Vibration Isolation

Motodude · Apr 13, 2007

I have an '05 FS650c Supermoto converted for the street and like to take it for long rides. The engine vibration is O.K.for short rides, but noticeable after 100 miles or so. I believe a modification could be made to the front two mounting plates where the engine bolts to the frame to rubber isolate most of the vibration.

The lower attachment point uses a tube between the frame and a long bolt tightens the plates between the frame members. The upper attachment could be converted to this same method and rubber washers installed to isolate the engine vibration from the frame, yet still allow the engine to be securely bolted without crushing the washers. You would have to cut the frames bosses (about 3/8") to allow room for the rubber washers to fit in.

Before I go cutting on the frame, has anyone tried doing such a thing before?

Taffy · Apr 13, 2007

no i don't think so and i wouldn't advise you to do it either!

you aren't actually rubber mounting the engine yet you are taking away strength from the frame.

regards

Taffy

k-dub · Apr 13, 2007

You could run a rubber mounted top triple clamp, anti vibration bar inserts or the Fasst Co. Flex bars vs. chop, cut, oooh sh$t. Right Taff! I bet you have an opinion on those $200 bars.

Taffy · Apr 13, 2007

the trouble i had when using them at moab for two days was that i didn't know what it was like before hand. the bike felt 100% normal to ride with them fitted though!

i did however ride coronaberg's 500 the third day, vibration wise they felt the same but i didn't get the bumps coming through the bars.

motodude
i would consider stripping the engine and having it rebalanced. you would need to change the balance factor to help you at high revs. in the doc we have balance factor figures from dale BUT i don't know which end of the scale helps higher revs.

with dale away the only peon i know of that can help is simon.

PM him if you're serious!

regards

Taffy

Maddel · Apr 13, 2007

Motodude said:
I believe a modification could be made to the front two mounting plates where the engine bolts to the frame to rubber isolate most of the vibration.

Interesting but what's about the rear section?
One attachment keeps together frame, engine and swing arm...
Which is about 70% of the whole chassis... IMHO

Motodude · Apr 14, 2007

Haven't studied the swing arm attachment, only the front. There's more mass back there which should provide dampening. I decided to forego frame cutting and concentrate on changes to the mounting plate and fasteners. For instance, thinner or off-set mounting plates would allow the space needed for rubber washers. The engine is not a stressed member so it can be rubber mounted and all it needs is support in the vertical plane to hold it up. Food for thought. Would be nice to have it as smooth as the new KTM 690.

fryguy · Apr 14, 2007

Motodude

I would guess that the 690 has more mounts than your berg as well, like a head support etc. I would go with the bar system and a tall seat to dampen. I've seen a full dual sport FS 650 from Alternate Cycle in Kamloops, BC, with even a gel seat.

Motodude · Apr 15, 2007

I unbolted the two plates which mount the front of the engine to the frame. They came off easily and the engine didn't move, so I ran it for a test. The engine was now free to vibrate without transferring anything to the front of the frame. However, there was no benefit as the additional engine motion was merely transferred additionally to the other mounting points (swingarm, carb & pipe). Conclusion: rubber vibration isolation could be done, but it would need to be done at all contact points in order to be effective.

In last month's Motorcyclist Magazine the writers concluded one reason the 690 was so smooth was that the frame was "tuned". If so, that is quite a feat and was probably done more by trial and error than with mathematics.

wildbill · Apr 15, 2007

Try changing gripes,bars things you come in contact with. Think you could make some good improvements going that way.

ORANGEBERG · Apr 16, 2007

Motodude said:
I have an '05 FS650c Supermoto converted for the street and like to take it for long rides. The engine vibration is O.K.for short rides, but noticeable after 100 miles or so. I believe a modification could be made to the front two mounting plates where the engine bolts to the frame to rubber isolate most of the vibration.

The lower attachment point uses a tube between the frame and a long bolt tightens the plates between the frame members. The upper attachment could be converted to this same method and rubber washers installed to isolate the engine vibration from the frame, yet still allow the engine to be securely bolted without crushing the washers. You would have to cut the frames bosses (about 3/8") to allow room for the rubber washers to fit in.

Before I go cutting on the frame, has anyone tried doing such a thing before?

Try the dampened bar clamps from KTM POWERPARTS also avail from force depot

Simon · Apr 17, 2007

A couple of very simple solutions to consider are:

1. change your gearing (to change the engine speed at which you ride)
2. change the resonant frequency of your bars by adding heavy weights to the end of them - like a few guys have already suggested

The idea of rubber mounting the engine will take some of the structural integrity out of the frame and it will make it less rigid.

The other option is the simply go and get your engine re-balanced to take the annoying vibrations away from the rev range where you typically ride it, or it takes the vibrations in a different direction so that although they are still there, you just don't notice them very much anymore.

Regarding the KTM, it is perfectly feasible someone sat down and did the maths and there are a number of computer tools out there that will predict quite accurately resonant frequencies. However, they will also have done balancing work to the engine - the old LC4 used to be quite a lump - the 660 almost bounced down the road, so they'd have to do some internal work to get it smooth.

Handling wise, if it has been built right, I'd suspect the 690 is stonking :wink:

Cheers,
Simon

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Vibration Isolation

Motodude

Taffy

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Taffy

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Motodude

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ORANGEBERG

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