Crank Shaft Side to side free play

[79XS11F]

Question guys.
I can't find any spec in my manual for the maximum allowable side to side movement of the crankshaft. All 3 of my engines have side play and I would like to know how much movement is too much movement.
The center main crankshaft bearing includes the thrust bearing so on a new engine or new bearings is there no side play?
Rob

[Crazcnuk]

1/2"


J/K but basically, in my experience, the thrust bearing has far less force on it than the main bearings themselves, so in order for it to wear out, your mains would have to be shot as well.

I was trying to think of what would actually happen if that thrust bearing did wear out, badly enough for us to worry...

Have you used a dial guage and measured the play? I would think it shouldn't much more than a few thousandths of an inch.

[79XS11F]

I will have to check the manual to see which side of the center bearing the thrust lip is on. If it's on the side that has the crank against the lip when the bike is on side stand then excessive side stand idling could wear it out and create the side play I feel.
I am talking more then 1000s of an inch here. Like approaching 1/32 of an inch and all 3 engines are about the same with different mileages on them. or does the crank "load up" to one side where that lip is when it's spinning? If this is too much then I need bearings on both my engines with the backup engine not being a concern.
Rob

[Crazcnuk]

Well, as I said, I can't imagine why, or how, the thrust bearing could wear out before the main it's attached to.

There are really no forces playing sideways, it's just that there has to be SOME movement there so it doesn't bind up.

If all your bikes are about the same, I would assume that what you are seeing is 'normal'.

Even idling, on the sidestand, doesn't put any forces sideways, other than gravity. If main bearings wore out from gravity, we would all be in trouble.

Remember that the same bearing that takes side thrust also takes every bit of power it's two adjacent cylinders can put out, so, relatively speaking, side thrust is nothing.

[79XS11F]

Well there must be some sideways force or they would not need a thrust bearing would they? Unless it's just to keep the crank somewhat centered in the engine. In any case I would like to know what is or is not normal. As you know i am trying to determine where my "BUZZ" is coming from and I want to correct or eliminate this as a possible source.
Rob

[Crazcnuk]

I believe it's just to keep things centered.

Because it's a rotating assembly, they can't just leave it with no designated rub surface.

I can't see this causing any kind of buzz. At worst it will hit the covers on one or both sides of the engine causing a rubbing noise or squeel.

It would definately be nice to know what the spec is, I will check my manual, but it's probably the same one you have.

[79XS11F]

BUMP ... come on guys I need at least 2 dimes worth of your 2 cents' before I can close the book on this one.
Rob

[TopCatGr58]

Hey Rob,

TrBig/Tod asked the same question a while back and also got no definitive replies even though we have several pro mechs on here, so that most likely means that there isn't any real value that Yamaha applied to that.

Note: There is a special thrust bearing (insert) located in the No.4 main bearing housing in the upper crankcase. The function of this insert is to provide a bearing surface for crankshaft side thrust.

Sounds like they are just allowing for "some" side thrust! So...unless you have signs of actual xsive side wear on the crank journals and bearing caps and such, then it does sound all normal.
T.C.

[79XS11F]

well that's what I'm trying to discover .. .what is "excessive" side play (wear). I have about 1/32 of an inch on all 3 engines that I have here.
Rob

[snowdog51]

side play

most piston engines have some play i would not worry about what you have
chev v8 with alot of miles have almost .25
and still run [inchs]. if you think about it
it would be hard not to have soms play.
as ever bill

[olebiker]

Rob it is more a worry if you don't have any. My buddies XV has none and is making an awful howl. I think we are gonna have to tear it down but I am worried that it will be possible not to find the problem. I haven't seen this one before. I don't think that the side play you have has any bearing on your buzz.

Carl