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Old 28-06-2016, 10:01   #16
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Re: Repeated Gearbox Failure Caused By Prop?

The 1000 RPM difference between WOT in neutral and in gear is too much. Normally indicates that there is too much prop for the engine. This can damage the engine (lugging) but don't know about it hurting the transmission. Most diesels have governors and you should get essentially the same RPM with or without load. Cruising around 400 RPM under WOT RPM is what many engine manufactures recommend.
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Old 28-06-2016, 10:57   #17
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Re: Repeated Gearbox Failure Caused By Prop?

V drives are very difficult to align, because you can't easily see and get to the shaft and bearings. That is made more difficult because it often impossible, through lack of clearance, to install a flexible coupling at the gearbox drive flange to absorb engine movement on the flexible mounts. It could be anything in the drive train, but after replacing all of the broken or worn bits and pieces, including the engine mounts, I would concentrate on alignment and if you can find a flexible coupling that will fit, install it. It sounds wrong, but I'd even consider replacing the engine mounts with one grade stiffer, to reduce engine-gearbox assembly movement, even at the cost of a bit more vibration being transferred to the hull.

If it was bad enough, I'd even think about replacing the v-drive with a saildrive.

Good luck

John Mardall
Vetus Group.
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Old 28-06-2016, 11:24   #18
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Re: Repeated Gearbox Failure Caused By Prop?

This string has me thinking, i have the same problem. Reading my manual, my boat came with the folding prop, however i get a vibration and noise when in gear, and just replaced the drive on my volvo md22l. How do you check propeller size and secondly, if the shaft bolts up with no apparent adjustment for alignment, it seems the coupling John describes would be standard.

John, I looked at your site, gonna be giving you a call.
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Old 28-06-2016, 13:58   #19
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Re: Repeated Gearbox Failure Caused By Prop?

We have a flexible coupling at the gearbox flange. Engine mounts were replaced 18 months ago. Cutlass bearing replaced and re-aligned last year. After all the gearbox rebuilds I am pretty good at setting up the alignment, so I am confident that it's not an alignment issue. I am curious though - how does poor alignment cause thrust washer wear?
The guy who did the last rebuild suggested that more oil would make the box run cooler, and even put a new mark on the dipstick about 3/4" higher. We followed his advice, but I now think he was wrong. The box actually ran hotter with excess oil, and the seals leaked. He also recommended using 10W40 instead of the ATF spec'ed by Hurth. I tried it during the last stages, and had to change straight back to ATF because it made the slipping much worse. Not sure if it would help on a new box. You would think Hurth knew what they were doing with the original spec.
Thrust washers assembled back to front would be an issue, but the current repairateur should pick that up. I'll ask him. Would it cause steel particles in the oil? I didn't see that.
Has anybody seen cases of gearbox failure due to folding prop or prop too big?
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Old 28-06-2016, 14:35   #20
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Re: Repeated Gearbox Failure Caused By Prop?

If you have room, add one of those "drive-saver" donuts. they take up any minor misalignment.
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Old 28-06-2016, 16:14   #21
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Re: Repeated Gearbox Failure Caused By Prop?

Quote:
Originally Posted by Jumbalara View Post
We have a flexible coupling at the gearbox flange. Engine mounts were replaced 18 months ago. Cutlass bearing replaced and re-aligned last year. After all the gearbox rebuilds I am pretty good at setting up the alignment, so I am confident that it's not an alignment issue. I am curious though - how does poor alignment cause thrust washer wear?
The guy who did the last rebuild suggested that more oil would make the box run cooler, and even put a new mark on the dipstick about 3/4" higher. We followed his advice, but I now think he was wrong. The box actually ran hotter with excess oil, and the seals leaked. He also recommended using 10W40 instead of the ATF spec'ed by Hurth. I tried it during the last stages, and had to change straight back to ATF because it made the slipping much worse. Not sure if it would help on a new box. You would think Hurth knew what they were doing with the original spec.
Thrust washers assembled back to front would be an issue, but the current repairateur should pick that up. I'll ask him. Would it cause steel particles in the oil? I didn't see that.
Has anybody seen cases of gearbox failure due to folding prop or prop too big?
This is purely theoretical, but according to the manual:

"The thrust force required for obtaining positive frictional engagement of the clutch discs is provided by a servo-automatic system.

