LongJohn

Shift interrupt switch

34 posts in this topic

I aquired this pristine 1984 Chaparral 172 with a mercruiser 140 when I purchased this Lake house in Feb. 2016 The boats owner passed away and his mom let the boat go with his house.

She said the boat was last used summer of 2015 and the alternator went out. Her son a mechanic by trade kept the boat in great mechanical condition. I replaced the alternator & started it up with muffs & it ran great.  My question is when I engaged the shift lever the engine would die. Did this also in reverse. This boat has been garage kept year round. Does the boat need to be in water for the shift interrupter switch to work properly.  This is my first I/O boat & not familiar with this. Thought I would get some thoughts on this before putting it in water.

Thanks for any information..

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The short answer is no, the micro-switch interrupter actually engages less when there is no water resistance. Adjusting these things can be a pain, and you must follow the prescribed procedure to the letter. There is a simple spring loaded rocker bracket that the micro-switch is mounted to. As you attempt to engage the shifter, the cable deflection will force this titter/totter to rock either forward or backward, momentarily shutting off the engine so that the dog clutch on your Alpha drive can fully engage. They call these things dog clutches but in fact there is no clutch at all, just a set of stationary teeth and a set of spinning teeth that you are trying to jam together. As you switch is holding the engine off for too long in both forward and reverse, adjustment may not be the issue. I'd look at two things. First is the idle speed being too low, as the engine flywheel has to be spinning fast enough to actually restart the engine after the ignition is re-established. The second possibility is the rear shift cable. If it's too stiff, it will cause the interrupter switch to deflect too far, shutting off the engine too soon in the shift cycle, and not recovering fast enough after shifter travel is satisfied. There is much less micro-switch action going into gear then when pulling it out of gear as there is less resistance.   W

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The lever moves very smoothly. When I was shifting I was easing the lever slowly. Maybe this was the problem. Also I noticed that the trim & position sensor wires were fried in two. Don't know if this has any possible effect.

Thanks W for your response.

Edited by LongJohn
misspelled word

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The shift cable that Wingnut mention is what I had problems with on previous boat. I had a mechanic replace it and everything was good.again. When it isn't working right it is a pain, because the motor will die just when you need it to be running.

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22 minutes ago, LongJohn said:

Thanks Mike for information. I will be able check things out more thoroughly next weekend. 

Thanks again

Long John.

Yea, you don't want to shift an Alpha slowly. One positive, deliberate move and the "clunk" you hear is both normal and preferred.  The shifter on an Alpha is in the foot, and when it's under water you don't hear it as much as when you are running her on a hose in the driveway.  W

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OK, Will do this. Boat was supposedly running & operating fine. A few months setting up should not cause a problem. Still concerned about the trim limit & ;positioner wiring being fried in two. Is this a major concern to have?

Thanks, W

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7 minutes ago, LongJohn said:

OK, Will do this. Boat was supposedly running & operating fine. A few months setting up should not cause a problem. Still concerned about the trim limit & ;positioner wiring being fried in two. Is this a major concern to have?

Thanks, W

Trim limit just prevents you from over-trimming while underway. As long as you start out full down and trim up in small increments until you find the sweet spot you will be fine. Never trim higher than that  (over 40% up) unless you are at idle speed as your out drive has very limited side support at that angle. I am wondering how the lower range of trim up is working without the limit switch, unless the sender wires have been twisted together leading to the trim pump relay. Usually the only way it would work with a bad sensor is if you were using the "trailer" detent. Trim indication is just that. On your ride it is a simple helm indication. Nice to have but not tied into a "ships system" like on the new "Smart Craft" offerings. Replacing the senders is a challenge without first removing the drive, and pulling the gimbel bell, but it is doable if you are handy and take your time.  W

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One thing I noticed is trim switch on lever will lower but not raise drive & trailer switch will raise but will not lower drive. Is burnt wiring causing this. Would like everything to work properly if needed.

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That is exactly what you should expect. Trailer button is an over-ride that allow trim above what the trim limit switch on the drive allows. It has no effect on trim down as it is wired into the trim up relay circuit only. Replace your trim limit and trim indicator sensors over the winter and you will be fine.  W

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Ok,  

Believe I can handle this. One more thing. Can't tell where the wires connect to inside the motor area. Don't see any existing burnt wiring.

Thanks, You've been a great help.

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9 hours ago, LongJohn said:

Ok,  

Believe I can handle this. One more thing. Can't tell where the wires connect to inside the motor area. Don't see any existing burnt wiring.

Thanks, You've been a great help.

