2007 YZ250 Weird Fork Issue

11/18/2020 4:20am
So I was riding my freshly rebuilt YZ the other day and my buddy wanted to trade up bikes, so we did. I jumped on his minty, hardly ridden 2007 YZ and ripped on it from the start. Wasn't the best decision I've made..really immature really, I should've ridden it slow just to feel it out. Well, immediately the front end felt a little stiff to me but I figured he just had it set up differently from me. Then...I slammed into a solid face and the front felt like a total brick. After making sure I was good, haha, I inspected..

I stopped, held the front brake, and tried to compress the front end. It would only go down about 2.5" or so. Literally, would not go down any further. Nothing sounds weird, it just won't compress.

What do ya'll suggest for issues? I haven't seen this one before. I'm thinking could be over torqued pinch bolts, an axle that isn't square. All weird issues because he hasn't ridden the bike in a long time and it was fine before. Its a good mystery.
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FWYT
Posts
3305
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5/25/2014
Location
San Diego, CA US
11/18/2020 4:34am
Did you bleed the air out?
1
FGR01
Posts
5091
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10/1/2006
Location
AZ US
Fantasy
1334th
11/18/2020 6:59am
Inner damping chambers were likely not bled properly. There is probably excess oil in the upper part of the inner chamber causing hydraulic lock. Either that or something is broken or there is about 3x too much oil in the outer chambers.
1
11/18/2020 7:17am
FGR01 wrote:
Inner damping chambers were likely not bled properly. There is probably excess oil in the upper part of the inner chamber causing hydraulic lock. Either that...
Inner damping chambers were likely not bled properly. There is probably excess oil in the upper part of the inner chamber causing hydraulic lock. Either that or something is broken or there is about 3x too much oil in the outer chambers.
Thanks guys.

My first question was had the forks been bled. He said yes.

To me it seems like oil is bleeding off to somewhere it shouldn't be and continuously doing so because it seemed to get worse (less travel over time).

A disassembly is in order, I'm sure.
asax771
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21
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11/9/2020
Location
SE
11/18/2020 8:01am
Is it plush in the beginning then suddenly stops, or is it more linear? Anyway I would guess the front axle is pinched. Does the thicker part of the axle stick out from the clamp? Bad sign in that case.

One other less plausible root cause that I am ashamed to know is that a 46 mm fork seal is possible to assemble to a 48 mm fork leg. It is however not possible to compress the fork afterwards 😂
2

The Shop

11/18/2020 8:10am
It seems totally normal then just hits a stop so I would say not linear. Its fine then brick wall. So freaking weird. The last time he rode it, it was fine. Only thing that's changed is it sat up for awhile.
11/18/2020 10:07am
What FGR01 said and add a bad inner cartridge seal. Oil form the inner cartridge leaks out into the outer chamber and you end up with hydraulic lock of the outer tubes. You won't notice the loss of dampening because the "air spring" effect is so high and then the lock point hits.
2
11/18/2020 11:08am
This is sounding like a culprit to me! Thank ya'll for the help on this.
Paw Paw 271
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3640
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4/3/2013
Location
Benton, LA US
11/20/2020 3:02pm
Too much oil in the outer chamber. Remove about 35cc of that oil and see how it does.

Paw Paw
silver753
Posts
137
Joined
5/18/2010
Location
Brick, NJ US
11/21/2020 12:06pm
You can drain 100% of the inner chamber into the outer and it's not enough to cause hydraulic lock on those forks. Most likely a front axle pinch bolt binding issue, or maybe a bent or dented fork tube.
1

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