Nissan 6 HP 4 cycles

[Bill]

Just exactly what caused the overheating, I don't know.

Failure to regularly fresh water flush an ob can lead to salt build up in the ob's water pump and its water cooling channels. Been there, done that. Almost ended up on the beach! The old Johnson, however, stopped running before it started melting anything.

[c_amos]

I just took a look at a Merc 6 (Of course same as the Nissan & Tomatsu) and noticed that the zinc is a TINY little square on the side of the lower unit. It look about 1" square.

Has anyone had a problem with them eroding really fast? It seems like it is about 1/4 the size of the one on the Yahama... seems like it would go really fast?

What have you seen?

On edit; Did find some discussion on OB motor zinc's here. Nothing addressing the little zinc on these motors though....

[c_amos]

Well, I just pulled the trigger on getting the little Tohatsu 6hp from onlineoutboards.com.



The price was right at $1265 with free shipping. They are out of stock on both of their lower pitched props.

I notice they have both a standard 6" pitch prop (~$65) and they also carry a new 5.99" 'High thrust' prop (~$100). The high thrust prop has large flat blades like the Yamaha high thrust prop does.

So now I have 2 questions for the users of the Merc / Nissan / Tohatsu 6hp.... I am still wondering about the zink, and would like to hear from anyone who may know if the new 'high thrust' prop is worth the extra $135?

Thanks,

[Tony G]

Craig

Hubba-hubba. Is that the extra-long shaft? With the charging system? And the verticle pull??

Long, long ago Mike made a well grounded point that the prop pitch we wanted for our boats, running a small HP 4-stroke was a 7" pitch. Something about allowing the engine to run in the proper RPM range without getting a lot of slip.

Sorry I can't add anything useful to the zinc question. Would composition of the metal the zinc is attached to make a difference in the rate of oxidation/disolution?

As soon as the O'day sells online gets a hunk of money from me too!

[c_amos]

Got the motor in the other day. Nicely packaged, looks to be pretty good gear.

Couple of interesting things I noticed. First, the fuel connector is not the same on the tank and the motor. The motor connector is the 'nissan' connector, kinda like the OMC, but not quite, nor does the Yamaha connector fit (although it is close). The tank connector looks exactly like the older (round) OMC type connectors... but I bet it is slightly different too. Not a big deal, especially since the motor comes with a new tank and line.

I opted for the 20" (really 22") shaft, not the 25"(27"). My Yamaha was 20" and never came out of the water. I see no reason to go 5" deeper, and pick up more drag, probably more crab pots, and not be able to stow it in the lazy-rat....

I did get the charging system. They charged me $145 for it. Again, had it on my last motor and it was nice to get a couple amps while motoring.

I went down to the boat today, was going to motor for a couple hours to make myself obey the break-in period (10 min at idle, 10min<1/2 throttle, 2hours <3/4 throttle, 3hours at 3/4 throttle.) Was a perfect day, with 10-12k and not too warm. Ran the motor a grand total of an hour.... Had a nice sail though.

Motor smoked a bit, guess that is to be expected while the rings seat. There was a bit more vibration then the 2stroke had, but then it also was a 2 cyl.

I had a consistent 3kt, at less then 1/2 throttle. I have no doubt that it will push the boat to hull speed as others have reported.

I did just order the 'High Thrust' prop, it is a 5.9999" pitch, but it has the wide blades like the Yamaha 4 strokes do. I would have had the motor delivered with this prop, but no one offered swap outs. This is not the same prop as the 6" pitch prop, but a different animal all together (bet that .0001" pitch makes all the difference.

OBTW Tony, I found the reommendation Mike made on the 'outboard' thread;

Mercury ,Nissan & Tohatsu ( same motor, all made by Tohatsu ) recommend a 8x7 prop on the 6 ,5 & 4hp for displacement hulls ( the 4 comes with it ) the 6 & 5 come with a 'square prop' 8x8 ( actually 7.9x7.9 ).
My mechanic , from his experience , say to skip the 7 and drop to a 6 or 6.5 pitch . He's a licensed Nissan service center and seems to know what's up .
I'm going to buy a 8x7 try it and log with the GPS what it does then have it re-pitched to 8x6 and see what that does .
The following is over-simplified and not scientific;
at 4000 rpm the 8x8 prop is trying to go somewhere between 20 and 30 knots . Not going to happen on an Ariel .
At 4000 rpm the 8x6 prop is trying to go somewhere between 12 and 20 knots .
now you have slip and losses that can be 50% which brings you down to 6knots which is close to hull speed .
All that wasted revolutions on the 8x8 is like spinning the tires on a car , not getting you anywhere fast , the 8x6 is like switching to a fatter tire with more tread ,or a lower gear, that delivers all the bite to the road and propels you forward & stops you when you engage reverse.
The only drawback about downpitching ;
If you use the same motor on a dink or skiff that planes , it wont go as fast because you have shifted to a lower gear .
It only takes 5 minutes to switch props so buy a spare and have it pitched lower .

