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Thread: 1925 JD Cannonball Bike

  1. #1
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    Default 1925 JD Cannonball Bike

    I am currently on a mission to build a 1925 JD to run in the 2012 Cannonball Run. When I was given it 30 years ago it was mostly complete but taken somewhat apart. Over the years a lot of it got away from me for various reasons. This is a picture of most of what I had before Davenport. At Davenport and shortly after I added most everything I need except a left side foot control.


    I am currently trying to fit the engine to the frame and found out one of the at least 2 reasons it was taken apart sometime before WW2. The engine had come loose in the frame and the motor mount tabs are worn. The original thickness seems to have been about .500 of an inch (1/2 inch). The front motor mount is worm almost .040" and when I pull the rear bolts tight the front mount is about .060 from the frame tab. I suspect that the additional .020" is caused by uneven wear on the rear mount pulling the case to the right.



    Front engine tab:



    Rear engine tab:



    I also have the problem of the holes being wollered out on the rear tab. My question is - what is the recommended fix for these tabs. All opinions welcomed.

    Jerry
    Last edited by Jerry Wieland; 11-20-2011 at 08:48 AM. Reason: speeling

  2. #2
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    are your frame tabs in the same plane. you can weld the motor mounts up and re drill them. you may find that your frame is bent. call harbor vintage for your foot control.

  3. #3
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    Thanks rwm - I was hoping to hear different ideas on the motor mounts but this must be the only one that is used.

    In the knucklehead and wl service manuals there is a procedure for roughly checking your frame for correct alignment - does anything like this exist for JD?

    ...and lastly - what is the original finish on springer rockers.

    Jerry

  4. #4
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    Drop a line to Mark Masa. He has a 22 alinment table as fas as I know. Bob L

  5. #5
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    Bob I have been in some contact with Mark. I recently traded him the last piece he needed for the table - the fork holding casting.

    Jerry

  6. #6
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    We have had to deal with this on Silver Ghost crankcases where the motor mounts use shouldered bolts that pass through 'ears' so that the engine can be aligned with the transmission. These holes get elongated over time and have to be restored or the engine will move in its mounts -- very bad. A few folks have tried to weld and re-cut the holes, but with very bad results. We try never to weld on crankcases if it can be avoided and welding on aluminum that may have oil in the pores and is an old casting to begin with... risky.

    Our method for repair is to bore the holes oversized and then sleeve with a good aluminum alloy bushing.

    The challenge is in locating the holes, because before boring you have to locate the original center of each hole before it became worn. Then bore the hole over in order to fit a sleeve/bushing with a wall thickness of c. 0.075". That's a basic minimum wall thickness for an aluminum sleeve. You could also use a bronze sleeve which will be much stronger and allow a smaller wall thickness (less aluminum removed.) The down side is electrolytic action over the long term. But I would use a good aluminum alloy such as 6061, which will be much stronger than the original casting and still last a long, long time.

    Once the holes are bored, make the sleeve OD oversized for about a .003" interference/press fit. Use some red Loctite when you press it in. Then, because the ID will shrink some because of the press fit, you use a pin hone or a reamer to exactly fit it to the cross bolts for the mounts.

    To get the holes really lined up, the boring and then the final honing should be done with the cases bolted together and torqued. Putting them together for the boring will be an interesting fixturing job... most crankcases are a pain to fixture.

    As folks mentioned above, refitting the repaired cases will require your frame to in correct alignment/straight or the bolts won't line up and stressing the ears on the case is very bad -- they can break off.

    It's not a hard process, but you need a machinist who really knows his way around a mill and you need the original dimensions of the holes and their center distances. A DRO helps a lot!

    There are other approaches, but this one is safe for the cases as it requires no welding and is very straightforward.

    Feel free to PM me with any questions. I have a '27 JD 74ci which I think is basically identical to the one you are putting together. Your '25 will be great for Cannonball!

    Cheers,

    Sirhr

  7. #7
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    Sirhe Now you are talking. I had already run both of these ideas thru my brain as a way to minimize the effects of welding the motor mount tabs. I am leaning to making my own bolts with the correct size shoulder. Luckily I noticed that the JD motor mount bolts seem to have the head on the right and the nut on the left which is perfect for this. I could do the hole sleeving trick neither method has a strength advantage that I can see.

    I do not see any real problem with it as I have a fully equipped machine and welding shop at my disposal plus my own shop where I have a lathe, mill and surface and shaft grinders and every kind of welder commonly needed.

    I had thought that I would weld the metal back for the mating surface but had also looked in to some kind of a shim to recover the original thickness.

    The frame basically looks real good but I am in the process of building a fixture to be able to measure if it is exactly straight.

    Jerry

  8. #8
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    If the thickness of the tabs has been changed (if it was moving in the mount, odds are some fretted away) that should be restored as well. I'd be very cautious about welding to any old casting. They tended to have some porosity. And over decades, oil gets in -- even on external tabs. And when you start welding, the aluminum can just start slumping off... Your shim idea is probably the best one. You can control the thickness very exactly. While boring the holes in the casings, you can also true the faces of the tab, so that your shim is fully-bearing on the tab.

    One fixturing suggestion which we use for odd castings like large manifolds (which are horrible to fixture) is a plaster box. Castings like these, without special jigs to hold them, will distort when you put enough clamping force on them to hold them. And there is often no good place to get a flat when they are bolted together. Done one at a time, you have a great flat surface and as long as your head is 'gibbed' right, no problem if your math is right on with the holes. But it's a lot safer to machine them bolted together, as it ensures your holes are dead on. But What we do is to use a wood box. We lightly fixture the part inside it, but we don't use a lot of pressure on clamps, etc. After we get the area to be machined dead square with the table/head, we'll fill the box with plaster of Paris and let it set up for a couple of hours. Plaster sets very fast. Then tightly clamp the box down on the table and you can hold odd-shaped or delicate parts very tightly. After you are done, wash/chip the plaster off. It comes right off. Fixturing in plaster lets you hold all kinds or odd-shaped things very well.

    Cheers,

    Sirhr

  9. #9
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    Right now I am leaning towards welding up the motor mount instead of a shim. I have to weld the right case anyway because the reason this motor was tore tore down 70 years ago is because the breather broke out of the hole after ingesting a big piece of piston debris.

    I have welded HD alumimum (mainly knucklehead and Panhead vintage) for 30+ years with liveable results. Only when there is corrosion do I have a real problem with it. You kind of get used to the oil exploding and spitting back at you.


    I really appreciate all the info just the same. Fixturing should not be a real problem as I work in a factory with a huge fully equipped machine and welding shop. I have had to do stuff like that on a regular basis for years for my job.

    Jerry

  10. #10
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    Will be attempting to repair a pair of Indian crankcases through a process that I'm not real familar with but it is a cold process that was developed for Honeywell and is used in aircraft engines. I'll post after the vendor visit next week. Wish I knew more about it.

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