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Discussion Starter · #1 ·
OK, so here is the deal. I'm build up a street tracker out of my grandad's old Sportster and it needs forks that work.

Lots and lots of chopper guys bore the stock 39mm trees to take later 41mm HD forks, and a few people have bored to 43mm and put on R6 forks. Considering that 39 to 43mm is only actually 2mm of metal taken off, and those weirdos that use sporties for stunt bikes all ride that setup I think its safe.

This how ever leads me to my question. How big can I go? I've still got the original forks from my 900rr (R.I.P.) before I put USDs on it. They've got fancy internals, and are 30mm shorter than sportster forks so they fit my design perfectly. Problem is, they are 45mm!

Do you guys think I could take the 39mm trees out to 45mm? Here is a pic.
 

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Super Moderator
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How thick is the clamp part of the triple clamp now?

Later, Doug
 
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Just my opinion but I would only bore 2mm max & even doing that would be based on the amount of material left, just because others have done it don't mean its right or structurally sound

There are a lot of jap yokes I wouldn't bore at all as they are already made as thin as possible in the wall for weight reduction & while there may not be a problem now the stress a bottom yoke is under could cause problems after years of use

Its difficult to comment more without knowing the measurements of the yokes you are thinking of using or the quality of the material, its a judgment call really but from the look of it I'd say no you cant go that big safely
 

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UnicycleMode
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I would just get a basic set made. Plenty of people out there do that for all sorts of Harley applications, just the other week I was looking at a set of custom billet units for a Sportster that were designed to hold USD's. Can't be that expensive either especially with the payoff of adjustable RSU's off of a 900RR.
 

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:dito: yup six holes bored in two lumps of ally is dirt cheap & day or 2 with a grinder, jigsaw, file, tap etc will get you a presentable set of one off yokes that can take the stem of your choice :)
And some swole forearms too... really though, is it that "easy"?
 
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And some swole forearms too... really though, is it that "easy"?
The difficult part is rough cutting the shape so I tend to start with the minimum of surrounding material I can get away with but after that its pretty easy but slow

I drill & tap the clamp bolt holes before cutting the slots to allow it to clamp up then cut the slots with 2 blades on the hacksaw then drilling the first part for clearance

Done it a few times now & not had major trouble yet, slow & steady wins the race :)
 

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The difficult part is rough cutting the shape so I tend to start with the minimum of surrounding material I can get away with but after that its pretty easy but slow

I drill & tap the clamp bolt holes before cutting the slots to allow it to clamp up then cut the slots with 2 blades on the hacksaw then drilling the first part for clearance

Done it a few times now & not had major trouble yet, slow & steady wins the race :)
Thanks, sorry for the thread jack... its something ive been considering for my bike. Just wasnt sure about the actual clamps design and what not.
 

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V4's FTW
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I've a couple of yokes with 45mm holes going cheap, no where to put bars tho, strictly clip ons
I'm sure you could add something to make bars work?

900RR forks are 45mm, as are 03-04 CBR600RR... both great conventional forks!
 

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Discussion Starter · #13 ·
I'm thinking of going R6 forks. Lots of flat track guys use them and they are 43mm so only 2mm overbore from stock.
 
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