has overdrive...What is does have is a 21 front tooth and a 42 rear tooth hub

I am staring at my 71 T120 that wheelies great...19/47 stock sprockets. I installed a 21 on the front of my last T120 and it was a world of difference, but not enough (70mph=4400rpm/K70 Tire/ 2367fpm average piston speed 19/47 vs 4200rpm/2260fpm)

I live in Norther California like a few others here. Riding on the freeway is a dangerous proposition and almost mandatory.If you are below 70mph and tempting fate for longer than a few minutes you are in for an interesting experience to say the least. being able to cruise 75-80 regardless of the legalities would be a welcome modification for long day touring.
- and getting run over by a truck is not a conversation I want to be the subject of.

Has anyone tried the BSA 42T QD rear hub on the OIF swinger? basically a QD rear wheel assembly on a Triumph with an integrated sprocket brake drum piece instead of the later Lightning/Hornet type removable sprocket. I have swapped the 2 for one another on a BSA with no issues as it seems they are the same with different drums.

I am not enthusiastic to take my riding bikes apart at the moment with my other machines in pieces. I plan on my major services in Spring and maybe then I can line em up for a taste test.

Interesting searches showed the K70 tire on the 18" rim was the tallest tire available from Dunlop, Metzler Avon, Bridgestone and Heidenau.

P.S. I am not at all worried about lugging the machine. It makes more power than a refreshed original...the old girl will pull the front wheel and makes for really cool 1-2 wheelies during spirited rides. To keep my front wheel down, my highway rpm low (3600rpm/70mph/ 1937fpm mean piston speed) and my engine alive for more than 15k miles I would like to do this swap.

Thanks for your input! I would like to know if it is a direct bolt up or if you had to made adjustments to the parts for chain alignment, brake operation etc.

Denis J





Bikes
- Triumph’s- BSA’s- Norton’s- Matchless’s - Scott’s- A Weslake racer...many others from all over the world.
If it has 2 wheels I might need it.
“You can wheelie any bike if you just try”
Broken Motorcycle Mechanic at The Vintage Monkey in Sacramento, CA ...Old Motorcycle Specialists
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Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761111
01/01/19 9:05 am
01/01/19 9:05 am
Joined: Dec 2004
Posts: 9,846
Scotland
kommando Online content
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I have seen a B44 QD hub fitted to a Trophy Trail OIF, looked good but needed access to a lathe to make spacers.

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761119
01/01/19 12:31 pm
01/01/19 12:31 pm
Joined: Jan 2006
Posts: 2,028
Asheville, NC
Mike Baker Offline
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I had a 45t sprocket made for one of my conical hub bikes. Had to use allen head bolts to clear the chain. Perhaps that along with a bigger countershaft sprocket would do what you want it to do.
Rebel Gears

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Mike Baker] #761148
01/01/19 5:29 pm
01/01/19 5:29 pm
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Posts: 189
Blue Ridge, Georgia, USA
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Rob Harper Online content
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Blue Ridge, Georgia, USA
I have the same clearance problem with a conical. I didn't think of allens as a solution. Where did you get them?

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761234
01/02/19 11:06 am
01/02/19 11:06 am
Joined: Jan 2006
Posts: 2,028
Asheville, NC
Mike Baker Offline
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McMaster Carr

Grade 8

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Mike Baker] #761307
01/02/19 10:52 pm
01/02/19 10:52 pm
Joined: Jun 2015
Posts: 40
kern county ca
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jon powers Offline
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kern county ca
Originally Posted by Mike Baker
I had a 45t sprocket made for one of my conical hub bikes. Had to use allen head bolts to clear the chain. ......
Rebel Gears


My memory is that I noted that for my 45 tooth sprocket build the 5 mounting holes can be indexed with the open space between the chain outer links (5 times 9 = 45 teeth) and the hex heads fit with no need for allens.

