Hurth ZF-25 Problem

[Rocketman]

Hi all, I am looking for advice on a ZF-25 transmition that I just aquired. I found a replacement engine and transmition for my boat. The engine was removed because it was "Froze Up" but it was suppost to have a new or nearly new transmition. The ZF-25 in question. After looking everything over I could see that the transmition looked new or nearly new and the engine also looked great but like the guy said the engine would not turn over. After getting it home for indepth evaluation, it now seems the transmiton is Froze Up and the engine is turning over great. I removed the transmion and the propeller end turns freely while the engine end will not turn at all. The engine turns great without the transmition. So before I tear into the transmition does anyone have a rebuild manual for it and and ideas why a nearly new transmition would freeze like this. It is posible the transmition was ran without oil. Also the shifter seems to work great, it shifts into nuteral, forward and reverse easily but like I said before the motor end will not turn in any postion.

[Tynesider]

Hi Rocketman

Not sure about the ZF-25 but I have a masters degree in the Bloody ZF 10 !

Just a long shot but what about the thruster plate? it will not be the first that I have seen to be the root of many problems and one of the last places to look.
Good luck

[Rocketman]

Mike
Thanks for the reply. Are you talking about the plate that is attached to the fly wheel? Or is there something in the transmition that is called the thruster plate? When I pulled the transmition off the engine, the shaft that goes into the splines of the flywheel will not turn at all. With the transmition not connected to the engine in any way the motor turns over easy and actually runs great.

[perchance]

He may be referring to a thrust bearing or washer.

[Sailmonkey]

If the input shaft on the transmission doesn't turn but the output shaft does, you more likely than not have seized bearings. If neither input nor output shafts turn you've got stuck clutch plates.
It's easy to open up the transmission to have a look inside, just pull all of the bolts and nuts from the perimeter of the housing, then remove the bearing cap bolts, and seperate the housing. Whatever the problem is should present itself.

[Tynesider]

Originally Posted by Rocketman

Mike
Thanks for the reply. Are you talking about the plate that is attached to the fly wheel? Or is there something in the transmition that is called the thruster plate? When I pulled the transmition off the engine, the shaft that goes into the splines of the flywheel will not turn at all. With the transmition not connected to the engine in any way the motor turns over easy and actually runs great.

Hi Rocketman

Yes thats what we call the 'drive plate' or 'Thruster plate' is attached to the flywheel, there are usually two types one with a like Polypropylene disc as on mine and picture below or the other type which has springs in it.

Most likely on your larger gearbox you will have springs, If the springs are broken or siezed then you will not get drive from the engine to the gearbox, if the box has siezed it 'might' also have sheared the drive plate mounting bolts.

In any case 'IF' you need to replace the gearbox (hope not) I would also recommend replacing the thruster/drive plate as 'if' that goes in the future you will have to take everything out again.

I am not sure who's drive plate you have, you need to check the part number that you will find on the plate whichever type it is, maybe a ZF or R&D, this is the company that actually makes the drive plates in the UK and you can buy direct:
R and D MARINE : Marine Damper Drive Plates


Hope this might help
Mike

Spring Type drive plate

Disc type drive plate

Thruster plate connected to the engine

Thruster plate installed ready for gearbox and coupling

Complete installation