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Front fork damping

Submitted by peter_maple on Sat, 27/02/2016
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Heavy Twins

Hi Noccers.

I decided to check my front forks while the bike (1962 Dommie 99) is in hibernationover the winter and I am at a bit of a loose end. So,I removed the forks from the bike then removed the springs from the stanchion tubes before reassembling the forks (without the springs). When compressing the forks, by hand,I found there wasn't much damping effect but, when extending them it took quite a bit of effort and the vacuum created tended to pull the two halves back together. Is this how it should be? I thought there should be two-way damping. By the way, the fork action seems quite smooth with no side play. The springs measure 19 inches and I was using 20 grade oil. Does this sound right?

Any comments appreciated. Peter.

Submitted by john_holmes on Sat, 27/02/2016

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2 way damping means it has different damping rates compression vs rebound, before it was the same both ways which is not what you want. So when you have 2 way damping you have a light damping for compression, light because assisted by the spring force, heavier for rebound as it is against the spring pressure. So everything sounds normal for these forks, have a play with them and pull and push them a small amount say 1/4", this will show no damping at all as this is the internal valve moving from compression to rebound and back and you get no damping when the valve is moving.

Submitted by dan_field on Sat, 27/02/2016

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The dampers in short roadholders were fairly rudimentary, there are lots of threads about how to upgrade them, especially to stop the topping and bottoming.

Submitted by peter_maple on Sun, 28/02/2016

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Previously john_holmes wrote:

2 way damping means it has different damping rates compression vs rebound, before it was the same both ways which is not what you want. So when you have 2 way damping you have a light damping for compression, light because assisted by the spring force, heavier for rebound as it is against the spring pressure. So everything sounds normal for these forks, have a play with them and pull and push them a small amount say 1/4", this will show no damping at all as this is the internal valve moving from compression to rebound and back and you get no damping when the valve is moving.

Thanks John, now I knowthe operation of the forks seems to be pretty much normal I have the choice; follow the sage advice of If its not broke don't fix it, and leave them alone, or strip them down for the hell of it. Thanks Dan. I will look at the threads to see if I can make any improvements.

Submitted by ian_cordes on Sun, 28/02/2016

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I fitted RGM uprated damper tubes to the short Roadholders in my Dommie, and also, after trial and error, increased the quantity of 20w oil to 180cc per leg. They now have a very plush 2-way action.

 


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