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Old 18 March 2018, 23:54   #1
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Fitting outboard questions

Hi
planning on fitting outboard next week and just wanted to get some views/advice. i was told that when fitting outboard to transom that its better to have the outboard not fully resting on the transom ( so not to have all the weight resting on top of the transom ) and by doing this it can help reduce vibrations. example raised 5mm above the top of the transom. So my plan was to put a 5mm plate on the top of the transom before i mark the bolt holes then remove plate before bolting up.

but then i have also heard ( youtube ) you shouldn't let the weight of the outboard be on the bolts alone i don't believe this to be true as why would there be additional bolt holes inlace on the outboard to raise or lower the outboard, this would end up with the outboard not sitting on the transom top, so back to my original way i guess ?

before bolting down fully, what would you recommend for filling the bolt holes and putting a seam around the outboard bracket before finally bolting in place ?
your help and advice is appreciated
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Old 19 March 2018, 08:31   #2
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Id start with the engine vertical at the boats in water attitude and the cavitation plate slightly above the keel line of the boat (10mm ish) and drill for one of the centre holes then you have adjustment up or down as required.No problem with engine hanging on bolts Id seal the holes with sikaflex or similar but wouldnt seal around the bracket
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Old 19 March 2018, 08:41   #3
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Ok.

1) DON'T drill any holes. The original ones should line up. (International standard)

2) Raising and lowering the position of the engine is about trim and performance and it's position should now be defined by which holes in the engine bracket you choose to use. It's nothing do do with "resting on the transom" etc. I'd do a bit of googling on "outboard mounting height"

3) There is no need to "seal round the bracket" it's the bolts that need sealing.

There'll be more replies with more detail coming
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Old 19 March 2018, 08:45   #4
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There are different schools of thought depending on who you speak to.

I've had an engine sitting on the transom and on bolts only and never noticed difference. Height of cav plate is all that matters.

I've also had an engine fitted that the holes were drilled much bigger and some sort of epoxy used to fill it and then drill the normal hole through it. This way you are guaranteed no water gets into the transom. Only 1 outboard shop done this I've been to but I've read of it being the normal for some builders.

Most of my outboards were purely done with some sikaflex round the bolts and call it good.

One thing to consider is if you are going to offset the engine, different schools on that too.
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Old 19 March 2018, 09:48   #5
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Ok.

1) DON'T drill any holes. The original ones should line up. (International standard)

2) Raising and lowering the position of the engine is about trim and performance and it's position should now be defined by which holes in the engine bracket you choose to use. It's nothing do do with "resting on the transom" etc. I'd do a bit of googling on "outboard mounting height"

3) There is no need to "seal round the bracket" it's the bolts that need sealing.

There'll be more replies with more detail coming
this would be good if i don't need to drill new holes, i would have thought different makes of outboard mariner, yamaha, Honda would have been different.
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Old 19 March 2018, 09:56   #6
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my plan was to have the cav plate around a inch above keel, as the outboard im fitting is heaver then the one they were originally fitted with. after watching some youtube vids i did see one that showed drag at the level with cav/keel and performance was better around a inch above keel. i was thinking this might be a good option due to the weight difference in the outboard
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Old 19 March 2018, 10:42   #7
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this would be good if i don't need to drill new holes, i would have thought different makes of outboard mariner, yamaha, Honda would have been different.
Consolidated in mid 70's. Yamaha was last to go but they're all the same.
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Old 19 March 2018, 10:51   #8
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this is music to my ears, fingers crossed. i will get tape out and check later
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Old 19 March 2018, 11:49   #9
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Quote:
Originally Posted by arkamelis View Post
my plan was to have the cav plate around a inch above keel, as the outboard im fitting is heaver then the one they were originally fitted with. after watching some youtube vids i did see one that showed drag at the level with cav/keel and performance was better around a inch above keel. i was thinking this might be a good option due to the weight difference in the outboard
Sounds like a good plan we used to keep moving up till we got the best performance without too much ventilation
Theory is less engine in the water then less drag up to the point where the prop starts to grab too much air
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Old 19 March 2018, 19:16   #10
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re fitting

brilliant i now have some ideas to go with, if all goes well i will be fitting this weekend, so thank you all for your help and advice, you've been very helpful, i will keep you posted. again thanks
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Old 21 March 2018, 20:43   #11
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Have you got this fitted yet? I thought the older force engines used their own hole pattern.
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Old 21 March 2018, 20:45   #12
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Have you got this fitted yet? I thought the older force engines used their own hole pattern.
hi there, i have a good feeling your right, no offence to the other members, but were talking about americans
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Old 21 March 2018, 20:47   #13
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no not yet my plan is to do it this saturday, ile be taking drills and drill just incase
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Old 21 March 2018, 22:13   #14
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This is what the bolt pattern should be.

The top pair of holes are spaced 12-7/8" on center.
The bottom pair of holes are spaced 9-7/8" on center.
The spacing between the top and bottom pair of holes is 8" on center.
The centerline of the top holes is 2-inches below the top of the engine bracket therefor the holes in the transom should be no greater than 1-7/8" and no less than 1-3/4" below the top of the transom.

"(Courtesy Hull Truth)" BIA standard
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Old 21 March 2018, 22:25   #15
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The force engines were a reincarnation of the old chrysler designs which was an old very basic range of engines bought by Brunswick to cheaply power the bayliner range I doubt they cast new brackets to conform to a new standard
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Old 21 March 2018, 23:01   #16
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The force engines were a reincarnation of the old chrysler designs which was an old very basic range of engines bought by Brunswick to cheaply power the bayliner range I doubt they cast new brackets to conform to a new standard
Could be but the early 70s Chryslers still used clamp bolts with securing bolts at the bottom of the brackets. They must have moved on to make them "height adjustable" at some point and the standard was based on a 60s Johnson so the pattern was around then. They wouldn't have had anything to spend on development until Brunswick bailed them out early 80s so I'd guess that was when any change would be made.
Don't know, but worth measuring out.
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Old 22 March 2018, 21:09   #17
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ok been over to the boat today, and nothing seems to match at all, the two top holes already there are approximately 245mm apart from centre of holes, from the top of the transom there approximately 35mm down again to the centre of hole ( they are 12mm holes ).
the next two lower holes are 240mm apart and look to be 10mm holes not 12mm and from the top of the transom there 220mm down.
i have no idea what outboard was originally fitted to the boat, but i am going to have to fill holes and start from fresh and put in the new one for the yamaha which straight away are totally different to whats there
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