John, Here is a link to the Mercriuser Alpha I MR style drive unit like yours. As far as the sender wires go, there will be 2 pair of wires with plugs, wire tied near the top of the bell housing, just behind the engine. They may be tagged trim limit, and analog trim, but on a boat that old likely the tags are gone. Does not matter as new senders will have plugs on them that only fit one way. If you have a question, tie one pair together and see if the trim switch starts working in the lower range from the normal trim switch. If so they are the trim limit wires. If not, the they are the trim indicator wires.They plug into the sender wires that pass through a waterproof passage fitting that goes through the transom plate just above the driveshaft. The attached manual will detail their location.

http://boatinfo.no/lib/mercruiser/manuals/mercruiser6.html#/20

This is the part number for the replacements for the senders. They come as a kit and the trim limit mounts on the port side, and the trim indicator to starboard. About 80 beans for the pair. Amazon has them, just be sure to buy OEW Merc, and not knock-offs.   W

Mercruiser Trim Tilt Sender Kit Alpha/Bravo   #805320A03

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Wingnut, 

Here is an update. I did as you suggested when shifting. The engine still died in forward & reverse.  The shift switch is moving out of the detent spot but slowly returning so engine is dying. I held my hand on it while my brother operated the shift lever & I manually moved it back quickly & it worked. Something is causing the switch return to move slowly back to run position. Everything seems to be in order but I have no experience with the mechanical workings of cables etc. I will do some more reading on this.

Hopefully someone might be able to diagnose this problem from past experience.

Thank you,

LongJohn

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Sounds like a stiff rear shift cable, the one the runs from the switch lever to the transom plate, and into the gimbel. Disconnect it and see if shifting still causes the engine to die. Drive won't shift, but you will have your answer.   W

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On 10/8/2016 at 1:02 PM, Wingnut said:

The short answer is no, the micro-switch interrupter actually engages less when there is no water resistance. Adjusting these things can be a pain, and you must follow the prescribed procedure to the letter. There is a simple spring loaded rocker bracket that the micro-switch is mounted to. As you attempt to engage the shifter, the cable deflection will force this titter/totter to rock either forward or backward, momentarily shutting off the engine so that the dog clutch on your Alpha drive can fully engage. They call these things dog clutches but in fact there is no clutch at all, just a set of stationary teeth and a set of spinning teeth that you are trying to jam together. As you switch is holding the engine off for too long in both forward and reverse, adjustment may not be the issue. I'd look at two things. First is the idle speed being too low, as the engine flywheel has to be spinning fast enough to actually restart the engine after the ignition is re-established. The second possibility is the rear shift cable. If it's too stiff, it will cause the interrupter switch to deflect too far, shutting off the engine too soon in the shift cycle, and not recovering fast enough after shifter travel is satisfied. There is much less micro-switch action going into gear then when pulling it out of gear as there is less resistance.   W

Same situation years ago, my issue was the shift cable corroded at the out drive. Replaced it with the new designed cable, no issues since.  Denny.

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9 hours ago, Denny said:

Same situation years ago, my issue was the shift cable corroded at the out drive. Replaced it with the new designed cable, no issues since.  Denny.

Thanks Denny, I this cable difficult to replace or should I have it done professionally?

LJ

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6 hours ago, Bt Doctur said:

The shift interupt should never move on land shifting into or out of gear.Only in the water with a load on the prop COMING OUT OF GEAR

I have a video that shows how the shift cable works, Best thing to do is pull the drive and inspect all the moving parts.

http://vid57.photobucket.com/albums/g219/BtDoctur/DSCN2491_zpsea1cc235.mp4

I've heard this before, but some say it should work out of water with the water muffs on. Boat was operating just fine last summer. I will put in water to check it out. This is a new experience for me. Just acquire the boat thru purchase of lake house.  Thanks for your feed back.

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on muffs there is no load on the prop. and the switch should not move. To change the cable you will need a really deep 9/16 socket or 2 welded together

Get yourself an old control cable core from a shop. or the complete old cable and remove the solid inner core

Remove the drive, the inner core, and insert the solid core to act as a guide for the new cable sheath.Then unscrew the old core and remove it leaving the solid core.

put solid core into new sheath and vise grip the core. lubricate the brass end and force thru the shift bellow A person pulls the core while you push the core.

install and tighten new cable casing, install the new inner core and complete the reassembly

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This is something I can do. Sounds like a little work but that's OK. Thanks for the video link also.  My switch does move and kills the engine. Not sure what you mean by not moving.

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1 hour ago, LongJohn said:

This is something I can do. Sounds like a little work but that's OK. Thanks for the video link also.  My switch does move and kills the engine. Not sure what you mean by not moving.

Gotcha Bt Doctur.  Seems though when you shift the lever the switch has to move being connected to the cables. What would keep it from moving?

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remove the cable with the brass barrel from the lever, Try to move the black plastic sleeve. You should be able to move it easily with 2 fingers.In the video I posted I`m moving the slide with 2 fingers. Thas how easily it moves. When the cable binds up ,the outer core is moving the switch.

 

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After a year I finally got back to work on this boat. Changed out the lower shift cable & everything works fine. Putting it in water tomorrow. Do have one question. Have to prime carb for cold starts. I noticed the electric choke works backwards. When engine is cold butterfly wide open. As engine choke heats up  butterfly closes. I'm thinking a linkage problem somewhere. I have not touched the carb. I'm assuming its the original carb. Any ideas would be appreciated. Thanks everyone....

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