vibration dampening motor mount (yet again!)

C

callahoochy

New Member
I know most experienced builders say to avoid trying to dampen vibration and mount the motor solidly. But I think I have a twist to previously mentioned methods that may actually work, and not result in broken mounting studs. Bear in mind that;

- studs have been replaced with US made 6mm all thread
- the pads are designed to absorb vibration transfer from skateboard trucks to the rider

A typical motorcycle motor mount uses rubber or urethane between two metal plates. This method seems very similar to my non-engineering mind. Why will it work or not work? OK, let me have it!

See pic. Thanks!
 

Attachments

  • motor mount w pad.jpg
    motor mount w pad.jpg
    85.9 KB · Views: 755
Your theory is much closer to the concept used in motorcycle and automotive engine mounts. Whereby there is no metal to metal contact. The trick will be to have a material that is firm enough to keep the engine from moving yet resilient enough to actually absorb vibrations.

The problem with other methods advocated by some is that the rubber, urethane, whatever, is often placed between the engine mounts and the frame utilizing common mounting fasteners and that's where the weak point is. The vibrations are still there and get transfered directly to the mount and fasteners. You idea isolates the two.

Just curious what your plan is for the rear mount. If it is used as designed, mounted solidly to the seat tube, then you've defeated the purpose of your idea. Both mounts will need to be fabricated the same to achieve what you're after.

Give it a try and please report back with the results of your findings.
Tom
 
I see one large problem with this, but don't get me wrong, I hope it works.

The problem is, what keeps the motor torque from twisting the rubber sideways out the left side of the frame?

I sold a bike to a guy who brought it back to me because he kept snapping chains. Turned out the front motor mount had gotten loose, and the motor had twisted to the left. The chain no longer lined up with the rear sprocket. I just worry you might have the same issue if your material isn't just right.
 
The material is nearly rigid laterally, and with 2 mounting points per plate, I don't think it will shift or rotate, but it can be bent by hand with force across the width. It's about the size of a deck of cards, and a little softer than a hockey puck. It feels about right. Guess I'll find out. Thanks for your thoughts.
 
I think you'll find it works best using your method on the front mount, and using the stock rear mount.

Actually the best thing to do is balance your crankshaft.

Just in case it vibrates like heck when you're done, try it the other way. I think you'll be surprised.
 
I'm an industrial designer, not a bike mechanic. It's about all I can do to mount a motor kit and keep it running, but I appreciate the education. I was lucky enough to get a reply from a former product development engineer at Harley Davidson. He told me that isolating the motor from the frame via a vibration absorbing material will work, provided the material is in the correct durometer range. The pads I'm using are considered 'soft' by skateboarding standards, so if it shakes too much or skews out of alignment I can replace those with harder ones. The shaking of the engine and any resultant additional wear is another matter.

Thanks for everyone's suggestions. I'll let you know the result.
 
RandyWhite said:
I see one large problem with this, but don't get me wrong, I hope it works.

The problem is, what keeps the motor torque from twisting the rubber sideways out the left side of the frame?

I sold a bike to a guy who brought it back to me because he kept snapping chains. Turned out the front motor mount had gotten loose, and the motor had twisted to the left. The chain no longer lined up with the rear sprocket. I just worry you might have the same issue if your material isn't just right.
Click to expand...

Solution for engine torque.....
 
leather belt from thrift store $.50
cut a piece to fit between motor and frame $.00
(x2) front and rear mount
to ride problem free= priceless
the leather will not break down like rubber and has great holding power!
the belt has to be of good thick leather (the real leather, not pleather).
 
Timing belt from cars seems to work good. Cut off the 'teeth' and you have a solid heat resistant rubber strips that protects your frame. Best of all it's free from motor shops. You'll have to cut it to size. I think some of these Timing belts use kevlar so it's very durable and can last long. Better select a timing belt from a high end car. You'll also have to use a very sharp cutting knife.
 
