Cota 247 Fork behavior after reassemble

[Niro]

Hello,

I redid the forks on 1970 Cota 247. 
 

I only had the bike for a short time and don't know how the forks should fill/ behave.  
 

Currently I reassemble the forks and put 190cc fork oil (15W) in each. 
 

what I noticed is:

1. The forks compress (goes down) quite easily the first few mm, feel like they bottoming, but I never experienced this behavior before so I don't know if this is the case, or it's a normal behavior. 

2. It seems the fork doesn't bounce all the way up. They do bounce up but I can pull them up few mm more. 

3. When I compress the forks, I can hear air goes out from the top of the left fork (I believe it's from the cap). I don't hear any air hissing from the right fork. (I open and clean each cap). Should I hear air goes out or not?
 

Can you please help me to address those issues? Thanks 

Edited November 17, 2021 by Niro

[feetupfun]

1 I can't understand your question.

2 There are usually anti-topping springs on the damper rod that have this effect. The intention is to avoid harsh metal to metal impact when the forks extend fully (like when you riding up a steep bumpy hill). It's also possible that the fork spring preload is too small to hold the forks at the top of their travel.

3 Some fork caps have vent valves that hiss when you compress the forks. Some caps don't have venting. Sometimes with vented caps, the valve sticks shut and doesn't let air out. If yours are the vented type, you should be able to find a small (1 mm) hole on the cap where the air comes out.

[Niro]

Feetupfun- Thank you for your helpful answer!

I would appreciate if you can help me with the related questions:

1. I will try to rephrase my question: how I can I tell if the forks compress correctly and not, let say, sagging down?

2. This is a photo of the fork damper assembly- can you tell if this damper has the anti-topping spring that prevent the metal to metal impact?

3. This is the fork caps that the bike has. Can you tell if this is the vented type caps that releasing air?

Thank you.

 

  

 

 

 

 

Edited November 18, 2021 by Niro

[b40rt]

1 hour ago, Niro said:

Feetupfun- Thank you for your helpful answer!

I would appreciate if you can help me with the related questions:

1. I will try to rephrase my question: how I can I tell if the forks compress correctly and not, let say, sagging down?

2. This is a photo of the fork damper assembly- can you tell if this damper has the anti-topping spring that prevent the metal to metal impact?

3. This is the fork caps that the bike has. Can you tell if this is the vented type caps that releasing air?

Thank you.

 

  

 

 

 

 

Take a wide guess what the hole in the top is for .........

[woody]

3 hours ago, Niro said:

Feetupfun- Thank you for your helpful answer!

I would appreciate if you can help me with the related questions:

1. I will try to rephrase my question: how I can I tell if the forks compress correctly and not, let say, sagging down?

2. This is a photo of the fork damper assembly- can you tell if this damper has the anti-topping spring that prevent the metal to metal impact?

3. This is the fork caps that the bike has. Can you tell if this is the vented type caps that releasing air?

Thank you.

 

 

If that is how your damper rod is assembled then it is correct. The top out spring is the small spring you can see. It doesn't stop the forks topping out if they aren't set correctly with oil but it cushions the impact - you will still hear the metallic bang

If you think the forks aren't working correctly drain all of the oil out and then, with the bike on its wheels, push the forks right to the  bottom. With no oil you should easily be able to do this in a smooth fashion with no binding. If there is resistance one or both tubes could be bent or there could be an incorrect length spacer on the front wheel which is pulling the bottom of the forks together or pushing them apart, which can also cause binding.  Assuming they push to the bottom normally, push them sharply to the bottom and let go. The spring should be strong enough that they rebound quickly and maybe right to the top so that you hear the metallic bang as they top out. It's possible the old springs have lost strength and don't fully extend, if not pull on the bars to check they top out.  This will show whether you have full travel up and down on the forks.

With the bike standing on its wheels the forks may drop (sag) by maybe 20-25mm under the bike's own weight. Pull up to full extend the fork and to see how much they sag. If it is a lot more than that it's possible your springs are weak so may need some extra preload spacers which is trial and error. It could even have the wrong springs.  

The fork caps letting air out when you compress the forks also affects the rate at which the forks compress. If they don't vent, the air pressure gives extra preload, if they vent it weakens preload - and can also spew oil out as well as air. Personally I think they are not needed and block the holes off to make them solid caps.

 

[Niro]

Woody,

Thank you so much for the information provided! I sure learned a lot from it 😎