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NoTies · 15-11-2012, 13:46

Quote:

Originally Posted by thaisail

To answer the question posed by others, I have only one cutless bearing and the new 27 HP Beta engine is mounted on rubber engine mounts.

OK, whole different ballgame. If you have only one shaft bearing and flexible engine mount then you MUST NOT use a flexible coupling. It is a surviveable mistake to use one but much better for drivetrain lifespan to use a solid coupling.

philocat · 15-11-2012, 14:27

Suggest you look at Vesconite, a high density low expansion type of nylon? plastic used on big ships too!

Quote:

Originally Posted by Acushla

Jd1
The earlier post advising the use of Vesconite is a good one and worth doing when you need to change the bearing.

After recently being quoted ~$150 for a duramax rubber type (shipped interstate within Aus) I opted for a vesconite one. Cost $94 for 250mm 35mmID OD55mm for machining to 1-1/2" shaft and will almost make 3 bearings. Since you will need to turn the OD to suit like me the extra cost of machining the ID to fit shaft is no issue. I suspect you may be able to buy cheaper in States with the inflated retail situation here in aus. The vesconite can even run dry or more commonly in water ( or oil in my situation) depending on the PV (pressure velocity ) requirement and avail in many sizes

motion30 · 15-11-2012, 15:26

Why replace the shaft ? propshafts are straightened all the time, find a machinst who will do so no big deal

delmarrey · 15-11-2012, 16:22

Quote:

Originally Posted by thaisail

Excellent information that confirms all the things that I have learned so far. The problem in Phuket and all over Thailand is the same as all the fake Rolex watches. How do you know if the shaft material is 316 or 304? I asked the guy at the shop that had the 316 shafting for documentation to prove that the stainless was 316 and he just laughed at me. However, another Thai friend who has another machine shop told me about an acid that I can buy locally that when applied to the stainless 304, it will turn red and when applied to high grade 316, it will turn black. Has anyone heard of this? Or any other way to identify the grade of stainless.

Get a strong magnet like what's used on pen magnets. 304 will have just a little bit of pull, where 316 will not have any pull. It would be best to have the two metals side by side as a standard.

And nitric acid will turn a yellowish color fairly quick on 304 and not so much on 316. I don't know of anything that will turn SS black except salt water, black oxide or a SS patina. And nitric acid will turn a greenish color on monel.

thaisail · 21-11-2012, 17:07

Quote:

Originally Posted by NoTies

OK, whole different ballgame. If you have only one shaft bearing and flexible engine mount then you MUST NOT use a flexible coupling. It is a surviveable mistake to use one but much better for drivetrain lifespan to use a solid coupling.

Now, I am in big trouble. My friend just bought a brand new Centaflex coupling and we are installing it today on his boat to replace the original type that had been on the ship with the old engine since it was new. I new Beta engine bobtail was fitted on flexible engine mounts and bolted up to his old Hurth gear box. From what you are saying, he should direct couple his shaft to the gear box and you are the 2nd person to advise me to do the same. But there are plenty of others who are qualified engineers who still recommend the use of this type of Centaflex coupling including the Beta marine engine factory who sell the coupling with their engines and recommend them, even for those of us with only one bearing. Please can you explain in more details why this Centaflex coupling is not recommended before I install the second one on a different boat. I can see the point of having a dynamic between the rubber engine mounts and the rubber coupling. Perhaps that was the cause of the vibration that I had when my boat sat in the water for more than 3 months without rotating the shaft!

delmarrey · 21-11-2012, 17:22

Quote:

Originally Posted by NoTies

OK, whole different ballgame. If you have only one shaft bearing and flexible engine mount then you MUST NOT use a flexible coupling. It is a surviveable mistake to use one but much better for drivetrain lifespan to use a solid coupling.

Not entirely true!
I ran my old VW (pathfinder) motor with a single cutless bearing with a flex coupler for lots of hours. When I pulled everything the coupler still looked new. For small motors I haven't seen or heard of any problems. It's the big HP motors on power boats where flex couples have a problem.

BTW All motors have flexible engine mounts. Some just softer then others. e.g Yanmar. And a lot of people change those over to the R & D mounts from PYI.

Cheechako · 22-11-2012, 11:44

Quote:

Originally Posted by DeepFrz

Identification Tests for Stainless Steels
Leave it to google...