Jon

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: jon powers] #761331
01/03/19 2:25 am
01/03/19 2:25 am
Joined: Apr 2008
Posts: 189
Blue Ridge, Georgia, USA
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Rob Harper Online content
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Blue Ridge, Georgia, USA
I replaced the hexes with allens today, and while the hexes did work when aligned exactly right, the allens gave better clearance by far. So a $9 fix

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761338
01/03/19 4:42 am
01/03/19 4:42 am
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Posts: 706
Pleasant Hill, California USA
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TR7RVMan Offline
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Pleasant Hill, California USA
Hi Denis, I have great interest in this subject. I live in Pleasant Hill east of San Francisco & know exactly what you mean about riding on the freeway. I've ridden to Sacramento & El Dorado Hills a few times. I've ridden highway 5 & 80 on occasions as well. I have '73 Tiger 750 with 20x47. I tend to cruise 62-65. but always run with traffic at interchanges which means 75+ mph.

I'm most familiar with Sacramento area. Now what gear do you run up hwy 50 Rancho Cordova to El Dorado Hills? +What speed do you usually run on that stretch?

Up 80 to Auburn what gear & speed do you run up those?

On those I find I need to keep at 70+. mph to really keep the motor spinning. If I get below 65 I need to down shift 1 gear. As I'm sure you know your 4&3 are the same ratio as my 5&4 gears so that part of trans is equal.

Last summer going east out of the town of Clear Lake on hwy 20 up the pass was 105f. 2 bikes melted pistons on that grade. They were in high gear. I couldn't find out gearing, but rear looked like 46t. Many downshifted as I did & were ok. Another bike T140 melted piston going to Alice"s restaurant on the peninsula south of San Francisco going up a grade. 20x47 gears. In standard form these bikes tend to ping with our 91 fuel. The standard points AAU is full advance 2k rpm, Boyer is full advance 3500rpm. So we can't count on retarded timing at freeway speeds to help with ping or detonation. A little over rich mixture of course is a must, but even that has a limit.

This is why I was wondering what gears you now climb those hills in.

I'm not so sure these bikes can pull such a tall gear as you are looking for in high gear. As you know the wind in the valley can be horrendous especially on hwy 99.

Michael Raber put a 21x46 on his 650 Bonnie & felt it was too tall to pull properly.

I've been debating about 4 years on whether to put 21 front on my bike, making 21x47 which gives 4180rpm @ 70mph. But what about 60-62 mph which is often the speed on the city freeways or open 2 lane roads. Even small up hill or head wind might demand down shifting...??? That has been my dilemma!


I've put 20t front on many 650 dry frames to get 20x46. Codeman has T140 in dry frame 20x46. I've ridden these enough to feel 20x46 is very desirable overall, but as you state, motor is spinning fast at 70mph with these gears. One tooth larger at rear to 20x47 adds 93 more rpm at 70mph which is noticeable & can bring vibration down somewhat.

I feel just going to a 20 in front will give a big improvement. Most my friends back in the 70s changed to 20 up front. We had not hear of 21t back then. With 100 octane fuel ping was never an issue. Nobody melted pistons on Triumphs that we knew.

Please follow up on the changes you make as I'd like to get a more comfortable cruising speed. Thank you.

On a side note are you going on the BSA owner's club Norther California Delta ride Feb.23,2019? I plan to. We can compare bikes real time if you can make it. I hope to do Mother Lode ride out of Eldorado Hills early spring. No need to be a club member to join rides. Just don't be late as we leave promptly 10am. About 100 miles. I usually just ride to start point. Rain cancels for me. Do web search BSAOCNC & find ride calendar.

Don


1973 Tiger 750
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761339
01/03/19 5:01 am
01/03/19 5:01 am
Joined: Jan 2017
Posts: 706
Pleasant Hill, California USA
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TR7RVMan Offline
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Pleasant Hill, California USA
Hi Rob & Mike, I'm most interested in how you mounted smaller sprocket on standard OIF conical hub.

Or are you talking about putting 45t on cast iron brake drum? I'm not clear on what/how you are doing that.

