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Thread: Pete's TF125 build

  1. #16
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    12th February 2004 - 10:29
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    Balance was the BIG thing I forgot to mention. You need to reduce the balance factor. I did it by pressing a slug of aluminium into each of larger holes in each crank wheel. If your crank is anything like mine you will have a hole in each web each side of the crankpin. One hole is larger than the other. Opening a balance hole will INCREASE the balance factor which is opposite to what is required.

    With weeks between sessions on Pete Sales dyno, inbetween which I pressed in the slugs, Pete commented immediately after the first rev of the motor about something being different. It is really obvious the difference.

    The bike also went from breaking brackets, chambers, and even the frame through vibration to being nearly turbine like at revs.

  2. #17
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    25th March 2004 - 17:22
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    Ohhkay. Funny with the MB on your advice I followed the path of boring holes either side of the pin which really helped. I guessed the same way but was surprised to see such large holes there. Hmm. Maybe I should build a jig. Or maybe just push some ally in the hole.
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  3. #18
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    12th February 2004 - 10:29
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    The MB "had" a balance shaft which added to the crank balance factor in the direction of piston motion and subtracted from it at 90deg to piston motion.

    The TS has no balance shaft and as you have already mentioned the TS motor is tuned and balanced for it's intended purpose of creeping around the farm, at lowish revs. With any such motor the balance factor needs to be reduced if you are repurposing it and will be operating it at elevated rpm. Remember that the reciprocating forces increase proportional to speed whereas the revolving forces increase with the square of speed. You just have to change things so that the 2 lines intersect at the rpm you want, probably about 11,000rpm now versus 5,000rpm originally. With all the factors affecting the feel at the end including chassis/engine geometry there's no point getting too technical. Suck it and see, just push the alloy in, it will work.

  4. #19
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    Roger Roger. Thanks forgot about the balance shaft.
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  5. #20
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    7th June 2009 - 13:29
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    Quote Originally Posted by speedpro View Post
    ... just push the alloy in, it will work.
    Pretty much what Rick Ford did. Worked Ok.
    Factual Facts are based on real Fact and Universal Truths. Alternative Facts by definition are not based on Truth.

  6. #21
    Quote Originally Posted by speedpro View Post
    Remember that the reciprocating forces increase proportional to speed whereas the revolving forces increase with the square of speed. You just have to change things so that the 2 lines intersect at the rpm you want
    Happy to be shown I am wrong here (and apologies for dragging this off track), but my understanding is that this is a common misconception. All of the motions of masses are made up of sinusoids. The rotating crank is just the a mass moving back and forth and up and down sinusoidal 90* out of phase. The piston moves up and down with the sum of the big end height added the effective conrod length - as these are added (and therefore of the same units) and not multiplied/divided, there is no way that a factor of crankshaft speed is going to drop out of the mix.

    It is my contention that the vibration 'sweet spot' that bikes have is due to harmonics in the bike/engine system. Changing the balance factor changes the directions and amplitudes of imbalance forces and so excite different harmonics in the bike at different RPM points.

  7. #22
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    Thanks Mike you may have saved me going the wrong direction. Crank is just being finished so will push in some ally tonight.
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  8. #23
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    18th May 2007 - 20:23
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    Quote Originally Posted by Moooools View Post
    It is my contention that the vibration 'sweet spot' that bikes have is due to harmonics in the bike/engine system. Changing the balance factor changes the directions and amplitudes of imbalance forces and so excite different harmonics in the bike at different RPM points.
    Perfect explanation of why one size does not fit all and you have to find the best balance factor that suits your bike by trial and error.

  9. #24
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    I seem to recall you bored the holes bigger in the GP cranks. Pretty hard to search these days. Or did you fill those too?

    The MB was OK without the balance until you revved it a bit more. With holes bored by pin it went to being buzzy at race speed to - a bit annoying in the pits (4000 blipping) but good on the track.
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  10. #25
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    Quote Originally Posted by Moooools View Post
    All of the motions of masses are made up of sinusoids. The rotating crank is just the a mass moving back and forth and up and down sinusoidal 90* out of phase.
    When you combine 2 sine waves that are 90* out of phase, as when 2 signals are combined on an oscilloscope, the resultant is a circle. Forget that the crankshaft is a crankshaft and consider it to be a rotating mass with an extra lump on one side. Calculate the force generated by that lump at a certain rpm and then calculate the force at double the rpm. The basic formula to use is something like F=(mv*v)/r. V squared but I don't know how to get a proper "squared" sign. V is the tangenital velocity of the mass concerned so double the rpm = doubles the V, which is squared.


    Quote Originally Posted by Moooools View Post
    It is my contention that the vibration 'sweet spot' that bikes have is due to harmonics in the bike/engine system. Changing the balance factor changes the directions and amplitudes of imbalance forces and so excite different harmonics in the bike at different RPM points.
    Changing the balance factor does not change the direction of imbalance forces. Taking the whole engine /chassis package and changing the engine balance will alter perception of the imbalance. Vibration in one plane is more irritating than vibration in an other.

