919 fork piston mods..... - Wrist Twisters
 
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post #1 of 3 Old 10-03-2015, 12:14 AM Thread Starter
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919 fork piston mods.....

I have left over from when I had my 919 a pair of comp pistons. Having spent so time since then mucking about with these fork carts in my other bikes I decided to mod some 919 ones for Kiwiboy. I spoke to him about this ages ago but only got round to it today.

So the first pic is the stock pistons. Pretty much as I can make out they run 1.6mm ports for the comp side. Tiny compared to anything else I have worked on. They have a basic shim stack of 4 shims.

As an experiment I have taken the ports out to 2mm although I may see if I have a 2.1 drill. 2.5 is to close to the sealing edge for my liking. Added a small taper on the top side of the ports. I also ground a approx 1.5mm port as a low speed bleed and to help the high speed. This was nothing like as tidy as I would like so if this works out for the next one I will drill a bleed in the cart body as per Roger Ditchfields "Rogering" mod.

I will give this to Kiwiboy and tell him to run 5w oil. If it works and I think it will he will owe me 2 coffees when we go out for a ride with my beloved. If it doesnt I will pay for the fork oil to swap it back.
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File Type: jpg Piston1.jpg (116.8 KB, 29 views)

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post #2 of 3 Old 10-04-2015, 06:21 AM
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I remember paying a tuner a lot of money to drill bigger holes in my Blackbird pistons. You really have ot know what you are doing but on the other hand it seems pretty hard to make the front any worse

2007 919
2003 CBR1100XX
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post #3 of 3 Old 10-05-2015, 12:10 AM Thread Starter
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Quote:
Originally Posted by Ditch View Post
I remember paying a tuner a lot of money to drill bigger holes in my Blackbird pistons. You really have ot know what you are doing but on the other hand it seems pretty hard to make the front any worse
Stock setup is not good. Its almost an orifice damper with a couple of shims thrown in for good measure.

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