I've had a 650 cast iron drum bolt on 46t sprocket hanging on my garage wall for a few years. I'll have to enlarge center & drill new holes to fit conical hub.

As you know bolt holes don't line up. Calculations show it's possible to fit with allen head bolts. It looks like a few of the casting bosses will have to be filled down to prevent side link of chain from hitting them, but I didn't get that far.

Where did you get 45t? The ones I've seen have offset on one side which looks like may prevent a fit on my conical hub after I machined the center out.

I've searched for years to find a 45 or 46 that was already drilled & machined to fit my conical hub. I've heard people say they exist, but I'm not found any.

Did you have to remove alloy from hub to clear chain where bolts go through? Seems with a 45 that would be a must?

Of course this is all mute if you are talking cast iron drum.
Thanks! Don



1973 Tiger 750
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761341
01/03/19 5:12 am
01/03/19 5:12 am
Joined: Jan 2017
Posts: 706
Pleasant Hill, California USA
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TR7RVMan Offline
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Hi Again, On a hypothetical note, I'm always pondering what causes more motor wear.....

Spinning 4389rpm at 70 mph. Or.... Lugging motor slightly pulling too tall a gear??

As my motor screams down the freeway I think about this sort of thing.

RPM per mile or more ring pressure, that is the question.

More RPM per mile might mean more wear on cams, bearings, valve guides etc. Also more RPM raises stress in rods & moving parts.

More cylinder pressure presses rings out much harder, puts more side load on pistons & force on bearings as well as chain & transmission.

Does it matter?? Maybe it's a wash.

For now I'm relying on Mobil1 v-twin 20-50 to protect the parts at high rpm & lower loads with 20x47 gears. Am I kidding myself?

Any thoughts?
Don

PS my Honda 350 lasted 70k miles. It spun 7000 at 70 mph! It would have gone longer, but I sold it to my brother in law & he never adjusted timing chain. It wore a hole in cly making big oil leak. New motor was cheaper than cyl & pistons. Was ridden 60 miles a day on freeway as a commuter bike.

Last edited by TR7RVMan; 01/03/19 5:13 am. Reason: forgot word

1973 Tiger 750
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761346
01/03/19 7:41 am
01/03/19 7:41 am
Joined: Jun 2007
Posts: 6,287
Maui Hawaii
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My thoughts on the subject; Tune your bike for the type of riding you do most. For example, if you like to cruise at 70mph for long times, de-tune the bike a little, up the gearing. If you ride curvy roads a lot, a hot bike is fine with stock gearing.

High speeds for long intervals exposes your bike to failure if your bike is highly tuned. The margin of error is very narrow and if you bike strays out of tune, or if anything goes wrong, like an intake leak, or closed valve clearance, you don't get much time to find it and compensate for it when you're blasting down the highway at 4500rpm at 70mph. You just won't hear it before it's too late.

A seizure at 70mph is serious business. You just might hit the pavement.

If you can, have two bikes. One for highway cruising and one for sport riding. One for when you feel blue, and one for riding on rainy days. One for show and tell, and one for your buddies to ride.

A whole fleet of them if you can.

If I had to have only one Triumph, I would probably get a mid 60's Thunderbird or TR6 and try to set it up as a compromise between the two types of riding that I do mostly.

My current ride is for lazy Sunday cruises on back roads and sightseeing. I have other bikes for the highway.

For the most part and serious changes in gearing have to be done at the countershaft sprocket. For example the difference in gearing between the pre unit 43 tooth sprocket and the 46 is hardly noticeable.

Cheers,
Bill




Last edited by HawaiianTiger; 01/03/19 7:45 am.

