eccentric/idler shaft issues

cml · Post by **cml** » Tue Mar 30, 2010 10:21 pm

I installed a 10-24 bolt and washer, and it fixed the problem of eccentric bushing walkout. It still walks out about 1/16" until it hits the washer, but that seems OK. I have my lower case ears tightened just enough so that I cannot turn the eccentric bushing to tension the belt by hand (and so it doesn't come loose under operating conditions.) I have the poly-V belt tensioned to about 1/4" of deflection on both sides.

I ran the motor at about 80% throttle for 3 or 4 minutes, and the idler shaft is VERY hot. It doesn't seem too warm on the inside of the machine where the belt rides, but the shaft part that protrudes from the eccentric/idler bearing gets too hot to touch for more than a couple seconds.

Is this normal? I am wondering if I overtightened it before and damaged the idler bearing. The shaft spins smoothly and easily by hand, and does not make any noise under power.

-Chris

PS- Thanks for the info on couplers, JPG

billmayo · Post by **billmayo** » Tue Mar 30, 2010 10:43 pm

cml wrote:I installed a 10-24 bolt and washer, and it fixed the problem of eccentric bushing walkout. It still walks out about 1/16" until it hits the washer, but that seems OK. I have my lower case ears tightened just enough so that I cannot turn the eccentric bushing to tension the belt by hand (and so it doesn't come loose under operating conditions.) I have the poly-V belt tensioned to about 1/4" of deflection on both sides.

I set both the eccentric bushing and idler shaft bearing againest the washer (lightly tighten the eccentric bushing set screw if present) and turn the eccentric bushing for 1/8" to 1/4" deflection on one side of the belt. The factory spec is 20 in/pd for the eccentric bolt. I use a lock washer under the bolt head where I can see the split and stop when the lock washer is flat.

cml wrote:I ran the motor at about 80% throttle for 3 or 4 minutes, and the idler shaft is VERY hot. It doesn't seem too warm on the inside of the machine where the belt rides, but the shaft part that protrudes from the eccentric/idler bearing gets too hot to touch for more than a couple seconds.

Yes, the idler shaft bearing can operate quite hot. I find if I can keep my finger on the housing for 1 sec., it is OK for me. If too hot for holding 1 sec, I replace the idler shaft after checking several things. I look down from the top of the headstock to insure the belt is tracking straight. There will be a budge on one side of the belt as it goes over the idler sheave pulley if not straight. The belt being too tight or the eccentric bushing set screw too tight can also cause too much heat.

cml wrote:Is this normal? I am wondering if I overtightened it before and damaged the idler bearing. The shaft spins smoothly and easily by hand, and does not make any noise under power.

Only over tightening the eccentric set screw can damage the idler bearing. However, If you do not feel or hear any noise when turning by hand, I would believe you are OK and would not worry about it.

Bill