Backlash Question

911231 · 06-29-2009, 05:26 PM

We seem to have solved our rod bolt problem from earlier... thanks to you who responded with answers. However, we have another problem...

We are preparing to seal the case. we have installed the 8 crank bearings and the crankshaft, and all the bearings for the intermediate shaft assembly/oil pump. We put in the assembly tonight and performed the backlash test. We could not feel the intermediate shaft have any play (although I know that the amount it is supposed to travel to contact the crankshaft is extrememly small - between .01 and .04 mm?!). Should we be worried? what steps should we take? Could it possibly be that the bearing holding the intermediate shaft is slightly too big and therefore allows no play? Thank you and we look forward to hearing from you all.

Al and Chris

Eagledriver · 06-29-2009, 07:35 PM

Are you talking axial play or play between the gears. I don't see how a bigger IMS bearing would change the gear play. It would just bind the shaft in the case. Did you put a new gear on the shaft? I put a new gear on mine and the play was almost imperceptable. If you have the right gear (0 or 1 as appropriate) and the gears don't seem to bind then I wouldn't worry about it. The aluminum gear will quickly wear to the point where you'll have plenty of backlash.

-Andy

911231 · 06-30-2009, 01:48 AM

The gears mesh smoothly and there is no axial play. There is no binding. It is just that we cannot feel or measure any backlash.
Al

docrodg · 07-03-2009, 06:01 AM

Feeling the backlash can be difficult, so is measuring. I prefer the ASE principles for ring gear backlash measurement I learned back in college adapted for this application. Rig a strap on the back of the crankshaft to a tranny stud and tighten well to prevent ANY play in crank. Then set up a dial indicator with a wiggle arm to amplify the measurement and get more toward center of the gear tooth. Gently rock the intermediate shaft and read the gauge. Divide the result by the wiggle arm ratio and you have your backlash. Using the wiggle arm (I have a 4:1 arm) really makes a difference, as .01 suddenly becomes .04 and .02 is read as .08 so you can read the lash easier. Just preload the dial indicator well and ensure it is not going to move at all in it's mount. Often there is play in the mount that will cause a bad reading. My personal preference is to tighten it down well and measure, then fully remove and re-install the thing and couple times. Whatever readings are repeated are the accurate ones. If 3 in a row match I am happy with it and continue building.

911231 · 07-05-2009, 05:40 AM

THank you for the help. We reinstalled the crank and now "feel" a little back lash. We will try to measure it. Thanks Al and Chris