Bikes
1974 Commando
1985 Honda Nighthawk 650
1957 Thunderbird/T110 "Flying Tiger"
Antique Fans: Loads of Emersons (Two six wingers) plus gyros and orbiters.
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761348
01/03/19 7:59 am
01/03/19 7:59 am
Joined: Apr 2008
Posts: 189
Blue Ridge, Georgia, USA
R
Rob Harper Online content
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Joined: Apr 2008
Posts: 189
Blue Ridge, Georgia, USA
I got my 45 from Rebel Sprockets (many years ago) and it bolted right up to the conical on my '71 TR6C. The front is whatever is stock on that model. The hexes did clear, just barely, but I was always concerned that when the sprocket wore the chain would begin to touch the bolts, so the allens were a cheap and easy fix, and improved the clearance to about 1/8 inch

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761356
01/03/19 11:26 am
01/03/19 11:26 am
Joined: Jan 2006
Posts: 2,028
Asheville, NC
Mike Baker Offline
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Mike Baker  Offline
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Asheville, NC
You're right, Don, I did clearance the bolt bosses on the conical hub. Had forgotten that....
Just me, but I prefer to have at least 1 odd number sprocket as I feel that 2 even numbers makes for uneven sprocket wear.
The bike that wears the 19-45 dyno'd right at 40hp. It rarely sees highway use but is the smoothest running Triumph I have and seems to like running in the 4-5K range. Got lucky with that one......

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761369
01/03/19 1:46 pm
01/03/19 1:46 pm
Joined: Apr 2008
Posts: 189
Blue Ridge, Georgia, USA
R
Rob Harper Online content
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here's where I got my 45 tooth sprocket for conical hub

http://rebelgears.com/officialrebelgearshome.html

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: TR7RVMan] #761372
01/03/19 2:23 pm
01/03/19 2:23 pm
Joined: Nov 2012
Posts: 306
Sacramento, CA
Denis J Offline OP

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Denis J  Offline OP

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Sacramento, CA
Originally Posted by TR7RVMan
Hi Again, On a hypothetical note, I'm always pondering what causes more motor wear.....

Spinning 4389rpm at 70 mph. Or.... Lugging motor slightly pulling too tall a gear??

Does it matter?? Maybe it's a wash.

PS my Honda 350 lasted 70k miles. It spun 7000 at 70 mph! It would have gone longer, but I sold it to my brother in law & he never adjusted timing chain. It wore a hole in cly making big oil leak. New motor was cheaper than cyl & pistons. Was ridden 60 miles a day on freeway as a commuter bike.



- Rpm wears - Lugging Kills
- It is not at all a wash
- A 350T has a piston speed under 2400fpm at 7000. A Triumph at that same piston speed is spinning 4300. Same barrel wear..different valvetrain wear


Bikes
- Triumph’s- BSA’s- Norton’s- Matchless’s - Scott’s- A Weslake racer...many others from all over the world.
If it has 2 wheels I might need it.
“You can wheelie any bike if you just try”
Broken Motorcycle Mechanic at The Vintage Monkey in Sacramento, CA ...Old Motorcycle Specialists
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: TR7RVMan] #761373
01/03/19 2:42 pm
01/03/19 2:42 pm
Joined: Nov 2012
Posts: 306
Sacramento, CA
Denis J Offline OP

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Denis J  Offline OP

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Joined: Nov 2012
Posts: 306
Sacramento, CA
Originally Posted by TR7RVMan
Hi Denis, I have great interest in this subject. I live in Pleasant Hill east of San Francisco & know exactly what you mean about riding on the freeway. I've ridden to Sacramento & El Dorado Hills a few times. I've ridden highway 5 & 80 on occasions as well. I have '73 Tiger 750 with 20x47. I tend to cruise 62-65. but always run with traffic at interchanges which means 75+ mph.

I'm most familiar with Sacramento area. Now what gear do you run up hwy 50 Rancho Cordova to El Dorado Hills? +What speed do you usually run on that stretch?

Up 80 to Auburn what gear & speed do you run up those?

On those I find I need to keep at 70+. mph to really keep the motor spinning. If I get below 65 I need to down shift 1 gear. As I'm sure you know your 4&3 are the same ratio as my 5&4 gears so that part of trans is equal.

