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Thread: 420 build offset grind or billet ??

  1. #1
    4 Cycle Advanced User
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    420 build offset grind or billet ??

    getting things around for a predator 420 for next year.
    Not sure if we will put it together or have it built, so getting our education now

    Is there a stroked crank for the 420 available? (stock appearing, can't modify the block outside)
    Should we look at billet crank if so who makes it??
    if neither are readily available, what would be the suggested of set of the grind, and how far can we cut and still be able to find a rod for it?
    Parts suggestions appreciated.

  2. #2
    4 Cycle Advanced User
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    buy one already built an save yourself a lot of money

  3. #3
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    Quote Originally Posted by oldloco View Post
    buy one already built an save yourself a lot of money
    who's building them?? I know it's not a common build, so they are not advertised much..

  4. #4
    4 Cycle Advanced User
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    A 390 has a 64mm stroke crank. A 420 has a 66mm stroke crank. A 460 (from Vegas Carts) has a 69mm stroke crank. They sell the cranks fairly cheap but takes a little work and know how to get it to work flawlessly in a 420 block. ARC sells a billet crank, not sure of the stroke, but at $500 is not cheap. Price has prevented me from playing with one though I am sure its a high quality part. Not sure what your end goal is but Vegas Carts offers 460cc gx "style" engines pretty cheap. I think BullFrog Motosports (Notice No R) as well as NR Racing offer parts and pieces for 390, 420, 440, and 460s. You can spend a pretty penny on this type engine and get it to run but it will NEVER be as dependable or make near the power a 450ish MX engine will. If your rules allow for welding on the exterior, find a welder to start bracing it now. You will need it.

  5. #5
    4 Cycle Advanced User
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    We build a few genuine Honda 390s each year. We also stock the parts for them (ARC, JE, Comp, etc.)
    jsstump has it correct on price and reliability. They are a fun engine to build/run if you like the industrial engines over the bike engines, but they'll never compete head to head. Then again, you used to be able to gut the transmission from a 450mx'er and have at it, now guys are spending big bucks modifying those as well.



    -----
    Thanks and God bless,
    Brian Carlson
    Carlson Racing Engines
    Vector Cutz
    www.CarlsonMotorsports.com
    28 years of service to the karting industry
    Linden, IN
    765-339-4407
    bcarlson@CarlsonMotorsports.com

  6. #6
    4 Cycle Advanced User
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    Look around classifieds, guys are always selling the big block engines for fair prices. If I were to build one I would likely find a good seasoned gx390 Honda on a pressure washer, generator or something like that and put the Vegas karts 69mm crank and a stroker rod in it, bore it out as big as possible without sleeving the block, and focus on a well built head and carb combo with a good cam and springs and billet flywheel. That will make for a pretty reliable and dependable big block that makes good power and doesn't break the bank. Scrapyards usually have all sorts of engines laying around on broken down power washers and other equipment, and usually the engine is just seized up if anything, sometimes nothing even wrong with the engine itself but the equipment it is on may be tore up....those are good finds. If you buy new you'll be spending quite a bit, expect to spend at least $1500-1800 on a decent big block build

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