rod growth rate

Discussion in 'Performance Mods' started by liquidesnake2, Nov 22, 2014.

  1. liquidesnake2

    liquidesnake2 New Member

    hi i building a motor i want it to rev to 11,000 rpm and i was wondering if anyone knew how much the con rod grows during hi rpm operation. i have a billet head im turning down because the last motor was having some real bad detonation and killed the motor. it looks like the edges were sand blasted and also i want to set the squish band to .5-.8 mm to help prevent detonation. any input is appreciated

  2. MotorBicycleRacing

    MotorBicycleRacing Well-Known Member

    What "billet" head do you have?

    Squish band is set by milling the top of the cylinder, not by turning down a hopefully well designed head.

    How are you going to get your motor to 11,000 rpm?
    Why are you aiming for 11,000 rpm?
  3. butre

    butre Well-Known Member

    little, if any. mine revs just a bit past 10,000 rpm and I haven't had an issue with connecting rod growth. I have, however had an issue with the head studs stretching while using the stock studs. some stainless studs will prevent that from happening.
    liquidesnake2 likes this.
  4. liquidesnake2

    liquidesnake2 New Member

    i have Jake's billet diamond head form the Jake bike store. i milling the head to get rid of that rough finish from all the detonation and im not sure what the squish band angle is at but i might change it to more suit high rpm. i have a 2 stroke performance tuning book where i am getting my information from. it is the second addition. i am aiming to land peak power at 10000 rpm but i don't know how far past that it will rev.
  5. liquidesnake2

    liquidesnake2 New Member

    i might want to run an 18 degree squish band angle.
  6. HeadSmess

    HeadSmess Well-Known Member

    if youre concerned about squish angle at this stage in the game... without mentioning piston crowns, gaskets, and whether youve skimmed the top of the cylinder... i can only suggest getting a different(possibly third) edition of this tuning manual... and reading it again...

    pondering over the issue of measuring a conrod.... some maths, some scales, some sorta jig and a press of some kind, combined with a dial can do their own tests on conrod stretch, if its really a concern...

    no mention of what engine it is either... what sort of port times are being used, any crank mods, any other mods, blah blah. a standard chainsaw hits 11k quite easily... unloaded.

    if its a HT, this thread should be placed in the "jokes and humour" category...

    nah. just chuck on a high compression head and a mikuni vm24 and it will be a 12k firebreathing dragon... maybe use a jag cdi for ultimate highpower supremacy... :rolleyes:
  7. liquidesnake2

    liquidesnake2 New Member

    well i have a vm18 mikuni thinking of boring it out to 19 and i am planning on using the jag cdi.
  8. liquidesnake2

    liquidesnake2 New Member

    i couldn't find a third edition but i found that people recommend Gordon Jennings two stroke tuners handbook but its 120 bucks.
  9. HeadSmess

    HeadSmess Well-Known Member

    ;) good for you. im sure youll be hitting 12,000 rpm any minute now... :jester: and make, maybe, what? 9 horsies or so? :joker::rofl:

    120? was free last time i downloaded it, the links on here somewhere at least five times, and any quick search on google will find it...

    *rolls eyes so far back that he can see his own rear end...*

    all right, ill come right out and say it, rather than snide implications and innuendos...

    if you think you can get 11000 rpm from a HT engine, go for it, but you wont get any help from on here :)

    the few that COULD do it, know its a complete waste of time, if not impossible. therefore, wont be handing out any useful information to achieve results. we will say things like " you cant open the exhaust up to 70% of the bore and/or raise the timing to a nice 170 degrees or so because there simply isnt enough metal there to remove".

    we will say "you cant stuff anymore air down a 14mm diameter tube than will go down a 14mm tube"... regardless of what size carb you stick on, physics stays physics... therefore, what good is an 18mm carb on a 14mm tube? or a 19mm carb for that matter? unless the port is bigger than the carb...its a waste of time. bling, gimmicks, and lighter wallets...

    the rest will just keep whispering sweet nothings into your ears while you get more and more frustrated or...ambitious. or theyll take your money while smiling :) gobbedley-**** is a really good way of ensuring people will give you money. baffle em with BS and its like hitting the jackpot!