I also ordered a few spare zink's and a waterpump rebuild kit. I looked at the 'vertical pull' option, but at $129 I think I am fine just pulling at a bit of an angle. It is funny, I recall reading someone here say that the nissan vertical pull option routed the pull cord out the top of the cowl, the one offered now does not do that... it is just an elbow that screws to the recoil starter and comes out the front and turns up... seems like it would add a bunch of friction and chafe to me.. maybe they have some special stuff in there. For the price, maybe so.

Overall happy so far, will report the performance of the new prop when it arrives.

[c_amos]

The new Tohatsu is sitting out in my shop right now, the oil is still draining from the first oil change. It has taken me almost 2 months to get the 10 hours on the motor, since I usually only motor a few minutes at a time to get in and out of the slip.

I had some oil burning in the first couple hours, mostly noticed it on start up. I think it was just the rings seating. I did notice that it was worse for the first couple minutes after starting, which normally would indicate leaky valve stem seals... but I think it had more to do with the fact that the motor was stowed on it's side in the lazy rat. (yes I did only stow it on the side with the tiller handle as per the manual.)

The motor starts on the second pull every time, and has a short warm up time. I like the angle of pull through the original cut out in the cockpit and am no longer interested in the 'vertical pull' option. I think it would be awkward for me, and looking at the $100 + kit I notice that it does not have a pulley to change the direction of pull, but just a curved tube. I wonder what the friction would be like... but don't think the option is something I want anyway.

I opted for the 20" shaft (really more like 23"). My Yamaha had a 22" shaft, and did not cavitate even in much chop so I saw no reason to go longer. It is a close fit in the lazy-rat hatch anyway, so I would not want the 25" shaft for fear it would not fit (or at least be tougher to put in).


I do notice a bit more vibration then I did with my old motor (2 cyl, 2 stroke Yamaha 6). Not so much that it is distracting. A 1 cyl inboard vibrates much more then this outboard.

I do like that I can close the lazy-rat hatch and not have the motor choke out on it's exhaust like the 2 stroke did. I have not tried to do this for prolonged running so I don't know that it can't happen, just that it does not happen as quickly.

I did get the optional charging system. I have seen 2.5a on my Link battery monitor, but suspect that the charge rate would be higher if my solar panel were not keeping the battery nearly full all the time.

The zink has only spent about 3 weeks in the water total. I pull the motor and lay it in the lazy-rat when I am sailing every day or nearly so. I was disappointed to see that the zink was nearly 2/3 gone after a total of 3 weeks. I used to get 6 - 9 months on the Yamaha zink but it was at least 4x as large. I also don't know how hot this marina is, so that might have something to do with it.

I Did buy the 'high thrust' prop (5.999 x 8). I changed it out pretty early in the break in period so I have to re-mount the stock (7.8 x 8) prop to do a real comparison. I bought the prop as much for it's big flat blades as anything, as the one I had on my Yamaha seemed to back better. I did notice some difference in the backing, but will do more testing later.

Let me see if I can post some pictures.

[Orca]

Yup, the first one eroded very quick a (about 2 months) and then the bolt broke off trying to change it, then I drilled through the plate with a bigger one that was sacrificial enough, so I ended up ruining the lower end. Tohatsu 6hp long shaft #1.

[Orca]

Above was in reference to the the question some time ago about the zinc. In a more general review of the Tohatsu/Nissan/Merc 6 HP I will say that they seem to have really small jets and I am having trouble keeping the motor running more than 4 weeks. I started the season with new gas after having had the engine serviced for trouble last season. I treated with Stabil Marine and within 4 weeks the carb was clogged with white mush. I cleaned it a few times and used Sea Foam. It started running again but 4 weeks later it was so clogged that I took it to a marina along with the line and the tank. They pronounced my gas fine, cleaned the carb and now 4 weeks later the carb bowl has white mush in it again and the motor wan't run. The marina talked me out of using aviation 100 low lead saying it would clog the rings but if I get that thing going I'm switching to ave gas and if that fails I'll sell that and move on. Which which other motors fit because I've had enough of this one? I didn't have much time to use it so basically this ruined the season. I've had guests waiting on board the last few times which we aborted when the motor wouldn't run. Basically we can't make a motor on its third season run more than occasionally. I'm going to take the carb off the old tohatsu with the ruined lower unit and try to make it to the marina to pull out for the season. AAAGH!

