Author Topic: Crankcase won't go back together, help please!  (Read 392 times)

Offline shill1000

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Hello,

I have taken the crankcase apart to deal with the dreaded sludge trap and I am pleased I did! Anyway fast forward when I try and put it back together the crank will not turn when bolted back together!

I haven't needed to replace anything as from what I have been told and from what I can see all bushes ect are fine and were replaced recently. I put it together loosely and it will turn. Bolt it up and it gets stuck. I have tried starting with the drive side down first, then timing side down (as suggested in the book). Then gradually tightening opposite side nuts at a time, Then a few.  *pull hair out* I hope I am missing something simple as I can't understand what I am doing wrong. Logic suggests it's an alignment problem, I can't see why and it was fine before, or any other way of doing it.

Any help would be greatly appreciated.

Many thanks, Stephen.
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Online Greybeard

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Re: Crankcase won't go back together, help please!
« Reply #1 on: 13.05. 2020 20:57 »
Hi Stephen and welcome. When you have a minute will you go to Introductions and give us some information. Your bank account and passcode would be very useful  ;)
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Offline muskrat

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Re: Crankcase won't go back together, help please!
« Reply #2 on: 13.05. 2020 21:09 »
G'day Step,  *welcome*
 There are a few reasons so first a few questions.
Which model? Plunger, early or late swingarm? Not that it should matter much.
Did you remove the inner drive side bearing off the crank when doing the sludge trap?
Are they a matched pair of crankcase halves?
Cheers.
ps: I'm off to work now so I'm sure you will have a few replies before I get back.
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'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Offline Swarfcut

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Re: Crankcase won't go back together, help please!
« Reply #3 on: 13.05. 2020 22:52 »
Hi Stephen. Welcome to the last chance saloon.

 Like all problems, the answer is easier with a little more history. Was it ever a runner, or someone's problem project?  On the basis of your single post I can only assume this was a previously assembled and running engine. If it won't go back together now, it can only be a simple assembly problem. If parts have been replaced, that is the cause. If it's never run, then the basic assembly and set up is wrong.

  With all original parts, does the camshaft turn, but the crank locks?  Both locking up, it's crankcase mis - alignment. There should be a locating dowel where the crankcases join, above the camshaft. If the cam turns fine, the cases are aligned OK.

  Usually some jointing compound is used between the cases. None, or less thickness than originally will make the cases closer together, and with a tight setting for the crank endfloat, this will trap the crank when the cases are tightened down.

   Another cause is the drive side bearing, either replaced without setting the endfloat or the original drive side main bearing inner race moved away from the crank web, effectively increasing  the overall length of the assembly.  Closing the cases clamps the crank.  If this seems the problem, assemble just the drive sleeve onto the crank, and tighten it down with the cush nut. This will move the bearing inner race back towards the crank and restore the original running end float.  The crank should now be free to turn, if it was a previously running engine. Plenty on the forum about setting the endfloat the need to seriously tighten this nut on final assembly.

 Have a look at the front of the cases, just below the dynamo cradle. Matched cases will have identical stamped numbers, side by side.

 If the bike is a S/A variant, the three front primary chaincase screws can lock the crank if they are too long, the threaded holes enter the crankcase, rather than being blind holes. Earlier Plunger design does not have this feature.

 Swarfy.
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Online KiwiGF

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Re: Crankcase won't go back together, help please!
« Reply #4 on: 14.05. 2020 08:04 »
Hello,

I have taken the crankcase apart to deal with the dreaded sludge trap and I am pleased I did! Anyway fast forward when I try and put it back together the crank will not turn when bolted back together!

I haven't needed to replace anything as from what I have been told and from what I can see all bushes ect are fine and were replaced recently. I put it together loosely and it will turn. Bolt it up and it gets stuck. I have tried starting with the drive side down first, then timing side down (as suggested in the book). Then gradually tightening opposite side nuts at a time, Then a few.  *pull hair out* I hope I am missing something simple as I can't understand what I am doing wrong. Logic suggests it's an alignment problem, I can't see why and it was fine before, or any other way of doing it.

Any help would be greatly appreciated.

Many thanks, Stephen.

Con rod nuts hitting?  *dunno* did you replace them?
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Offline muskrat

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Re: Crankcase won't go back together, help please!
« Reply #5 on: 26.05. 2020 09:38 »
G'day Stephen.
How'd you go with it  *????* Find the problem  *????*
Cheers
Now get over to Introductions and give us your story.
Cheers
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'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Online RichardL

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Re: Crankcase won't go back together, help please!
« Reply #6 on: 26.05. 2020 12:43 »
Well, that's a lot of reponses to the question without a word back for some time. Stephen, if your fingers are trapped in the crankcase just nod.

Other possibilities:

Timing-side bush pulled out a bit and resisting going back.
Main bearing outer race pulled out a bit and resisting going back.
Shims behind inner race have become distorted, preventing seating the race to original position (per Swarfy's advice).
Others, even more obscure.

Richard L.
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Offline ianbsa

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Re: Crankcase won't go back together, help please!
« Reply #7 on: 01.06. 2020 11:17 »
Bit of obscurity here.
If nothing has been replaced bearing wise and all is as is and clean the only thing I can think of and this happened to me is forgetting to nip up the top stud nut inside the cases over the cam.
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