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  • Engine balancing, add mass to counterweight

    Loving flying the kite, but one job Iíve been putting off is balancing the crank; Briggs Vanguard installation was plagued at first by minor vibration related issues, so the alloy bracket on the oil cooler radiator cracked, exhaust mounting bolts worked loose and had to be increased, and a bracket pinned with a Sellock pin to stop it shifting and working loose. Oil cooler is mounted on rubber strips now so fixed that problem, and coils are on bigger fixings as well.

    A quick check during assembly showed even a crude balance reveals the crank counterweight is too light, maybe the cheap stock rods and pistons are lighter than Brian Fallow's beefier ones?

    SoÖthe other day I unearthed the original balance weighing done on the pistons and rods, the V-Twin for perfect balance you take 100% of rotating mass, (both big ends and lower rods) and 50% of the reciprocating mass (piston and upper rod) and balance that against the counterweight.

    For your interest the numbers for Brian's beautiful billet rods and shallow pistons are:-

    BALANCE REPORT, BILLET RODS AND A.R.T. PISTONS FITTED

    1) Rings 16 grams, Piston 304 grams, Big end 111 grams

    2) Rings 16 grams, Piston 304 grams, Big end 112 grams

    Total Rotating mass = 223 grams x 100% 223
    Total Reciprocating mass = 640 grams x 50% 320
    Counterweight total 543

    Note; reciprocating mass includes small end, Gudgeon (Wrist) pin and clips (weighed with piston fitted to connecting rod)
    So when building the engine I wasnít certain if the thing would fly at all, and put off doing a balance until it was tested, a Ducati specialist wanted £180 for the work and maybe more if he had to add weight to the counterweight on the crank using heavy metal.

    Iíve ordered the 12-point Facom socket to suit the racing big end bolts.

    Queries that Iíd be really grateful for having last stripped the motor two years ago and reliable since:-

    Iím open to ideas to increase the mass of the counterweight, thinking of bolting a steel cheek-plate or banana strip onto the crank weight using threaded bolts and locked by peening with a centre punch or even a tack-weld?

    Hope you guys donít mind me throwing this open, but I love flying the thing, just need to do a static balance as it is waaaaay out and improving this will seriously civilise the operation and reliability of accessories.

    Kev
    G-KEVA
    BMAA 5696

    "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

    R.J. Mitchell :- Designer of the Supermarine Spitfire

  • #2
    Engine balancing, add mass to counterweight

    Interesting... "a thousand years ago" in my misspent youth, on occasions I have been known to do something similar on an old "1200cc Cortina" 3 bearing engine, with vertually no flywheel, running at just under 10,000 rpm because I thought the "vibrateion" meant that it would not balance in spite of drilling bits out etc:-)

    Bolts screwed in the crank webs and held with locktite... not too successfull.............. but a "loverly blow up"!!!:-(

    Turned out that the "out of balance" problem was dynamic and due to the 3 bearing crank "flexing"... primarily due to "weak" bearing caps. Cured by machining the bearing caps "flat" and bolting a "bloody great" lump of steel across the cap with a few thou "pinch" in the centre... lasted around 4 seasons and won quite a few races........

    "You won't know if it works till you try it":-)

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    • #3
      Engine balancing, add mass to counterweight

      Way back when I worked on two stroke development contracts, we used to use lead, melted into large machined recesses in the full disc flywheels, sealed in by welsh plugs. The welsh plugs were probably unnecessary, but were a belt and braces thing. Later we used machined weights made from tungsten - one of the few
      metals heavier than lead, but personally I never thought that the advantage of using tungsten was outweighed by the simplicity of using lead (11.3 SG for lead against 19.3 SG for Tungsten) in this type of construction, but if you machine holes and plug them with lead, you can always lighten them a bit or make heavier easily.
      A 25mm dia. hole x 20mm deep in a steel flywheel; filled with lead, will be 34 gms heavier, as a guide.

