Rod Movement!

[gthoma23]

I thought i'd ask, even though i think i know the answer to this question. is the connecting rod suppose to have any free play from side to side? cuz mine moves a little, but i don't think it's suppose to.

and how would i fix this if it's a problem? do i have to split the case and replace the crank? or is the problem just in the bearings or seals?

thanks!

 

[btm1948]

the rod is not supposed have any movement side to side i would replace the bearings first and see if that fixes your movement problems

 

[IndyMX]

it should have a little bit of free play side to side..

Check your service manual for the proper amount.

 

[steve.emma]

the rod is supposed to have some sideways movment. if you look in a service manual you will see they give you a spec for how much there should be. remember when the motor is assembled the rod cannot really move side to side as the piston stops it from happening.

 

[gthoma23]

my service manual it has 2 measurements, big end axial/radical play, and connecting rod big end side clearance? i hate these manuals, cause the discriptions suck. so i'm thinkin it's the big end side clearance, but the pic shows him measurin with a feeler gauge from the bottom of the crank. that service limit is .9mm and the axial/radial play is .03mm. do either of those sould right?

 

[steve.emma]

you are correct its the side clearance you're talking about.
.9mm sounds about right, when i did my last top end job i checked mine and it was .8mm. checking the axial play is harder to do but basically if you can feel any up and down play of the rod in the big end bearing then theres a problem.

 

[cujet]

Big end side clearance is necessary on 2 stroke bikes. Some people claim that side clearance can indicate bearing condition.

For instance, if new, the side clearance was X but now, after a season the clearance is more than X and close to the published limit. It indicates the rod/bearing/pin should be changed. I will not dispute this.

You probably do not know the exact figure your crank started out as. So my above method is not helpful to you right now. But, remember to measure any "new" crank and write it down.

Another point, setting up a new con rod to the "tight" end of the side clearance settings often results in shorter bearing life. The theory is that oil flow is reduced.

 

[gthoma23]

this might sound like a stupid question, but what's the best way to measure the end clearance? should i just try and stick a feeler gauge in the gap between the rod and crank? or is it better to measure it up by the small end bearing, and if so, what is the best way to do it?


thanks for the feed back