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Elitest thrill junkie
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Or why these MOFOs making these semi-bath forks don't include valves in the footnuts that allow you to quickly change the semi-bath fluid without taking apart the fork?

Probably a good reason for that, they wouldn't sell as many forks, seals, and replacement stanchion-steerer assemblies.
 

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I've started doing this with my 2010 Revelations and get the hssst noise when I compress the fork and then really smooth buttery movement.
 

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Unless there is a defective seal in the air cartridge allowing high pressure air to leak into the lowers, there is no reason to purge air out of the lower legs.

Any oil bath fork, coil or air, when assembled, has a sealed lower leg. The oil seal at the top and the crush washers or O-rings at the foot nuts form a sealed chamber. When the stanchion tubes are inserted, at the top, air is trapped in the lower tubes. When the fork compresses and the stanchion tubes travel into the lower legs, the stanchions take up volume, and the air in the lower legs is compressed. Yes, this results in a slight ramp up of pressure in the lower legs. This is normal and inevitable. It does not pose an impediment to performance because at the top of the travel you are starting at 0 PSI and the amount of pressure built up at the approach of bottoming out is just a slight cushion. Depending upon your riding weight and style, the effect will vary, but that is why you adjust the air spring pressure for your particular situation rather than just going by a shock chart.

You can absolutely compensate for this slight air cushion by adjusting your air spring pressure and damping accordingly.

The video that was posted showing the zip tie "procedure" is a horrible example of how to "solve" a problem that does not exist. Worse, it's a good way to create a problem. Notice that the air being "purged" is at the bottom of the stroke. They are venting out the air pressure as the stanchions compress the air. This means when the air spring is charged and the fork extends, the lower legs will be in a vacuum. All this does is provide the temporary effect of having a negative air spring. Sure, it feels plush for a bit, but it needs to be repeated later. Why? Because the vacuum gets filled. In other words, the air gets sucked back into the lowers. Depending on where you are riding, guess what else gets sucked into the lowers? Moisture, dust, or whatever.

I can't see the point in running a zip tie past the seals on regular basis to get some temporary gimmicky effect while risking damaging the seals and contaminating the oil. Simply accept that fact that a slight ramp up occurs inside the lower legs and adjust the air spring and damping accordingly. Then, ride your bike and stop wasting time performing unnecessary "procedures."

Again, if significant air pressure is building in the lowers, that would be different and would indicate a loss of air from a pressurized part of the fork to the lower leg. This calls for a repair of the problem, not a quick zip tie purge.
 

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Discussion Starter · #46 ·
Unless there is a defective seal in the air cartridge allowing high pressure air to leak into the lowers, there is no reason to purge air out of the lower legs.

Any oil bath fork, coil or air, when assembled, has a sealed lower leg. The oil seal at the top and the crush washers or O-rings at the foot nuts form a sealed chamber. When the stanchion tubes are inserted, at the top, air is trapped in the lower tubes. When the fork compresses and the stanchion tubes travel into the lower legs, the stanchions take up volume, and the air in the lower legs is compressed. Yes, this results in a slight ramp up of pressure in the lower legs. This is normal and inevitable. It does not pose an impediment to performance because at the top of the travel you are starting at 0 PSI and the amount of pressure built up at the approach of bottoming out is just a slight cushion. Depending upon your riding weight and style, the effect will vary, but that is why you adjust the air spring pressure for your particular situation rather than just going by a shock chart.

You can absolutely compensate for this slight air cushion by adjusting your air spring pressure and damping accordingly.

The video that was posted showing the zip tie "procedure" is a horrible example of how to "solve" a problem that does not exist. Worse, it's a good way to create a problem. Notice that the air being "purged" is at the bottom of the stroke. They are venting out the air pressure as the stanchions compress the air. This means when the air spring is charged and the fork extends, the lower legs will be in a vacuum. All this does is provide the temporary effect of having a negative air spring. Sure, it feels plush for a bit, but it needs to be repeated later. Why? Because the vacuum gets filled. In other words, the air gets sucked back into the lowers. Depending on where you are riding, guess what else gets sucked into the lowers? Moisture, dust, or whatever.

I can't see the point in running a zip tie past the seals on regular basis to get some temporary gimmicky effect while risking damaging the seals and contaminating the oil. Simply accept that fact that a slight ramp up occurs inside the lower legs and adjust the air spring and damping accordingly. Then, ride your bike and stop wasting time performing unnecessary "procedures."

Again, if significant air pressure is building in the lowers, that would be different and would indicate a loss of air from a pressurized part of the fork to the lower leg. This calls for a repair of the problem, not a quick zip tie purge.
Chris I'm not sure you are understanding the issue. I agree that purging the air at the bottom of the stroke does seem like a bad idea. For whatever reason, air pressure does in fact build up in fork legs, such that even at full extension, there is significant pressure in the fork leg. The anecdotal evidence in this thread suggests it happens on a range of models, and of course, many DH forks have a provision to bleed air out of the fork lowers. You could probably account for why this happens better than I could, but it definitely is an issue than can amount to a dramatic alteration of the spring rate of the fork.
 

