Rubber plugs between cooling fins, purpose or just for shipping?

[ElDorado]

Not sure where to post this question so I'll start here. I have a '99 Yamaha XT 350 I bought to take on camping trips. I ride it rarely, and am not much of a dirt biker. I'm pretty handy and if you ask my kids "What can your daddy fix?" They'll answer, "Anything." :-)

The other day, I was checking the valves (for the first time) on the bike and once I had it all back together I was inspecting for oil leaks and noticed these round rubber things stacked in order between the cooling fins. A couple of them were about to come out and I easily removed one and thought "Hmmm, I've seen these on my garage floor. So, THAT's where they've come from!"

There are smaller ones inserted in the upper fins, which are closer together and larger ones below. Some are obviously, and clearly missing. The one I took out is about the diameter of a time and about four nickels thick.

What is the purpose of these rubber inserts? To protect the fins during shipping or are suppose to be there to protect the fins while riding? Seems they are merely wedged in, and they certainly can take the engine heat while in place.

What are they for?

Thanks,

E

[t_shuffle]

Those help keep engine noise down. Serious.

[holeshot]

Those help keep engine noise down. Serious.

Yep, that's all they're for....just stops noise from the fins. I remember losing one from my Suzuki 125 street/trail bike in the early seventies. My Dad thought they had some other mysterious function, so he made me go back on the streets and retrace my path to find it. Believe it or not, I found it on the street about 1/2 mile from home....... ?

[NYMXer]

They are to stop the cooling fins from rattling to death. The vibration of the engine will make the fins rattle and then break off. The rubber inserts stop that. I wouldn't remove them.

[holeshot]

They are to stop the cooling fins from rattling to death. The vibration of the engine will make the fins rattle and then break off. The rubber inserts stop that. I wouldn't remove them.

Hmmmm...I wonder why none of the motocross bikes (before water cooling) had those plugs in the fins - just the street legal models. I didn't see any broken fins on the MX models (and I had several - including the RM125, which had the same fins as my street/trail 125, but no rubber plugs).

But you never know though..... ?..... but I wouldn't get too excited about the few that were lost already.

[NYMXer]

The old air cooled mx bikes had them too. They were just smaller for whatever reason the factory had. Some were just little plugs between the fins. I have seen a few broken fins over the years. Maybe on yours someone took them out.

[RCannon]

They made a big difference on noise. Sometimes we used chunks of fuel line or split radiator hose for the same purpose.

[ElDorado]

Well, now that y'all mention it, uh....duh. I should have thought of that. Makes total sense. I've lost a few of the plugs during involuntary dismounts, but I think most are still there.

Thanks all, now I can sleep at night. :-)