bottom end assembly problems

Discussion in 'General Questions' started by dotcom, Jul 6, 2014.

  1. dotcom

    dotcom Member

    Hi, I was wondering why when I put the crank in the housing and when I put the bolts in and tightnen them, there seems a significant amount of friction on the crank. Could it be the proper size screws being in the wrong place because there are a couple different sizes but they all look almost the same. When the crank part is in and the housing is together and I try moving the crank arm, it seems good but once I tighten the bolts there is some friction problems. Is it in fact the bolts are in the wrong places because nothing like this was happening before I took it apart.. Thanks in advance
     
    Last edited: Jul 6, 2014

  2. HeadSmess

    HeadSmess Well-Known Member

    the HT i assume?

    i shoulda taken pics, i was doing this last night...

    one, did you replace or remove the gasket? as a quick trick...i SCAN my cases for gaskets. clean em up, lay em on, cover with dark heavy blanket, scan, cut to profile. use thick paper. like 200gsm+. scanners are cheap nowadays :) of course, ive had no ink for a few weeks so i didnt do it this time :(

    change bearings? etc? why exactly was you digging around down there?


    but...when you pull it apart this time,

    1, check the bearings are free. one of mine had seized(lets say i forgot about the gasket and bearings when i pulled it apart last year and rebuilt it the other day and had to scratch my head for a while :p)

    2, remove all the SHIMS from the ends of the crank. there is usually two or three on each side.

    3, replace crank without shims, tighten case screws. dont put sealant on gasket just yet.

    if the shaft slips side to side,dismantle, then re insert one shim only.

    repeat if necessary until its just stopped the endplay, adding one shim to alternate ends each time. without clamping on the crank. loose is better here... ie, if you run out of shims, dont stress.


    all the bolts are same, bar three...two just under the cylinder that come in from the other side, and one right at the bottom of the case. thems be short ones. but no, they cant interfere with the crank, you just wont get some in if wrong...
     
  3. dotcom

    dotcom Member

    chinese engine from boygoesfast. Im replacing the crank seals and I also replaced the gasket since it needed it after opening. Im not sure exactly sure what the shims are you are referring to but I will try and check again this process over again
     
  4. HeadSmess

    HeadSmess Well-Known Member

    you will see them when you have the crank in your hands unless they fell on the floor. really thin washers.


    they are installed on initial assembly, a bit of selectivity, to make up for slack china tolerances.
    dont have to split it for doing the seals, but is an idea to use sealed bearings on the crank, just pop out the inside seals first. extra sealing never hurt noone!
     
  5. dotcom

    dotcom Member

    I must have lost those small washers you are talking about because I do not see them anywhere and im guessing without them, I will not have a motor so until I find out, I will need another bottom end which I am planning on getting from boygoesfast on ebay for $65 unless anyone here has a better place I can get one. Also, I do not need the covers or magneto or coil or piston.
     
  6. HeadSmess

    HeadSmess Well-Known Member

    if its crushing up the bearings and there arent any shims there at all, tis rather peculiar. they are on the crankshaft itself.

    of course, if the gasket isnt there either, it will crush the bearings. the gasket is quite thick. though you say you replaced it...

    it was fine before you pulled it apart...so whats different now? gasket, thats what.

    two gaskets always works at a pinch. or getting the crank pressed together just a touch. hint....try jacking up the house, with the crank in between the jack and house/ground... yep, thats my press :) overdo it and then itll clamp down on the conrod instead. oops.
     
  7. dotcom

    dotcom Member

    Yeaah I don't see any bearings and the new gasket seems fine but I have already sealed it onto one end so my only guess is these shims that I have never seen is what's causing the friction
     
  8. crassius

    crassius Well-Known Member

    I've opened several that had no shims - they are only put in when needed. Did you say you put in seals? if so, they may be in too far and binding when the cases are tightened. Try putting them in after the cases are together.
     
  9. dotcom

    dotcom Member

    already attempted this method
     
  10. dotcom

    dotcom Member

    this did not make a difference with the binding
     
  11. HeadSmess

    HeadSmess Well-Known Member

    true, only used when needed, and sometimes not.

    meh. smart person would have already tried cutting another gasket (or 3) from some paper and fixed the issue, but hey...


    here endeth the lesson on "dry trial assembly first"
     
  12. crassius

    crassius Well-Known Member

    look for rub marks on the edges of the housing in the case that goes around the outer shell of the main bearings - I've seen crank cheeks rub there when there is no shim
     
Loading...