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FRANTIK1

09 yz450 front fork question.

5 posts in this topic

I bought an 09 YZ 450 last summer that had leaking fork seals. I was pretty shocked at the dealers price to replace, so I bought the tools, watched a Youtube video from Rocky Mountain and did them myself. It went easy , but now the forks seem too harsh. I used 5w Maxima fork oil. I ride woods and trail and not track, so I want the forks a little on the plush side like they where when the forks were leaking, lol. I put the recommended amount of fork oil in from the manual. So my question is do I run fewer cc's of oil in the fork? Do I run less in the inner chamber or outer chamber, or both? Bike is stock and I weigh 235. Clickers were all set back to original settings (they were stock).

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The inner chamber oil has to be filled completely full and free of all air, which is why you bleed them after filling.

The fork is quite sensitive to oil level in the outer chamber. The base amount is 12 ounces each side (355cc). dropping the level as little as 5-10cc per side can make a noticeable difference, and you can run as little as 295cc (10 ounces). The effect is that the air trapped within the fork behaves as a spring, adding to the overall spring rate, especially deeper in the stroke. You soften the "air spring" by reducing the oil level in the outers, thus increasing the volume of air and lowering what you might call the "compression ratio" of the fork.

I typically run 325cc (11 ounces) in mine. If you find that you bottom excessively, but don't want to turn up the compression damping to address it, you can try running a heavier weight oil, like a 7 or even 10wt in the outers only. The only effect this will have on the fork behavior is to slow the fork as it enters the last inch of travel at the bottom.

Oil can be removed by pulling the forks and dumping a measured amount out of the vent screws.

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Thanks gray. Thats the info I needed, and explained very well! I put 350cc's in the outer chamber. The amount of old oil I dumped out was (visually) not that much. Who knows how long the seals were leaking before I bought it. The oil that was in there seemed very thick.

Well now I know where to start. Thanks.

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You mentioned the oil that was in there was very thick. You might be surprised that just changing the oil with a fresh batch will make a world of difference. Even without the oil level change. We just changed my buddy's fork oil that had been in there for about a year and a half and it was very thick. When we went out to ride at the track he said the forks were plush again. We didn't change the fluid level, just fresh fluid. I personally try and change my suspension fluid, both front and back, twice a year to keep the fluid fresh. But then we ride motocross and while I'm not that fast, we do ride pretty hard and fairly frequent. Just my 2 cents worth anyway.

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You mentioned the oil that was in there was very thick. You might be surprised that just changing the oil with a fresh batch will make a world of difference. Even without the oil level change. We just changed my buddy's fork oil that had been in there for about a year and a half and it was very thick. When we went out to ride at the track he said the forks were plush again. We didn't change the fluid level, just fresh fluid. I personally try and change my suspension fluid, both front and back, twice a year to keep the fluid fresh. But then we ride motocross and while I'm not that fast, we do ride pretty hard and fairly frequent. Just my 2 cents worth anyway.

I agree, and I plan to change the fork oil out next winter again. I don't get to ride as much as i'd like too. My problem was that my forks were plush with the thick gunk, and became too harsh with fresh fluid. Grays post made me see what my problem is. I'm sure the leaking seals reduced the fork oil level enough to make them softer. Not to mention how many cc's that were put in there from the previous seal change. The previous owner told me they had been done the year before he put it for sale by a dealership. He told me they were leaking before I noticed it.

Thanks for the help.

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