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Author Topic: Finally replacing the Martec prop  (Read 204 times)

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Robert Mann

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Finally replacing the Martec prop
« on: September 08, 2020, 08:20:08 PM »

I have finally got around to replacing the Martec prop and PSS bellows.  Coupling came off easier than i had planned, PSS came out as expected, the propeller needed a little heat, 3 jaw puller and a good rap on each side to spring it loose.  Then came the unplanned surprise. To fit the Martec the installer cut off the end of the shaft where the cotter pin fits, meaning there is no cotter pin hole in the threaded part of the shaft.  I have just sufficient threads for a narrow and thick propeller nut, so that's good, but i will have to drill through the outer nut and the stainless shaft threads to lock the nuts with a cotter.  Has anybody any experience in drilling stainless with a hand drill?  Or has anyone tried different locking methods for prop nuts? I don't want to consign my nice new Campbell Sailor to the deeps.
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Catalina 34 MkII, Indigostar, 2002 no 1622

KWKloeber

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Re: Finally replacing the Martec prop
« Reply #1 on: September 08, 2020, 08:55:22 PM »

My experience is that the key to drilling s/s is what my s/s fabricator buddy taught me 15 yrs ago.

* Use a cobalt drill.
* Start small and enlarge the hole with subsequent larger bits.
* Buy extra bits, they dull and can snap if gotten stuck.
* Use moderate pressure and slow speed, donít try to Trush it. Heat buildup will cook the bit.
* Use a cutting oil that has sulfur content. That dissipates the heat of drilling.

The friction of a correctly lapped prop/shaft it what keeps the prop on the boat and out of the deep. See http://tinyurl.com/LAP-PROP

You can use a prop nut and jam nut to lock it (if they both fit.)

-k
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scgunner

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Re: Finally replacing the Martec prop
« Reply #2 on: September 09, 2020, 09:48:37 AM »

Robert,

Under the heading of different ways to skin a cat, I'd take it to a machine shop.
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Kevin Quistberg                                                 Top Gun 1987 Mk 1 Hull #273

Robert Mann

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Re: Finally replacing the Martec prop
« Reply #3 on: September 09, 2020, 02:09:46 PM »

Ken, that's about where I am with it.  I'm going to lap the prop to the taper, then torque it up with big nut, remove the nut, add red loctite to the small nut and tighten it up, do the same with the big nut. After that, drill through the big nut and the shaft with 1/8" drill and cotter  pin it.  That way if I have a drill casualty half way through, the combination of well lapped, tight, loctite and a busted bit should hold it in there.  Red loctite gives up with a little heat so if there's a next time that's the way to remove the prop or cut the shaft and replace

Scgunnar, the problem isn't the machining of the shaft that's a simple project if it's out of the boat, it's the time and space to drop the rudder to get the shaft out.  Believe me, I would rather replace the cobbled up shaft, but it ain't happening this time.  I can't see sneaking the stainless shaft past the the rudder on a Mk2.Sent

Note to anyone fitting a Martec folder.  The standard shaft will need cutting and there is no return to a normal prop without the above process, or replacing the shaft.  Plan accordingly!
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Catalina 34 MkII, Indigostar, 2002 no 1622

Noah

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Re: Finally replacing the Martec prop
« Reply #4 on: September 09, 2020, 05:05:57 PM »

Donít know about a MKII, but on a MK I, you can remove the shaft without dropping the rudder IF YOU REMOVE THE CUTLASS BEARING FIRST.
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Robert Mann

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Re: Finally replacing the Martec prop
« Reply #5 on: September 12, 2020, 03:24:49 PM »

So here is what I did.  I removed the offending folder and lapped the new Campbell Sailor prop to the shaft, using fine valve lapping compound.  Got a pretty even and complete engagement with blue.  After that I fitted the key and tightened the prop using the big nut and a block of wood against the hull. Then I realized that the brass nuts were not really well machined and they did  not touch the prop face evenly, neither the big or small nut.  In addition, I chickened out of drilling through the big nut and the stainless shaft in one go, figuring that was a good recipe for a broken drill bit.  I faced off the big nut by 1/8" and then installed it, with the machined surface against the prop making a complete contact.  I added a little Loctite and tightened both nuts.  I'm sure we can debate the fat nut, thin nut order topic, but...  Then I filed a flat through the threads on both sides of the shaft and center punched and drilled it using a Cobalt drill bit from Milwaukee Tool, bought at Home Depot and plenty of good quality tapping and cutting oil.  If you try this use the slowest speed the hand drill will turn and you will get a nice spiral chip, indicating a good cut.  It took probably 20 minutes to get through 3/4" of shaft.  I used 2 bits, because I got paranoid just before breakthrough, 1 would have done it.

I replaced the PSS dripless bellows as they had been in place for 17+ years, which is too long.  The bellows looked good but I was getting some water past the seal in reverse when backing down, so the spring could have degraded.  Interestingly the initial installer failed to put the safety grub screws into the stainless seal face and had positioned the bellows too far down the shaft log, but it all held together for 17 years.  I was going to install a Buck Algonquin split coupling, but when the PSS was correctly positioned room was at a premium and I didn't want to risk damaging the PSS by forcing it all together.
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scgunner

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Re: Finally replacing the Martec prop
« Reply #6 on: September 13, 2020, 01:56:36 PM »

Robert,

It looks very pretty, the problem I have with it is the gap between the end nut and cotter pin. There's nothing to keep that end nut(followed by the prop nut)from vibrating loose and working it's way down to the cotter pin. I think I'd find a taller crown nut to replace that skinny end nut, that way you could drive the cotter pin through the shaft and top of the crown nut for a snug fit. If you can't find a crown nut tall enough for your application you could always use washers to achieve the desired fit.
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Kevin Quistberg                                                 Top Gun 1987 Mk 1 Hull #273

Robert Mann

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Re: Finally replacing the Martec prop
« Reply #7 on: September 13, 2020, 03:17:15 PM »

SCGunner, you are correct, I have washers on the shopping list this week, just to make it look good.  However, the original shaft had a non threaded part on the end, which as you can see was turned off the shaft to fit the bucket nut from the Martec, into which the cotter was fitted.  This means even in standard form they never would have had a snug fit.  Believe me, if this lot moves at 30 ish HP I would be very surprised.
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scgunner

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Re: Finally replacing the Martec prop
« Reply #8 on: September 14, 2020, 07:33:04 AM »

Robert,

I was thinking more of vibration than horsepower, let's hope you're not surprised.
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Kevin Quistberg                                                 Top Gun 1987 Mk 1 Hull #273
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