Sprung front engine mount - your thoughts?

Discussion in 'General Questions' started by CARROT-The DESTROYER, Jun 10, 2008.

  1. Hey,

    Somewhat new to the forum, but after much research, one of the main repetitive problems I had read about was vibration.

    So for my first build, I made a sprung front engine mount to try to aleviate the vibration problem.

    Being I have never ridden an MBC yet, - hopefully tomorrow!! - I have no previous experience to base my design upon.

    Do you think this design should work? - Or can you suggest any improvements?

    The spacer I used in the center does not go all the way to the top. It has about a 3/8" gap to actuate the spring. So it should also act as a stop gap as well.

    I also used rubber at all engine mount points between the clamps to reduce any vibration.

    Take a look at the pic's, tell me what you think.


    Troy Fitz.

    Attached Files:

  2. HoughMade

    HoughMade Guest

    Well, I always appreciate new ideas and only trying it will tell if it works well. I sure does look good. My only concern is whether the extra movement allowed at the front mount will create stress points at the rear mount...but like I said, using it will tell the story.
  3. eljefino

    eljefino Member

    To do it "right" you'd need another spring between the head of the bolt and the mount. As it stands now you're only getting half the vibration wave and it's going to slam the bolt head repeatedly... with more force than if you just had no spring to begin with.

    Also in addition to a spring you need some sort of dampener... Think of a car suspension that has both springs and shocks... the shocks/dampeners keep vibrations from continuing forever.

    I hate to be a wet blanket but this looks like a bad idea.

    +1 to what's said above about being hard on the rear mount too.
  4. No worries: -
    I asked the question to get feedback good or bad. I appreciate the good, but only the well reasoned critique can actually be useful for improvement.

    I understand what you are saying. It makes sense, and it's a good suggestion.
    The spring is pretty heavy duty and already has a load on it. Since I am automotive inclined, my thought was that it would be more akin to a valve spring. If it's strong enough it should be able to keep pace with the movement of the engine as it vibrates. A larger spring to eliminate valve float in higher RPM's. Or in this case increased vibration at higher speeds.

    What do you think about this; since the spring already has a load on it, If I was to add a neoprene washer/grommet to the top stud, do you think that may be able to absorb some of the residual vibration? -(maybe two washers).

    Appreciate your input,

    Troy Fitz.
  5. eljefino

    eljefino Member

    Neoprene would work well but fatigue fairly quickly. It will last long enough for "proof of concept". I used neoprene from an old mousepad as a sandwich between my motor mount brackets and the frame. It collapsed and I retightened the mount bolts so it probably may as well not even be in there.

    I put some new shock absorbers on the rear of my cutlass ciera and they came with new "rubber" doodads the bolt went through. I reused my old doodads as I'm lazy. These doodads would be just about perfect for what you're doing.
  6. I am very familiar with the "HELP" section in any automotive store. That is actually where my spring came from. I debated for awhile between rubber or a spring. Due to the strength of the one I chose, I figured it would have greater endurance than any type of poly-rubber material. The material I am referring to would be pretty much what your "doodads" were made from. Very strong. I'll take a trip back to the store tomorrow to see what I can find.

    Thanks for the follow up,

    Troy Fitz.
  7. Quick update

    At this time, I have 30 miles on the bike w/ no changes to the top bolt. I have gone up to 22mph at times w/ no vibration at all. The rear mount seems to be just fine.
    So far, it's a great mod.
    I will give further updates after the bike is officially broken in.


    Troy Fitz.
  8. JinbaIttai

    JinbaIttai Member

    The mount looks great, IMHO. I wish I saved my old bump stops (doodads) last shock change on the car. I will definitely be doing something like this when I get my mb.
  9. Scottm

    Scottm Guest

    All I've read in the last year here is that rubber fails. The shock absorber "doodads" are bushings. http://www.energysuspension.com/pages/shockbush.html .The spring looks like an awesome idea. Please keep us up to date on how it works. You could always go to the junk yard and pull some off a wrecked car.
    From what I understand, the Happy Times are so unbalanced in the bottom end that there's not much we can do.
    BTW I love the black engine, you did a great job on that build.
    The spring is a brilliant idea.
  10. bushido

    bushido Member

    how has this mount been working out for you? any plans to build a sprung rear mount as well?
  11. JinbaIttai

    JinbaIttai Member

    Anybody have any luck with polyurethane instead of rubber?
  12. 2nd update:

    I have been riding my bike just about everyday, and I have about 120 miles on it now.
    I am still in a partial break in stage - haven't even used my first gallon of gas yet:grin: - and have taken it up to about 34 miles per hour once or twice just to see how it would do at higher speeds. I usually cruise it at about 25 mph most of the time - no problems w/ vibration at all - I don't even notice it has a motor on it.
    At 34 mph, I started to get some vibration, but again nothing that I felt was detrimental to my safety. I think the majority of that may have been due to my rear sprocket isn't exactly trued. It's about an 1/8" off balance.
    So at this time my tests are still inconclusive.
    The sprocket spacers I got were cut at a diagonal; so I think that may have something to do with it. I need to get some new ones.

    When I get things perfect, I will submit another post.

    Thanks for the renewed interest,

    Troy Fitz.

    Q: "how has this mount been working out for you?
    A: see above.

    Q: any plans to build a sprung rear mount as well?"
    A: Not at this time. I had considered it, but I felt the motor still needs to have sturdy base as well. If it floats too much, I think it would create all sorts of problems. Such as chain tension slack, or even more imbalance if the motor is constantly pulled on the chain side.
    And, at this point, it doesn't seem necessary.
  13. erickster

    erickster Member

    that sounds pretty darn good to me. When I'M done riding, my butt is numb.
  14. bushido

    bushido Member

    where did you get the spring?
  15. bushido where did you get the spring?

    In the "help" section at Autozone. I had two springs in the package. One that was conical in shape, and the one I wound up using. I was actually going to use the other one, but this one fit the need much better.


    Troy Fitz.