Chain hitting the plastic cover

[jarda]

My two months old Model D erg makes an occasional knocking sound at the extreme end at the catch position. I think this basically only happens when I overcompress, so I am not very worried about it. I take it as my over compression warning. I was finally able to trace it to the chain hitting the plastic return mechanism cover bellow it. Basically, the chain is slack and when I start pulling on the handle, the chain vibrates and hits the cover. Again, this only happens when I get very close to the chain guard. Probably too close. I tried replacing shock cord, but that did not help. Taking the plastic cover out obviously helps, but that's probably not a solution.

I am trying to sort this out through Concept 2 support, but I was also wondering if maybe it's something that's relatively common. Normally, I'd go to a gym and test Model D there, but somehow, with the lockdown, that's not possible. So, does anybody have experience with anything similar? If you go extremely close to the chain guard while rowing, do you get a chain hitting the plastic cover?

Here's one short video demonstrating the issue: https://photos.app.goo.gl/kT8nmG5AMaNZRgRk8

[jamesg]

Let the chain pull your hands forward, during the recovery, rather than trying to push it; it has to stay tight.

[Dangerscouse]

It does sound like there is some sort of resistance on the chain on the drive, and your issue hasn't happened to me unless I'm rating at 40+

How old is it? When did you last oil the chain? There are far more knowledgeable minds than mine who will hopefully offer some advice

[jarda]

Let the chain pull your hands forward, during the recovery, rather than trying to push it; it has to stay tight.

I think the chain stays tight. There's a tension in the chain on the whole recovery period and I don't push it. Maybe it's not obvious from the video, but there is never a slack on the visible part of the chain. The speed of recovery doesn't seem to have an impact on the knocking sound, though it never happens from the static position. Ie. if I stop at the catch long enough. The only thing that will completely eliminate the knock is if I stay farther away from the chain guard.

It does sound like there is some sort of resistance on the chain on the drive, and your issue hasn't happened to me unless I'm rating at 40+

How old is it? When did you last oil the chain? There are far more knowledgeable minds than mine who will hopefully offer some advice

It's new. Bought in March new and I think the sound was always there, I just didn't want to spend time debugging it, since it doesn't seem to have functional impact. I haven't oiled the chain yet, but it was well oiled from the factory - in fact, there's oil residue on the plastic cover where the chain hits it: https://photos.app.goo.gl/gs1Df6JTjjujHB8m6. Does this seem normal?

But yes, after eliminating the shock cord, the chain is another possible culprit. I'll try oiling oiling it.

[jackarabit]

Referencing C2D parts schematic, there are two chain idler pulleys (part # 1024) in the ‘cat’s cradle’ of the chain drive and return mech. The one yoked to the bungee takeup presents no problem ime. The pulley nearest to the fan axle has been known to throw the chain on to the idler shaft (part # 1305) where it continues to track on drive and recovery. Pull the plexi slide from the U-channel again to check chain location and lift chain on to idler pulley if found to be necessary. Fire for effect.

[jarda]

Referencing C2D parts schematic, there are two chain idler pulleys (part # 1024) in the ‘cat’s cradle’ of the chain drive and return mech. The one yoked to the bungee takeup presents no problem ime. The pulley nearest to the fan axle has been known to throw the chain on to the idler shaft (part # 1305) where it continues to track on drive and recovery. Pull the plexi slide from the U-channel again to check chain location and lift chain on to idler pulley if found to be necessary. Fire for effect.

I am worried my Model D is newer than the schematic. There's a plastic part that I cannot find in the schematic, but it's screwed to the screw that is also holding generator base (part #1029) and wraps around the chain idler pulley - apparently holding it centered and completely preventing the chain from ever slipping off the pulley: This is the best photo I could get: https://photos.app.goo.gl/mhwg7KYJLPU3SK246.

You may be onto something with the idler pulley though. It basically seems to me now that something is introducing vibration to the bottom part of the chain. The chain always vibrates on the recovery and getting closer to the chain guard means it gets more amplitude, to the point where it hits the plastic cover once I start applying force on the drive. I really wonder what could be responsible for this.

Thank you all for helpful suggestions! I'll keep exploring.

[puffyp]

I have had a similar experience and was able to establish that the chain was coming into contact with the plastic shroud on the left hand side. i solved the issue by simply moving my right hand a fraction towards the centre of the handle, maybe 5mm, issue resolved. This may not work for you and will probably depend on the point in the stroke that contact is made. Fingers crossed, no cost solution and anyone can do it!

[Hans]

I had the same ? experience in the past. The problem was the plexi slide at the u-channel that didn't fit well. At one side it
was resting on a nut and on the other side resting on the frame. That made a 1 centimeter diference in height. I made it
fit better and the noise was gone.

Hope this is of any help.

[tobypearce]

I had this issue too. My C2 is 10 years old (and by the way, still as brilliant as the day I got it). The plastic sheeting had bowed upwards over the years, so I took it out, turned it upside down and put it back in again. This created about an extra centimetre and the rope now runs free

[jackarabit]

I had the same ? experience in the past. The problem was the plexi slide at the u-channel that didn't fit well. At one side it
was resting on a nut and on the other side resting on the frame. That made a 1 centimeter diference in height. I made it
fit better and the noise was gone.

Hope this is of any help.

Think Hans may have it! My 2012 model D has press-in ‘nutserts’ in the flanges of the u-channel which receive the bolts in the rear strut of the front leg. The plex slide may or may not ride on these if not persuaded to seat instead on the flanges and the result is elevating the slide into contact with the chain return mechanism.