Resonant Frequency?

Has anyone else found an RPM range that sounds/feels like crap?
What I mean is, between 5,000 and 5,500 rpm (any gear) my Seca has a horrible vibration and sound. It's not extremely loud or a very pronounced vibration, but it sets my teeth on edge.
Up to 5k its smooth and quiet, and over 5.5k it smooths out again. At first I thought it was noise from the gauge cluster or vibration from the after market wind screen. I have tried different postitions on the wind screen and will be dismantleing the gauge cluster to clean and lube everything. I don't think that this is the source of my irritation though.

Any thoughts or first hand observations from Seca riders?

 

Yes, the dentist drill feeling is standard on the 650s and 750s.

You can think of it as a loose fastener test. If it feels like a dental drill everything is fine. If the motorcycle sounds like it's disassembling itself at 5k you have a loose exhaust bolt.

 

If you don't have the rubber wedges inserted all over the cooling fins ... that will do a lot in quieting down that frequency.

The Factory knew that the Cooling Fins on these Bikes required High Freq Dampening.
Rubber Wedges were installed in an "X" Pattern on both sides.

If you can find a package of Wedges ... install them.
The effect is immediate!
That Frequency is muffled and makes the ride a lot less fatiguing.

 

Well that sets my mind at ease!
There are 6-8 rubber pieces installed between the cooling fins on either side of the heads. There does not seem to be any pattern, just random placement and there are none on the jug fins.
Is there an optimum placement for these?
Is there and OEM # or does Len have these parts?
I'll pm chacal.

 

Set them so that they work with each other.
If the noise is really bothering you ... add a few!

Make a row supported by wedges above and below.
Like and X.
The top, middle, and lower fins muffled.

If you have any more, stuff some extra around the Cylinder Head.
The Cylinder Head is what's making all the racket, anyway.

 

Insulators-R-Us:


yy5) OEM Yamaha rubber Cylinder Fin Rubber Insulators. These are the small, rubber, wedge-shaped noise absorders that fit between adjacent levels of the cylinder head cooling fins at various places on the heads. Usually hardened or missing from original motors. Replacing these insulators with new ones really helps to quiet down an engine, and especially eliminates the fin "ringing" which can sound very much like valvetrain noise, while giving your engine that authentic, original appearance.

HCP1280RH OEM cylinder fin Rubber Insulator, for the RH side of engine. Differs between models, but normally use 8-10 per engine on the right side. Fits all XJ550/650/700/750/900 models. Each:
$ 2.50

HCP1280RHSET10 OEM cylinder fin Rubber Insulators, for the RH side of engine. Set of 10:
$ 21.00


HCP1280LH OEM cylinder fin Rubber Insulator, for the LH side of engine. Differs between models, but normally use 15 per engine on the left side. Fits all XJ550/650/700/750/900 models. Each:
$ 2.00

HCP1280LHSET15 OEM cylinder fin Rubber Insulators, for the LH side of engine. Set of 15:
$ 27.00

 

Just looking at those numbers per side...

10 on the right and 15(!!??) on the left.

15 sounds like a lot - maybe I'm missing a few insulators but I have nowhere near 15 or even 10 on either side of the engine. I was thinking of getting a few more - I probably have maybe six on either side. Sounds like the noise improvement is worth adding a few more.

Can anyone clarify this issue - I reckon 8 - 10 on either side would do the trick. Not even sure where I'd put 15 on the left side although I'm sure there's plenty of space between the fins.

 

Well, as I said, the number used per side differs by model, BUT.......

For USA XJ900RK Seca models the original parts fiches specifies a total of 14 to be used on the LH side, and 8 on the RH side!

 

Thanks Len,
I hadn't gotten around to PMing you yet.
I'll be picking up a set or 2 of the insulators next payday. I'll pm you for a quote then.

Wow 15 to a side! And the few are present on my sled are certainly original and probably hardened.

 

Thanks luv......by the way, they start out life as a very hard rubber compound to begin with!