    ambition is great. so is perseverance and determination! as long as the end result is worth it! cropdusters may dream of winning races... but they cant :)

    get gordon jennings book (download) read it. five or more times. find graham bells book. read that one too. if you cant rewrite both books and condense all the important points into one concise page... read them again. for such small books,they cover so much!

    then blairs book. you can just scan that one...its hard to "read" as such...and is actually possibly confusing... makes one go chasing geese rather than concentrating on the basics. its also based on early computer programming, ie...its a uni level textbook for computer modelling of two stroke engines. very complex. so, unless youre conversant with earlier computer languages...avoid.

    then reconsider this project of yours :) forget about squish bands for now. forget about their angles, their dimensions, and their ratio of squished area to combustion chamber... think about airflow, breathing, and port timings.

    you havent even said if you have a decent exhaust on this thing yet... thats the second thing to think about, after port timings...

    for conrod stretch, still no definite answer, is there?

    why not weigh the piston and pin. figure out the g-forces at 11krpm- pretty easy, you know the stroke and the rpm and the weight...

    then get a rod, make a jig so you can hang the appropriate weight off of it, and measure the distortion with a dial indicator...

    also remembering the rod isnt as stretched on a 2stroke as it is on a 4 stroke, as its always under compression... its very hard to find any reference to rod stretch in any application other than fourstrokes... 4 strokes have an exhaust cycle.

    yes, im nasty. yes, im rude. yes, im negative.

    just suggesting to start at the beginning and work your way up, not just dive into the deep end chasing geese... far more rewarding :)
  10. liquidesnake2

    liquidesnake2 New Member

    we i have a decent exhaust im fabricating a few and trying them i have already been practicing porting these barrels and i am making a custom intake manifold that is exactly 18mm or 19 if i want. i already figured out the breathing part. i actually have add epoxy to the out side of the barrel to raise to transfers to the height i want its a lot of work but i like doing it. i asked about the rod because it dosent mention it in the book. actually my friend that builds four strokes told me to find out how much the rod stretches but he dosent build two strokes so he didn't know. Ur right about reading those book lots of info.
  11. keatonx

    keatonx Member

  12. Robot

    Robot New Member

    RPM ranges don't change the dimensions
  13. Fabian

    Fabian Well-Known Member

    You have no hope at all of getting a Chinese 2-stroke bicycle engine to give any meaningful engine life if attempting to rev it to 11,000 rpm.

    As soon as you hit 7,000 rpm, even just once, the damage is done, and it's only a matter of time (much sooner rather than later) when the engine will need a replacement crankshaft.
  14. butre

    butre Well-Known Member

    11000 rpm isn't happening with an 18mm carb anyway
  15. liquidesnake2

    liquidesnake2 New Member

    well i balanced the crank and im completely changing all the port heights and shapes and im making and expansion chamber to suite 10k. if it brakes it brakes its more of an experiment now its not like n need it for transportation anyway. one of the cheapest engines to screw around with.
  16. butre

    butre Well-Known Member

    18mm can't support 10K either, not without some nasty intake trickery at least. somewhere in the 9000s is as good as you'll get
  17. liquidesnake2

    liquidesnake2 New Member

    hmm well with that info in mind i will change the plan to tune peak power at 8k rpm than. i dont feel like buying a new carb. i also will re balance the crank to 8k
  18. Fabian

    Fabian Well-Known Member

    You may very well make peak power at 8,000 rpm, but engine life will be no longer than the concept of preserving virginity in a brothel.
  19. liquidesnake2

    liquidesnake2 New Member

    okay how about 6k wont be a screamer like i was wanting but it is a compromise. it will be more ride-able too
  20. liquidesnake2

    liquidesnake2 New Member

    "As soon as you hit 7,000 rpm, even just once, the damage is done, and it's only a matter of time (much sooner rather than later) when the engine will need a replacement crankshaft."

    why will the engine need a new crank can the needle bearing not take high rpm or just vibration from an unbalanced crank?