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I am hoping the collective wisdom of the forum can help me deal with an issue that has come up regarding my transmission and prop shaft.
I need to replace the Hurth HBW50 transmission on my 1995 Catalina 320. The way I read the spec sheets, the current ZF transmission that is required to handle the rated 29HP on my Perkins M30 is a ZF10M, which looks to be about 25mm longer than the HBW50. The result would be to push the prop about 25mm further from the cutless bearing in the strut underneath the boat.
I have seen some references on-line to a "rule of thumb" that the distance from the bearing to the prop shouldn't be more than 1-1/4 times the diameter of the shaft. (I have a 1 inch shaft, so no more than 1-1/14 inches back.) I think I am pretty close to that distance already, although I can't measure with the boat in the water.
My question is: what is the risk if the prop is more than 1-1/4 inch behind the cutless bearing? It seems like the potential problem would be prop shaft whip if the prop is out of balance. However, I replaced the original bronze shaft with an A22 shaft 2 years ago, and I'm hoping that it might be able to handle the additional distance. In any event, I'm thinking that I'd be able to see or feel vibrations from any problem that might develop.
Also, if a problem developed, is there any reason to believe there would be any permanent damage if I then used the engine to motor to my preferred yard (which is a full day away ), to have the boat hauled, remove the shaft, and shorten it?
Not to drag this off topic, but why does your current transmission need to be replaced? The HBW50 was used in a LOT of boats, and they are rebuildable.
Not to drag this off topic, but why does your current transmission need to be replaced? The HBW50 was used in a LOT of boats, and they are rebuildable.
I am told that the re-build kit for the HBW 50 is $900, and labor would be another $300 - $400. I have a quote for a ZF6 at $1627, and have seen a quote for a ZF10 at $1,750. For a few hundred dollars more, I'd like to have a new transmission and a warranty.
Also, the HBW 50 failed after only 1300 hours, and looking at old spec sheets, I think it too is rated for less than the nominal 29HP of the M30. So I'm thinking the upgrade to the ZF10 might avoid a future failure.
You can cut off the extra length, you might need to replace the shaft flange anyhow.
Prop shafts come in standard lengths so it common to adjust length during replacement.
Master Overhaul Kit for Hurth HBW 5/50/100 Transmissions. It Includes Overhaul Gasket and Seal Kit, Bronze Plates and Steel Plates. This item replaces OEM: 500437.
The above kit includes both the plates and the gaskets...
Meatal Clad Seal for Shift Lever on Hurth Marine Transmissions Fits the following HBW models: 5, 10, 20, 50, 100, 150, 150V, 220, 250 Replaces Hurth original equipment part # 106864
Hmmm. The $900 was quoted to me as ostensibly coming from ZF. But maybe there are better prices available. The quotes you included look like they're aftermarket parts, but I'm not necessarily oppose to that if it saves me $400+, and avoids the problem of the longer transmission. Where did you get those quotes?
shortening the shaft, presuming it can be reused after forcibly divorcing it from the old coupler, is do-able. Need to cut a new keyway in the end, tho.
The Hurth 50 discussion comes up regularly in any forum where lots of a given make of boat use the Universal diesels. Catalinas and Ericsons by the score, and probably others.
I have one of these transmission models on my M25XP with 2200 hours. Might be on borrowed time, no way to tell.
I figure that if the trans croaks, I will decide between some sort of replacement with all the shafting problems... OR just replace the whole drive train with a new Betamarine 25 hp.
YMMV, as they say on the internet.
shortening the shaft, presuming it can be reused after forcibly divorcing it from the old coupler, is do-able. Need to cut a new keyway in the end, tho.
For what it's worth, I would check the specs on the transmission and avoid approaching the upper limits of it's rating. Everyone eventually ham fists the throttle to prevent impact with a dock or need a sudden stop for conflicting traffic, etc. These little trannies take a beating. Beefier is better. Be sure to match the reduction ratio, if you're upgrading.
As for the length, that's a very simple cut at the flange end. The stress can be getting an old flange off, but if it's severely corroded on due to age, your shaft seal and cutlass bearing are probably due too. Perfect time to think about a dripless shaft seal, if you don't have one. At the least, replace the rubber on what you have and start the clock over.
Rebuilt trannies are only as good as the shop that does the work. I have a rebuilt tranny that began leaking fluid in 12 months and the shop does have a good rep. That saga hasn't been resolved yet.
I bet you'll also need a new damper plate, whether you rebuild or go new.
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