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Author Topic: Having trouble with new Fork  (Read 5658 times)

Indiana Dave

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Having trouble with new Fork
« on: June 01, 2012, 06:25:10 AM »
So I've got my new=to-me bike built up, and have been on a few rides. This is my first experience with full suspension (besides an old Wallyworld bike) air shocks and hyd. disk brakes.
I've got a Marzochi Bomber Marathon front fork.

I've read many tutorials on setting sag, etc. I've got the rear set up, and am happy with it.
However I'm having trouble with the front.
I set it at a base of 75psi, with the rebound set right in the middle.
Sag seems about right, and it rebounds fine.
However, the front fork just doesn't soak up any of the sharp roots, rocks, etc. It moves on more flowing bumps, but doesn't react quick enough over the harder more abrupt bumps. I get a loud "BONG" sound. and the front tire bounces up off the ground, which completely defeats the purpose of having a shock.
Any ideas? I'll be at Ft. Harrison this afternoon around 2:30-3:00 to ride if anyone wants to meet up and maybe help me out.
I'd like to get it figured out before the race Sunday in BCSP.
David
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Fett

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Re: Having trouble with new Fork
« Reply #1 on: June 01, 2012, 07:39:27 AM »
I think I know the answer if the Marathon is like many other Marzocchi forks.  If there is no external compression damping, you may have to change the weight of the fork oil to a lighter weight. When you do this, it will also speed up rebound damping, so you may need to readjust that to slow it back down to where you want it.
Not a quick task, but may be your only option to adjust compression damping.
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jdncpa

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Re: Having trouble with new Fork
« Reply #2 on: June 01, 2012, 12:41:15 PM »
If it is used it would probably be a good idea to give an oil change anyway.  I may have a Enduro Fork Seal kit that will fit it.  I bought it a few years ago then sold my bomber.  You can have it on the cheap if you want it.


There are lots of tutorials online that show how to rebuild forks.  It takes time but usually not that hard.

Indiana Dave

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Re: Having trouble with new Fork
« Reply #3 on: June 01, 2012, 05:47:50 PM »
I bought it brand new. I'm only 150lbs, so if it's set up for the "average" guy, it might be a little stiff. I lowered the air pressure, but all that does is lower the sag. The reaction to bumps is the same.
Sounds like a thinner oil might be the solution.
David
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Ed Strobel

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Re: Having trouble with new Fork
« Reply #4 on: June 01, 2012, 06:55:20 PM »
Adding to the oil weight like Fett said, I think on most Marzocchi forks you can change up the shim stack if all else fails to get you the wanted result.

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Re: Having trouble with new Fork
« Reply #5 on: June 01, 2012, 09:48:32 PM »
I bought it brand new. I'm only 150lbs, so if it's set up for the "average" guy, it might be a little stiff. I lowered the air pressure, but all that does is lower the sag. The reaction to bumps is the same.
Sounds like a thinner oil might be the solution.

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getsometrail

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Re: Having trouble with new Fork
« Reply #6 on: June 02, 2012, 08:30:02 AM »
Maybe more doughnuts??

 
I don't care who you are that's funny!  Dave I'm not sure what weight fluid you looking for but I have plenty of 10wt and 7wt fork fluid in my garage if you need some.
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Indiana Dave

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Re: Having trouble with new Fork
« Reply #7 on: June 02, 2012, 01:08:16 PM »
I have been trying to figure out what weight oil is in it. The Marzocchi site says 7,5... So it could be 7 or 5 weight?
Also, by the numbers on their site, I should be running 95psi in the fork for my weight. That seems really high. Might give it a shot, but it seems liek it would have the opposite affect.
David
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Ed Strobel

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Re: Having trouble with new Fork
« Reply #8 on: June 02, 2012, 01:32:29 PM »
7,5 would be 7.5 translated to us in the States.  They also do things like spell "tire"  with a y instead of an i.

Indiana Dave

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Re: Having trouble with new Fork
« Reply #9 on: June 02, 2012, 03:31:33 PM »
Is bike shock oil like motor oil? Is the higher number a lighter oil?
David
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Ed Strobel

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Re: Having trouble with new Fork
« Reply #10 on: June 02, 2012, 04:27:53 PM »
Peter Verdone has a lot of stuff at his site that can fill in way more than you might be looking to know. He has motocycle stuff, frame building, all sorts of things.
http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid

Indiana Dave

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Re: Having trouble with new Fork
« Reply #11 on: June 02, 2012, 06:07:58 PM »
That's a great link. Thanks!
Ironically, that site claims Marzocchi forks tend to work better with a thicker oil. Sheesh!
David
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Indiana Dave

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Re: Having trouble with new Fork
« Reply #12 on: June 03, 2012, 03:41:57 PM »
So, I survived the Dino race today... That's all I did is survive...
This fork is horrible on the BCSP trails. Might as well had a rigid fork on it. I rode behind some clydes just so I wouldn't be tempted to ride my normal pace and end up hurting myself. Once we were past the really rough stuff, I passed them, and a few others but felt like I was on the verge of crashing every bumpy turn.
Actually took one big crash just into the north tower downhill as I got into the woods... Knocked the wind out of me, and cracked the plastic on my helmet. Going to be shopping for a new one.
The tech guy there said that the factory may have overfilled it with oil.
I'm going to try to check it, and maybe drain some out and see if that changes anything.
David
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moondawg

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Re: Having trouble with new Fork
« Reply #13 on: June 03, 2012, 09:58:19 PM »
Is bike shock oil like motor oil? Is the higher number a lighter oil?

All oils are rated the same.  The larger the "weight" number, the thicker the oil.

a 5-weight oil is much thinner than a 90-weight oil.


Incidently, the "w" in motor oils doesn't stand for "weight," it stands for "winter"  It has an additive in it that improves "pour time" in cold temperatures.
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getsometrail

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Re: Having trouble with new Fork
« Reply #14 on: June 03, 2012, 11:01:17 PM »
Sorry to hear about your troubles at the race today.  You should be able to find oil volumes for your fork online however I don't know how you could tell how much is in there unless you drained it all and replaced it with measured amounts.  Is your fork under warranty?  Might be worth a call, they might service it for you at zero cost.  You'd just be without a fork for a while :(   
Roads...?  Where we're going we don't need roads!  Travis Eacret 2008 Giant Trance X2.

 

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