Topic: Question about Rubber "plug" near crank sprocket.

[Lostboy Steve]

The rubber seal that can get eaten up by an oring chain was eaten up by rust instead. There wasn't much left to it at all. I wire wheeled the entire area a little bit to get all the rust off of the metal behind it. It is fairly pitted now and all that is left is the rubber around the edges of the metal plug. I cleaned up the whole area and sprayed it with silver engine enamel to try to keep it from rusting any further. The area wasnt leaking oil before all this, and again it was mostly just Rust covering the plug. So, my question is what is the significance of the rubber that was deteriorated and only had a small section left hanging on like a loose tooth? Is this something to worry about? Is it common for this plug to rust like that and "blow out" the rubber on top of it? Thanks Guys.

[dave500]

if it aint leaking itll be fine,its a sort of a half arsed up date,on the earlier 500 model that plug has a centre hole with a lip seal that the clutch rod runs through,with the 550 that was all changed and not required,my guess is to lessen the expence of re tooling the case and delete that opening just change that seal to a holeless one?the rubber coating is just a hangover aswell?dont worry if it aint leaking!ive reused these over and again no sweat,this is a reassembled bottom end with the old seal reused,you can clearly see the old o ring chain tell tale scrub mark?

its not an "active seal" like if it had a spinning shaft through it, or the clutch action rods lateral action that will wear it out and by all rights should be replaced as a matter of course if you split the cases,its a static one and lasts forever more or less,much like a freeze plug.

[Lostboy Steve]

Perfect Dave! THANKS! Yes, mine was rusting under the rubber and "blew" it out. There was barely any rubber left.

[Lostboy Steve]

While in that area, what would cause this? Remember the bike had a 15t sprocket and I haven't changed it yet.

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[TwoTired]

That rubber coating is a rust preventive.  To prevent rust, it either has to be oil/grease coated or coated with some other material.

Liquid vinyl, RTV, JB weld, or epoxy are possible restorative avenues.  Or, you can hope some chain lube fling-off keeps the rust at bay.

[dave500]

the rubber around its edges also forms the seal,probably just as easy to coat the whole piece than try and apply it just on the edge?just paint it if you want,looks like its had a chain come off at some time?