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Author Topic:   1975 MONTAUK Re-power; Problems in Mounting Modern Engine
RJG posted 08-22-2015 01:08 PM ET (US)   Profile for RJG   Send Email to RJG  
Has a vintage [1975 Boston Whaler MONTAUK boat ever been] re-powered with Suzuki 90-HP four-stroke-power-cycle outboard engine? Were any problems [encountered in re-powering a 1975 Boston Whaler MONTAUK] with the engine mount? We chose [to re-power a 1975 Boston Whaler MONTAUK with a Suzuki 90-HP four-stroke-power-cycle outboard engine] as it seemed it would be an easy trade out. ([The boat previously was powered by] a 1989 Suzuki DT100 outboard.) I got a bit concerned when I went by the dealer and his technician seemed to have difficulty with the mounting bolt layout.

[The technician said] the splash well was a bit shallow, and it would mean raising the engine [quite] high? Does this sound right? I would think this would be a common setup? Thanks in advance.

jimh posted 08-22-2015 01:44 PM ET (US)     Profile for jimh  Send Email to jimh     
Questions about the engine mounting of modern engines using the standard BIA engine mount hole layout on older Boston Whaler boats are frequently asked. An answer has been prepared in the FREQUENTLY ASKED QUESTIONS article. See

Q8: How Does the Engine Mount to the Transom?

Read closely the section under the heading, "Problems specific to Boston Whaler boats."

Most modern engines, and I would include a 1989 Suzuki outboard in that group, have the same engine mounting bracket hole layout. Perhaps the old Suzuki engine had a blind hole mounting option, and that is no longer used on the c.2015 Suzuki engines.

jimh posted 08-22-2015 01:47 PM ET (US)     Profile for jimh  Send Email to jimh     
It is hard to know how high the technician at your dealer plans to mount the new engine because the description of the mounting height as "[quite] high" is a bit hazy.

How high is the technician at your dealer planning to mount the new Suzuki engine on the transom of your 1975 Boston Whaler MONTAUK?

Was the location of the mounting holes on the engine mount on the new c.2015 Suzuki different from the their location on the 1989 engine? I would have thought they would be the same. How high was the old engine mounted?

You should know that it is very common to mount an engine on a MONTAUK at least one-hole up from the lowest position, and mounting two-holes up is not unusual.

contender posted 08-22-2015 03:05 PM ET (US)     Profile for contender  Send Email to contender     
I would raise the engine so the cavatation plate is about 1-3 inch above the bottom of the boat. I understand what you are saying for I have the same boat/hull. The problem is that they no longer have the blind hole in the engine bracket for doing this. Last year I mounted a 60 Suzuki 4 stroke on the same whaler in the bahamas, We ended up using only the top two holes in the engine bracket and filling in the lower ones on the transom. Some people use lags in the bottom holes from the outside, I would not do this. Moving the engine up two holes you might be able to use the bottom holes on the bracket (Im not sure), but moving the engine to high you will lose performance and it will be harder to plane. The only way I could be sure you could use all 4 holes is by using a bracket,(I would use a manual one 4 inch would be plenty) this would also give you the choice to move the engine up and down with ease. Those years hulls (73-84) the splash wells were just to shallow and the engine designed has changed as well since then...good luck
RJG posted 08-22-2015 03:57 PM ET (US)     Profile for RJG  Send Email to RJG     
The technician was trying to use a metal template to mark the mounting holes. I would have thought the new engine would have been able to use the existing mounting holes but he seemed to think the bottom mounting holes on the new engine were lower than on old engine thus the new mounting
RJG posted 08-22-2015 04:08 PM ET (US)     Profile for RJG  Send Email to RJG     
Yes, Contender, we have the same problem. Mounting the new engine using only 2 bolts sounds a bit dodgy particularly since my boys will be doing plenty of wakeboarding and I can't see running running lags either. A simple bracket may be the answer. Thanks for the input.
jimh posted 08-22-2015 05:14 PM ET (US)     Profile for jimh  Send Email to jimh     
Did you read the FAQ? Your technician needs to read it, too.
RJG posted 08-22-2015 07:09 PM ET (US)     Profile for RJG  Send Email to RJG     
I did. [The engine mounting to transom method described in FAQ Q#8 answer called the fifth-workaround] seems to be the answer. Thanks again!
jimh posted 08-23-2015 08:07 AM ET (US)     Profile for jimh  Send Email to jimh     
Yes, the fifth workaround approach is probably what was used in the previous installation. Your dealer's outboard engine technician probably placed a BIA template onto the transom and found that the existing holes in the transom did not align with the holes in the template. On the transom the lower pair of holes was probably located at a shorter offset from the upper pair than on the template, done intentionally to allow the bolts to emerge from the transom above the shallow splash well.
RJG posted 08-23-2015 10:29 AM ET (US)     Profile for RJG  Send Email to RJG     
This is how the old Suzuki DT100 was mounted befroe it was removed.

Forgive as I have forgotten how to post from a photo album

Tom W Clark posted 08-23-2015 10:48 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Yours is an FAQ. The solution is simple:

Fill the two lower bolt holes in the transom and drill two new holes that are 9-7/8" apart and 6-1/2" below the existing upper holes.

Mount the new outboard two holes up.


contender posted 08-23-2015 06:50 PM ET (US)     Profile for contender  Send Email to contender     
RJG: I remember seeing one time that a person used a stainless all-thread and ran it through the transom all the way to inside of the boat, it was done nicely, but I did not care for it. I would make a cardboard template of the engine bracket and play with it on the hull of the whaler. This way you can mark all the holes on the bracket and move it up and down to see if it will fit. If you have a problem with the template, the dealer [may] let you copy theirs or maybe borrow their metal factory template for mounting outboards. Good luck
RJG posted 09-04-2015 03:47 PM ET (US)     Profile for RJG  Send Email to RJG     
The install is complete and we are pleased with the result. The harness is a bit long but I think we can pull it back into the console and create a loop. suzuki%20motor%204_zpsogzb7dtt.jpg.html?o=3

dgoodhue posted 09-04-2015 06:40 PM ET (US)     Profile for dgoodhue  Send Email to dgoodhue     
The motor is mounted too low. Move the motor up one set of holes so that it is 2 holes up.
jimh posted 09-04-2015 11:35 PM ET (US)     Profile for jimh  Send Email to jimh     
From the image available at jpg.html

it appears to me that the installer drilled the lower engine mounting hole in the transom at a spacing reduced by 0.75-inch from standard, or 1-hole. It also appears the installer drilled the holes on an upward angle toward the bow to get the holes to exit above the bottom of the splash well. Both of these methods are suggested in the literature in the FAQ and in the resources linked from the FAQ.

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