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Falcone connecting rod

Discussion in 'MonoCylindrico' started by GT-Rx®, May 12, 2020.

  1. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    Engine rebuild underway !

    What is the collective experience and advice with fitting needle bearings to the big end of the rod. After placement and nesting the bearings in the complete circumference would there be any gap before first and last bearing? I'm using bearings that seem to measure in a range of 3.27 mm to 3.30 mm. Is that to much of a range?
    Finally after rod is fitted to the crank and bolts torqued, how much lateral movement is acceptable?

    I hope I'm not rehashing something already discussed but if so I could find it.

    Wicker F
    Newtown Square, PA
     
  2. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    There should be no discernible radial play; not sure about lateral play. Mine had very little lateral play after grinding the crank pin, boring the rod and fitting oversize bearings. I used one less bearing for the oversize and I am quite sure that there was not a gap between the first and last roller. It has been over 10 years since I rebuilt the Falcone and thousands of trouble free miles, so my memory of the details is not the best. But here is what I do remember:
    I could not find any specifications for oversize bearings on the Falcone crankshaft so I used the specifications in the factory service manual to determine the original clearances by subtracting the diameter of the crankpin from the diameter of the bore and subtracting that number from the diameter of two of the rollers. That gave me the clearance between the crankpin, the rollers and the rod. By dividing the circumference of the circle that was halfway between crankpin and the rod bore by the number of bearings gave me the cleance between each bearing, Grinding the crank was a two-stage process. The first stage was to determine how much to grind to get past the damage. The second stage was to grind to the diameter dictated the size and number of the oversize bearings with the appopriate clearances. Then the rod was bored to fit the oversize bearings. Bear in mind that there will be slight difference in clearance between an odd number of rollers and an even number of rollers, but I believe that variance falls within the specified range. One caveat is that a crank re-grind may go past the case hardening of the crankpin. Your machinist can determine if that has occurred. My re-grind did not go past the hardened material. Also, there can be varying degrees of precision with the diameter of new rollers. i ordered twice as many as I needed and used the ones that were closest to one another in size.
    None of this is rocket science, but this exercise needs some precision. You may have to dredge up your high school math and re-kindle your knowledge of geometry. It helped me to make a large scale detailed drawing with exaggerated clearances,
    Alan in Roberts Creek
     
  3. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    Thanks Alan!

    Terrific write-up and appreciate the effort. The machining of the crank and rod was already done when I received them but the needle bearings are a mystery with respect to diameter and the number of them. I have dropped them in place only to find about a 1.7mm gap between the first and last. So my initial question to the group is whether this is acceptable. I'm finding a a surprising range in the diameter of the bearings that came out the existing engine and the bearings supplied with the newly refinished crank and rod. I will study a bit more based on your comments.

    All the best
    Wicker
     
  4. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    Hi All,
    I would be very reluctant to use needle rollers with any variation in size
    I have not seen a length quoted for the rollers ? are the ends rounded?
    On another make of bike I obtained oversize rollers from
    http://www.peters-bearing.de/produkte_neu.php?klasse=8&#data
    Not all the rollers in the list are available though
    I could not measure any difference between any of the rollers that were supplied
    The road to destruction of crowded roller big ends is if the rollers skew sideways
    Flat ended rollers are kept to a tight tolerance between the crankpin shoulders on other makes to keep the rollers parallel to the pin
    I prefer a caged roller bearing design, On my Rudge engine's big end the needle rollers are caged, the cage is made in two halves which is a design that would work on a Guzzi

    Keep Safe
    John
     
  5. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    One approach is to alternate normal sized rollers with an undersized
    ones, the undersize rollers acting like a cage.

    --
    Paul Compton
    www.morini-mania.co.uk
     
  6. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    Hi, to help with this I have produced the table below from information in the Falcone workshop manual.

    FalconeRodMsrmnts.jpg

    The table relates to a touring Falcone which has 3 possible over size big ends. The second column shows the three con-rod eye diameters, the bold is the nominal size and the figure below shows the maximum size allowing for manufacturing tolerance. The third column is the crank pin diameter showing the nominal size in bold and the max and min diameters allowing for manufacturing tolerance. The fourth column is the maximum clearance obtained by taking the difference between the largest rod eye diameter and the smallest pin diameter. The fifth column is the minimum clearance between the smallest eye diameter and the largest pin diameter. These clearances accommodate 2 roller diameters so it can be seen that the top row shows that half the clearance is between 3.130 mm and 3.117 mm. The recommended roller diameter in this case is 3.1 mm leaving a radial gap of between 0.030 mm and 0.017 mm. Columns 7 and 8 establish the length of the circumference of the mean diameter of the bearing. Dividing this by the roller diameter, i.e. 32.02 / 3.1 produces a result of 32.45. The number of rollers is the integer below this number, 31 leaving 0.45 of a roller diameter as the total circumferential clearance. this amounts to a gap between each roller of 0.044 mm.

    The other over sizes are treated in the same way. The third over size seems to have a lot of circumferential clearance. The workshop manual states the maximum wear on the rollers to be 0.02 mm so any rollers out of tolerance should be discarded as the rollers will not be equally loaded and the load carrying capacity of the bearing will suffer. When assembled there should be no discernible play in the bearing.

    One good feature of this bearing design is the use of a long roller (as with Velocettes). It is common for big ends to have three short rollers instead of one long one. This reduces the effective bearing width and the capacity of the bearing. The sport Falcone big end has a larger clearance than the touring model to allow for a higher oil feed rate. Hope this helps, best wishes.

    Biran A.
     
  7. GT-Rx®

    GT-Rx® Administrator Staff Member GT di Razza Pura

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    I agree with John you want minimum size variation in rollers. The thing (a main thing) that destroys roller big ends is deformation of the pin surface by the high local pressure along the top rollers on the firing stroke (brinelling) because the contact line pressure is so high. So one oversize roller carries all the load and it is not shared with its neighbours.

    And so the rollers should be as near as dammit the same diameter. The figure quoted in this thread by Whicker of a range of 3.27 mm to 3.30 mm seems unacceptably high. (to me).

    Roger Moss, the great vintage two-stroke Scott motorcycle racer, and impeccable engineer, told me to get the rollers all within 1/10 of a thou of each other. [Sorry - I have gone Imperial - I mean American - here] - but he is a perfectionist. I sat down with a hand micrometer and a pack of rollers from a good bearing supplier which they promised were Swedish and not Chinese, But they were variable by at least 0.8 thou or so. After an hour or so I was getting quite cross-eyed and not sure what I was seeing anymore because a 1/10 of a thou is quite challenging to measure repeatedly with a hand micrometer. But I was fairly confident that eventually I got 2 sets of rollers that fell within a range of 1/3 to 1/2 a thou of each other and built the engine with them. It ran great and I believe it still does, though I stupidly sold the bike.

    I have just translated the millimetre range of your roller diameters h into thou which I should have done before I wrote. It is 1.1 thou which gut feeling suggests is ok for a mild engine like Falcone. If you had enough spare rollers to eliminate the outliers and create a more uniform set if could be better, but if not personally I wouldn’t worry.

    Hope this helps a bit.

    Andrew N.
     

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