Resurrection of a Mongrel /5

Discussion in 'Airheads' started by cameron110, Apr 25, 2013.

  1. bpeckm

    bpeckm Grin!

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    I say "Aha!" to your comment that, in spite of it being more difficult to begin with, having the BLOCK milled will give you further options down the road....

    I like your attitude... how far can I bend this before it.....(fill in the blank)....:evil

    :D
    #41
  2. disston

    disston ShadeTreeExpert

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    That is a great story Cameron. I think that Mr Collier is about to get much more of this Airhead work. Do you fell it appropriate to share contact info?

    I also agree with the block modification being preferable when there is a choice.
    #42
  3. cameron110

    cameron110 Been here awhile

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    I don' have a good read on how he would feel about doing mail order work so next week I'll call and ask him about it (I'm back at work tomorrow and through the weekend so It will have to wait for Monday.

    If I don't post an update one way or the other by the middle of the week I've forgotten and reminders would be welcome.
    #43
  4. disston

    disston ShadeTreeExpert

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    I would understand somebody trying to be "retired" may not want to do mail order. He could also just allow people to do what you have done and bring stuff in. Maybe the Airhead business won't be over whelming but the boring the block out to 99mm should have some interest in these pages and many others.

    It would be much easier if he only accepted stripped blocks for boring. That could easily be a stipulation.

    Feel him out on it for sure. Maybe get him to agree to doing just a few more? To see what the demand would be.

    Here's what has been happening of late. The idea of fitting later cylinders, 99mm, to an early bike comes up all the time. Several people have investigated it but you are the first to finish the machining part of the conversion in years. Maybe I'm missing something but I don't think there is anybody else that is readily available for this work.

    I'm not in the market myself so I will probably drop out of this completely. I just know there are going to be a couple right away at least.

    As another point I think his price may be too cheap. Others that have experience in doing this stuff will know but the price you got I kinda think is a special deal because he wanted to not over charge. I'm not sure what the price should be but think he should get a fair price.

    Maybe you could wait on approaching him till another rider speaks up and thinks he could follow in your foot steps?
    #44
  5. Plaka

    Plaka Brevis illi vita est

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    it is not a difficult operation. You can do it on a vertical Knee mill with a big angle plate, or on a horizontal mill with a boring attachment. You do want a stripped block. Chips. Unless you have made up a dedicated fixture, the setup for the cut is slow. You have to square the block to the axis of the cutter and then center the cutting head. The cut itself is quick. might consult Randy Long.

    Mail order works if' you're set up with shipping containers. I have seen plans for plywood plates used for packaging blocks. Shipping adds quite a bit to the cost.

    if anyone wants to play I have a 75/5 short block I'm looking to sell...
    #45
  6. Lornce

    Lornce Lost In Place

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    That makes good sense and you've had the good fortune to find a guy willing to do the machining for a very reasonable sum. Hard to beat that. :thumb

    I went the other route and turned a few sets of Nikasil barrels (800 and 1000cc) to suit /5 blocks. I built a fairly simple lathe fixture with facility to securely attach the cylinder using the two cylinder to head studs. Worked well and helped me achieve one of the critical steps in modernising an old R75/5.
    #46
  7. disston

    disston ShadeTreeExpert

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    I think that is the reason that turning cylinders would be more common. You can use a lathe. To do the bores in the block you need a mill. I think the lathe and the knowledge to use it are more common than the mill and the knowledge to use it.

    I never realized before though that there would be a reason to chose block over spigot machining. The idea that the block can be used with any number of cylinder changes now is a definite advantage in my book also.
    #47
  8. Lornce

    Lornce Lost In Place

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    I turned the barrels because the rest of the motorcycle was still intact. I didn't see any point in removing the motor from the frame and stripping it to the bare block casting.

    If you consider the work involved in stripping the motorcycle and engine block and the cost of five or six hours machining in a modern machine shop (unless you can do the machining yourself), the convenience of future barrel options begins to blur.

    But there's always more than one way to skin a cat. :thumb

    :norton
    #48
  9. disston

    disston ShadeTreeExpert

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    Agreed Lornce, most will choose this option for the same reasons. The OP's block was already off the bike and already stripped I think. And then he just happened to run into somebody who would do either. Not going to happen that way for too many others I think.
    #49
  10. Plaka

    Plaka Brevis illi vita est

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    And the big cc cranks and cams fit? Gee, I may rework my /5 block...
    #50
  11. disston

    disston ShadeTreeExpert

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    Nope. There is a limit to which crank can go in which block. I don't know the story but it involves specifically early blocks and early cranks. Swapping is limited by the fact you can't get just any crank to fit just any block.

