Aluminum or Steel ?

Discussion in 'Frame Mounted Engines' started by ezrider, Aug 12, 2016.

  1. ezrider

    ezrider Member

    Supposedly its recommended to mount an engine on a steel frame...rather than an aluminum one. Curious to hear the pros and cons on this one.

  2. FurryOnTheInside

    FurryOnTheInside Well-Known Member

    Aluminium work hardens over time when exposed to vibrations and becomes brittle.
    Cro-moly steel is used to make helicopter frames, so it does not work harden.
    I presume that hi-tensile steel does not work harden either, and it is a popular material in older bike frames.
  3. KCvale

    KCvale Motorized Bicycle Vendor

    I have no issues with good AL frames at all.
    Giant and Trek make a few good AL bikes.

    I've been building on the GT2 in-frame gas tank AL frames lately, no issues with them either.

    By good I mean something Wally World or gasbike doesn't sell ;-}

    Vibrations? Pffttt...
    Well mounted good engines just don't vibrate that much!
    A well mounted engine is one that can pass the 'Shove Test'.

    Hold the top of the frame above the engine with one hand and your engine head with the the other hand, then shove it back and forth as hard as you can.
    If it moves AT ALL that is a failed mount.

    Though I am a firm metal to metal mount with nothing in between like old tire tubes guy, I must admit the Skyhawk 2-stroke solid rubber block between the front mount and frame is pretty cool...


    The best part is, it's light, that bike only weighs 60# wet, and that's with 3" tires!

    Anyway, don't be afraid of AL frames, just mount your engine right.

    Last edited: Aug 13, 2016
    FurryOnTheInside likes this.
  4. Wolfshoes

    Wolfshoes Member

    Champion riders of trials motorcycles recently did a trick motorcycle halftime show in county fair in Wilmot, WI. These riders could to flips, jump over 5 people on a level surface, ride on either one wheel, hop jumps up high blocks of concrete, ect. It was mentioned the full suspension motorcycles were 300 cc two cycle and weighed 150 lbs. They were whisper quiet without mufflers being visible from the stands. At 150 lbs, it would be safe to say the frames were not steel, probably aluminum. What is apparent is light weight alloy frames can be strong enough to replace steel in larger displacement motorcycles. Using alloy frames in smaller displacement motorized bicycles should not be all that hard of a thing to accomplish. Marketed steel frames may be overbuilt heavy in order to skip long term testing of a lighter design and cost less to make.