British Customs 19-Tooth Front Sprocket Conversion
April 30, 2012This weekend I had a chance to change my 2008 Triumph Bonneville front sprocket from the stock OEM 18-tooth one to a 19-tooth version purchased at British Customs (Part: BC704-001-19).
19 Tooth Front Sprocket from British Customs
I had to purchase a motorcycle jack to complete this upgrade, but that was something I needed to do anyway. I ended up getting one (and ratchet action safety straps) from Harbor Freight Tools on sale, and it worked great!
Once I had the motorcycle up safely and securely on the jack (with the help of the safety strap), I removed the front chain sprocket cover, then the rear foot pegs and mufflers, and chain guard.
Bonneville on new Motorcycle Jack
Although not required, I also removed the seat, side covers and gas tank just to do some other small maintenance tasks and cleaning.
At this point, I realized I did not have the correct 36mm socket to remove the front sprocket retaining nut, so I went to my local Sears and purchased a 1/2″ drive Craftsman socket. I flattened the washer that was holding the nut in place using a hammer and chisel.
The manual says to have a partner stomp on the rear brake while applying pressure to loosen the nut. I did not have this option, so I inserted a 2×2 wood bar between the spokes on top of the swing arm to keep the rear when from turning. This enabled me to loosen the retaining nut.
Once this was removed, I then loosened the rear wheel axle nuts which allowed the wheel to slide forward. loosening the chain tension. This allowed me to remove the front sprocket, and then spend some time cleaning and lubricating the chain. I then turned the rear wheel alignment adjuster bolts forward 5 complete turns. This allowed me the extra room to installed the new sprocket on the shaft, using the original nut and locking washer.
I then backed out the rear adjuster bolts until the chain was the correct tension, and tightened the rear wheel axle bolts.
After some other maintenance (adjust spark plug gap) and cleaning I put everything back on the bike: gas tank, seat, side covers and sprocket cover. I left the chain guard off. I carefully lowered the bike and removed the jack. After visually inspecting everything again, I took it for a short test run to make sure everything was working properly.
This morning I had a chance to ride it 10 miles to work on side street and the highway. I did not notice any lack of power to start in 1st gear, but did notice the changes in shifting at different RPM’s. Most noticeable is the change at higher speeds. It have more power at higher speeds as the engine is turning slightly less at those speeds. I’ll be interested to see if this affects my gas mileage.
Hope this helps you if you ever try this change. Let me know if you have any questions, or a different experience or outcome.
Harbor Freight Tools 1500 lb. Motorcycle Jack
Hey, great write-up! I have an ’08 Bonnie Black and I’m looking to do the exact same thing to my bike. Did you notice any difference in top speed? My Bonneville seems to strain at anything over 55 mph. Is that normal? I know this article was written a year ago, but I’m just now finding it. How has the 19 tooth sprocket held up for your needs over that time period?
Thanks again,
Wayne in Utah.
Hi Wayne,I replaced my 18 tooth for a 19 tooth, and do a lot of miles on long open roads and it really made a great difference.
No looking back for my 2010 Bonnie it loves it.
So much so a mate is doing the same to his.
Regards Mark
North Queensland
Australia
Wayne, Yes there is a difference in top speed… you can go faster at the same RPM! 🙂 I know that’s a “Duh!” but it lowers that “strain” and to me it seems more natural for the bike. Of course I’ve done other things to increase HP, so that contributes as well. And the sprocket is holding up just fine. You can buy them from many sources now… BC, NewBonneville, BellaCorse, etc. Let me know how it goes and what you think after you do the switch.
Why did you take off guard muffler and foot peg?, I did not and it worked, Bonus! sprocket cover off easy to adjust,back brake rod
Keith, with my particular exhaust setup, I need to remove the muffler/peg to be able to remove my rear wheel. Without doing that, I can’t slide the axle all the way out.
Did you notice any increase in chain /sprocket noise?? I have put on aftermarket sprockets, and was annoyed by the extra chain noise coming from the front sprocket.
Jack,
I did not notice any change in chain noise with any of the times I have changed a front sprocket from 18 to 19 tooth, on my bike or on friends bikes. They only thing I can think of that might cause extra noise would be if your chain was stretched (they do this over time), and that was the cause of the noise. You might try changing the sprocket and the chain at the same time.