      Comment


      • #4
        Engine balancing, add mass to counterweight

        Quality input Ted and Wally, one American tuner uses old tungsten milling cutters chopped up with a grinder and pressed into holes, I've also found another method whereby a crescent shaped cheek plate is bolted to the side of the crank weight.

        This looks the easiest using standard materials, probably countersunk screws to retain the banana profile steel plate, and a light tack weld or two to ensure the heads can't spin.

        Once found an online centrifugal force calculator which should help when sizing the fixing screws

        Cheers gents

        Kev
        G-KEVA
        BMAA 5696

        "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

        R.J. Mitchell :- Designer of the Supermarine Spitfire

        Comment


        • #5
          Engine balancing, add mass to counterweight

          More research results

          Am trying to locate a supplier of the rigs with overlapping wheels that allow the crank to roll freely on stands, but most seem to be USA only

          Got the weight addition part more or less sussed, and am digging to find the removable clamp-on bobweight makers, again easy to get in the USA but none-existant here, maybe the balancing people buy their gear in the US and sell their services rather than trust you to do it.

          Found a cheap and natty rolling stand that looks promising so ordered one to try

          http://www.amazon.co.uk/5079-Black-Range-Pocket-Balancer/dp/B00FE6OF6U/ref=lh_ni_t?ie=UTF8&psc=1&smid=A1ZRIB9CX045Q0

          Cheers

          Kev

          Attached files
          G-KEVA
          BMAA 5696

          "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

          R.J. Mitchell :- Designer of the Supermarine Spitfire

          Comment


          • #6
            Engine balancing, add mass to counterweight

            Kev
            I am sure you know, but if you outscource your balancing, make sgure you know to what tolerance they balance......... there is "balancing" and there is "balancing!":-)
            Some companies actually "balance to "half a brick"
            I used to have my cranks/rods/pistons balanced to "a millimeter width of thin paint" on the webs, but I did run "5000 rpm engines to around 10,000 rpm":-)

            Maybe I should have my Kohler Lawnmower balanced so that I can bring the record back to the UK..:

            http://www.foxnews.com/leisure/2014/04/02/honda-sets-lawn-mower-top-speed-record/

            Go for it:-)

            Comment


            • #7
              Engine balancing, add mass to counterweight

              Best kit I have found for balancing is the knife edged roller balancers for the big grinding wheels but you would not want to buy one. Maybe ask your local grinding shop if you can borrow one. You soon notice if a grinding wheel is out of balance.
              Obviously you could make a simple rig with large dry roller bearings but they can be fiddly to use and keep mounted flat when in use.
              Usually any balancing brings an improvement.
              Interestingly it is not unknown to tune the balance to suit the frame mount so perfection is not always good in fact some of the old single Manx engines had a hole in the crankcase to get at a bolt in the flywheel so they could change the balance weight without stripping the motor!
              One thing else that sometimes gets forgotten when fixing things to the flywheel rim is oil drag which can consume a lot of energy.
              Mick Broom
              Member 909
              Shadow G-MWTN

              Comment


              • #8
                Engine balancing, add mass to counterweight

                Quality input as usual Mick

                I got quite close using the dry rollers, then rechecked using knife edges and that was way more sensitive; the knife edges were made from aluminium extruded channels fixed into a frame and checked for level, even after ages fiddling with the rollers the knife edges got a better result, with a more definite rolling motion when even a couple of grams were hooked in position to sort the balance.

                Flywheel plate idea is in the bin, I'm using tungsten carbide 10mm rod off eBay (from Israel!) and putting slugs of the stuff into holes reamed two thou" undersize so the weight can be press fitted into the counterweight, easy to do but hard to fuigure out, but google and the USA tuning websites helped. Apparently the stuff is impossible to cut, even with a grinder, but easy to snap, any input appreciated as I'd need to work out the mass and thus length of rod needed and pay the supplier to do that before posting.

