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Author Topic: Mating upper & lower halfs of different bikes  (Read 1088 times)

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Offline Sgt Wonderful

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Mating upper & lower halfs of different bikes
« on: November 22, 2008, 04:05:01 PM »
Question:
I'm assembling a 1971 CB 750. Upon close examanation I notice the crankcase is cracked. I obtained another crankcase  (lower half) from another bike, and want to mate it with my upper. Will I have a problem when it comes to getting main bearing to fit?
Any help or constructive comments will be appreciated.
Thanks,
John
« Last Edit: November 22, 2008, 06:12:35 PM by Sgt Wonderful »
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Offline FunJimmy

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Re: Mating upper & lower halfs of different bikes
« Reply #1 on: November 22, 2008, 09:02:23 PM »
John

I may be wrong, but don’t they line bore the crank journals as a matched pair?
I’d try to get the other case half from the same engine if it where me.

Jimmy
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Offline bill440cars

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Re: Mating upper & lower halfs of different bikes
« Reply #2 on: November 23, 2008, 09:22:32 AM »
Quote from: FunJimmy on November 22, 2008, 09:02:23 PM
John

I may be wrong, but don’t they line bore the crank journals as a matched pair?
I’d try to get the other case half from the same engine if it where me.

Jimmy

        I would be thinking that you are right Jimmy. Since the bearings appear to set in each case half, no way would I consider using another case half, without getting it checked by a machine shop and  maybe you could get it mated up. I think you might get by with it if it was a 2 cylinder if they have another piece that actually holds the crank in the upper case half. Far as I know, anyway. ;)

                                Take care, Bill ;)

     
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Offline boatsdickson

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Re: Mating upper & lower halfs of different bikes
« Reply #3 on: November 23, 2008, 04:43:01 PM »
Quote
I may be wrong, but don’t they line bore the crank journals as a matched pair?
I’d try to get the other case half from the same engine if it where me.

Ive heard the same as for matchin and grinding the halves as a set. I currently have the same issue with a bad lower case but a good upper. Also a problem might come about trying to match different halves with the different K models.

By the way, anyone have a good K8 I could buy?  :)

Good luck Sarge...
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Offline Sgt Wonderful

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Re: Mating upper & lower halfs of different bikes
« Reply #4 on: November 23, 2008, 04:45:14 PM »
Thanks guys, Thats what I figured you all would say. I'll get the other half. I started to think about it when I was trying to figure out what kind of bearings to get. I looked on the crank and got the letters and looked at the case and got the letters and started to figure it out. I plan on putting in standard size bearings.  Mains one, two four and five were green, number three was yellow. Now all I have to do is find a place that sells them. ANY SUGGESTIONS..
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Offline boatsdickson

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Re: Mating upper & lower halfs of different bikes
« Reply #5 on: November 23, 2008, 04:51:01 PM »
http://forums.sohc4.net/index.php?topic=743.msg4704#msg4704

Since your posts are low, its hard to tell if youve lurked a while or not. Have you looked at the above topic yet? Should be alot of cross reference info there.
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Offline Sgt Wonderful

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Re: Mating upper & lower halfs of different bikes
« Reply #6 on: November 23, 2008, 07:46:16 PM »
I'M BRAND NEW HERE, JUST BEEN HERE A FEW DAYS NOW.
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Offline 754

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Re: Mating upper & lower halfs of different bikes
« Reply #7 on: November 23, 2008, 08:48:59 PM »
Boat, do you mean cases or whole bike??

I might be able to sell a set of 78F cases, but I am way up in Canada.
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Offline boatsdickson

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Re: Mating upper & lower halfs of different bikes
« Reply #8 on: November 24, 2008, 06:32:49 AM »
Nope. Just needing the cases of a k8. Welcome to the group.
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Offline Sgt Wonderful

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Re: Mating upper & lower halfs of different bikes
« Reply #9 on: November 24, 2008, 04:15:45 PM »
I've got a cracked one you can have.
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Offline boatsdickson

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Re: Mating upper & lower halfs of different bikes
« Reply #10 on: November 25, 2008, 05:07:24 AM »
 ;D ;D ;D ;D ;D

Ive also got an f2 case thats cracked you can have. Merry christmas.  ;D ;D
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Offline Sgt Wonderful

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Re: Mating upper & lower halfs of different bikes
« Reply #11 on: December 02, 2008, 09:11:31 AM »
Got my crack welded. I'm lucky, my son is an Aluminum welder of the highest caliber. He Tig welded it and it almost looks like it came that way. He's a layed off auto worker with lots of time on his hands for my little projects. It was cracked where the drive sproket was. Looked like a chain came off and cracked the case.
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