Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  Engine Mounting Hole Alignment

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Engine Mounting Hole Alignment
billh1963 posted 09-22-2003 08:42 PM ET (US)   Profile for billh1963   Send Email to billh1963  
Please explain to me what is mean by hole alignment when repowering? I will soon be repowering an 1984 17-Montauk with 90 Evinrude (currently has a 80-HP Mariner). I've searched the threads and I keep reading about "move the motor one hole up". What does that mean?

Also, everyone says to keep the anti-cavitation plate level with the bottom of the hull. Will that occur naturally with the engine resting on the transom or is it necessary to use wedges to get it to the proper height?

Sorry for the stupid questions :-)


jimh posted 09-22-2003 09:00 PM ET (US)     Profile for jimh  Send Email to jimh     
The recommend practice for mounting outboard motors is to drill one set of holes in the transom, using the template supplied by your outboard engine manufacturer. (Your dealer should give this to you when he delivers the engine.)

The engine mounting bracket will be pre-drilled with typically four sets of mounting holes. If the engine is mounted in the lowest possible position, the topmost set of holes will be used, often called "No. 1" holes. This will place the engine at rest or almost at rest on the transom's upper edge.

The motor can also be mounted in higher positions on the transom by using different sets of holes on the engine's mounting plate. For most Boston Whaler boats, the recommended initial mounting position was "one hole up", that is, with the engine raised about 0.75 inches and mounted to the transom using the second (or "No. 2") mounting holes on the engine bracket.

The position of the anti-ventilation plate (AV plate) should generally be no lower than the bottom of the boat when the motor is trimmed down to its lower limit.

Depending on the motor, its lower unit, the boat, etc., it may be possible to raise the motor so that the AV plate aligns above the keel of the boat. This is often determined experimentally, and the precise limit to how high the engine can be raised depends on many factors.

In a general sense, you want to raise the engine in order to reduce the amount of drag caused by the lower unit being immersed in the water. Once the boat comes to hydroplane, much of the power of the engine is used just to drag its own lower unit and propeller though the water.

Care must be taken in raising the lower unit so that the water intake port does not become ineffective. Loss of cooling water through the engine can cause serious and expensive damage.

Often your outboard motor owner's manual will provide you with valuable information about the mounting holes and their location, particularly where to drill them in the transom. The engine maker's advice will typically call for the engine to be mounted using a set of holes that place it lower than the position that gives best performance. The engine maker is concerned with the position of the water intake.

billh1963 posted 09-22-2003 09:03 PM ET (US)     Profile for billh1963  Send Email to billh1963     
Thanks, Jim.

The engine is used and I won't have a template. I have read on some threads that Mercury Marine and OMC share mounting patterns. Is this correct? Also, could OMC provide a template for an older motor?

Thank you!

arnereil posted 09-22-2003 09:44 PM ET (US)     Profile for arnereil  Send Email to arnereil     
I'd just use the motor mount as the template. Put the motor on and use a couple of big C clamps to hold it against the transom (scrap plywood on the front of the transom). Drill the holes in the transom through the top holes in the mount. Then you can raise the motor up another hole or two if you want. If you use a lower set of holes you will not be able to raise the motor as much, or not at all.

When i jacked up the motor on mine, I used a floor jack under the mount to slide it up. Because of the black rubber trim (i did not want to remove the motor to cut the trim), i made a spacer out of 3/16 plywood, and raised the motor as high as it would go. Once the bolts were in place, i cut a block of wood to fill the space between the top of the transom and the bottom of the motor mount....

If anyone sees a fault with the above, please chime in..

Dick posted 09-22-2003 10:34 PM ET (US)     Profile for Dick  Send Email to Dick     

I think that you will find that the holes drilled in the transom will fit the new motor. So no new holes should be needed.

Whaler suggests one hole up for a 90 on a Montauk. Thats a good place to start and then adjust as necessary.


Post New Topic  Post Reply
Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.