Tohatsu 6hp Outboard 350 Hour Service

It took 3 years to put an additional 225 hours on the Tohatsu since that last service (see previous post). In that time the motor has run flawlessly, always started and never let me down. It was running so well that I put off doing the scheduled services (as I'm sure most owners also do). But the hours were mounting up and I felt I could not put it off any longer. One problem that had developed was that there appeared to be wear in the mounting bracket such that the outboard could clunk slightly side to side on its mount. I did not like that at all and expected that I would need to replace the mounting bracket.

Parts all over the kitchen (of course)

I went through the awkward ritual of getting the motor off the boat and into the dinghy. It went better this time because I rigged a bridle of ropes to carry the outboard horizontally. Rather than having to manhandle the outboard vertically with its long 25" leg getting in the way, I could lift it in a horizontal orientation and lower it into the dinghy (no pics).

Carburetor

I tackled the carb first, pulling it apart and finding that it looked really clean. I attributed this to always draining the carb after use so that water accumulated in the gas cannot corrode the fuel bowl.

It does look very clean, but as I was to find out later, looks can be deceiving.

I removed the float and all of the jets and blew out the passageways with carb cleaner. I measured the float level and found it to be in spec, but decided to change it anyway as I had paid for an expensive carb-rebuild kit which included a new float and valve. I soon regretted this as the stainless pin that holds the float was stuck firmly. I had to drive it out using a very small punch and started to send it the wrong way, despite having a workshop manual to consult.

Float pin comes out to the right.

Anyway, I finally got it right and installed the new float and valve and reset the float height. Then the card was reassembled with a new o-ring for the fuel bowl. In hindsight it was not worth purchasing the pricey carb rebuild kit. The only item I really needed was the o-ring.

Fuel Pump

The carb had been cleaned once previously, but the fuel pump has never been off the motor. The manual said it needs to be cleaned at 300 hours, so clean it I did. The pump had been working fine and was very clean inside. The pump diaphragm was OK, but I would have been happier replacing it with a new one. I hadn't bought one because the genuine diaphragm is something like $40, while a whole new pump is $65. I think I will get a whole new pump as a spare in case of failure. Next I took out the wafer-thin valve elements (still in the pump body in the picture) and cleaned them. The flutter valve elements are very flimsy and fragile but I managed to get them apart and back together again. The only part that the workshop manual says has to be replaced is the o-ring that sits between the pump and the engine block. I had pre-ordered the o-ring and fitted it.

Diaphragm, valve element (in the pump) and valve cover.

Mounting Bracket

After dismantling the bracket and giving it a good clean, there was no sign of excessive wear. The sloppiness was just because it needed to be tightened a bit. Problem solved. I had wasted hours on the internet looking up the cost of a replacement bracket for nothing.

Water Pump

Next was the water pump which was way overdue for replacement. The bottom section came off easier this time than the last due to copious greasing of the bolts. Given that it had been running for 200+ hours the pump impeller still looked in good shape, but the base of the impeller housing was badly scoured, I'm guessing from mud getting sucked through the impeller. The water pump replacement kit is much better value than the carb kit and comes with everything you need include a new impeller housing, gaskets and new bolts. 

Worn water pump cover after 200 hours.

It is tricky lining up everything to refit the bottom section: the drive shaft, water pipe, gear shifter shaft and shift lock-out pin all need to find their home in the shaft housing. I found that having the housing to one side allows all four to snug home easily, but on the other side it is difficult. I can't now remember which was the easy side, but when you get it oriented the right way, the lock-out shaft in particular kind of falls into the right position.

New gasket and impeller.

Tappets/Cover

I then reset the tappets, which (again) only required minor adjustment. A corner of the tappet cover was very rusty, so sanded, primed and painted it. The only paint I had on hand was Rustoleum Brown Hammered Finish - not very pretty, but effective.

Tappet cover prepped for paint.

Hammer glaze?

Flush

The motor was then run up so that I could flush out the case with a water and vinegar mix. The motor started and ran but had a big miss off idle. I carried on and ran it in a vinegar bath for a while, before flushing with copious fresh water. I should have stopped right then and figured out why the motor was missing, but convinced myself that it was just clearing its throat after not running. I was in a hurry to get it done and back on the boat so that I could take the Little Helpers out to Angel Island the next day. Big mistake.

Note the new fuel filters. The large one is an add-on.

Reinstall and Run

We headed to the boat the next day, and Little Helper #1 waited while I fitted and restarted the motor - it would not start. I started to get breathless from pulling on the starter cord. It caught and started to run, but had  a massive flat spot off idle and would only run at high revs. Then I had to apologize to Little Helper #1 for using bad words. For the first time since I got the boat, we were prevented from going on a trip because of a mechanical problem.

A few days later, I tried to figure out what was up. At first I was convinced that I had damaged one of the delicate flutter valve elements in the fuel pump, but pulling the starter cord it was clear that fuel was flowing. Next I took the carb off and convinced myself that the fuel bowl screws were not tight - I refitted the fuel bowl cover and it made no difference. I took the carb off again and took it home for another clean.

This time I soaked the carb overnight in a container filled with carb cleaner (what I should have done first time around). When I removed the jets again I found the problem - a big lump of junk blocking the idle jet! So, when I cleaned it the first time I had just loosened the dirt inside so that it could move around and block the idle jet the first time I tried to run it. Lesson learned - spend time soaking the carb and getting it very clean.

As soon as I refitted the carb, the motor ran sweetly and has done so for quite a few hours already (this post is months behind the actual work). I'm looking forward to another couple of hundred hours of reliable running from the Tohatsu.