Aligning crankcases, removing crankcase studs

eric

eric

Senior member
Location
solihull west midlands
        l have been informed that the top and bottom halves of triple crankcases, are machined as a unit, and that two different halves

        won't align, does anyone know if this is true? Also, how do you remove crankcase studs? l've looked in the archive, but can't find

        any information, any help would be deeply appreciated,

                                  thanks,  eric
 
I think the horizontal bearing holes are machined as a pair.
If you were to mix crankcase halves there is a risk that the hole would be oval leading to too tight a fit or even too slack a fit on the bearings, with nasty consequences.
To remove crankcase studs use 2 nuts on the top threaded section. Lock them together very tightly (using 2 spanners) then unscrew the stud.
 
          Thanks Grant, l've already tried the two nuts and two spanner trick, but they aren't budging yet, l'll soak them with wd40 and

          have another go tomorrow, doesn't look very promising for the crankcases then. l'll have to track down the original, some hope!

          l think someone else must be riding around with it, l wonder how they're getting on with different halves? Do you know if they

          can be re-machined?
                                              thanks eric
 
Try heating the casing around where the stud enters.
Aluminium expands faster than steel with heat.

If you re-bore the bearing holes then you will need very slightly larger OD bearings. Good luck with that.

It would be easier to buy another set of matching case halves. I have a spare set.
 
Eric, it was always a no no using different crankcase halves but I've seen it done on old 60's Hondas a few times with no apparent ill effects. Mind you Honda made good castings even though the material was poor.
 
            lt's a 120 Jota, the chain snapped and smashed the top crankcase, which has now been welded, .....so its about matching

            numbers and keeping the integrity of the bike, its taken some time to find a 120 bottom half, in vain by the look of it.......

                                    eric
 
Hi Eric - a long time ago I heard a comment that the crankcases are never going to be rigid enough to clamp the crank in place as it flails around - rather, the crank holds the cases in alignment (or not, depending how true the crank is)!  :o  

The factory machined the two halves as a matching pair, but doubtless you will have seen photos of bearings that have spun or fretted in their housings over time; also bearings being built up with coper plating to acquire the right amount of nip when fitted.  It may be useful to bolt the two halves together and check the housings for ovality if you have a tame engineer with the requisite measuring kit.  Ideally a suitable diameter bar could be machined up to assess their alignment too...perhaps Keith; Phil or Piet may have a view?

Various stud extractors are available if heat doesn't do the trick - if you don't fancy Snap-On prices then Sealey do one
http://www.sealey.co.uk/PLPageBuilder.asp?gotonode=ViewProduct&method=mViewProduct&productid=14205

Good luck - would be good to see that 120 rise from the detritus!  :D
 
As Red has stated, you need an incredible amount of luck to have odd halves match at all 3 shafts.  Very difficult and time-consuming machining them to get the bores in line, definitely not for the faint hearted.  Not sure if a single coat of copper on bearing races will suffice in every case.

A certain amount of ovality/wear can be compensated with specialist adhesives, misalignment is a whole different matter.  Simply pulling them together will just open the next can of worms...

If the welded matching case can be salvaged, by all means.  Otherwise, grab Grants' offer!

piet
 
eric said:
            lt's a 120 Jota, the chain snapped and smashed the top crankcase, which has now been welded, .....so its about matching

            numbers and keeping the integrity of the bike, its taken some time to find a 120 bottom half, in vain by the look of it.......

                                     eric
Click to expand...

Just make a good bike Eric..screw the numbers...An engine with matching crank cases or a top crankcase that matches a stamp on a frame hmmmm

just my tuppence worth ;)
 
            Well, l've got the studs out, (plenty of heat) believe it or not, I have two or three options open to me, none of them cheap,

            one of them is to give the crankcases to my mate who has an aviation engineering company, and see if he can ''ream'' the

            horizontal bores. l have posted before, that my eyesight is failing, so my other bikes will have to be sold anyway, but that would

            fund the 120 project, l would like to keep it with matching no's, but obviously, if the two halves won't align and he can't align

            them, l haven't lost anything, and will move on to plan 'b'

                                  thanks,      eric
 
If you're all OCD about matching numbers, you could change the crankcase, grind off and re-stamp the original number. It's not as if you're doing anything dodgy, you're just replacing the original case with an identical part and restoring the engine number to what it was. Might save a bit of paperwork at the vehicle registration office too. What they don't know about won't bother them.
 
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