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Race bikes, track bikes, broken rods, et al

Discussion in 'Motorcycle Racing and Track Days' started by maelstrom, Jul 15, 2014.

  1. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    Hi All,
    I have seen quite a few stories about broken rods on race/track bikes recently and so I just want to point something out that a lot of readers may or may not know.
    Load increases at the square of the engine speed.
    As an example of what that means, if you calculate the load on your connecting-rod at 10000 rpm then at 18000 rpm the load has increased 3.24 times. It is 9 times greater than the load at 6000 rpm. Just think about that. From 6000 to 18000 you have tripled the rpm, but your engine is coping with 9 times the load.
    This is quite relevant for the 250cc bikes because they tend to have their necks rung, so to speak, for extended periods. Whereas it would not be so easy to keep a 1000cc sports bike pinned.
    My two cents would be to fit Carrillo rods and other precautionary measures if you want your engine to stay together under such stress, or buy lots of engines.
    cheers
    Blair
     
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    maelstrom, Jul 15, 2014
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  2. Phil

    Phil Senior Member Contributing Member

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    Hey Blair
    Enjoyed reading your thoughts and comments on racing and track bikes. Needless to say I concur 100% with your findings. Every time I look a the tacho on any of 4 cylinder 250cc motorcycles and see the redline commencing at 18k and above, I tend to ponder what's happening internally and shake my head in disbelief!

    I have seen first hand the damage that can ensue when revving these little gems to the limit and it isn't a pretty sight.
    Having said that, I admire the technical prowess of the Japanese engineers who designed and built these machines over a quarter of a century ago, very talented people.

    If the bikes were brand new, see no issue with pushing these levels whatsoever, however they aren't new and 9 times out of 10 we have limited data on it's previous life so problems, some very major ensue. Just a quick peruse on our forum illustrates some of the problems we all face. Problem being, we want to experience the effect of revving to the redline, we want that sound, the power.........and the speed! Alas this at times comes at a price.

    The issue facing most of us is this, we try to keep our expenditures to a minimum (oh to be rich!) hence the band aid approach kicks in, patch and go is probably more the reality. Hey, forgot to ask! are we still having fun.......????????
     
    Phil, Jul 15, 2014
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  3. cal

    cal Well-Known Member Premium Member

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    tell me more of these "Carillo rods"
     
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    cal, Jul 15, 2014
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  4. maelstrom

    maelstrom LiteTek Staff Member Premium Member 250cc Vendor Contributing Member

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    As Phil said these engines are getting old. Poor little things.
    Regards the rods you can find everything you need to know about them on the net. Some of the little known things are that Fred Carrillo was a bike nut and his company had a policy of doing bike rods cheaper than those for the cars. Apparently, since he has died that is no longer the case. They also do custom and one-offs, a lot of them. Over the years I have used these rods many times. I used to have custom rods made for Ducati singles (the Ducati big end bearings and crankpin are complete rubbish). I would buy a complete Yamaha XT-500 rod kit and throw the rod away. Then get Carrillo to make a new rod with all the appropriate dimension. This was in the days of telegrams and snail mail. You young people don't know how lucky you are. :p
     
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    maelstrom, Jul 15, 2014
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  5. cal

    cal Well-Known Member Premium Member

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    yeah :( they are getting old and sloppy - and i am having trouble sourcing parts for my engines bottom end...

    got a cool idea of sending my crank away for balancing and get new bearings, rods, pistons, rings etc..
    but unfortunately this idea may never come about due to parts availability
     
    cal, Jul 15, 2014
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