Randy
I can’t find an oem 19 tooth sprocket with the rubber sound dampener, so I will try a regular steel oem 19 . The bike only has 25 miles on it so chain is new. I was just going by past experience , and other riders that they thought the plain steel sprocket made more noise, so I was going to try to get a rubber mounted one just in case. Will let you know if weather ever turns good enough to ride again. Had another snow storm last nite.
Jack,
I don’t believe Triumph makes an OEM 19 tooth front sprocket, so I don’t think you’ll find one with the factory looking rubber sides. At least I’ve never seen one. If the bike has the stock front sprocket cover on it, and you’re wearing a helmet, I don’t think you are going to be able to tell any difference in the chain noise… at least I never have.
Hope the weather breaks for you soon!
Randy
I have a sprocket from British customs, 19 tooth, part #BC704-001-19, but it is for a 532 chain I think or maybe a 525. My chain and original sprocket both say 520. Where am I going to get a 520 19 tooth sprocket. The dealer I am dealing with is 50 miles away, and doesn’t seem to be able to get what I need , or doesn’t care, don’t know which. I live in cheyenne Wy. the closest dealer is northern Euro in Ft. Collins Colorado. He says he can’t locate any sprocket that I need from any of his dealer network parts dept.
I allready have way too much money invested in this sprocket with shipping and all. I’m about ready to forget the whole damn thing and stay with the standard oem sprocket and chain. Cost way too much to convert every thing to 532 size . My bike is a 2016 , but apparently one of the last models made with a 520 chain.
Looks like my only option is to do a complete conversion and get a new rear sprocket, chain and front sprocket, for about 250 bucks. I don’t think it is worth that just to gain a few rpm’s at highway speed.
This is turning into a real cluster #### if you know what I mean.
I already have nearly 40 bucks invested in a sprocket that sells for 22 bucks, and don’t know what kind of refund they will give me.
Don’t know what to do at this point.
Jack,
I think you meant that your Bonneville is a 2006, not 2016 as they are not out yet. I do not think Triumph has changed the OEM Bonneville chain size since 2001. They all shipped with OEM 525 chains. If your bike actually has a 520, then it was modified – and perhaps you didn’t realize it. This would explain the perplexed dealers trying to locate a non-standard part.
There are plenty of discussions about the 520 chain conversion online:
http://www.triumphrat.net/twins-technical-talk/135364-520-chain-conversion.html
http://www.triumphrat.net/twins-technical-talk/168602-520-chain-weight-comparison.html
http://www.triumphrat.net/twins-technical-talk/64664-considering-520-conversion-2.html
If you verify that you actually do have a 520 chain setup, you can keep it and buy 19-tooth 520 sprocket online here:
http://sprocketcenter.com/street-sprocket-applications/triumph/865-bonneville-2006-2014/520-conversion-sprockets.html = $33
Hope this helps explain what has happened and to clarify things. Good luck!
Randy
Jack I have a 2015 Scrambler and it has a 520 oem setup. I too bought the British customs drink sprocket which is for the 525 chain they used for years. I emailed British customs and they refunded me without even having to send the old sprocket back. My new problem is finding someone who carries the 520 version???
Andrew,
i just purchased a 19 tooth front sprocket for a 520 chain here: http://sprocketcenter.com/catalogsearch/result/?q=88801
Randy
Hi there, great right up and very useful link to the 19T sprocket for a 520 chain, thanks. I have a 2015 bonneville T100 which has a 520 chain, that link above to the sprocket center is for a Thruxton front sprocket, I assume that it would also fit my Bonnie?
I bought my 19-tooth here – https://www.speedmotoco.com/ProductDetails.asp?ProductCode=19-smc-525 They also had the 520 for the later models.
Has any 1 with a 2014 scrambler done 19 front sprocket want to know how much it alters the speedo
Norm, the Scrambler has the 865cc engine (but with a 270 degree crank) and the same stock gearing as the Bonneville and Thruxton. So, the 19 tooth front sprocket will have similar effect to that described in this post.
How much would your R.P.Ms drop at 60 mph., when you install the 19 tooth after market sprocket ? Also how far out will the speedometer be
Robert, This post was written over 10 years ago. I no longer have a Bonneville with a-19 tooth front sprocket to check for you. But if my memory is somewhat accurate, there was a 300-500 RPM drop. It was enough to increase MPG and make cruising more comfortable.