Nissan 120 trim unit issues

Hi,
I recently got a mako 228 with a pair of 120 nissans. I'm trying to get everything running with a minimum of expense because I don't want to sink money into a project without knowing just how bad everything is. I plan on eventually doing carbs, plugs, gear oil, control cables, electrical, etc. In the meantime I have both engines running off a portable fuel tank and keeping idle, which is good enough for me on that front. Next I am trying to sort out the trim on the starboard engine (port works fine) and cooling on both engines. One pees poorly and the other not at all.

The trim unit: the motor whirs, but it doesn't move up or down. I tried filling the reservoir, but no difference in operation. The service manual leads me to think I need to have the motor tilted up to pull the unit out, but the manual valve release might as well be welded shut. I removed one of the bolts holding the motor to the hydraulics in an attempt to get the pressure to release, but the bolt head sheared off with depressingly little torque. No pressure loss, and I'll just have to deal with that once the unit is out. My current plan is to drill out the center of the pressure release bolt as precisely as I can. However, the bottom pin attaching the trim unit to the bracket seems very stuck. After looking at a couple used ebay parts listings this seems like a common problem. An alternative seems to suspend the motor and take the mounting bracket apart from around the trim unit. Is there a trick to getting that lower pin out? I don't want to destroy the manual release valve if I will end up taking the bracket apart anyway.

Lower units: The bolts are very rusted out. A couple came out by hammering on sockets, but for the rest I think I will have to grind them flush and then pull them out using the threaded stubs exposed by removing the lower unit. I'm not too concerned about that, but who knows what I will find when I actually get to the impellers.


Also, I heard that these engines can be brought up to 140hp output by modifying the throttle stops and ignition timing. Is it worth doing this, or will I see problems with fuel economy and reliability?

I can't get the forum attachments to work so here is the imgur link: https://imgur.com/a/FoB1DSl

Possible that the manual valve is already open. New valves are still available for about $75. If the lower pin is seized, you will likely need heat and/or a press of sorts. Yes, you can up to 140, and of course, it will burn more fuel at those throttle positions.

So, I tried tapping the valve with a left hand thread so that I could get a better bite on the hex head. the tapping went perfectly but when I started applying real torque to the bolt the head sheared right off. I tried drilling the bolt shaft out and broke the drill bit. At this point I am just trying to get the damn thing lifted up so I can work on it. Torching the lower pin didn't achieve much, at least just when hitting it with a hammer. Do you have any ideas on how I can move forward? Thank you.

More heat and a bigger hammer when they are seized.

I figure I would give an update to anyone reading who may have the same issue in the future. I ended up clamping a collar on the shaft and welding a couple tacks so that it couldn't slide further up the shaft, and using a piece of steel to jack against and pull the shaft and bearings out of the housing. I was worried that the pinion gear might've been what was sticking, but it was pretty clearly the bearings. Now I'm worried about the clearances putting everything back together. The manual says that the backlash specs are in table 3, but table 3 just lists the available shim thicknesses! I also don't have the specialized tool for setting the pinion gear/shaft height. I didn't seperate the forward gear from the bearing, so any shims there will be the same. I'm guessing I will just have to do it by feel and guess at if the amount of backlash is acceptable since I don't have any way to measure it or any specs to even set it to.



This was a lot more work than I was expecting. If I had known at the start, I would've just replaced the bad oil seal on the prop shaft and did a couple oil changes in the hope that it helped clean up the sticky bearings.

The trim unit replacement did go ok. The ticket was to just take the two brackets apart and not try to push the lower rod out.

Next issues:

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Lack of coolant: The telltale doesn't piss any water at idle, but plenty of smoke (not steam). I tried both running it with earmuffs and with a barrel, no change. If, however, I pull off the thermostat housing and leave it uninstalled, plenty of water comes out of the thermostat housing and also even the telltale! I wish the manual had a diagram of the coolant water flow because I really don't understand how it circulates, but that test should tell me that the water pump is pumping, right?

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Copious amounts of smoke and oil: the manual says this is usually a too-rich condition, so I need to rebuild the carbs. My first instinct was that this was a serious problem like a blown head gasket but then I remembered it was a 2-stroke, so I can only hope nothing is actually destroyed.

I think I found the issue with the smoke, one of the carb floats was stuck and flooding the whole intake. However, there seems to be something weird about the throttle linkage mechanism I don't understand and the manual doesn't directly address. there is a lot of free movement for the ignition advance and oil pump to ramp up before the cam actually starts to engage the throttle butterflies. Is that normal? it seems counterintuitive for the oil to be enriching the mixture and the timing to advance before the carbs even begin to admit more air.

I would just adjust as per the FSM.