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Thread: crankcase

  1. #11
    crazypj's Avatar
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    Splitting crank is actually a lot more difficult on that motor as it has a steel plate on left side to direct oil from main bearing to big end. Earlier bikes (CB350 et.al.) had a 'lip' on flywheel so caught oil centrifuged out of main bearings to lubricate big ends. (they are not pressure fed) The 125 version of the motor had left side big end failures if oil was not checked regularly and kept between middle and top mark of dipstick. (125 also has a 12,500rpm redline) I have changed left big end bearings on 125 but it isn't easy. Freezing the crank and applying local heat to outside of flywheel may enable the plate to be removed without damage but it's a difficult crank to fix.
    If you want to split cases, just make a tool from some flat plate and a few nuts and bolts. If it isn't coming apart relatively easily you either still have some bolts in place or your using tool wrong.
    Last edited by crazypj; 12-20-2016 at 01:39 AM.

  2. #12

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    Oldie,
    Please see attached. This outlines the method of separating and rebuilding a pressed up crank.
    crankcase-alfa-cranks_page_01.jpgcrankcase-alfa-cranks_page_02.jpgcrankcase-alfa-cranks_page_03.jpgcrankcase-alfa-cranks_page_04.jpgcrankcase-alfa-cranks_page_05.jpgcrankcase-alfa-cranks_page_06.jpgcrankcase-alfa-cranks_page_07.jpgcrankcase-alfa-cranks_page_08.jpgcrankcase-alfa-cranks_page_09.jpgcrankcase-alfa-cranks_page_10.jpg

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  4. #13
    crazypj's Avatar
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    I was wondering when the Alfa Bearings instructions would appear. Kudos for taking the time to upload it.
    I've used the instructions in one form since around 1979 or so. ( I taught pressed up crank building/truing at MMI for several years as a 'machine shop' instructor) It's easier to make a 'press plate' to separate the halves
    As I previously mentioned, Honda use what is referred to as a 'tin can' crank on 125~200 twins so crank pins are not seen until covers are removed (they used similar concept on CR125/250) The instructions work when you have access to crank pins but there are no instructions on removing the covers without damaging/destroying them. It's been such a long time since I did 125 twin crank I can't remember how I got plate off left side without damaging it (it IS possible though)


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