Hi fellow MTBR members. Sorry for the very wordy post, but I wanted to lay out all the details in advance in case anything that I consider non-relevant is the root cause of the problem with my fork.
First I would like to say that I am a fairly skilled bike tech and have several years of bike shop experience in addition to working on my own bikes. I was out on a ride recently and was hoping to improve the settings on my Lyrik RC2DH. Before I could even get to the trails I wanted to use as a testing loop to dial the damping, I went off a small (2', maybe 3') drop to a steep transition, not to flat. I noticed that the bike came down really hard, the front fork had bottomed. I looked at the o-ring and it was sitting just above the 30% sag indicator on the right stanchion (maybe 40% of total travel). I pulled the front brake and compressed the fork which had a noticeable hard stop at that point in the travel. Giving up on my ride for the day, hoping not to do any further damage to the internals I went home and took things apart.
The first thing I noticed was that when I deflated the air chamber, the fork compressed to about 20% sag (never noted exact amount). After removing the top caps and knocking the bolts loose on the lowers I unscrewed the air side bolt and there was a large pop, with oil spraying all over the place, so there was some sort of air leakage from the upper to lower chamber in the fork (possibly time for new o-rings?).
Leaving the left side to drain into a pan, I drained the right side lowers. The oil was a little murky but not too bad. Note, I have maybe 15 days of riding on the fork since I last rebuilt it. Once it had drained I flipped it over to pour out the oil in the top side of the rebound and a good amount of oil started draining out of the left leg (despite it sitting for around 20 minutes).
I then pulled the lower shafts out of the stanchions and while it is nearly impossible to see, there are two very shallow dents in the rebound shaft, roughly mid way (likely the same point where the fork had the hard stop in travel). The two dents run perpendicular to the shaft and about half of the circumference of the shaft. I presume this was done by the plastic spacer that clips in to the lower stanchion, and that when the fork bottomed the shaft somehow buckled enough to cause the dents.
Now, that's all the information I have, everything else on the forks looks fine internally. Any ideas why the fork would have bottomed mid-travel like this? The pop and oil pressure in the lowers is likely due to not 'burping' them as some people suggest is required periodically with this fork, but could the fork have had so much air in the lowers that it effectively locked the travel at 40%? The bottom out sensation when I compressed the fork was quite abrupt, but there appears to be no other internal damage to any of the parts, everything was as clean as could be expected, and still lots of grease on all the threads and o-rings, with no signs of anything binding. Even the shaft with the two small dents was very slippery and the black spacer moved very easily from the top of the rebound valve to the end of the shaft.
At the very least, I will have to try and purchase a new rebound damper shaft (or assembly) but have no answer as to what caused the loss of half the travel that resulted in the bottom out and presumably the damage to the rebound shaft.
Any insight would be most appreciated as I'm quite sure my LBS won't have a clue as to what went wrong and will suggest I buy a new fork.
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Thread: Lyrik RC2DH issues