Engine Mounting and Bolt Orientation

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
Oldslowandugly
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Engine Mounting and Bolt Orientation

Postby Oldslowandugly » Fri Apr 17, 2020 4:03 pm

[This topic has been separated from another repair topic. This topic is discussing the method of mounting an engine. To discuss how engine mounting height affects performance, please see the PERFORMANCE forum. This discussion is in regard to the process of mounting, particularly the location and oreintation of bolts, not the process of optimizing boat speed and performance from adjustments of mounting height. The FAQ discusses engine mounting height in detail. See

Q8: How Does the Engine Mount to the Transom?
http://continuouswave.com/whaler/reference/FAQ/#Q8
Q9: What is the Standard Transom Hole Layout?
http://continuouswave.com/whaler/reference/FAQ/#Q9

The FAQ discusses use of blind holes and elevated lower mounting holes, particularly in regard to Boston Whaler boats with shallow transom splash wells where the lower bolts would exit the transom on the inboard side below the splash well bottom. Reading the FAQ is highly recommended---jimh]

When I bought my boat it had a Mercury 60-HP c.1985 engine. The location of that engine's mounting holes were not even close to what I needed for my 1993 Evinrude 48 SPL. I filled the old holes and drilled new ones.

I rested the 1993 Evinrude 48 SPL outboard engine on the top of the transom for support. That location put the engine [anti-ventilation plate] where I wanted it [in relationship to some unspecified reference point].

I used two lower engine holes that [were not part of the notched slot that is located in the BIA recommend position range]. Using those holes put the mounting bolts safely above the splash well curved bottom.

transomEngineBolts.jpg
Fig. 1. A view of the transom engine bolts on inboard side, also shown in Figure 4.
transomEngineBolts.jpg (11.11 KiB) Viewed 952 times


engineMountingBolts.jpg
Fig. 2. Transom mounting bolts on outboard side
engineMountingBolts.jpg (11.53 KiB) Viewed 951 times

biggiefl
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Re: Engine Mounting and Bolt Orientation

Postby biggiefl » Mon Apr 20, 2020 11:34 am

No offense, but that is not a correct mounting either. You should raise the engine OFF the transom and use the slots below the blind holes.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

dtmackey
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Re: Engine Mounting and Bolt Orientation

Postby dtmackey » Mon Apr 20, 2020 12:18 pm

Ideally [an outboard engine] should be in the third hole for the most efficient mounting location. There is less gear case in the water , and that allows for better efficiency. [This mounting height] also prevents the bolts from being buried in the bottom of the motor well.[I believe here the intent is to say the engine mounting height should be two-holes-up. Describing mounting holes using ordinal numbers causes confusion as no direction if specififed.--jimh]

If you are swapping to an F70, have the dealer mount [it as shown below, in the two-hole-up from lowest position]. And utilize the blind holes in the transom bracket.

Image
FIg. 4. Engine mounted in the two-holes-up from lowest position.

Image
Fig. 5. I need to fill the old mounting holes with something more permanent. I will fill with a composite material, glass over front-and-back, and re-spray with Awlgrip.

Image
Fig. 6. The top bolts are double nutted, the lower bolt screws directly into the blind hole in the outboard bracket.

In full disclosure, the boat is a mess and I just pulled it out of winter storage on Sat and getting my to-do cleaning and prep list together now.

Image
Fig. 7.
Image
Fig. 8
D-

jimh
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Re: Engine Mounting and Bolt Orientation

Postby jimh » Mon Apr 20, 2020 12:58 pm

Re engine mounting height description, please use the method of description in terms of number of holes up from lowest. Using ordinal numbers (first, second, third and so on) to describe the hole is not always clear as it depends on which direction the ordering is from hole and how many holes there are in the engine mount.

See the permantly top-listed article

ENGINE MOUNTING HEIGHT
viewtopic.php?f=7&t=739

jimh
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Re: Engine Mounting and Bolt Orientation

Postby jimh » Mon Apr 20, 2020 1:05 pm

Re the orientation of the machine screws in the engine mounting:

The instructions for engine mounting from EVINRUDE, a company that has over 100-years of experience in outboard engines, specify that the engine mounting bolts are installed with the bolt HEADS on the inboard side of the transom, and the nuts are on the outboard side of the transom for mounting larger engines. See diagram below:

evinrudeMountDiagram.png
Fig. 9. Drawing from Evinrude showing engine mounting details with bolt orientation. Note the use of retaining straps to hold the mounting bolts in place before the engine is lifted onto the transom. From "Predelivery and Installation Guide "for E-TEC engines.
evinrudeMountDiagram.png (48.75 KiB) Viewed 933 times


Were I to install an outboard engine, I would follow the method that Evinrude requires, rather that adopt an opposite orientation of the engine mounting bolts through the transom.

By using the method required by Evinrude, I see advantages in the application of sealant to the portion of the bolt that is passing through the hull. The bolts can be pre-installed in the holes and pre-coated with sealant.

In Figures 1 and 2 above show the engine mounting bolts are installed in the opposite direction than recommended by Evinrude.

In Figures 4, 5, and 6 above the engine mounting bolts are installed in accordance with the recommendation by Evinrude.

jimh
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Re: Engine Mounting and Bolt Orientation

Postby jimh » Mon Apr 20, 2020 1:36 pm

Oldslowandugly wrote:When I bought my boat it had a Mercury 60-HP c.1985 engine. The location of that engine's mounting holes were not even close to what I needed for my 1993 Evinrude 48 SPL.


Your experience is a good demonstration of the need to standardize engine mounting bracket hole locations, which is what occured when the BIA (Boating Industry Association) adopted a recommendation for standard engine bracket mounting hole locations. I suspect that the Mercury engine you report as c.1985 may have been older than that. I believe the BIA standard was already in use by 1985.

A date of 1984 is often mentioned as being the epoch when engine mounting bracket hole location began standardizing on one layout. Of course, since Mercury's mounting bracket needed to change to meet the new standard, it is very possible Mercury continued to make engines with their old mounting brackets for some time after 1984.

jimh
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Re: Engine Mounting and Bolt Orientation

Postby jimh » Mon Apr 20, 2020 1:55 pm

A further advantage of following the Evinrude recommendation is elimination of bolt ends sticking into the splash well area. Bolt heads extending into the splash well area can create snags for engine rigging hoses or cables, or for steering cables.

Oldslowandugly
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Re: Engine Mounting and Bolt Orientation

Postby Oldslowandugly » Mon Apr 20, 2020 3:21 pm

I have always mounted the motor with the bolt heads on the outside. The reason is that the motor "lip" that overhangs the transom keeps the motor from being removed cleanly from the transom without removing the bolts. If you mount the motor raised that is possible, but I don't, I rest it on the transom. Thus, since the bolts must be removed anyway, I find that having the nuts on the inside protects them from sea water induced corrosion. Then the nuts come right off and the bolts cab be driven out the rear freeing the motor. I also use anti-seize and then paint over them for protection from sea water. Of course to each his own. This is what works for me.

biggiefl
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Re: Engine Mounting and Bolt Orientation

Postby biggiefl » Mon Apr 20, 2020 3:33 pm

I put the nuts on the outside as it makes adjusting the engine much easier as you can just drive the bolt in a couple inches instead of removing it. I also usually use a flat plate on the inside to spread the stress and keep the bolts from damaging the gel. I have never had corrosion problems using SS hardware. Like Jim stated, the jagged bolts on the inside are great knuckle scrappers and may get in the way of rigging.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).