[pbryant]

Above was in reference to the the question some time ago about the zinc. In a more general review of the Tohatsu/Nissan/Merc 6 HP I will say that they seem to have really small jets and I am having trouble keeping the motor running more than 4 weeks. I started the season with new gas after having had the engine serviced for trouble last season. I treated with Stabil Marine and within 4 weeks the carb was clogged with white mush. I cleaned it a few times and used Sea Foam. It started running again but 4 weeks later it was so clogged that I took it to a marina along with the line and the tank. They pronounced my gas fine, cleaned the carb and now 4 weeks later the carb bowl has white mush in it again and the motor wan't run. The marina talked me out of using aviation 100 low lead saying it would clog the rings but if I get that thing going I'm switching to ave gas and if that fails I'll sell that and move on. Which which other motors fit because I've had enough of this one? I didn't have much time to use it so basically this ruined the season. I've had guests waiting on board the last few times which we aborted when the motor wouldn't run. Basically we can't make a motor on its third season run more than occasionally. I'm going to take the carb off the old tohatsu with the ruined lower unit and try to make it to the marina to pull out for the season. AAAGH!

Be sure to disconnect the fuel tank line from the engine at the end of the day and allow the engine to run until the bowl is emptied and the engines stops from fuel starvation. The owner's manual actually recommends this. The procedure accomplishes two things: it allows the engine some cool-down time to reduce thermal shock and -- more importantly, it empties the carb bowl so the fuel doesn't evaporate in the bowl every time you run the engine and eventually develop a residue.

100 "low lead" ("100LL") av gas should really be called: 100 lots of lead. It has more lead than leaded car gas once had. It will foul your plug. Yes, 10% ethanol gas will absorb water, but I doubt the water content is causing the fouling.

[Orca]

Be sure to disconnect the fuel tank line from the engine at the end of the day and allow the engine to run until the bowl is emptied and the engines stops from fuel starvation. The owner's manual actually recommends this. The procedure accomplishes two things: it allows the engine some cool-down time to reduce thermal shock and -- more importantly, it empties the carb bowl so the fuel doesn't evaporate in the bowl every time you run the engine and eventually develop a residue.

100 "low lead" ("100LL") av gas should really be called: 100 lots of lead. It has more lead than leaded car gas once had. It will foul your plug. Yes, 10% ethanol gas will absorb water, but I doubt the water content is causing the fouling.

I only ran the motor twice after the carb was serviced and I ran it dry. I disconnected the fuel line and tank and put them down below on the cabin sole in case water was permeating the line or something. I've been running 100LL in my scooter for about a month, I'll pull the plug and see what it looks like. Quite honestly if 100LL cut the life of my motor by 30% I'd never notice it. I seems like it would last a real long time never running which is the present situation. A plug would be easy to change, carb, not so much. I did think of keeping an extra carb on board though as its a real pain in the butt to load that motor into a dinghy from my mooring and row it to the beach.

[pbryant]

I only ran the motor twice after the carb was serviced and I ran it dry. I disconnected the fuel line and tank and put them down below on the cabin sole in case water was permeating the line or something. I've been running 100LL in my scooter for about a month, I'll pull the plug and see what it looks like. Quite honestly if 100LL cut the life of my motor by 30% I'd never notice it. I seems like it would last a real long time never running which is the present situation. A plug would be easy to change, carb, not so much. I did think of keeping an extra carb on board though as its a real pain in the butt to load that motor into a dinghy from my mooring and row it to the beach.

I installed a "Racor SNAPP One-Piece Snap-In Fuel Filter Water Separator - Filter Assembly w/ Bracket & Drain - 2 Micron" between the fuel tank and the engine two years ago. It has a clear bowl that allows you to see if any water has accumulated. Pilots will know this device as a "gasculator." They're common on most airplanes. I have yet to see one drop of water in the inspection bowl. But it made me feel good to install it.

The engine problems I had were:

1) I failed to recognize that after the engine is shut down while bouncing around in swells that the fuel would run down hill out of the carb bowl back to the tank - making me pull the cord about 10 times before the fuel pump would refill the bowl. Solution: squeeze the primer bulb until it's "stiff" before restarting the engine.
2) Since my fuel tank is slightly below the carb bowl, fuel doesn't feed the carb by gravity. The fuel pump MUST be able to draw against a partial vacuum to be effective, and... I wasn't getting an air tight seal where the fuel line connects to the tank. Solution: clean the connection at the fuel tank regularly with a wire (bronze) brush.
3) The fuel cap was a fancy CARB (California) approved type that required a partial vacuum in the tank before the air vent would open. That vacuum was too great to allow fuel to flow. Apparently, California thinks a few fuel molecules evaporating out of the tank is a major source of pollution. I discovered this after the engine died about a dozen times -- always obeying Murphy's Law by failing at the harbor entrance, near rocks, while crossing in front of big boats, or on final approach to my slip, -- and I finally saw the sides of the plastic tank pop out when I removed the fuel cap - along with a loud whooshing sound when air rushed into the tank. Temporary solution: screw the cap on very loosely. Permanent Solution: Find an old-style cap that fits the tank that has a simple non-pressure controlled vent (please don't report me to the CARB).

I have about 300 hours on my engine, using 90 octane / 10% ethanol fuel (it does seem to like 90 more than 87 octane - but that might be my imagination), and I've had no problems yet besides the problems above that someone smarter than me would've spotted sooner. I always let the engine run out of fuel at idle throttle at the end of every sail.