What does the tilt/trim limit switch do?

jopakent

Recruit
Joined
Apr 21, 2010
Messages
5
After a month of trials and hassles trying to first remove and then repair my old tilt/trim unit, I got a tilt/trim unit last week from eBay. Huge discount, and when I received I found out why. The lower mounting pin was stuck in the unit. I contacted the seller and they explained that “all” I had to do was disassemble the transom bracket and slide it in.

Without an engine hoist, and assuming that even with the engine in the air, getting that bracket apart was going to be a huge headache, I took the part down to a machine shop yesterday and they were able to use a large press to punch out the pin. Cheers!!

Last night I did a pseudo install to see if after all the fuss, I was going to have a working unit. I installed just the lower pin and the servo wires and happily, when I plugged it in and hit the relay, it responded by raising the main piston up and down perfectly.

So, on to the question… when I removed the old assembly, I got a little “snip-happy” in removing the old wiring. My plan was to restore it all when I re-installed. Well I did a great job on the blue green pair that drive the servo motor, and an even better job on the pair that route from the limit switch. That’s the problem, I did a really thorough job of installing crimp connectors with heat shrink over the connections, and then heat shrink over the pair, and then a nice split plastic protective cover over the whole thing; but…. I lost track of the wire colors.

So the question is, what does that limit switch do? I “thought” it sensed when the motor was getting lower and applied a step-down to the servo drive. In the past, I’ve noticed that when the lower unit is almost down the servo changes speeds. That is, it goes fast until it reaches the last couple inches of travel, and then slows down until it gets to the bottom. When it gets to the bottom, it doesn’t stop, but you can hear the motor labor. That’s the way it worked before anyway. I’m not sure if the change in lift speed was triggered by that limit switch or by the small pistons that engage at about that same point (or maybe the two work in concert?).

At any rate, my plan was to plug the thing in, raise and lower the motor a couple times and see what happened. I figured if I have the limit switch wired backwards, the thing would perform just like before, but in reverse. So, like I said the main piston raised and lowered beautifully last night, but when I triggered the limit switch manually, it didn’t affect the motor speed either way; it seemed to have no effect at all.

So lacking any additional insight, I removed the tilt trim unit and prepped it for paint. Got the primer on last night and applied a top coat this morning, so I'm hoptin to install it tonight. I’m curious about how the limit switch and those two smaller pistons are supposed to work. Can someone tell me how they all are supposed to work together? I guess it’s possible that the limit switch is not functioning. I could put a meter on the leads while manually triggering the switch, but I’m not sure what I’m looking for. For instance, does the limit switch only do something when the relay is working?

Sadly, no clues on this end.

Thanks in advance for any suggestions.

JPK
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,870
The limit switch was installed because on some boats / installations the cowling would hit part of the motor well.--------So that switch limits the total UP travel.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
37,870
On the way down the unit slows down because it switches to the trim cylinders.---These 2 trim cylinders have more volume so it takes longer to move the oil.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Am wondering if you the switch you are referring to is the trim gauge sender. The trim/tilt mechanism that mounts inside the two transom brackets serves two functions. The "trim" system functions from a minus 5 or 6 degrees, to a positive 15 degrees. While in this range, the two trim cylinders can force the engine backward while under full power-effectively raising the bow for increased speed and fuel efficiency. The trim system is designed to vary the angle of the engine when under normal power. While at rest, the system can also be used to "tilt" the engine out of the water, from 16 degrees, up to approx. 50 degrees. This is performed by the single tilt cylinder. That cylinder has the force to lift the engine only. If you try to throttle the engine up while in gear in the "tilt" range, the forward force of the prop can cause the lower unit to slam down onto the two trim pegs, at 15 degrees. You may be able to idle the engine (while in shallow water) when in gear and in the "tilt" range. The multiple functions of this trim system afford the operator many options for various boating conditions. A great invention.
 
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