chimivee

I'm fixing up a ~1990 Trek 800 with low-end 200GS cranks. On the drive side, there seems to be plastic that envelopes the entire crank arm and extends over the face of the spider. I don't see any assembly joint/fastener aside from a molded seam—it's as if the crank arm is "coated"; yet it seems to be one continuous piece with the spider cover... if that makes sense.



Anyway, can this plastic cover be removed somehow? The chainrings are bolted (not riveted) together, so I if I can get this cover off, I can access fully disassemble. Also, any tips for restoring the plastic are welcome.

Thank you!

aggiegrads

I am not familiar with that particular crank, so I can't say how (or if) the plastic should be removed, but I have found mineral oil inexpensive and helpful in restoring some plastics.

You can also find protectants in the car aisle at your local Walmart, Meijers, etc.

Bill Kapaun

Isn't that a self extracting crank?
Never had one.

Crankycrank

The only diagram I've found of your crankset doesn't list any type of fasteners for the chainrings which would suggest it's riveted onto the spider. EV-FC-M202-1191.pdf (shimano.com) You mentioned there are bolts holding it together so why not just undo them and see what's behind the plastic type piece which may just be a factory coating over metal.

Andrew R Stewart 

I strongly suspect this crankset uses riviets to hold the rings. Some rivets have a stamped in hex shape mimicing a hex wrench socket.

The plastic coating is likely molded on and might come off with a fair amount of knifing cutting and scraping. But expect the underlying metal to not have had any finishing and might well be purposely rough to better offer the plastic cover a "bite".

The retaining bolt has a plastic ring about it's head to look flush and neat. It's no self extracting device (and if it were it would need some method to grab it to thread it into the arm, like pin holes as many do have).

BTW that middle ring has some significant wear. Watch for chain suck when shifting over the rings. Andy

chimivee

It's the chainrings I'm trying to remove, which is why I'm trying to access the bolts under the plastic. I've already pulled the cranks off the BB. Yes, self-extracting.

chimivee

Sorry for the confusion, I just meant that the chainrings are bolted to the spider (vs riveted). To access the allen head on the big ring, I need to remove the plastic cover.

Andrew R Stewart 

I've never seen one as you describe. After you remove the plastic and take the rings apart can you post the shots? Andy

chimivee

The chainrings are definitely bolted with they typical hex bolts + slotted nuts. The plastic does seem to be molded—you can see a seam. I just can't figure out how they got the rings on after the fact, since they cover the outer chainring bolts. Chicken vs egg.





I can pry up the plastic cover a bit... I wonder if I can cut an "L" allen wrench short enough to fit under there to hold the bolt while, I turn the nut from the back side. Or maybe drill a neat little hole right through the plastic. Just feel like I must be missing something here!

This bike is total budget Trek, and isn't worth this effort, but I'm doing it more for my own amusement and to give it a second life. I've got a bin of spare parts, but would rather keep this low-end crank on this low-end frame, vs throw something nicer on. Might make it a 1x... if I can get these damn rings off.

Thanks!

Andrew R Stewart 

Well I learned something today. Thanks, Andy

Bill Kapaun

That's a new one for me too.

aggiegrads

My guess ( and it is a guess) is that the cover is snapped on. In order to be molded on, that process would have to happen after the crank arms had already been installed. That is an unnecessarily complex process for high-volume manufacturing. I find it more likely that the cover is aesthetic only and it is either bonded with and adhesive that has already failed near the spider, or it is snapped on. Either way, I would do some prying to get it off so that you can change the rings.

The cover adds no structural value to the crank. It is either there to improve aesthetics, prevent you from replacing the chainrings, or adding the plastic cover was cheaper than the finishing operations for the crank. I would not be surprised if there was an aggressive thread locking compound on the threads which will be very difficult to remove.