This essentially comprises a number of balls which, by the rotary movement of the external disc carrier, are forced against inclined surfaces provided in pockets between the guide sleeve and the external disc carrier and in this way, exert axial pressure. The thrust force, and as a result, the transmittable friction torque are thus proportional to the input torque supplied.

Due to the cup springs supporting the clutch disc stack and a limitation of the range of axial travel of the external disc carrier, the thrust force will not exceed a predetermined value."




You don't indicate the nature of the failure, other than worn thrust washers, but if it is also slippage, it seems that the above paragraphs might indicate that it could be the combination of a small input torque and a large propeller (folding or not) that is causing the problem. It is possible that the transmission is oversized for your application, and that a smaller prop could give you a longer service life for your existing transmission.

Are the used friction discs glazed but otherwise close to specified thickness?

I would rely on Hurths' specifications for oil (ATF), especially in your application, as it seems that in your case you require more friction, not less.

Again, this is purely hypothetical, but is based on a lot of mechanical experience.
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Old 28-06-2016, 22:57   #22
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Re: Repeated Gearbox Failure Caused By Prop?

I have an HBW25 on my boat, wore out the friction plates in 1 season because the linkage was not adjusted properly. When I shifted to forward it did not go all the way into gear allowing a little slippage,and I had a rebuild after 1 year. It lead to a very different anchoring experience, I got into the old harbour in Mazatlán and shifted to neutral, when I went back into forward, nothing, so I shifted into reverse and backed up doing circles till I could drop the hook ( really bad prop walk )
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Old 29-06-2016, 06:57   #23
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Re: Repeated Gearbox Failure Caused By Prop?

That mechanic wanted to find fault with all VeeDrives short comings. His suggestion didn't pan out, but the addition of an oil cooler and changing the oil at half time won't have any negative consequences.
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Old 29-06-2016, 08:43   #24
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Re: Repeated Gearbox Failure Caused By Prop?

I would say check both shaft alignments and oil levels. altho I did have a friend bought an old boat and had a mechanic install a new drive train. It had a Vdrive and they had gotten a right hand prop. so the mechanic just reversed the gear shifter and the owner was non-the wiser, till the V drive burned out. luckily he had the reverse gear checked and only had to do a minor rebuild on too. They are not made to go in reverse for long periods. He now has a left hand prop and has turned the shift leakage back around, with no problems for the past year. He motors the ICW and the tenntom quite a bit.
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Old 10-08-2016, 02:21   #25
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Re: Repeated Gearbox Failure Caused By Prop?

An update for anyone still following this thread:
The expert mechanic in Noumea stated that the box was "like new inside" and he couldn't say why it was slipping. He reassembled it and I re-installed it. A bit worrying when I pulled out the dipstick and found it coated with dirt from his bench. Also noted that the little plug at the front that you open to check end float had not been touched. Anyway I filled it with oil and tried it. Forward sounded rough but OK. Reverse stalled the motor. Pulled it out, drained it, and gave it back to the mechanic. Checked the oil and found visible specks of foreign material. Not happy, but didn't make waves because we are at this guy's mercy at this stage. He is not a bad mechanic, just not as expert as he thinks he is. I'm thinking "bush mechanic", he thinks "experienced gearbox expert". Anyway, second time round it worked OK except for a massive oil leak through the quill shaft. Not really his fault, this is a design fault in the Hurth vee drive which they fixed in the ZF vee drive. Third go, with some sealant on the quill shaft thread and we called it good enough, paid the (reasonable) bill, changed the oil twice, and cleared outbound for Australia. Now in Brisbane, 30 engine hours later, the box still works but sounds rough at idle. We don't trust it to last, so we have taken the plunge and ordered a brand new ZF15MIV from ZF in Sydney. The one with the same reduction ratio would have been 2 months shipping from Italy, plus $1800 extra to cover the shipping. Bearing in mind the comments to this thread about the engine lugging due to being over-propped I inquired about the next ratio, and hallelujah they had it in stock.
This thread asked the question "can the prop cause gearbox failure?". I'll try to remember to report back in a couple of year's time whether our gearbox woes were fixed with the new box, or if they aren't whether the prop is still one of the suspects.
Thanks everyone who contributed.
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