13mm Master cylinder guts

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May 21, 2006
I notice that someone is sleeving the stock M/C to 13mm to increase the "leverage" on the caliper. Does anyone on the forum know what Jap this kit fits, and where I can get one? I can have my M/C sleeved if I can determine what I need in parts.
Thanks, Ron T.
Ron, instead of messing about with an original m/cyl, why not use a Brembo? They are available in a range of piston sizes, and body styles, and lever types. Modifying the internals could be dicy safety wise. Better to put the effort into matching levers on a factory part, or chasing down the perfect Jap m/cyl, if you don't like Brembo's.
Frankly, I would put the custom effort into replacing the stock brake rotor with something better.
Also, you don't know how it will feel with the different piston size, and it's a lot easier to swap different cyl assy's to get the correct feel/effect than it is to modify parts. There are a lot of variables that should be considered, besides piston dia. : lever ratio, hose type, pad material, rotor material & surface & diameter & floating/solid, brake switch type, one or two rotors, riding style, riding conditions, fluid, costs, time, etc...

FWIW, I'm speaking from personal experience. A bad combination of brake components put me and my pristine Guzzi BOTT racer shiny side down while braking for turn #4 at Sears Point. it was going to be retired after that race, but I decided since it wasn't perfect anymore, I would continue racing it :lol:
13mm master cylinder

I have installed a resleaved master cylinder along with the braided st. stl. brake line from Old Britts, www.oldbritts.com last year. Its one of those things I wanted to do but for awhile but didn't because of the time/money involved finding what I needed. The Old Britts unit is a modification to the stock master cylinder.
If you're looking for more than the 13mm master cylinder Colorado Norton Works offers a complete system.
73nortonron said:
Does anyone on the forum know what Jap this kit fits, and where I can get one?

As far as I am aware there's no 'Jap' parts available to directly convert the standard master cylinder. The early modified master cylinders used a machined sleeve along with a modified Kawasaki M/C piston, although the later pistons seem to be purpose made.
The kit is available from RGM (or Norvil) in the UK, the master cylinder needs to be drilled and tapped to take the reducing sleeve, or the unit can be sent to them and they will install the kit, the brake lever needing to be sent along with the unit.
I recently had the master cylinder kit (now an improved type with a pusher) fitted by RGM and have no complaints.

RGM kit: http://www.rgmmotors.co.uk/images/full/full_713d.JPG

Norvil kit seems identical http://www.norvilmotorcycle.co.uk/050136.htm
Thanks for all the info! I have a machinist friend eager to do the conversion (s) and the the kit for $55 (US) seems to be the least expensive way to go. I have a '72 Roadster and 3 Triumphs to do, so cost is an issue. My hope was that some standard M/C rebuild kit arround 1/2" would just pop up, and be maybe $10 or $15; so much for dreaming.
Again, Thanks much, you'll hear from me lots when I get back to transforming a rusty old relic I bought for $500 25 years ago, rebuilt and rode the wheels off of for five more years, and has been sitting in the shed for the last 20.
Regards, Ron T.
73nortonron said:
I have a '72 Roadster and 3 Triumphs to do,

I don't know if you were thinking of trying fit the Norton kits to your Triumphs or not? But I'm fairly sure it's not suitable for Triumph master cylinders.
Actually, this is why I am looking for just the internals. As you may know, the Triumph uses a steel M/C that threads into the lever housing, and the reservoir attaches to the M/C also. If I can find a suitable “rebuild kit”, I can bore all four and fix a sleeve with a 13mm bore in them.
But, don't think I'm ungrateful for all the help; if my quest proves to be futile, there is much usable info here, Thanks again, Ron
I don't know of a piston kit that would be suitable for Triumphs (I am also a Triumph owner) and whatever you decide to do, the piston assembly for the Norton unit will need to be different to the Triumph type due to the different lever arrangements. If I can find any info on a piston kit suitable for Triumph master cylinders I will certainly let you know.
from clubmanracing.com

Master Cylinder Resleeving Kit - One of the reasons for the Commando’s poor braking is the size of the stock master cylinder. Replacing the standard master cylinder with our Grimeca 13MM unit improves braking, but is unacceptable to those trying to maintain a stock appearance to their bike. This kit reduces the bore of the standard unit to 13MM. From the feedback we have received, it works well and greatly improves braking, however as you must now drill and tap the end of the bore to install the new sleeve we strongly suggest professional installation. - #C024

guess you could buyone and have your machinist buddy make you more or pickup some Hon/yam/Suz master cylinder and use them..
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