Last summer going east out of the town of Clear Lake on hwy 20 up the pass was 105f. 2 bikes melted pistons on that grade. They were in high gear. I couldn't find out gearing, but rear looked like 46t. Many downshifted as I did & were ok. Another bike T140 melted piston going to Alice"s restaurant on the peninsula south of San Francisco going up a grade. 20x47 gears. In standard form these bikes tend to ping with our 91 fuel. The standard points AAU is full advance 2k rpm, Boyer is full advance 3500rpm. So we can't count on retarded timing at freeway speeds to help with ping or detonation. A little over rich mixture of course is a must, but even that has a limit.

This is why I was wondering what gears you now climb those hills in.

I'm not so sure these bikes can pull such a tall gear as you are looking for in high gear. As you know the wind in the valley can be horrendous especially on hwy 99.

Michael Raber put a 21x46 on his 650 Bonnie & felt it was too tall to pull properly.

I've been debating about 4 years on whether to put 21 front on my bike, making 21x47 which gives 4180rpm @ 70mph. But what about 60-62 mph which is often the speed on the city freeways or open 2 lane roads. Even small up hill or head wind might demand down shifting...??? That has been my dilemma!


I've put 20t front on many 650 dry frames to get 20x46. Codeman has T140 in dry frame 20x46. I've ridden these enough to feel 20x46 is very desirable overall, but as you state, motor is spinning fast at 70mph with these gears. One tooth larger at rear to 20x47 adds 93 more rpm at 70mph which is noticeable & can bring vibration down somewhat.


Don


At this moment 70 mph (70gps, speedo reads 75ish) is my sweet spot and keeps me in the 4200-4400 rpm range when meandering. Hills are as such and our machines in stock form are underpowered to run high speeds consistently( squint for the barrage).
- Please don’t get me started on ignitions. My experience - electronic ign is not for a long distance touring machine. Sorted points for [email protected] works perfect
My cruising fuel is right at 13:1...it pays to check..most bikes are rich down low and lean up top
A 95 degree day is no different to me than a snow day...my bikes are parked or I’m already home from a sun up ride. I tell all my customers avoid hot days. It’s hard on the equipment (old and new)

Making an inspection window in a piston is not normal and has little if nothing to do with gearing...you prob know this already

21/47 Was excellent in all riding up here, but I want just a bit more. The 45 rear is intriguing, but a QD rear hub is also. Pondering....
20/47 is just fine..but reminds me that I’m not riding to Santa Cruise or Eureka on this one. A sacrifice in acceleration is ok with me.
More is better 21/42 sounds perfect

This is good stuff

Remember gents... If you hear pinging..downshift!....if you still hear it...Jump off!


Bikes
- Triumph’s- BSA’s- Norton’s- Matchless’s - Scott’s- A Weslake racer...many others from all over the world.
If it has 2 wheels I might need it.
“You can wheelie any bike if you just try”
Broken Motorcycle Mechanic at The Vintage Monkey in Sacramento, CA ...Old Motorcycle Specialists
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761385
01/03/19 4:27 pm
01/03/19 4:27 pm
Joined: Nov 2012
Posts: 306
Sacramento, CA
Denis J Offline OP

BritBike Forum member
Denis J  Offline OP

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Joined: Nov 2012
Posts: 306
Sacramento, CA
Just ordered 2 of the 45 tooth rears from Rebel. Great guys.

I'm keeping one for myself and this upcoming testing. Call in while they still have 2018 pricing. I paid $85 shipped

Testing 20/45 first then 21/45

Maybe a 21/45 is the ticket. Save some grief making spacers and taking my Beezer apart for testing. Great help from you all!


Last edited by Denis J; 01/03/19 4:29 pm.

Bikes
- Triumph’s- BSA’s- Norton’s- Matchless’s - Scott’s- A Weslake racer...many others from all over the world.
If it has 2 wheels I might need it.
“You can wheelie any bike if you just try”
Broken Motorcycle Mechanic at The Vintage Monkey in Sacramento, CA ...Old Motorcycle Specialists
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761401
01/03/19 6:08 pm
01/03/19 6:08 pm
Joined: Jun 2015
Posts: 40
kern county ca
J
jon powers Offline
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Joined: Jun 2015
Posts: 40
kern county ca
Originally Posted by Denis J
...

