Help Required - Hurth HBW100

[ciclon1942]

I have a problem with a Hurth HBW100 gearbox which is leaking oil from the back seal near to the coupling. The gearbox is attached to a Westerbeke 4-107 which I understand to be similar to a Perkins 4-107.

There are a couple of things, firstly the leak, which although a problem does not stop me going out. I am sure there is no problem with the oil as we are now running a constant loss system. If possible I would like to know if by replacing the seal we will cure the problem or is the leak a sign of a far worse problem?

I also think that the prop which is currently on is of the wrong pitch as our speed reduces from about 5.5 to 2.5 knots when we head to windward in anything aproaching 20 knots. The CAV pump on the engine indicates that it is rated at 1850 RPM but I am able to rev the engine a couple of hundred RPM higher than that if required but with no increase to the speed.

I have been offered a ZF12M which I am told will fit straight in if this is the case could anyone tell me what size prop and pitch I would require if I were to change gearboxes.

Any help would be much appreciated.

[S/V Elusive]

Titles are important - I've changed yours to be descriptive of your problem instead of so vague.

[perchance]

The engine and propshaft are out of alignment. A common cause of output shaft seal failure.

[Mark Zarley]

The rear seal failure is usually caused by an out of spec bearing on the output shaft of the trans. The failure of the bearing could have been caused by mis- alignment with the output shaft. Replacing the seal will not fix the problem.

[shakey doug]

If the rear gbox bearing is noisey or showing any sign of movement or has had bilge water around the rear of the box you may have the cause of the seal leak as previously mentioned shaft misalignment will also cause this problem.The windward speed of your vessel is dependent on so many variables boat size, gbox reduction ete, most pleasure boats run 2:1 ratio boxes most 4107s cruise at about 2.200 --2400rpm or a sweet spot there abouts. Unloaded max rpm should be around 3600 rpm could be to 4000 depending on fuel pump setup. A ballpark on prop size with 2:1 box 16''x12'' again there so many variables before a correct size selection can be made.

Doug.