Compression Tubes
30 March 2019 | St Marys, GA
Capn Andy | Summer Like
So I bought the Chinese 2 stroke outboard motor for $40 and confirmed it didn’t run. It looked like it had no time on it, basically brand new. The seller wasn’t the original purchaser, it came with the boat he had purchased, so he wasn’t a source of info about the motor. He had someone look at it and say it had no spark. We confirmed that by removing the spark plug so that the pull starter could spin the engine fast and then holding the spark plug against the engine so there would be continuity to allow it to fire, but it did not.
.
I have a DVD with service manuals for all Yamaha 2 stroke outboards from 1997 on. Since this outboard is mentioned on the internet as a clone of a 1990‘s Yamaha 2 stroke, I began researching the ignition system. This Hangkai outboard is specified as 6 horsepower, but the Yamaha 6 is a two cylinder motor, so I looked at the smaller Yamaha’s, 4 and 5 horsepower. Perhaps this Chinese motor is a clone of an even earlier Yamaha. The service manuals give ohms readings from the engine’s electrics and voltages of generating coils.
.
The ignition system on the Hangkai 6 HP is very simple, there are two coils near the flywheel, one outside that is a trigger or pulser that feeds a pulse to the CDI unit, the other is the charge coil or stator located under and inside of the flywheel and it sends AC voltage to the CDI unit. The CDI unit also gets a dead man’s key signal from the safety switch and the dead man’s key at the front of the motor. When the key is removed from the switch it shorts to ground and that signal kills the engine. This safety feature can prevent ignition but can easily be taken out of the system by simply unplugging the wire where it goes through a connector to the CDI unit.
.
On the output side of the CDI unit is an orange wire that connects to the ignition coil and from there a spark plug wire goes to the spark plug. So simple. Comparing ohmage values in the Yamaha manuals with what I was getting on the Hangkai motor showed that the charge coil or stator on the Hangkai was very low, about 4 ohms. No Yamaha motor showed such a low value for their charge coils. When I spun the motor with the pull starter and attached an AC voltmeter to the connector from the charge coil, the voltage was low in the 3 or 4 volt range. With it all hooked back up again, the orange wire from the CDI was putting out a similar voltage to the ignition coil. It looked like the charge coil was bad and putting out too low a voltage for the ignition to generate a spark.
.
Geoff, the chemist, seemed to be fascinated by this motor and came by and did a compression check and also bore scoped the cylinder head. Not many people would do this for you unasked, and at the time I was in the woodshop fighting procrastination by playing some puzzles on the computer. Geoff came in and announced the compression readings and showed me the bore scope photos. I really have to get one of those. Compared to me Geoff is a rocket scientist and I’m no slouch. That Chinese motor doesn’t have a chance. We rode our bikes over to the Barn and talked about it some more.
.
I was working on the crossbeam and had to do a fairing coat of thickened epoxy which uses up a lot of epoxy and is a real effort. Geoff took off on his bike while I mixed epoxy. It was a nicer day for bike riding than for mixing epoxy.
.
After lunch I decided to borrow some tools from Radio Bill who always obliges, and began to remove the flywheel on the Chinese motor. First the pull start mechanism has to be removed, 3 10mm headed bolts, then there is a kind of cup device that must be for an emergency rope pull start also held by 3 10mm headed bolts. Then there is the flywheel nut which was too large for Bill’s socket set. His largest was 17mm, so it was probably 19mm. I cycled over to the metal shop where some tools were lying around. Let’s see 19mm, one inch is about 25mm, so 19/25, or 76/100, and there was a 3/4 deep socket and ratchet handle sitting right in front of me. A quick ride back and a tough nut was backed off, the socket fit perfectly.
.
I needed a gear puller, but I noticed that the emergency rope start cup and its 3 bolts could be a gear puller if I could get something to fill the hole in the cup and bear against the flywheel shaft. It had to be thin but strong. I began my search at the woodshop where there were many strange offcast metal objects. One of these was an offcut of my VHF antenna mount. It had a rounded end and when I came across it I had the emergency rope start cup with me and compared the rounded end with the bolt holes. Hmm. It looked like a perfect match. One bolt hole was obscured by the mount, but rotating it aligned a hole in the mount with a hole in the cup. How perfect.
.
Back at the motor I could put it all together. The cup, the flywheel shaft nut back on its bolt, adjusted to the proper level, and the piece of antenna mount in between, perfectly aligned. As I tensioned the cup’s bolts, evenly, there was a sudden pop, the flywheel was free.
.
I removed the flywheel and removed the stator coil underneath. It is a simple coil of wire around a kind of bar of layers of metal and it looks just like the stator of some of those Yamaha engines. I ordered one of them from an outboard motor salvager in Pasadena, California.
.
Now we have to consider that the Yamaha charge coil output might not be compatible with the Chinese CDI unit. Why not just get a Yamaha CDI unit, so I did. It was expensive, $38 including shipping.
.
The final layers of glass had been laminated onto the new crossbeam and a fairing coat of thickened epoxy smoothed it out, some. Once again I achieved a workboat finish.
.
Defender Marine was having its annual sale so I purchased fiddle blocks for the new mainsheet and a couple of swageless stud wire terminals. When the bill was tabulated I could see that now they are charging sales tax, so maybe I wasn’t saving so much. I had to buy more wire terminals, toggle forks, but now I compared prices at Rigging Only and it turned out they were less expensive than Defenders, even with the sale pricing. Line for halyards was cheaper at Defender, so I ordered that from them.
.
It was time to work on the mast and I had to recalculate where the fittings for the upper shrouds, running backstays, lower shrouds, and diamond spreaders would go. The actual work only took a few hours. Schedule 80 stainless pipe had been cut to form compression tubes whose length was exactly the same as the thickness of the mast. Retainer plates had already been cut out, drilled, and ground. Now they were bent in the 55 ton hydraulic press to match the curvature of the mast. The holes for the compression tubes were drilled out to match their outside diameter and then the holes on one side of the mast were taped over with fiberglass packing tape. The mast was flipped over and each position was finished off by dropping a compression tube into the open hole and working it around so that it was resting on the tape on the hole on the other side of the mast. Then a retaining plate was positioned on the mast and thus covering the compression tube also, and then a 1/2“ pin was put into the plate and the compression tube, lining them up. First one 3/16“ hole in a corner of the retaining plate was drilled into the mast and then a stainless pop rivet was set in that hole. Then the hole in the opposite corner was drilled and pop riveted, making sure the pin was loose and the plate wasn’t binding it against the compression tube. Then the two remaining corners were riveted and the mast was flipped over, the tape removed, and the plate on that side installed the same way.
.
The photo is of the inner forestay tang and the compression tube retaining plate that will be for the running backstays.