F3680 Center Blade Intermittent Problem

[ProjectKing]

Good thought but No cross threading of the blade bolt. Threads are perfect

When you tighten other blades do they try to turn drive shaft? The fact the drive shaft tries to turn when you have blade block demonstrates why blade isn't mowing. It's loose for some reason and not being properly clamped by bolt and washer assemblies.

 

[kthompson]

At least the ones I have seen the belt on the middle blade runs around the pulley using the back side of the belt while the outside blades use the inside of the belt. It could be the outside of the belt is worn heavy while the inside is in better shape or it could be there is an idle pulley to help route the belt around the center pulley that is the issue. Either is damaged, missing or needs adjusting.

 

[1bush2hog]

When you tighten other blades do they try to turn drive shaft? The fact the drive shaft tries to turn when you have blade block demonstrates why blade isn't mowing. It's loose for some reason and not being properly clamped by bolt and washer assemblies YEP.

The other two blades on the outside do not turn when I tighten the blade bolt if I have them blocked

 

[art]

There are times the cups need to be replaced!

 

[1bush2hog]

At least the ones I have seen the belt on the middle blade runs around the pulley using the back side of the belt while the outside blades use the inside of the belt. It could be the outside of the belt is worn heavy while the inside is in better shape or it could be there is an idle pulley to help route the belt around the center pulley that is the issue. Either is damaged, missing or needs adjusting.

I checked belt, pulleys, tension arm and tension spring and all are OK. The fact that the spline in the mower gearbox, and the pto shaft from machine to mower gearbox both continue to turn after I have blade blocked is the concern.

I would think that once the middle blade under the gearbox is blocked, nothing should turn except the blade bolt.

I'm wondering if these machines have a "slip clutch" :muttering:

 

[1bush2hog]

There are times the cups need to be replaced!

Understood, but is it normal for the PTO shaft to turn when trying to tighten them?

 

[kthompson]

Understood, but is it normal for the PTO shaft to turn when trying to tighten them?

If the blade is not turning as it should something is slipping for some reason. If one blade is slipping when the other two are not then issue is with that blade, washers, spindle, belt or pulley.

As to is it normal for the pto shaft to turn when you are turning bolts on the blade spindle, yes. You are turning the drive system. The bolt holding the blade onto the spindle is as much part of that system as the pto shaft is. What you want when you are tightening or losing a bolt is there to be enough weight in the drive system or such to keep your bolt from turning but...normally that is not true. But that is a good sign for it shows the drive train is easy to turn which it should be. It also takes a tight belt with good grip to have the full drive system to turn when you are turning one spindle using either the blade or just the bolt.

One thing I do not think has been suggested, remove the bolt from the center spindle and one other. Compare the two bolts are they the same length or by chance is the center one little longer? Does the other bolts have a washer this bolt does not? Take something even small Phillip screw driver and message the depth of the threads on both spindles. The center one may not have been drilled or taped as deep as it should have or they may be some foreign material in there. Swap the two blades, could be the center blade is not the proper thickness. Some after market blades are not as thick as the OEM blades are and that may be the issue.

I assume (dangerous) you have check to verify the blade mount is not broken lose from the spindle allowing it to turn. No idea if yours is welded on or has key or what.

 

[jcummins]

I noticed just today, an area which was quite a bit taller because I cut it ever, 2nd to 3rd time, wasn't cut as cleanly as it should have been....and yep, it looked like it was the center blade not cutting cleanly.

I need to do some checking on mine as well. Won't get to it until the weekend.

 

[JOHNTHOMAS]

Mine is now cutting terribly but all three blades are cutting. Grass this time of years gets like strings, tough strings and not sharpening blades also gives me that great bad cutting performance. Sharpen and inspect all three blades before deciding there is a problem with the mower and make sure your at full throttle and see if slower instead of faster makes a difference, jc.
The washer holding the blades on is cupped. Turn it upside down and it isn't going to hold. Don't get it tight enough and it isn't going to hold. Reason I use Ryobi/Craftsman battery or generic air impact wrench to remove and tighten blades on mowers.

 

[ProjectKing]

The other two blades on the outside do not turn when I tighten the blade bolt if I have them blocked

Yeah either cup washers are shot, the bolt is bottoming out, bolt or spindle thread is bad. The bolt washer assembly is not clamping down on the blade.