Maybe a 21/45 is the ticket. Save some grief making spacers and taking my Beezer apart for testing. Great help from you all!



On TR6R 1971 (with T120 head) I run the 21 by 45 and on the street - two up take off is a little fussy but otherwise downshifting at the right time works fine - I went through the 1/2 mile timing trap at Mojave in 3rd wound out at 99.2 mph so freeway speeds in third for hills and passing is fine. Off road though first is very high in ratio with 21/45 and I like the bigger rear sprocket 21/53 from the triple ( 37-3903 SPROCKET, REAR WHEEL, 53th 5 bolt T150V, CONICAL 13-F) then first gear is much better when you need to go slow.

Jon

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #761445
01/04/19 2:17 am
01/04/19 2:17 am
Joined: Jan 2017
Posts: 706
Pleasant Hill, California USA
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TR7RVMan Offline
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Pleasant Hill, California USA
Thanks for the replies. Lot to think about.

I've ran 20x46 for several thousand miles, commuting every day. My friends have ran 20x46 several thousand miles. I've not observed any worse chain wear compared to odd/even numbered sprockets. I would say chain/sprocket wear was basically identical. We all lube regularly.
Don


1973 Tiger 750
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #762226
01/11/19 2:16 am
01/11/19 2:16 am
Joined: Nov 2012
Posts: 306
Sacramento, CA
Denis J Offline OP

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Denis J  Offline OP

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Joined: Nov 2012
Posts: 306
Sacramento, CA
Sprockets In today! Here are pics with some hardware fitted for clearance....


6mm Socket head (Allen) bolt
1/4" Stainless Round head

I may install countersunk screws..these sprockets are very nice and worth the price
[Linked Image]
[Linked Image]
[Linked Image]
[Linked Image]


Bikes
- Triumph’s- BSA’s- Norton’s- Matchless’s - Scott’s- A Weslake racer...many others from all over the world.
If it has 2 wheels I might need it.
“You can wheelie any bike if you just try”
Broken Motorcycle Mechanic at The Vintage Monkey in Sacramento, CA ...Old Motorcycle Specialists
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #762232
01/11/19 5:06 am
01/11/19 5:06 am
Joined: Jan 2004
Posts: 4,044
ca, us
D
DMadigan Online content
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Posts: 4,044
ca, us
6mm bolts in a 1/4" hole? Not what I would do. You can buy half height 1/4" socket head bolts so the counterbore is not 2/3rds of the way through the sprocket.
If you want full freedom in sprocket teeth then put on a spool hub. Dirt track blanks are about $40 each. Then bore and drill for your hub.
Do not use flat head bolts on sprockets, they will loosen.
I doubt you will notice any difference in engine life with a couple teeth on the rear sprocket.

Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #762248
01/11/19 1:26 pm
01/11/19 1:26 pm
Joined: Oct 2012
Posts: 4,370
State of absurdity
Hillbilly bike Online content
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Hillbilly bike  Online Content
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Joined: Oct 2012
Posts: 4,370
State of absurdity
I agree with Dave, the loose fit of bolt 6mm bolt may let the sprocket move around creating another problem...On my 650 land speed race 650 Triumph I was using a 21/47 with a conical rear hub...Needed more speed at the same RPM so I went to a 19 inch T160 rear wheel with the "modern" type disc sprocket that's available in any tooth count with no issues. T140 18 inch rear disc wheel might be better.to keep stock tire sizes....Of course this would require a switch to a rear disc..........