The only thing I would add is that most 300 series SS's I have seen WILL BE magnetic to some dgree from slightly to quite magnetic if they have been cold worked. So a piece of 3/8 x 2" wide bar stock may be pretty magnetic if the bar stock had a cold pass at the factory. (which many bar stock shapes do)

NoTies · 23-11-2012, 16:50

Quote:

Originally Posted by thaisail

Now, I am in big trouble. My friend just bought a brand new Centaflex coupling and we are installing it today on his boat to replace the original type that had been on the ship with the old engine since it was new. I new Beta engine bobtail was fitted on flexible engine mounts and bolted up to his old Hurth gear box. From what you are saying, he should direct couple his shaft to the gear box and you are the 2nd person to advise me to do the same. But there are plenty of others who are qualified engineers who still recommend the use of this type of Centaflex coupling including the Beta marine engine factory who sell the coupling with their engines and recommend them, even for those of us with only one bearing. Please can you explain in more details why this Centaflex coupling is not recommended before I install the second one on a different boat. I can see the point of having a dynamic between the rubber engine mounts and the rubber coupling. Perhaps that was the cause of the vibration that I had when my boat sat in the water for more than 3 months without rotating the shaft!

With 2 shaft bearings the shaft is held in line with the engine, with only one bearing and a flexible coupling there is no satisfactory way of keeping the shaft inline with the gearbox output. This can lead to shaft whip. As I said, not a deal breaker, especially on a smaller engine if the alignment is spot on but I would personally not use a flexible coupling, if for no other reason than it is not needed and is another maintenance item.

NoTies · 23-11-2012, 16:53

Quote:

Originally Posted by delmarrey

BTW All motors have flexible engine mounts. Some just softer then others. e.g Yanmar. And a lot of people change those over to the R & D mounts from PYI.

Sorry but wrong. Solid engine mounting is very common, especially on commercial vessels. Flexible engine mounts have only relatively recently become popular.

mikereed100 · 24-11-2012, 07:37

Quote:

Originally Posted by motion30

Why replace the shaft ? propshafts are straightened all the time, find a machinst who will do so no big deal

I was wondering the same thing. Unless the shaft was damaged when removed it would be a simple matter to straighten it. I'm sure you know of a good machinist in Phuket. Luck, down Ratanachai way, comes to mind, as does the owner of AME in the Boat Lagoon.

thaisail · 24-11-2012, 19:00

Quote:

Originally Posted by mikereed100

I was wondering the same thing. Unless the shaft was damaged when removed it would be a simple matter to straighten it. I'm sure you know of a good machinist in Phuket. Luck, down Ratanachai way, comes to mind, as does the owner of AME in the Boat Lagoon.

Khun Luck has welded on the shaft 3 years ago when the new Beta engine was fitted. He does not want to repair again because he thinks that the shaft will be too weak from heat stress. Besides a new shaft of 316L in Bangkok costs only 1700 baht plus the machine work to put keyway, taper and threads. Khun Luck will also make a new brass nut! I think the total cost will be less than 3000 baht or $100. I am only worried about the quality of the shaft but they say that the shaft will have a factory stamp from either Japan or Korea. I think Luck is quite capable of making the new shaft. Also Khun Wiwat from AME as well. Thanks for your advice. You do recommend the best machine work of Phuket!

NoTies · 24-11-2012, 20:12

Quote:

Originally Posted by thaisail

Khun Luck will also make a new brass nut!

Please tell me they meant to say bronze nut, not brass.

captain58sailin · 24-11-2012, 20:46

I have worked on plenty of old commercial boats and they all had rubberized motor mounts. It is not enough flex to adversely affect the alignment of the gearbox/shaft coupler. There may be some initial inertial flex. On my own commercial fishing vessel the alignment was so good that it was smooth as a babie's behind underway so there was no need for the flexible coupler.

NoTies · 25-11-2012, 02:36

It may be a geographical thing. Most every commercial boat I have worked on over 40' had solid mounts.
BTW, flexible coupling in boat drive trains are not installed principally for anti vibration. They are there to ensure no excessive bearing wear on a multiple bearing shaft set up with flexible mounts. Salesmen and well meaning amateurs will tell you different but speak to an experienced marine engineer if you want the facts.