Ringing fins - rubber damping?

I generally like that air-cooled ringing sound, but my '83 250WR is HORRIBLY loud in this regard. Can't take it anymore. Motor is otherwise fresh and VERY tight, so I'm not suspecting any other mechanical cause. It's the fins. My 430's aren't nearly as loud and I run them with no damping at all. But this 250 really hurts my ears!!

Anybody got a good part number or idea for rubber damping? I Stuffed all the fins with sections of rubber fuel line, but the effect was minimal. I know some of the old Yamahas had a string of press-in rubber blocks, but it's been too long so I wouldn't know what to look for. Any other ideas?

I wondered the same thing as my 84-WR250 is also very loud. My 82-430 is also alot quieter.

Pick,
Saw the post and immediately thought of stuffing some hose. Knew you knew that old man trick though.

I know what i'm about to suggest is soooooooo "caveman" and really really outside the box and even goofy but here we go. How about sliding some rubber/heater hose (or equivilant) over a couple of long springs. Drill a couple of holes, attach and stretch springs across the head from side to side. Hose might dampen the head vibration somewhat. Might melt the hose. Who knows? Just throwing something out there. Seems like the shifter kart guys do something similar to mount up their pipes.

Cylinder fins are another issues. I too remebrer the old YZs had press in rubber blocks that fit in a vertical manner in between the cyclinder fins. They just slip fit between the fins and the pressure just held them on/in.

Its late and just scatter shooting - don't hold the sleeved spring idea against me plz - pretty off the wall. Good question though and I'm interested in a solution.
Rick

My 84 WR250 is loud too; nature of the beast I guess. Pretty much the same after replacing the original rubber dampers with new 5/16 diameter (I think) rubber fuel line too. Small improvement but not much.

Maybe if you remove the silencer you won't notice the fins ringing

If discover an alternate method, be sure and let us kow.

Picklito-
I know these would be similar to the hose you're using but these may be made of different material. Works well on ATK's - they're known for having ringing noises from the fins.
Items 42, 43, and 44.

Another option that works well was buying small rubber blocks from McMaster-Carr and cutting notches to match fin spacing. A real cheap fix too.

1989-1996 ATK406 part numbers:
830 453 Silencing Tube 9.5 x 14 x 70 mm
830 454 Silencing Tube 9.5 14 x 150 mm
830 452 Silencing Tube 9.5 x 14 x 35 mm

HWY,
Good job on the cross referance!

I like those old ATK`s almost bought one back in the day.

What kind of graphics do you do?

Thanks,
Yup- I've had 4 ATK's. Still have two. Reliable as a rock or XR's, whichever came first!

I won't hijack the thread with my graphics, PM and I'll tell you.

All great ideas guys (except for Schimmelaw... who wants to turn my beautiful classic 'ooska into a geeky teenager wearing braces!! JK).
Thanks for the input.

The rubber fuel line trick was much less effective than I had hoped. I wonder if those ATK parts are different material. Thanks HWY. I'll check with Motoxotica next time I'm there. They sell ATK parts and I bet Dan knows exactly what that material is.

If there are any more ideas out there, keep 'em coming...

I know that ultralight aircraft pilot's use this technique on their engines.
A slightly different approach using tubes that is effective on Rotax engines.

Hey Picklito,
Let me know how the ATK blocks work out.

Update:

While doing routine maintenance I found that the front engine mount bolts were loose. 3 were at about 15 ft-lbs, one I could almost turn by hand. Torqued them to 25. Swingarm pivot bolt was about 20, torqued it to 45 (I guessed at the torques - had greasy hands and no manual available at the moment, but the manual I do have says 29 up front and 44 at the swingarm).

Ringing has NOTICEABLY decreased. Still there, but tolerable. And I had taken out the rubber fuel line. Gonna put some softer stuff back in and see where that goes.

I think the softer the material the better.

Just like vibration dampners on tennis raquets, the dampners on my raquets are gummy silicone like material.

Hey Picklito,

Here's something else that may or may not matter. On my WR, the exhaust pipe has two steel plates (just below the gas tank) that encase a sheet of fiberglass cloth or something on both sides of the pipe. The plates are held on with hose clamps. I think your '83 has the same feature. A lot of times these are lost and not replaced, but mine are still there. The fiberglass cloth on mine is really worn out though and I am planning to replace it with thicker cloth from McMaster-Carr. I don't know if this helps cut down the noise level yet but I thought I'd mention it as a possibility.

Thanks for the torque specs. I did not have them but will also give that a try.

Tom

I am fortunate that the extra wall for the pipe is still there and in good shape. Have fresh fiberglass and snug clamps... it does make a difference. Thanks.

Picklito, you probably fixed your ringing issues by now (or sold the bike) but when I came across these:


http://www.cemoto.it/articolo.php?id=1055

I remembered this thread. Thought I'd post it up in case any use. Not sure of the dimensions. I may try these but I have more pressing noise and tuning issues to attend to first...

Kind regards
Lucien

Wow! Those look great! Thanks.

No, I sort of lost that pursuit. I tightened the frame up a bit as above, and that helped, but last few times I had it out my ears were killing me! I'd like to get some of those dampers. Several, actually, as I'm sure they'd help the 430, too (although the 430 doesn't ring nearly as loud, or maybe at a less annoying frequency). Will have to check around and see if anybody in the U.S. has them. Again... Thanks!

LOOK UP PART#'S 860 095, 860 090 for a Rotax 503 engine. I think they would work perfect. One is long and one is short.

Picklito...

check out this Bultaco site, I have ordered stuff from them for my Alpina.
Scroll down the fin dampners/anti vibration parts are near the bottom of the page

http://www.bultaco.com/Rubber.htm

I bought some fin dampers about 7 years ago. Cannot remember who from though.
They were sold as Husky ones, but I found that the pitch of the slots was wrong for my 390 motor. They just tried stretching out with wrinkles and lumps ! I stopped after fitting two of the strips. I did think of cutting them so they would span two or three fins at a time to lessen the crap look, but figured that would be defeating the object.
If I can find the two I have not fitted yet I will post a picture.
I am following this with great interest, as the ringing does wind me up.

Fantastic info guys! Rotax... yes... seem to remember those having the dampers. Will check that out.

Mike,
That Bultaco site is really nice. It looks like that chain tensioner wheel might work for us, too. Do you happen to have those rubbers on any of your bikes? Would be nice to know if they fit... would be a bummer to have grouty's experience.