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Old 08-30-2013, 12:42 PM   #46
Lornce
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Originally Posted by bpeckm View Post
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....
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.

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.
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Old 08-30-2013, 12:52 PM   #47
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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.
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Old 08-30-2013, 01:06 PM   #48
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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.

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Old 08-30-2013, 01:44 PM   #49
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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.
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Old 08-30-2013, 04:19 PM   #50
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Originally Posted by Lornce View Post
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.

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.
And the big cc cranks and cams fit? Gee, I may rework my /5 block...
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Old 08-30-2013, 05:15 PM   #51
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And the big cc cranks and cams fit? Gee, I may rework my /5 block...
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.
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Old 08-30-2013, 07:56 PM   #52
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And the big cc cranks and cams fit? Gee, I may rework my /5 block...
Never touched the bottom end. Bolted the 1000cc pieces directly onto the /5 block. It was never an issue.

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.

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Old 08-31-2013, 07:24 AM   #53
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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.
I don't believe this is accurate.

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


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Old 08-31-2013, 09:15 AM   #54
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I don't believe this is accurate.

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


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.
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Old 08-31-2013, 06:27 PM   #55
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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.
Well, which ones do you need to be worried about.

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.

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Old 08-31-2013, 10:34 PM   #56
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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.
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Old 08-31-2013, 10:50 PM   #57
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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.
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.

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Old 08-31-2013, 11:13 PM   #58
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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.
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Old 08-31-2013, 11:46 PM   #59
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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.



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Old 09-01-2013, 07:24 AM   #60
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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.
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.

Quote:
Originally Posted by disston View Post
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.
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.



Quote:
Originally Posted by disston View Post
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 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.
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