                For now I've drilled the iron counterweight 25/64" which just happens to be an off the shelf handy starting size, then bought cheapo reamers from 9.5 - 10mm from Amazon; being single use I don't need quality tooling to ream out to 9.95mm, will coat with Loctite bearing retainer as well and if still not happy put a grubscrew in from the outsdie and peen the hole.

                The Tungsten Carbide is 14.5 grams per cc and nodular iron crank 7.11 grams per cc, so swapping volume drilled out with filler in the heavier material sorts my balance weights.

                As for windage or oil drag, Paul Bailey once raised this and I found one of the crank makers puts streamlined edges on their crank weights so the cut the air like an aerofoil to gain a couple of hp, as some mass on the crank weights rises 'above' the crank centreline at Top Dead centre this mean grinding a round leading edge and tapered 'tail' to the crank weights actually reduced the weight needed to be added below the crank aat T.D.C.

                Why aren't the weights alrteady cast streamlined? you'd think the power gain and fuel burn reduction worth it?

                Cheers

                Kev
                G-KEVA
                BMAA 5696

                "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

                R.J. Mitchell :- Designer of the Supermarine Spitfire

                Comment


                • #9
                  Engine balancing, add mass to counterweight

                  April did a test-flight flight which was Ďpre-balanceí and Iíve just assembled and test-flown Monday Ďpost balanceí; results are that an action camera fixed to the front strut doesnít wobble cyclically as much, but am mildly disappointed to find that the main pulses from the engine combustion are still there.

                  Maybe being a four stroke V-Twin I should have expected this, so an engine with lightened flywheel and set in a light airframe on flexible mounts will still pulse and wobble, but the high frequency vibes that were causing wire terminals and stuff to work loose have gone.

                  Will test and report further after longer flights, but damage will be less to engine from vibes.

                  Cheers
                  G-KEVA
                  BMAA 5696

                  "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

                  R.J. Mitchell :- Designer of the Supermarine Spitfire

                  Comment


                  • #10
                    Engine balancing, add mass to counterweight

                    Hi Kev,

                    Possibility of two separate things maybe in the above.

                    Balancing is what it is and when correct will give an improvement, sometimes its not apparent because the vibration being energy has a collective direction which can work with or against the engine mounts used.
                    Theoretically the mounts should be in compression in the form of a cone passing through the CG. This usually comes with a weight increase and when I tried this with a HKS fitted to the back of a Shadow it did not have enough benefit to justify the arrangement.

                    Power pulses are another thing and you have a lightened flywheel plus a Vee twin arrangement which doe not help.

                    Engineers very often underestimate the problem which means that the transmission and mounts needs to be stronger ( heavier) , at a basic level we had to update the bearing size on the Hesketh engine as the collective loads act between the Vee in the cases , the transmission pulse tends to see the motor almost as one big single due to the firing spacings.

                    Specially spaced cranks/rods have been tried to help this in the bikes or you just add extra weight like the Harley to absorb the energy (that's the average American rider we are talking about). ;-)

                    You back in the air then young man after your bit of excitement?
                    Mick Broom
                    Member 909
                    Shadow G-MWTN

                    Comment


                    • #11
                      Engine balancing, add mass to counterweight

                      Rebuilding, my Lady was understandably somewhat slow to come to terms with my addiction, but has realised she gets peace when I'm in the workshop

                      Binned the wing, trike is surprisingly undamaged, apart from forks and keel tube, am renewing pylon and front strut too

                      Tough little beggars these Ace trikes

                      cheers

                      Kev
                      G-KEVA
                      BMAA 5696

                      "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

                      R.J. Mitchell :- Designer of the Supermarine Spitfire

                      Comment


                      • #12
                        Engine balancing, add mass to counterweight

                        Ahh - the secret of a long marriage and sanity - the shed
                        Mick Broom
                        Member 909
                        Shadow G-MWTN

                        Comment

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