"Don't be alarmed ladies and gentlemen, these chains are made of chrome steel" Carl Denham, 1932 ...
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: DMadigan] #762273
01/11/19 5:11 pm
01/11/19 5:11 pm
Joined: Nov 2012
Posts: 306
Sacramento, CA
Denis J Offline OP

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Denis J  Offline OP

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Joined: Nov 2012
Posts: 306
Sacramento, CA
Originally Posted by DMadigan
6mm bolts in a 1/4" hole? Not what I would do. You can buy half height 1/4" socket head bolts so the counterbore is not 2/3rds of the way through the sprocket.
If you want full freedom in sprocket teeth then put on a spool hub. Dirt track blanks are about $40 each. Then bore and drill for your hub.
Do not use flat head bolts on sprockets, they will loosen.
I doubt you will notice any difference in engine life with a couple teeth on the rear sprocket.



I’m not sure what you mean when you suggest low profile socket heads. I remember these to have wider heads than traditional socket screws. I assume it was to make up for the lack of strength available with a shallower depth.
Flat head bolts on sprockets are common in classic and late model machines. My late model dirt bikes use counterbore. Your suggestion about flat head bolts confuses me. Many machines I see in the shop use bolts, nuts on studs and counterbore.
I have included pictures for anyone interested in what we are talking about.

I am anticipating using counterbore (taper head) screws like many of the late model Japanese machines. Strength should likely not be an issue unless I am missing something?
Please I appreciate your advice.

Thanks for the tip on a spool hub and T140 rear wheel. The project was to keep a rear drum. To try a QD/42 and now a conical/45. The numbers for piston speed/rpm and cruising speed look great on paper.
..The 78 T140 project lays in wait when this is done

Here is a link to some pictures. Thanks again gents for the insight.

Pictures/dimensions of bolts and sprocket attachments



Bikes
- Triumph’s- BSA’s- Norton’s- Matchless’s - Scott’s- A Weslake racer...many others from all over the world.
If it has 2 wheels I might need it.
“You can wheelie any bike if you just try”
Broken Motorcycle Mechanic at The Vintage Monkey in Sacramento, CA ...Old Motorcycle Specialists
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #762276
01/11/19 5:20 pm
01/11/19 5:20 pm
Joined: Nov 2012
Posts: 306
Sacramento, CA
Denis J Offline OP

BritBike Forum member
Denis J  Offline OP

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Joined: Nov 2012
Posts: 306
Sacramento, CA
I prefer this option...please let me know if I am straying down a dangerous path.
I greatly appreciate you guys chiming in..you have the experience I am taking notes on
.. These setups have stayed together under severe load..in well developed trim a 2 cycle 500 makes upwards of 70ft lbs ATW.

[Linked Image]


Bikes
- Triumph’s- BSA’s- Norton’s- Matchless’s - Scott’s- A Weslake racer...many others from all over the world.
If it has 2 wheels I might need it.
“You can wheelie any bike if you just try”
Broken Motorcycle Mechanic at The Vintage Monkey in Sacramento, CA ...Old Motorcycle Specialists
Re: T120 With a 42 Tooth QD rear hub from a BSA? [Re: Denis J] #762292
01/11/19 7:05 pm
01/11/19 7:05 pm
Joined: Jan 2004
Posts: 4,044
ca, us
D
DMadigan Online content
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DMadigan  Online Content
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D

Joined: Jan 2004
Posts: 4,044
ca, us
The only problem you might encounter with the CR250 hub is the metric axle size. Modern bikes have been going to larger diameter tubular axles so you probably can make a sleeve for the wimpy British axle. Notice that hub allows the spokes to be replaced without dismantling the wheel.
Also called low profile head bolts -
https://www.mcmaster.com/standard-socket-head-screws
Flat head screws are generally used in tension or for location. In shear the force against the head pulls on the threads as well as shear. I am not saying that you cannot used them that way.
The bolts in your picture are button head which are large diameter than socket head. Useful when you need more support area under the head such as the three 1/4" screws at the valve pocket on a triple.
Many ways to do a QD axle without resorting to antique parts. Endurance and WSK wheels mount the sprocket on its own bearing carrier with essentially is an Oldham coupling. but without the floating interface.

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