Vibration on Kubota G1800

[cwhiley]

I recently purchased a Kubota G1800 riding lawnmower at an estate auction. 855 hours on it. Non running. Put a new battery in it, changed the oil, and my mechanic messed with the PTO switch and she fired right up. Mows great too. Got it for very little money ($425) and after the battery and paying my mechanic I’ve only got $600 in it.


Now for the bad. There’s a significant vibration. If I run it at full throttle or 100% it’s an intense vibration I can really feel in the seat. Sorta significant at very low throttle too but fairly smooth around 40-70%. Can’t be the PTO because it does it with it disengaged.

What’s the culprit? Have I got a major problem? Is it the driveshaft? Sorry I sound clueless as I’m not very mechanical.

 

[85Hokie]

S0,

engine idle - no blades spinning, vibration?

ramp up the rpms and the vibration increases?

Blades on - does vibration change at all?

Does the frequency increase with engine rpm?

Have you lifted the hood and looked to see if anything is amiss?

Check a motor mounts while engine is off

 

[Fordtech86]

3 cyls are naturally hard to balance.

 

[GeoHorn]

3 cyls are naturally hard to balance.

Yep! They VIBRATE!

Smooth out about 3K rpm.

 

[lugbolt]

there's a drive shaft that runs from the engine back to the transmission. It has 2 little bitty u-joints in that shaft assembly. 4 common points to address are the U-joints, the rear yoke, and the front stub (bolted to the crankshaft pulley) and it's yoke. all 3 points will cause significant vibration, exactly as you are describing. The front yoke assembly has a grease fitting on it that never gets greased. Similarly, the PTO shaft and the PTO drive assembly where it goes through the front axle.

That shaft is buried way up inside the chassis. Easiest access is to remove the rear fender and the mower deck. Probably a good idea to pull the fender anyway and power wash the transmission, as people often spill fuel and it runs down onto the trans and dirt sticks to it, creating a nasty thick residue that reduces transmission cooling capability. There's also a plastic fan on the drive shaft at the transmission end that should be inspected as well.