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Old 29-04-2017, 16:46   #1
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SD50 - Heavy Throttle Slips

Can anyone give me some insight into this? I have an SD50 that was run really hard with no prop for 10 minutes 6 months ago. Why? Long story,

So today I'm leaving Marsh and have both throttles engaged in forward and the STBD prop wasn't spinning. I took it out of gear and slid it into forward and I could see prop wash. I then throttled up and could hear a thud - and no proportion.

Any ideas? I have the SD50 apart now - first time - wresting with the peening on the end nut. Hoping it is just lapping the cones.....

Thanks for any advice or insight!! _steve
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Old 29-04-2017, 16:54   #2
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Re: SD50 - Heavy Throttle Slips

SD50 has cone clutches and after a while they glaze up and don't engage properly.

To eliminate other culprits, try unhooking the shift cable at the transmission and cycle the lever manual (with engine running) to see if it engages then. If not, you need to overhaul the clutches.

ETA - sorry, just saw you already have it apart. Might as well lap the cones anyway now.
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Old 29-04-2017, 17:08   #3
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Re: SD50 - Heavy Throttle Slips

SD 50's are well known for their cone clutches wearing and then slipping. Get the clutches re-lapped and they should go back to normal.
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Old 30-04-2017, 04:41   #4
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Re: SD50 - Heavy Throttle Slips

Either cone clutch or gear shift cable, happened to ours too
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Old 30-04-2017, 20:53   #5
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Re: SD50 - Heavy Throttle Slips

You said you are in marsh? Where is marsh? If you mean marsh harbor I might be able to help you, if you mean the marsh lands of New Hampshire, i can not.
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Old 30-04-2017, 21:04   #6
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Re: SD50 - Heavy Throttle Slips

I'm in Hopetown - going to take it to Lighthouse tomorrow to try to get that end nut off... if they can't help then I'm over to MH to head to that Yamaha shop as there is supposed to be a guy that works on this kind of stuff.

Can use any help for sure. I'm anchored outside of Hope between the lighthouse and Firefly._steve
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Old 01-05-2017, 06:52   #7
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Re: SD50 - Heavy Throttle Slips

Hi Steve,
I am at man jack. I have all the stuff needed if you need help. I have the lapping compound and the tools with me to get the nut off. I have fixed 3 of these since being in the Bahamas 🇧🇸 I learned on doing mine. We are thinking of heading out today. Let me know.
You can text me or e mail. 508 509 7264 or dan swift@exitrg,com
Good luck, dan
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Old 01-05-2017, 09:03   #8
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Re: SD50 - Heavy Throttle Slips

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Originally Posted by dan swift View Post
Hi Steve,

I am at man jack.

Hey Dan! I just texted.
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Old 01-05-2017, 09:25   #9
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Re: SD50 - Heavy Throttle Slips

Was run hard in gear with no prop. So there was no force to keep the cone firmly pressed and locked to the mating surface on the gear.

I suspect this rapidly wore the surfaces, though how much in ten minutes is the question. A careful inspection may reveal it to be beyond what normally occurs, but hope not. It may be beyond what a good lapping can restore.

A good picture of a brand new cone could help for comparison.
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Old 01-05-2017, 13:13   #10
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Re: SD50 - Heavy Throttle Slips

The Nut on top of the clutch pack can be a problem it is very hard to tap out the locking tab with tools I have on my boat.
REMEMBER THIS IS A LEFT HAND THREAD
I have found that a socket with a standard 1/2 drive breaker bar and a bit of muscle will get it loose.
I have reused the nut but also put locktite on the thread.

Another thing to be very careful with is when reassembling that you get the pinion to mesh properly with the clutch pack gear.
Its a good idea to measure the length of free thread on one of the 4 pinion release studs before initial loosening. it is quite easy to tighten this up when reassembling and for the gears not to mesh.
This is easily established by comparing to the previous measurement If this is the case you need to rotate either the input or output about 5mm this will allow the gears to mesh and then tighten and it will come back to the original measurement when tight.
As these 4 studs are only threaded into a tapped hole at the opposite end to the nut it is possible to unscrew the stud rather than back the nut off, this can give problems.
Ensure you wire brush the exposed threads of the studs before dismantling and put some lubricant on to ensure the nuts come off easily and when the job is completed put grease all over the thread to keep it in good condition for when next you have to relap the clutches.
It is amazing how little lapping you need to remove the glaze approx 10 turns is all thats needed.
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Old 04-05-2017, 07:22   #11
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Re: SD50 - Heavy Throttle Slips

Thanks all -! And Aqua - great insight.

I was able to lap the cones and re-install without too many issues. The second time will be MUCH easier....!

Tested the SD yesterday for 45 minutes without any slipping..... headed to FLL on Sat.... that will be the real test!
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Old 04-05-2017, 21:21   #12
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Re: SD50 - Heavy Throttle Slips

If you got 45 mins You will most likely get 250 hours. Well done. It is a good feeling when you are self sufficient,
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Old 05-05-2017, 07:06   #13
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Re: SD50 - Heavy Throttle Slips

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If you got 45 mins You will most likely get 250 hours. Well done. It is a good feeling when you are self sufficient,


You are right about that! Now to get the correct tools.....
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