OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Four Stroke Trimmers & Brushcutters Rattly BBT 4 stroke brushcutter

Found at tip, BBT Brushcutter, 36cc 4 stroke, clone of Honda UMK435, wasn't running when found but got motor purring perfectly with some carb TLC

Two problems, maybe just one though.

Problem One. Horrible rattle and shake at bevel gearbox end, goes all the way though the rev range.

Using same metal blades and line spools they spin perfectly on my three Hondas but not on the BBT so they aren't out of balance.

Took the bevel gearbox off the drive tube, pulled out the splined drive shaft, looks perfectly straight.

ProblemTwo. Where the drive tube enters the clutch housing there's a looseness. No axial play but the tube can wobble maybe 5 degrees around inside the motor/clutch housing.

I'm thinking the looseness or angulation at the motor end is inducing a harmonic along the drive shaft/rod causing the racket at the gearbox end?

I can't see if there's bearings or bushes inside the shaft which may be worn and can be replaced, or does the drive rod just sit between the female splines at the clutch end and the gearbox end?

Anyways would love to hear if there's a fix, the motor is running so nicely.

Not sure if it will work on this one but Bruce suggested I weld one up previously as I couldn't get a new housing. I didn't end up welding it I shortened the outer tube so the shaft could fit further along the spline

Hi MM and Norm,

You would have to take the engine connector clutch housing off and check the splines and if necessary as Norm
mentioned weld the shaft to the clutch drum if it's excessively worn also check the bearing in the the engine connector clutch housing.

There are usually plastic bushes in the aluminium tube but normally they don't need replacing.


Cheers
Max.

Thanks for the parts diagram Max.

I tried packing some steel strips in the annulus between the clutch housing and the aluminium tube to make it less wobbly but that didn't help.

Obviously although the BBT clone looks incredibly the same as the Honda they are cheap for a reason and the drive system is probably FUBAR. Pity as the motor goes so well.

Getting in to replace that clutch drum bearing looks a royal hassle and may not fix the problem anyway. Will probably just keep using it until it self-destructs.

It's easier than you think MM ,you undo 4 bolts and remove the circlip then get the clutch drum out and the bearing, if the bearing is
worn out ,but you could just find an old 2 stroke 52cc line trimmer at a tip shop for $10. and use the shaft assembly from that..

Cheers
Max.