Hurth HBW 50 R2 gearbox removal

[GrahamW]

Members of this form have recently give me some good advice re problems with my Hurth gearbox and I now want to remove it for sending off for a complete overhaul, i.e. new plates, seals, gaskets and thrust washer.

I am hoping to move the prop shaft back 3 - 4 inches to give me enough room to get the input shaft free from the engine, thus avoiding having to move the engine forward.

But I'm not clear how to uncouple the box from the engine itself.

Should I undo the bolts holding the large round plate to the back of the engine? See pic # 005 attached.

Or something else? Though at the moment I can't see much by way of alternative.

Apologies if this is a dumb question. I have got fold of a Hurth manual which gives great detail about how to assemble the internal mechanism of the box, but contains nothing on the basic nuts and bolts of how to detach from the engine itself. I am out in the wilds of Donegal where marine engineers are a bit thin on the ground and want to avoid making any basic errors.

Regards,

Graham

[perchance]

The bolts on the large flange hold the transmission to the engine. Remove those and any cables hoses etc. and it should come off.

[GrahamW]

Perchance,

Thanks for that. Do you know how the flange, ( I assume that means the large round plate on the back of the engine ), attaches to the transmission?

The flange is not shown in the Hurth manual as part of the transmission.

Graham

[sailr69]

done this, remove the adapter plate with the trans, the trans is bolted to the adaptor plate from the inside. also, before you send off for rebuild, make sure they have parts for this. I was told by rebuilder parts are not available anymore for the hurth version. the replacement is ZF but parts are not interchangeable, Trans input shaft goes into a dampener plate which is the same as a clutch plate without the clutch lining. replace this as well( not too expensive ) but will save you time in the future to replace it when it too goes bad. the spline goes into the dampener only perhaps a inch. all you will need to pull the trans.

BTW, get the water cooler for this trans, easy bolt-on from the outside and works wonders for cooling the unit. will last much longer

Good luck, ( not a tough job at all )
Gene

[GrahamW]

Thanks Gene

Just to make sure that I understand, am I right in thinking that by the adapter plate you are talking about the large round plate on the back of the engine?

Graham

[highseas]

The Hurth ZF 6 or ZF 10 is the replacement transmission for Hurth HBW50.Don't bother rebuilding,brand new can be had for around $1100.Remove at bellhousing,about 10bolts,remove hoses,cables,etc.Ihad to remove rear engine mount nuts,and raise rear of engine a couple of inches to remove lower bellhousing bolts. The transmission bolts right in,although output shaft is 1inch further back,meaning propshaft will extend rearwards 1in.,or remove and shorten shaft.Check your gear ratios when ordering.

[perchance]

Originally Posted by GrahamW

Thanks Gene

Just to make sure that I understand, am I right in thinking that by the adapter plate you are talking about the large round plate on the back of the engine?

Graham

You are correct.

[highseas]

Don't reuse the HBW50,it is way to undersized for anything but a small boat.

[sailr69]

yes, the big round plate, 4 bolts are attaching it to the trans. from the inside

[sailr69]

Originally Posted by highseas

Don't reuse the HBW50,it is way to undersized for anything but a small boat.

not true, change the oil every 1 hundred hours and if you install the water cooler it will last longer then you own the boat. DO NOT sail with the gearbox in forward. freewheel it or lock it in reverse. I had mine going on 21 years now. no issues.

[highseas]

Wrong,wrong,wrong.How heavy is the boat?

[sailr69]

Originally Posted by highseas

Wrong,wrong,wrong.How heavy is the boat?

OK, tell me what is going to fail? the gears, clutches, case, splined shaft, shift fork? seals

[highseas]

Clutches for starters,then the thrust washers.I rebuilt my HBW50 at authorized Hurth rebuilder 5 years ago in San Francisco.Finding parts then was almost impossible,finally did though.Lasted 900hrs.The 50 is discontinued,the ZF6 was the replacement until about 1 year ago,now it is discontinued also,and now the ZF10 is the standard replacement model.Did everything right .Always in reverse under sail,changed ATF every 100 hrs,fully in gear in use,babied the thing,as it was my second.Now about to install ZF6.Going synthetic this time.

[brutb]

Apparently Sailr69 is really good on maintaining his equipment since he has used his trans in a Corbin 39 (not a litght weight boat) for 21 years. Just goes to show you if you maintain your equipment it WILL last.

[highseas]

Check the ZF website ,it gives sizing tables,the 50 is a weakling.