Terrible Vibration with New 4 Stroke Engine

[moonlight]

I vote for unbalanced prop or prop shaft.  Something's going on w/ the bottom end, in gear only; and shouldn't be.  Drain and refill the gearcase, remove the prop and have it checked, and since it's off, set an index mark on something and turn the shaft, it should wobble NOT AT ALL.

[edbuchanan]

Hi All,

So, I went to the boat today to take a second look at the engine.  No mounting bolts or clamps were loose.  The runout on the prop was very tiny; the measurement was probably limited by the thickness of the paint on it.

It ran terribly, just as before.  The steering friction screw was useless for holding the engine straight at any speed.

An idea provided by mattman was useful: just let it run for an hour.  By the end of an hour of in-gear running (at dock) the steering friction was holding the engine steady and my family thought the vibration was greatly reduced.  My wife took a nap during the following one hour motor cruise (beautiful day!) and thought that the sensation was similar or better than our good 'ol 6HP Johnson 2 cycle, with the exception of very low RPM.  At the end of the cruise she declared it preferable to the Johnson.  Yes, I know this is subjective.

Just above idle the boat was pushed greater than 5 knots!  Maybe it is okay.  I still have three years on the warranty.

A new, stiffer 4 stroke mount will be installed next week.

Thanks for all the suggestions, they were greatly appreciated.

[BruceW]

Ed, glad to see your last note; a couple of us were talking yesterday about the motor. I have one, no issues, and the other guy has one on order. Funny thing, I went to start mine, and couldn't pull the cord. I knew it needed to be in neutral, but it just didn't seem to be working. Took the cowl off, messed around for awhile, and finally saw the position the linkage needed to be in to release the cord. Put cowl back on, and Veee-ola! Haha, I had sure felt panicky when it wasn't working; felt a sense of relief once it started, and we all agreed it was quiet and not having excessive vibration. Next couple times starting, had no trouble finding neutral.

I'll bet you were very relieved with the finishing status of your motor as well!

Bruce

[skip1930]

I'm guessing the mount has nothing to do with it.
I'm not a fan of four cycle outboards. I like two cycles.
Generally speaking the engine manufactures have to deal with the EPA who wants 'lean burn, no pollution' engines.
The smaller the engine displacement, the further away from 'lean burn' the engine will be.

This engine is rough because something is going on with this four stroke, in the combustion chamber.
a ...

read the plugs that should tell you exactly what is going on.

too cold
too hot  
fouled spark plug
wrong spark plug
poor fuel delivery
poor fuel
leaking one-way valves in fuel line
vacuum leak
cracked hose
plugged carburetor internal passages
full closed/full open butterfly action
full open/full closed choke
oil sump filled
oil delivery to moving parts failing or plugged
running rich
running lean
is exhaust feeling really hot
or really cool
feeling oily from unburned fuel
spitting water
How's the sound of the exhaust
Hit and miss or hit-hit-hit ...
running with the cover off and listen with a stethoscope from a pharmacy to the engine
or put your ear on a long handled screw drive and listen for the same engine sounds
should be able to hear the 'explosion' in each individual cylinder
put a timing light clip over a spark plug wire and watch the strobe light fire
does it fire continently or once in a while

after all this now tackle the electrical components

bad coils
spark plug wires are just carbon impregnated nylon strings
is the string broken under the insulation
has the carbon been broken
continuity
timing
pick-ups
rust
wet
shorts

You get the idea ... "Gotta run smooth. Says so in the book."

compression-fuel-ignition-timing

Side Bar: Back in 1967-68 H.S. our auto shop went to a Chrysler contest where three boy teams were each given a disabled Chrysler. First team to get her running wins. Our car would start by turning and holding the key, but died when we let-go the key. The starting circuit cuts out a ballast resistor so 'full' power goes to the plugs for easier start. A coil of wire was broken under the ceramic cover bolted onto the firewall. We were around #8. So thinking about it today  "We was Slackers'.

skip.

[edbuchanan]

Hi All,

I just finished an almost 2 week trip in the boat with the new Tohatsu Sail Pro 6.  A Garelick 71033 stainless steel mount was installed about 6 weeks ago, and the engine is much happier with this wider stance mount than the old 2 stroke Garelick aluminum mount.  Vibration is lessened, with only one resonance which I believe is also reduced in amplitude.  The old mount/Tohatsu combination made the boat seem like it was going to shake itself apart.  The engine is still louder than the two cylinder two stroke.

Fuel economy with this engine is great, using about one quart an hour at 5 knots.  Part of that leg was straight into 15-20 knot winds with head-on seas of 2-3 feet.  1/4 throttle yields 5.2 knots.  It also behaved perfectly with 2 dangerous draw bridge crossings.  In both cases a strong tide was running in my direction under the bridge.  I'm glad I ordered the 25" version as the propeller only escaped from the water twice. 

Many thanks to JonnyB for calling Garelick and discovering that the 71033 is secretly(??) rated for a 60 pound or less 4 stroke engine.