Single cylinder 4-stroke outboard vibration.

[Doug Rodrigues]

No one has mentioned it yet, but there is a problem switching from a two cylinder 2-stroke outboard, to a single cylinder 4-stroke outboard of similar horsepower or weight. My 56 pound 6hp Nissan single cylinder 4-stroke replaces a 48 pound 8hp Johnson two cylinder 2-stroke. The original swing-up engine mount cannot take the increase in vibration of the single cylinder 4-stroke outboard. That vibration hammers away at the mount.Yesterday, my engine mount broke another stainless steel bolt. The first time that happened, I replaced the broken bolt with a galvanized high quality steel bolt of the same size. After disassembling the mount today, I noticed that even that high quality bolt had wear after only approximately 5 hours running time. My plan is to modify the swing-up mount by installing the largest bolts that can fit the pivot points in the mount (with modification of the cushion material). Of course, that means that the brackets will have to be drilled-out to larger size holes. Still cheaper than buying a new $330 mount built for the 4-stroke engines, and going through the hassle of bolting it to the transom. Look at the West Marine pictures of the 4-stroke mount. Looks like the bigger bolts are what is required. Just giving everybody a heads-up on this problem.

 

[Tom Eckes]

Could it be the prop?

That seems extreme. Have you tried to run it with out the prop to see if the vibration is still there?

 

[Will Hunt]

Be careful with no prop.

Be very careful running any ouboard without a prop. The water pump assumes movement and the engine could overspeed quite quickly w/o the load from the prop. Borrow a prop!

 

[Doug Rodrigues]

Not the prop.

From day one, that single cylinder outboard had the "shakes." It isn't related to the prop. The engine runs great, for a single cylinder. I never had a problem with my old Johnson 8 hp two cylinder two stroke. That one ran smooth because of two cylinders and firing on every up-stroke. There were more power strokes per prop rpm to smooth the engine.

 

[Mic fry]

Out board

Hello Doug: You might as well get used to it I bought a new 4stroke 5hp Tahotsu (same motor) and it is a pretty bad motor, in my opinion. It shakes, runs poorly on Idle, and vibrates so badly that we feel it in our inflatable RIB. I took mine back to the dealer three times before they finaly replaced it now not only does it do all the other things I mentioned it now also wines (kinda like the owner). I dislike mine so much I won't use it. Good luck "MIC"

 

[Doug Rodrigues]

No problem with the outboard.....

Hey Mic,I like that outboard, vibrations and all. At reduced power, that thing can run almost 10 hours on one 3 gallon tank full of gas. I solved the broken bolt problem: I now have half inch galvanized bolts instead of the 5/16 inch soft stainless steel original ones. Try adjusting your idle mixture. My outboard can idle so slow that I can almost count the RPMs, but that's too slow. Easy to adjust the idle mixture, but whatever you do, DON'T OVERTIGHTEN THE MIXTURE SCREW! Just turn it lean until a slight drag is felt, and then assume that to be your starting point to turn 1 3/4 toward rich. If you do tighten down too hard, you'll never be able to adjust the idle mixture again! Also, don't allow gasoline to dry-out in the carburetor. It'll plug-up the idle circuit. Disconnect the fuel hose and use your choke until all the gas is burned up. Only then will it not matter if you don't run the thing for another year.Seems to me that the outboard manufactures could have invented a small four stroke with two cylinders instead of one. That would have corrected the vibration problem somewhat, but still not as good as a two stroke. I wonder how many people know that Tohatsu makes the Nissan and the Mercury outboards? Only difference is the paint job and the price.