---

Searched the forums and couldn't find this, specifically. I plan to remove the OMC and install a 2013 Honda BF90. Anyone have the specs on the BF90 mount bolt pattern? I'm trying to figure out whether or not new holes will be required in my transom.

If someone knows them, would you please reply with the specs:

Distance Between Upper Bolt Centers:
Distance Between Lower Bolt Centers:
Range Between Upper and Lower Bolt Centers (e.g., top hole to bottom of slot, and bottom hole to top of slot):

---

Sure,
We have lots of current threads on this one.
4th one below yours at this time right on the front page.
http://www.whalercentral.com/forum/vi...pid=114407

Also in the Articles link under Outboard Motors and Rigging:
http://www.whalercentral.com/articles...icle_id=82

You most likely will want to drill the "Green Holes".
However, layout the holes on the inside and view the clearance for the washers.

Also see this fairly current thread:
http://www.whalercentral.com/forum/vi...rowstart=0

Bottom Line, fill the Blind Holes and drill the Green holes making sure you have clearance at the bottom of the splashwell for the partial washer.

NOTE:
Because you have a 1986 model, you may be able to drill the Yellow or even Red holes.
However, make positively sure by laying out the holes on the inside of the transom.

We really need to add the info on when the splashwell got deeper.
It was around 1986 but we need more info from the members.
For everyone: see this article and let us know if you have the deeper splashwell so we can add that info to the list.
http://www.whalercentral.com/articles...icle_id=17

---

I just repowered from a 90HP Evinrude Ocean Pro to a Honda BF90D. The existing bolt holes matched the Honda perfectly. I do not know if the 70 hp OMC uses the same bolt pattern as the 90 OMC but I'm sure someone here will know. Good luck with the Honda its a great engine.

---

I currently have a 70 hp Johnson on my 17' Montauk. The motor weight is 256lbs? I see the new 90hp optimax has a weight of 374lbs and the 4 stoke is 369lbs. This seems to add a lot of weight. Should i be concerned?

---

Yes.

---

I just went from a 300lb engine to a 340lb engine on my 1979 17 Montauk. There is no doubt that these boats are trim sensitive. I can tell the 40lb difference but it is not a problem, the boat runs just fine. My guess is that your boat will handle the Honda just fine, but you may have to get used to how the motor affects the trim from the 70hp engine. The 70ho was a light motor and I am sure the boat jumped on plan and had no bow up even at low planning speed. I would say be ready for more of a bow up slow plane and a flat or bow down as you get into the power band of the motor. I think the old 70hp will have let you run flatter at slower speeds than the Honda will.

---

I repowered from a 90 Johnson VRO to a Etec 115. many have thought this was not a good move due to the weight increase. however, I have moved 2 batteries and oil tank into the console and have a trolling motor mount full time on the bow. I seem to be balanced out fine.

not knocking anyone else's motor - but the 4cyl Etec is a beast. I bought it due to the $$ savings over a 90 based on Evinrude offers at the time - free rigging, controls, prop, and discount and increased free warranty.

good luck.

---

rvschulz, did you mean "2cycl etec is a beast"?

---

I think he meant 4 cylinder E-Tec 115hp is a beast.
Meaning huge in size (to me) on a 16/17 model.

He doesn't show any new photos of his new E-Tec on his personal page.
Would be nice to get a look.

---

The original poster may find the Honda bolts right up to the OMC holes. Since the hull is a 1986, the engine did not need to be blind hole mounted, so perhaps it wasn't.

I have always thought that the splashwell was deepened at the same time they made other modifications to the hull, such as the bow locker cover size, making hull 100% desert tan color on the outside, and changed the center console. Wasn't that model year 1983?

---

Finne,

So far, the only photos and proof we have is a 1987 model Montauk with the deeper splashwell.
3C5156 stencil number but we do not know the HIN and rvshulz hasn't given it to us yet.
http://www.whalercentral.com/infusion...r_id=18198

We have been asking members help on this but so far, NADA, Nothing, Zip.
And no, I will not take someone's verbal statement. We need to see photos for proof.
Both inside and out is the best.
Anyone?

---

I have a Yamaha F80 on my Montauk 17. Weight is around 375 lbs. The drain holes in the motor well are well under water most all the time, except when the boat is up on plane.

I don't consider this a problem, but I am sure some people would.

Scott

---

Joe - the reason I think it was 1983 or 1984 model year (at the latest), is that for 1984 model year boats and engines, the B.I.A. bolt standard (invented and in use by OMC since at least 1974) was officially adopted for all engine manufacturers. As you know, Mercury never used the blind hole system, and beginning in 1984 the 75, 90 and 115 engines all had the new B.I.A. standard hole pattern brackets, containing 5 hole sets.

So with the engine manufacturers now using the B.I.A. pattern, including the newly introduced Yamahas, it would make sense that all boat manufacturers would need to have transom configurations that could accomodate this new engine convention, including Boston Whaler. That is why I am betting on 1984 model year Montauks. I have a friend with a 1985 Montauk, rigged originally with a 75HP 1985 Merc, all the way down, and the transom accomodates the lower bolts with no problem.

One way to tell would be to find photos of Montauks rigged with yellow/brown stripe Mercs (1984 & 1985) with engines all the way down on the transom. With no blind hole option, those boats would have to have the deeper splashwell to accomodate the 8" vertical pattern.

---

Yes, a Honda BF90 uses the same BIA bolt spacing as all other large outboards have since the mid 1980s. This bolt pattern was first used by OMC in 1960. Other manufacturers began copying it soon after. Mercury was the last but they switched over fully by 1985.

Some other manufacturers also copied the auxiliary bolt locations (aka "blind holes") but since one would want to use those today, it matters not if a new motor has them.

It also matters not whether a Montauk has a deep splashwell or not because there is no reason on Earth to have a motor set all the way down on the transom.

Identifying the year the splashwell depth changed, along with other mold changes like the bow locker is best left to a separate thread, but suffice it say here that all changes did not occur simultaneously.

---

yes I do need to update my pics since I have done a few other 'mods'. I meant 4 cylinders - i'm sure the 3 cylinder 90 is a very good motor. I appreciate the extra oomph getting up on plane.