Mercury Mark 5, first run, first problem

[Buccaneer]

Late last fall I went thru a Merc Mk 5, new bearings, seals, coils, etc.
Just got around to filling up test barrel today to try it out.

Good News – Started on the second pull and sounded good.
I let it warm up a while then proceeded to go "fast" to adjust
the high speed jet.

Bad News – Was okay for a little bit then it started "bucking and reving up".
Decided that the prop clutch must be slipping 😮
Pulled from test barrel and tried to tighten prop nut / clutch washers / spring.
Held the prop while tightening the nut, but prop shaft turns.
Guess I’ll have to drop the gear box, and put the drive shaft in the vise
as the manual mentions. It also mentions that shims can be added
under clutch / cone tension spring if needed.

The only other possibility I can think of is that the neutral clutch
spring could be slipping? Is that even likely or possible?
I overhauled a Mark 6 previous to this Mk 5 and had no problems
with slippage.

Tried to adjust "idle" speed so it would idle slower. Tried to "richen"
as one normally would, "counter-clockwise" to no avail.
Read manual after the fact, "clockwise" to richen 🙄

Any thoughts or suggestions on the slippage welcomed before I tear
into it.
Thanks!

Prepare to be boarded!

[dave-bernard]

could it be cavitation in the tank. I have the tool to test the slippage. did you clean the discs good.no oil grease/

[Buccaneer]

I thought about cavitation, but haven’t noticed that to be a problem
any other outboards in my tank. It’s a "half" of a 265 gallon fuel
oil tank, so lots of water.
Yes to "no grease" and yes that every thing was cleaned well.
I actually use the manual on this one!
I don’t have the "torque wrench to prop" tool, and believed I just
put the driveshaft in the vice and tighten up on the nut to what I
thought was prudent.

Prepare to be boarded!

[green-thumbs]

Mark 5 Neutral shift adjustment is covered by Service Maintenance Bulletin #170 issued May 6, 1953
I do not know if this is the problem with your Mark 5 but
Mercury believed their Dealers needed specific instructions to get it right
so may be worthwhile doing anyway.
If you believe this is worth checking out PM me
2 pages of instructions and 2 pages of illustration
so easy email
Louis

[richardg]

I mark a tourniquet out of a length of rope and use it with a screwdriver to pull the prop against the front of the lower unit. It makes it tight enough to be able to pull the prop nut up tight without the prop spinning on the prop shaft.

[Buccaneer]

Green Thumbs, PM sent.
Richard, interesting idea. Perhaps I will try that, or something
similar with clamps, etc.
First, I think tomorrow I’ll add another six inches of water to my test
barrel just to be sure I’m not cavitating like Dave? suggest.
Thanks all.

Prepare to be boarded!

[billw]

You can make the prop tool out of PVC pipe. Find a size to fit over the prop hub. Cut angled slots in the sides of the pipe, such that it will grab the prop blades. Glue on an end cap and drill a 1/2" hole in the end cap. Glue (I used Plexus) a 1/2" bolt and nut into the hole in the end cap. Now you can use a torque wrench and 3/4" socket to apply torque to the prop. Keep in mind it’s a lot easier to use a beam or dial-type torque wrench, than a click-type, in this case.

Long live American manufacturing!

[Buccaneer]

Bill, good idea on the homemade tool. I suppose one would
need 3 or 4 inch PVC pipe?
When the nut is properly torqued, would one be able to
slip (turn on shaft) the prop by hand with effort, assuming
the driveshaft was clamped in the vise?

Prepare to be boarded!

[Buccaneer]

I added more water to my test barrel and tried running
the MK5 again. That was NOT the problem. Something is
still slipping when the throttle is any higher that "Start"
position. I’m not so sure the neutral spring is adjust
correctly. When idling and shifted into neutral, I see
no change in the agitation in the barrel, nor hear
a change in RPMS. Have said service bulletin now,
so will play some more before I tear it back apart.

Prepare to be boarded!

[20mercman]

I had one that I worked on last year that I picked up at a swap meet in parts. In the process of building it from a pile of parts, I forgot to put in a thrust washer. 😳 The neutral spring then wound itself up on the drive shaft and it went from no neutral to stuck. I took it apart and the spring was fairly deformed, so I ordered a new one from marineengine.com. I got it all back together with the new spring, then all I had was neutral. 😕 I took it all back apart, and decided that the new spring had too long of a tang that was activating off of the housing instead of the lever. In anger, I decided to repair the original spring, and was able to get it back in proper shape quite easily. Put it all back together again, and it worked perfectly. I was able to return the spring to Marineengine.com. 😀

Steve

[Author]

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