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mike check

hurth gearbox or prop issue

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So ive got a thornycroft t33 mitsubishi 2 cylinder and a hurth gearbox. (

The engine runs OK.

but sometimes there is no power in the prop. Push it into gear and very little propulsion the prop shaft is spinning and no power (could prob move about 1/2 mile an hour on a good day with no stream). Pop it back into neutral then back into gear and the prop produces power. (However limited by the tiny engine but you know it moves).

Was thinking its not the gearbox because the prop shaft is spinning either way. But the boats in the water and not coming out for a while so gear bix might be servicable but prop shaft and bearings etc not atm.

Any thoughts appreciated...

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Its a Hurth so I bet its a slipping clutch or other internal problem. Just make sure the control lever is being pushed fully into position by the cable. Maybe time for a PRM mechanical box.

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My Hurth HBW 10 gearbox failed in exactly the same way. I couldn't change it for a PRM because i need more of a drop between the input and output than the PRM equivalent provides. Fortunately for me a good HBW 250 which has the same dimensions and very similar mounting hole centres came up on this site.

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Thanks for the suggestions.

I went to test it again earlier. Checked the control lever was engaing on the cable. Seemed fine.

Checked the prop. Was not fouled or loose.

Then ran the engine with the weed hatch open...(no i did not sink). And it worked in both gears each time.

Ran in in gear for half an hour and checked again. Forward and reverse. Almost annoying that it worked normally. I was moored  up during this test so my new thinking is the prop getting jammed up easily when moving.

Will take it for a propd spin  at the weekend.

Thanks

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The reason I asked about reverse was that my first Hurth failure sounds a bit like yours. The box would seemingly engage forward gear, and the prop shaft would spin at idle, but winding up the revs had little effect - the engine would speed up but the prop didn’t and the was no “oomph”. Reverse worked fine. Diagnosis was badly worn forward clutch plates. My second Hurth (actually a ZF) failed on reverse, when the prop picked up something solid in a hasty emergency stop, and stripped some of the teeth on the reverse plates. Symptom there was failure to engage reverse intermittently, with a horrible grating noise. Then I switched to a PRM :)

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