major vibration break thru!!!

2DOOR,

I've been looking into this frame braking thing pretty hard. Thought I'd post and say you are right in that it can actually crack frames. Now it will still reduce vibration "slightly" but in exchange for a broken frame and possibly ending up on your face at 30-40mph, it's just not worth it.

I'm one of those guys that needs a reason, because it does or i said so, will never be good enough for me. I did find out why this can happen if anyone's interested. There's two centered bolts clamping the the engine, allowing to rock ever so slightly. Essentially bending metal back and forth until it stretches breaks. IF there were four bolts it would be fine, but there's not so... I gotta agree it's just not a good idea/worth the risk.
 
i have built over 35 motorbikes for my customers in the last two years.
every build i have cut a 2" piece of garden hose then cut it in half long way.
i put 1 piece between the mount and tube front and back.
vibration is minimum if at all. i have never broken a motormount. the motor does not shift to one side from center.
about 6 of us ride a 100 mile loop every sunday and no complaints about tingling hands or butts lol.
this is in jacksonville florida, mostly no hills and paved.
we all belong to the 20 mph club.

stay dry
gubba
 
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This spray foam is a good idea. Some other points I can reflect here.

Aluminum frame no rust to worry about.

The crank bearings open or sealed units(like BMX trick cranks) when u wash your bike the crank bearings get wet moisture can develop if u have a steel frame the tubing with the foam can get wet and possibly collect (drain holes)

Vibrations still getting the best of you Gear your bike up with a shock fork up front just check that the diameters are the same on your fork you currently use and you want to check theres different sizes and the proper fork should be used and do a good clean job if you keep open cup style non sealed bearings.

I have a shock fork and am going to use it if it turns out to be a correct size. I will try this expander foam for shure because I have a aluminum frame.

CHEERS TO ALL
.shft.
 
The spray insulation to the inside of these bicycle frames is something I had recently thought about on my own, along with putting it on the inside "shell" of the rear mount spacer.. Spray insulation is waterproof, airtight, watertight, shape able once hardened so this substance will not create an increase of condensation in the frame tube! How well this works- somebody out there might have to do a street survey and let people ride both kinds..just to say which was smoother. ; ) All in all it comes down to what your individual preference is..Take Care
 
Nobody has nentioned fitting a head steady. The cylinder heads on every bike I've seen have no firm attachment to the bicycle frame; look at single cylinder motorcycles, most have the head attached to somewhere on the frame. Damping frame resonance with a filler is probably chemically ok, but adding a stay to the equation to tame the jiggling and shaking of an engine has been shown to help.
 
How would you do it? Makes perfect sense and having something perhaps pressing on the bar above the head would make me feel better about large bumps and pot holes. still scared to death that chain is going to pop off and spread me all over the road like peanut butter on bread.
 
Lazy Dog said:
There's no way, it's just not possible. I understand it doesn't get rid of the source. But any form of insulating that can absorb any kind of movement will reduce vibration. If this weren't a fact then rubber bushings wouldn't be the standard vibration/noise reducer for almost all machines and cars. From air compressors to CNC's, cars to planes, rubber bushings/insulators are used and are effective.

Now i get that one dopey little wrap with 3mil roofing rubber isn't going to be very effective. But anything that can absorb/dissipate the resonance will reduce vibration.
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Actually you're only partially right. Mounting these engines with rubber allows the motor to move fairly freely setting up a resonance. We've used rubber for three different motor/bike combos and they all have had terrible vibration, which stopped after the rubber was removed.
Compressor for example do use rubber mounts but they are attached to the base plate with coiled springs.

I've installed several machines that needed to be isolated from vibration. The key is not necessarily rubber but alternating materials with different densities, steel/rubber, steel/plastic, or my favorite steel/lead etc.

My old boss a retired engineer from Aerojet suggest we use delron or nylong sleeves and they work very well.
 
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Goat Herder said:
Your gonna bust the fasteners to the motor! Might read through this? http://motorbicycling.com/f6/rubber-not-27364.html
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I don't use any rubber. Granted I did upgrade my engine mounts from M6 to a 5/16-18 just because I thought it looked weak to begin with.

My bike absorbs a lot of the vibration but truly that doesn't mean it isn't still there. At certain RPM's the harmonics of the engine does transfer some.

The very best way to reduce vibration is to balance the crankshaft, which is probably beyond the scope of most builders.

When I used rubber, I found that it allowed too much twisting of the motor over time. The engine would shift and be cock-eyed, pulling to the left from the force on the drive chain.
 
I like to use hard leather on the rear mount if I'm breaking in the bike myself since the leather takes several days to shape itself into a nice firm seat. For bikes that are going right out to the customer, I'll use a piece of PVC pipe which forms up in just an hour or two. Same for front mount if needed. Never had a frame crack or scar with this.
 
I don't think rubber would 'increase' the vibrations maybe just allow the engine to vibrate but still the ONLY reason I'm using rubber on my mounts is to I don't scratch the **** out of my bike.
 
Gawdzahh said:
I don't think rubber would 'increase' the vibrations maybe just allow the engine to vibrate but still the ONLY reason I'm using rubber on my mounts is to I don't scratch the **** out of my bike.
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You can protect the paint with a couple of layers of vinyl electrical tape. No need for rubber.

Tom
 
Lazy Dog said:
I was going to keep my mouth shout about this but after doing 3 bike around mt house. I feel like I have to tell.

one day in a drunken argument with a friend (who doesn't even ride) say fill it with foam. You know the old light bulb click :) ding ding. SAME BIKE, SAME SET UP.


A little expanding foam in the down tube and seat tube "Fill'em up" has an amazing affect on vibration. Almost just absorbs it all, I do have the standard rubber motor mount raps but that did very little any ways.

Hope this can work as well for you guys as it does for me and my group.
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Here what I did:take the motor apart and rectify the flywheels (weights)from the crank.Eliminates the stress in bearings (they became loose),Stop shaking the carb.Install a reeds valve (billet) also cuts the vibs also improves the low rev torque(need a larger jet for some carbs).The rubbers should be between the tubes of the mount and the bike,applies for choppers and cruisers with separate mounting (not directly to the bike.After that you can use foam,and handlebar lead weights(like a scooter or motorcycle,mine were made out of fishing cast leads) for personal confort.Improoving the muffler and/or lighter (and perfect round..:)) flywheels helps too (better dem for semafors but less inertia for the ups.Cheers and keep it street legal.
 
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