    Maybe somebody who knows will elaborate? Or it might be on Anton's Web Pages? Or even Snowbum's if you get lucky?

    But swapping cranks is not the issue for using late model cylinders on a /5 block. The issue is the size of the spigot. 1969-1975 uses a 97mm spigot. 1976-1996 uses a 99mm spigot. The change happens during the /6 production years. 1976 /6 blocks use the larger spigot.

    In some applications the spigots have to be further clearance ground so the rotating crank misses the edge of the spigot. This applies to the larger /5 cranks I think.
    #51
  12. Lornce

    Lornce Lost In Place

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    Never touched the bottom end. Bolted the 1000cc pieces directly onto the /5 block. It was never an issue. :dunno

    Years before when modding a '76 R60/6 to become an R100/6 I tried to learn about any difference between the cranks (a local "expert" had told me the counterweights had different inserts) and never did get any definitive information. I swapped the cam to use a /7 308 and ran the /6 crank without issue. It was the smoothest 1000cc boxer I've ridden to date.

    I still don't know if there's any difference in any of the post '74 cranks. Think I checked once and they all had the same part number. :dunno

    :scratch
    #52
  13. Lornce

    Lornce Lost In Place

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    I don't believe this is accurate.

    I've mated turned Nik barrels to /5 cases without clearance issues.


    :thumb
    #53
  14. disston

    disston ShadeTreeExpert

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    Maybe it's not the /5 that hits the spigot. I've never done it. The issue is that some cranks hit the spigot. Check the fit of the cylinder you have against the crank in the block you have. Rotate the crank. If it hits you have to spend some time grinding.
    #54
  15. Lornce

    Lornce Lost In Place

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    Well, which ones do you need to be worried about. :dunno

    I've fitted 800 and 1000cc Nikasil barrels to /5 bottom ends without clearance issues.

    I've fitted 1000cc /7 barrels to /6 bottom ends without clearance issues.

    As far as I know, the cranks are all dimensionally identical. Have you run into this clearance issue you keep warning us all about. :dunno

    :scratch
    #55
  16. disston

    disston ShadeTreeExpert

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    Some cranks have larger throws or some spigots are deeper. In some applications a small notch or little bit of grinding needs to be done to clear. I'll try to find the info about which swap runs into this problem. I don't think it is even a rare problem.
    #56
  17. Lornce

    Lornce Lost In Place

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    Disston, every airhead crank from an R50/5 to an R100RS has the same stroke/throw. They're all the same.

    Only ones that are different are the R65/45 cranks, but we're not talking about those here.

    :brow
    #57
  18. disston

    disston ShadeTreeExpert

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    I believe the difference is in the counter weights. Some counter weights were larger, maybe they are heavier. Yes the stroke is all the same. But the counter weights also interfere with actually getting the cranks in and out of the blocks.

    I've only been searching the Snowbum site for half an hour. I'm only through the first article of the "Engine" section. I'll find it before morning if I don't fall asleep. :lol3
    #58
  19. disston

    disston ShadeTreeExpert

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    Here's one problem mentioned by Mr Bum but it's not the one I'm looking for;

    One last bit of information about the cylinders needs to be made here. In the later 1980's, BMW added a sort of "step" machined into the cylinder spigots, and a similar matching step was in the crankcase opening. If you try to fit late cylinders to an early bike, you MUST machine-off the step.



    #59
  20. cameron110

    cameron110 Been here awhile

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    I had a pile of parts type bike with no particular plan other than have fun, learn more about indepth work on airheads and create a town/fire road ripper. When I pulled the heads the bore on one side was pretty rough from sitting with water in it. We had a set of Nik 800cc jugs and pistons lying about, new rings for that set are much cheaper than new slugs and rings if I were go up one size on the origional jugs.

    With this project as much about learning more about airheads as anything else I was happy to strip the block and once I found Mr Colliers shop my course was set.

    That step he is referring to is the reason I had to go back to Mr Collier to get the O-ring step added. I contemplated having him just put a bigger chamfer on the corner to clear the "step" which would have worked, but I figure if it's going in the mill I may as well be able to run o-rings. The extra step in the portal can be seen in this photo, I'll try to remember to get a pic of the offending step on the spigot when I'm back in the shop on Monday or Tuesday.

    [​IMG]

    I seem to rememeber having heard or read about people having problems with the interference you are talking about in some cases. I havn't test fit the cylinders since getting the crank back in, I'll let you all know if I end up with contact. We also have a variety of cranks and jugs lying around so I'll try to rememeber to do some comparison measurements and see if I come up with anything interesting.
    #60