Tanaka hedge trimmer weird blade shuddering problem

[mulcher]

Tanaka THT-2000 hedge trimmer blades shudder at full speed.

 

Background

Water had got into the gear-case over the winter, causing the drive pinion and bearings to rust and seize solid.

 

I replaced the clutch drum & pinion assembly and both bearings, and cleaned up the cutters, the oscillating gear and the guide plate. (The clutch drum & pinion assembly and the bearings were driven into position using heat/cold method.)

 

The bearings & gears turn OK and the blades move easily so I can’t feel any binding; and at anything up to about two-thirds revs its all working perfectly with little or no vibration…

 

Problem

…But at full throttle the blades shudder every few seconds, shaking the whole machine. It’s hard to see exactly what’s happening due to the speed-blur.

 

What I’ve tried

I thought it might be clutch slipping and re-engaging due to the new clutch drum not bedding in with the existing centrifugal [metal] clutch. So I emery-papered the drum and clutch but it hasn’t helped.

 

I experimented with the cutter fixing bolts, slightly tightening then loosening either side of the required half turn out but that didn’t work either.

 

Help please – I’m at a loss to explain or fix this problem, has anyone come across this phenomenon before on this or other makes?

[Stubby]

Blade bent/out of balance ? Try another known good blade ........

[GardenKit]

A few things I would check

 

Make sure that cam spindle (item 6) is correctly set into the housing (item 1). if its loose then the cam teeth may be slipping against the pinion (item 5)

 

Ensure that the bottom plate (item 11) is on the right way up and not distorted. If its wrong it can allow the blades to slip off the edges of the cam.

 

But the most likely cause is damage to the clutch drum/pinion (item 5) when fitting. If the drum edge was tapped, rather than the pinion shaft when driving it into place its possible that the weld between the pinion and drum has fractured. The pinion will still stay sort of riveted to the drum, and may drive after a fashion, but slip under load. Worth a check.

[mulcher]

Thanks guys, I'll go back and check all of those things.

[mulcher]

A few things I would check

 

[snip]

. . . Ensure that the bottom plate (item 11) is on the right way up and not distorted.

If its wrong it can allow the blades to slip off the edges of the cam . . .

[snip]

 

That was it Mr GardenKit, the bottom plate wasn't the right way up!

With the plate's bevel facing outwards it left room inside the gear case for the blade to slip off the cam. Now I've corrected that it's running perfectly.

 

Thank you so much for the exceptional diagnosis, you're a star.