Crankshaft side play

[Cantab]

Does any body know what the service spec is for crankshaft side play?
I am talking about how much the crankshaft can move between the main bearings with the main bearings fully seated in the crankcase housing.

I assume there should be some clearance, otherwise there would be a problem with thermal expansion and contraction between the steel crank and the alloy case and possible side pressure on the main bearings.

Any advice would be much appreciated, using a micrometer it looks like there is about 1.2mm at the moment.

[stewart]

it should be a press fit  and not movable

[Wizzy214]

it should be a press fit  and not movable

if theres side play, you might have bearing failure.

[BDI]

Does any body know what the service spec is for crankshaft side play?
I am talking about how much the crankshaft can move between the main bearings with the main bearings fully seated in the crankcase housing.

I assume there should be some clearance, otherwise there would be a problem with thermal expansion and contraction between the steel crank and the alloy case and possible side pressure on the main bearings.

Any advice would be much appreciated, using a micrometer it looks like there is about 1.2mm at the moment.

If there is 1.2 mm of play something bad is wrong. I do know that when the kx500 was raced on a pro level and the engines were rebuilt on a regular basis, the crank would become worn and start floating in the main bearings.  Is your bike by any chance an old race bike...

[Cantab]

Sorry I should clarify.  Actually it is a brand new Hot rod crank, new NSK bearings and the crank halfs have been put on a bluing glass to take off any high spots. 

So the bearings are tight into the case halfs, and the bearings are tight onto the new crank rod.  The crank is definately not going to move sideways when assembled, unless forced.

The Clymer manual says that if the crank is hard to turn when the cases are just reassembled, then the crank is most likely slightly out of centre.  It says to tap the end of the crank until the gap between the case and the crank webs are even and the crank rotates freely.  To me this suggests that there is probably some side play in the crank between the bearings.

The reason I ask the question is the old factory crank (probably rebuild many times) is slightly wider than the new HOT ROD crank, by about 0.8mm.  Of course the Hot Rod cranks are supposed to be built to OEM standards, I am hoping I haven't purchased one that hasn't been assembled properly.  Also as mentioned in my first post, with rough measurements there seems to be about 1.2mm difference between crank and bearings.

I am trying to find out if there is some kind of service limit to any crank sideplay as I re-assemble it.  It probably won't matter as the crank isn't going to move, but I am kind of fussy.

[stewart]

the counter wieghts should be center in case with same distance on both sides ..when cases are pressed toghter and the crank does not  turn freely  with it centered then the counter wight s were not held apart  properly during the pressing together  of the cases try putting somthing between them oppiste  the rod pin and pushing them apart till the crank spins freely

[BDI]

when you press the cases together the inner bearing races wined up pushed appart from eachother causing the bearings to bind up. If you press the crank to one side and then back to center it automaticly spaces the center races on the crank the same distance appart as the outer races in the case, thus centering the balls in the bearing races and allowing the bearing to spin free. As for crank to case side clearance it is what it is once the crank is centered in the cases, 1.2 mm sounds typical. If you are concerned with your crank being pressed together wrong you can check the rod to counter weight clearance with a fealer gauge. Your clymer should give this spec but I wouldn't be surprised if hot rod thought that the stock spec was excessive and tightened it up some, You may want to call them and ask what they think. I do know that if it is to tight the big end rod bearing may over heat from not getting enough cooling gas and oil.

    P.S. all of this should be done with a crank installation tool in place to keep from knocking the crank out of true.