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Discussion Starter · #47 ·
Some additional information for my specific case: I live around 900' above sea level but routinely drive up to 5000' feet to ride and occasionally 8000'+ (Mammoth). I've wondered if frequent altitude changes exacerbate the issue.
 

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Chris I'm not sure you are understanding the issue. I agree that purging the air at the bottom of the stroke does seem like a bad idea. For whatever reason, air pressure does in fact build up in fork legs, such that even at full extension, there is significant pressure in the fork leg. The anecdotal evidence in this thread suggests it happens on a range of models, and of course, many DH forks have a provision to bleed air out of the fork lowers. You could probably account for why this happens better than I could, but it definitely is an issue than can amount to a dramatic alteration of the spring rate of the fork.
Hillharman: Thanks for zeroing in a very specific aspect. If air is actually building up inside the non-air spring lower leg of a fork, it cannot be due to a leak from a pressurized part of the fork. Hence your inferred question: Where is it coming from? The only rational explanation would be that somehow the main seal design is such that air is being "grabbed" during extension and then remains trapped and slowly builds up. I'm guessing something along the lines of what was happening with the Fox air chambers that were filling up with oil from the lower leg. The U-Cup seal was doing something similar with the oil. Anyway, that's the best guess I have for that specific situation. I've not had any reports of such air build up with our seals, but would certainly like to know if it is a seal-specific issue.

My main concern was that every fork will compress air in the lowers on the downstroke and that is not a problem. It's not going to be a good thing if everyone is shoving cable ties past their seals as part of normal "maintenance."
 

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This happens on all forks, not just Pike, especially when you go from low elevation to high elevation. They do it on some DH forks because they figure people are riding lifts all day at higher elevation. Trail bikes not so much. And what would your lowers look like if you were smooshing grease into them every ride for that extra plushness, eventually it would just be a ****y mess inside your fork. Nasty. No fork company in their right mind is going to incorporate that, warranty nightmare
 

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Discussion Starter · #50 ·
Hillharman: Thanks for zeroing in a very specific aspect. If air is actually building up inside the non-air spring lower leg of a fork, it cannot be due to a leak from a pressurized part of the fork. Hence your inferred question: Where is it coming from? The only rational explanation would be that somehow the main seal design is such that air is being "grabbed" during extension and then remains trapped and slowly builds up. I'm guessing something along the lines of what was happening with the Fox air chambers that were filling up with oil from the lower leg. The U-Cup seal was doing something similar with the oil. Anyway, that's the best guess I have for that specific situation. I've not had any reports of such air build up with our seals, but would certainly like to know if it is a seal-specific issue.

My main concern was that every fork will compress air in the lowers on the downstroke and that is not a problem. It's not going to be a good thing if everyone is shoving cable ties past their seals as part of normal "maintenance."






In this particular case, the root of the problem needs to be pinpointed and corrected because the last thing you need is your fork pulling outside elements into the lower leg.
I think we are on the same page. The only explanation that made sense to me was that it was somehow easier for air to enter the fork leg (past the seals) than for it to exit, resulting in a gradual build up. I agree that compromising the seals in order to solve the problem is a really bad solution, but it was to the point where my fork felt like garbage. I was running ~15 psi less than I was initially and it was still extremely harsh and only using ~80% of the travel. Equalizing the fork legs at full extension instantly brought me back to the out of the box feeling and more reasonable air pressures in the air spring.
 

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I think we are on the same page. The only explanation that made sense to me was that it was somehow easier for air to enter the fork leg (past the seals) than for it to exit, resulting in a gradual build up. I agree that compromising the seals in order to solve the problem is a really bad solution, but it was to the point where my fork felt like garbage. I was running ~15 psi less than I was initially and it was still extremely harsh and only using ~80% of the travel. Equalizing the fork legs at full extension instantly brought me back to the out of the box feeling and more reasonable air pressures in the air spring.
Well, if you ever want to see if it's seal-specific, let me know. Since you have the problem consistently, you'd be a great test candidate.
 

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Unless there is a defective seal in the air cartridge allowing high pressure air to leak into the lowers, there is no reason to purge air out of the lower legs.

Any oil bath fork, coil or air, when assembled, has a sealed lower leg. The oil seal at the top and the crush washers or O-rings at the foot nuts form a sealed chamber. When the stanchion tubes are inserted, at the top, air is trapped in the lower tubes. When the fork compresses and the stanchion tubes travel into the lower legs, the stanchions take up volume, and the air in the lower legs is compressed. Yes, this results in a slight ramp up of pressure in the lower legs. This is normal and inevitable. It does not pose an impediment to performance because at the top of the travel you are starting at 0 PSI and the amount of pressure built up at the approach of bottoming out is just a slight cushion. Depending upon your riding weight and style, the effect will vary, but that is why you adjust the air spring pressure for your particular situation rather than just going by a shock chart.

