bondy Posted August 31, 2013 Report Share Posted August 31, 2013 hi guys i have come across aproblem with my crank on my 198A (250) i have put it into the L/H crank case no problems dropt stright in when ive come to bolt both cases toghther the crank is really stif to turn. when i loosen the half case nuts it frees up i have noticed theres a biger gap on the other side were the crank meets the case. so i gess as am tightening the bolts its jaming up on the L/H side so ive strip it all back down. and this morning i have put the crank back into the L/H case but left a bit of a gap has anybody come across this before? are ham i doing somthing wrong? spoke to big john he has told me he has heard of this happening before think he as a friend who its happend to. so any help will be good cheers bondy. Quote Link to comment Share on other sites More sharing options...
sherpa325 Posted August 31, 2013 Report Share Posted August 31, 2013 First of all you should use C3 clearance main bearings, to provide a little bit of additional clearance. There are two methods of pulling the cases together. A couple friends use the method of gently heating the cases to expand the bearings just enough to allow the crank to slide into place with little force. I have a number of different lengths of pipe that go over the threaded ends of the crank, I then tighten the nut on the end of the crank, as the nut tightens on the pipe the crank is pulled into the bearing at right angles.You have to do both sides separately but I prefer the second method as I can pull the crank exactly as far in as I want without fear of bending the crank out of alignment. Cheers Greg PS It is fairly easy to 'bend' the crank out of alignment Quote Link to comment Share on other sites More sharing options...
pschrauber Posted August 31, 2013 Report Share Posted August 31, 2013 Are you sure that you have mounted the main bearings perfectly to the crank shaft? For mounting the assembly I prefer the heating / freezing method: - first mounting the kick start shaft and return spring, as we all know ..., - then put the left sidecase in the oven and heat the assembly up to around 150 - 180° - you can too put the crank assembly in a plastic bag and then in the fridge. Now mount the crankshaft in the left side case this should work out very easy, the crank bearing should pop in with ease, and when sitting completely in the left engine case everything should be OK. Mount the reminding shafts and gears, ... Now mount the right engine case, heat the case up to 180° and be sure to mount it parallel already from the beginning, some soft hits with a wooden or plastic hammer and the case should slip on. When the case has cooled down check if all shafts and the crank runs free. Quote Link to comment Share on other sites More sharing options...
bondy Posted August 31, 2013 Author Report Share Posted August 31, 2013 hi guys thanks for your help i have used the C3 bearings. i did the freezing methord wich works well but when i dropt the crank in the case its gone in to fare and was rubbing on the case i may have to have the crank checked in case i have bent it out it fell out the case when i was geting it back out but only onto the work bench dont know if this would do anything but to be on the safe side i will get it checked. ive been told off some one that says he has heard this a few times so hopfully he will let me know what to do cheers bondy. Quote Link to comment Share on other sites More sharing options...
stevem75 Posted August 31, 2013 Report Share Posted August 31, 2013 This is a common issue when assembling the crankcases. Sounds like you have assembled correctly with the use of heat etc etc. One thing that is overlooked is not installing the seal retainer in the left case. This sets the depth at which the crank with bearing will sit. When installing the right crankcase make sure that you've heated the case good and hot before assembling. It should just drop right onto the left case half withou the need to tap or draw it together with the crankcase nuts. If you find it isnt just dropping on then heat it again and make sure all your trans shafts and crank are sitting properly in the left case. Once you have the right case installed torque the case nuts to 5 foot pounds as we discussed earlier. At this point check to make sure the trans spins freely. In all likelihood the crank won't turn freely. This is ok because it will be sitting a little proud on the left crank case. Look at where the crank is sitting between the two case halves to determine this. Once you note where it's sitting you can tap the end of the crank with a brass hammer or the like to get it to center in the cases. Bultaco actually had a special tool for this and they pried the crank in the direction it needed to go. You will find with one or two good taps and the crank will free up and spin nicely. All you're doing is centering the crank in the case halves. Once done continue with reassembly. Remember that your brand new crank was pressed and aligned to a very high tolerance. I'm not suggesting to hit the crank so hard as to put it out of alignment but just a few love taps to get it into position. Sounds like you had it right. Just take your time. Make sure everything is aligned and the cases are heated sufficiently and all will come together Steve Quote Link to comment Share on other sites More sharing options...
bondy Posted August 31, 2013 Author Report Share Posted August 31, 2013 hi steve thanks for that. i did not have the L/H retainer on i didnt hit it that hard but it did drop on the soft mating on my workbench i will have it rechecked. cheers Quote Link to comment Share on other sites More sharing options...
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