  11. #26
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    I just got home and decided to weigh the std cast piston vs the prolite forged .5mm o/s piston.

    180g suzook
    185g wiseco

    Measured on my rickety scales, I have good ones at work but the fact is the amount of bananas is very similar.

    Did some porting with long reach carbide burr. Very hard not to get terrible vibration but with air drive can almost be controlled and stops quickly. Finished the inlet ports off with stones and sanding bits to get it smooth as I care to. Ie straight and not rough.

    Inlet ports are much higher and biggerer affording me some scope to fill the bottom of the ports, then I'll do final area measure and timing measure.

    I cut the manifold mounting area off and will make a plate the new manifold can bolt to which will be welded on a little and gap filled with JB Weld..

    Tonight I'll space the barrel to get the transfers right and measure the ex which I only roughly raised but got scared and need to measure properly. The new rod is longer so I'll need to make a spacer once its in.
    Don't you look at my accountant.
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  12. #27
    Quote Originally Posted by speedpro View Post
    When you combine 2 sine waves that are 90* out of phase, as when 2 signals are combined on an oscilloscope, the resultant is a circle. Forget that the crankshaft is a crankshaft and consider it to be a rotating mass with an extra lump on one side. Calculate the force generated by that lump at a certain rpm and then calculate the force at double the rpm. The basic formula to use is something like F=(mv*v)/r. V squared but I don't know how to get a proper "squared" sign. V is the tangenital velocity of the mass concerned so double the rpm = doubles the V, which is squared.

    Changing the balance factor does not change the direction of imbalance forces. Taking the whole engine /chassis package and changing the engine balance will alter perception of the imbalance. Vibration in one plane is more irritating than vibration in an other.
    Very aware that two sine waves 90* out make a circle. I was using that description to help illustrate the point that both the piston and the crank imbalances rise with the square of crankshaft RPM. I wasn't very clear there sorry.

    Two graphs below. The first shows the imbalance force inline with the piston throughout a cycle at varying RPM Each line is an increase of 1000 RPM (poorly labeled). Note the shape remains constant and the magnitude increases by the square of RPM.

    Second graph is the angle of the imbalance force with varying balance factor. This one is labeled a bit better, and shows the angle changing for different balance factors.

    Graphs made from a first-principles derivation of crankshaft forces. Engine specs 54mm stroke, 100g piston, 150g con-rod, 100mm con-rod, 100g big end weight of con-rod.

    Very apologetic for dragging this thread down Dave. I will give it a rest now.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  13. #28
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    Set the barrel to where the transfers will end up. Measured that 4mm on the inlet floor would take me to 185 inlet. Cleaned and centre punched some keys in the floor and warmed up the barrel and resin. Turned the old piston upsidedown and set it to 4mm up, flowed some resin to about right and left to set.

    I'd also checked the ex duration. Well, only another 3.4mm to raise the roof to get to my hardly radical 196*. Sheesh! Remeasured that a few times.

    I'd like to meet who. . . `ported' . . .this and ask what they were expecting. Sure had spent a bit of time getting the duct shiny.
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  14. #29
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    12th February 2004 - 10:29
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    Sounds like a mud bug or whatever cylinder. There was a version that had real low exhaust port. The shame is that it probably had the same oversize exit port to the pipe.

    I'd forgotten about the angle of the imbalance force. Suzuki probably didn't when they made the TS cranks as the holes on either side of the crank pin are different sizes. Possibly to counteract this. I don't have the maths to calculate it.

  15. #30
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    18th May 2007 - 20:23
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    Quote Originally Posted by F5 Dave View Post
    I seem to recall you bored the holes bigger in the GP cranks. Pretty hard to search these days. Or did you fill those too?
    Balance holes ether side of the big end pin on a GP crank are different sizes to each other too and the balance holes are bigger in diameter than the TF/TS crank.

    Click image for larger version. 

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    GP crank on the left, TF/TS crank on the right.

    After plugging with alloy and boring the 19mm big end pin hole for a 22mm (solid) pin we had to use a slug of Mallory (pure Tungsten) metal opposite the BE to get the balance factor for the GP about 50-55%

    Click image for larger version. 

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    The TF/TS crank wheels are thicker than the GP ones and their holes are smaller too. So their counter balance weight is proportionally much heavier than the GP. I suspect you can plug TF/TS balance holes with alloy and use a solid BE pin without needing to correct the BF with Mallory metal slugs.

    A whole lot of posts by Thomas on Balancing a single cylinder crank.

    https://www.kiwibiker.co.nz/forums/s...post1129267538

    https://www.kiwibiker.co.nz/forums/s...post1129267785

    https://www.kiwibiker.co.nz/forums/s...post1129267718

    https://www.kiwibiker.co.nz/forums/s...post1129269584

    https://www.kiwibiker.co.nz/forums/s...post1129364519

    You can tickle up the balance factor when the crank is re assembled by drilling shallow holes where needed, see the drill press picture in the post below.

    https://www.kiwibiker.co.nz/forums/s...post1129934876

    Work carefully and you wont get any dirt in the BE and if you do it washes out easily enough with a squirt from a spray can of CRC.

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