Did I just get a good engine, or something. Where's all this vibration coming from that some people need to isolate/eliminate just so they can enjoy their ride. I'm not being sarcastic; I really feel for those of you with numb hands. I just think there could be something wrong with an engine that vibrates so much.
I bolt mine right to the frame, and check back on it now and then. I almost never wear gloves unless it's a bit nippy out. I'm beginning to believe I have a DAMM fine 2-smoker. (Thanks, DAX!)
On my first bike I was worried about vibes from the beginning, so I used urethane strips between the mounts and the frame. When I later saw how much things were shaking down there, I went to direct-mount. Would you believe it actually REDUCED the amount of vibration I felt? I'm sure that's not true for everybody, but it got me thinking.
I'm sure motorcycle frames and their corresponding motor-mounts are designed for the vibration and torque they must endure. The fact that most of them are made of rubber is of little consequence when you must also consider: what kind of rubber? how big/how thick? where is it placed in relation to force or torque imparted upon frame and engine mount? etc. etc. We're just putting small engines on bike frames. We're not exactly designing a motorcycle. We have to be very careful with these motor mounts we come up with.
 
Last edited:
I believe the Matrix is having another Deva vu Morpheous LOL!

I used black RTV around my motor mounts sure seemed to work well for me...the stuff hardens and pretty much feels the same as a regular motor mount to me.
 
Allen_Wrench said:
I'm sure motorcycle frames and their corresponding motor-mounts are designed for the vibration and torque they must endure. The fact that most of them are made of rubber is of little consequence when you must also consider: what kind of rubber? how big/how thick? where is it placed in relation to force or torque imparted upon frame and engine mount? etc. etc. We're just putting small engines on bike frames. We're not exactly designing a motorcycle. We have to be very careful with these motor mounts we come up with.
Click to expand...

First of all not all motorcycles use rubber in the motor mounts in fact NONE of the ones I work on have any rubber in the mounts. Secondly there on some on this forum that use engines MUCH larger then some motorcycles. There are 50cc legal streetbikes out there and MANY up to 200cc. Most use motormount PLATES not U shaped clamps the shape and thickness of the tubes used in a frame has lots to do up what vibrations the frame will cancel out. Think of a frame as nothing more then a big tuning fork.

Most motors that have rubber motor mounts also have a harmonic balancer the 2stroke china dolls do NOT.

doing some research on how a motorcycle frame is designed will give you a better understanding of what how and why

here is an example of getting the harmonics of metal wrong...
http://www.youtube.com/watch?v=j-zczJXSxnw
Yes I know its a bridge but the lesson is still valid
 
Last edited:
Ibedayank said:
First of all not all motorcycles use rubber in the motor mounts in fact NONE of the ones I work on have any rubber in the mounts. Secondly there on some on this forum that use engines MUCH larger then some motorcycles. There are 50cc legal streetbikes out there and MANY up to 200cc. Most use motormount PLATES not U shaped clamps the shape and thickness of the tubes used in a frame has lots to do up what vibrations the frame will cancel out. Think of a frame as nothing more then a big tuning fork.

Most motors that have rubber motor mounts also have a harmonic balancer the 2stroke china dolls do NOT.

doing some research on how a motorcycle frame is designed will give you a better understanding of what how and why

here is an example of getting the harmonics of metal wrong...
http://www.youtube.com/watch?v=j-zczJXSxnw
Yes I know its a bridge but the lesson is still valid
Click to expand...

I am glad you mentioned all of this. It goes to show what a great deal of thought, planning, and math goes into motorcycle design. And I had nearly forgotten what a big role harmonics plays in the soundness of the design and solidity of the frame. My own knowledge of "true" motorcycles is getting a bit dated. Good motorcycle builders certainly don't throw things together. There's also much for us to keep in mind when we mount our own engines.
 
You must log in or register to reply here.
Back
Top