You can absolutely compensate for this slight air cushion by adjusting your air spring pressure and damping accordingly.

The video that was posted showing the zip tie "procedure" is a horrible example of how to "solve" a problem that does not exist. Worse, it's a good way to create a problem. Notice that the air being "purged" is at the bottom of the stroke. They are venting out the air pressure as the stanchions compress the air. This means when the air spring is charged and the fork extends, the lower legs will be in a vacuum. All this does is provide the temporary effect of having a negative air spring. Sure, it feels plush for a bit, but it needs to be repeated later. Why? Because the vacuum gets filled. In other words, the air gets sucked back into the lowers. Depending on where you are riding, guess what else gets sucked into the lowers? Moisture, dust, or whatever.

I can't see the point in running a zip tie past the seals on regular basis to get some temporary gimmicky effect while risking damaging the seals and contaminating the oil. Simply accept that fact that a slight ramp up occurs inside the lower legs and adjust the air spring and damping accordingly. Then, ride your bike and stop wasting time performing unnecessary "procedures."

Again, if significant air pressure is building in the lowers, that would be different and would indicate a loss of air from a pressurized part of the fork to the lower leg. This calls for a repair of the problem, not a quick zip tie purge.
Makes sense to me. It makes a strong argument for reintroducing adjustability of the negative air spring. The increase in small bump sensitivity was pretty nice with the vacuum.

So, with the Enduro seals you get a little bit of air trapped as well?
 

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Makes sense to me. It makes a strong argument for reintroducing adjustability of the negative air spring. The increase in small bump sensitivity was pretty nice with the vacuum.

So, with the Enduro seals you get a little bit of air trapped as well?
Yes, as far as initial air trapped during installation with pressure at "0" fully extended and ramping up slightly on compression that should happen with any seal that is actually sealing, including the Enduros.

As far as the "pumping up" effect described by some in this thread, where the air pressure builds up to where it exceeds the air pressure outside the fork--I have not seen that happen with the Enduros. On the other hand I have not had first hand experience with this phenomenon with any fork I have rebuilt.

The only fork I've opened had the lowers almost shoot off due to excess air pressure int the lower leg was due to a leaking postitive/negative air spring assembly. Magura sent out a new assembly and that took care of it.

I'd like to have someone that has a fork with this problem try a set of our seals and see if the pressure build up goes away.
 

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I'm in over my head here... but the question I beg to ask is, why then to achieve 30% sag after "equalizing" the fork with the zip-tie method, does the air spring increase by nearly 20psi over the previous "pre zip-tie" air spring?
 

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Elitest thrill junkie
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The pike would have to have some pretty amazing seals IMO to stay pumped up like that and base on my tear downs, it doesn't. Not like older marzocchis with the oil seals that seal harder the more pressure that's applied.
 

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I have been experiencing a slow decrease in small bump sensitivity and overall performance from my Pike. I've had it six months so I decided it was probably a good time for some maintenance. After pulling the damper I immediately noticed a problem, air in the system. Did a bleed and added at least 10cc's of fluid. Not sure if it leaked out or was not filled fully from the factory, kinda strange. Put the fork back together with some fresh bath oil and seals and holy buttery smoothness. Most suspension components really do benefit from routine maintenance, and I know many riders skimp on it, including me. So if your fork isn't feeling like it used to, it could be time for a rebuild.
 

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I Have Gnarly Potential
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Well, if you ever want to see if it's seal-specific, let me know. Since you have the problem consistently, you'd be a great test candidate.
Its got to be a side effect of how well the seals work at holding in grease/oil. They are good enough to keep grease from passing allowing the upper stanchions to remain dry when extended, id assume air is getting in when the seal is being pushed against the dry upper and then trapped when the seal pushes back down as air cant get past the grease coated stanchion seal surface on the inside.
 

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Discussion Starter · #58 ·
Its got to be a side effect of how well the seals work at holding in grease/oil. They are good enough to keep grease from passing allowing the upper stanchions to remain dry when extended, id assume air is getting in when the seal is being pushed against the dry upper and then trapped when the seal pushes back down as air cant get past the grease coated stanchion seal surface on the inside.
This was basically my thought as well. One side of the interface is better lubricated than the other.
 

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Its got to be a side effect of how well the seals work at holding in grease/oil. They are good enough to keep grease from passing allowing the upper stanchions to remain dry when extended, id assume air is getting in when the seal is being pushed against the dry upper and then trapped when the seal pushes back down as air cant get past the grease coated stanchion seal surface on the inside.
Definitely something like that. Only thing is, the seal is not supposed to be a one-way device. We've found someone that's consistently having the problem with the OE seals that is going to switch to our RS 35mm kit and we'll see what happens.
 

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Rocks belong
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So before this ride, I did the equalization at full compression... Which this thread says that would've put my lowers under vacuum and made my small numb über plush... Which it did.

This thread also says that my fork would "pumped" back up and lost small bump and sag during a ride... Which it did. I could feel the Pike stiffening up during the descent.

I feel the moral of my story is to equalize at full extension.
 
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