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Old 31-12-2010, 03:57   #1
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Outboard Motor Mounts

I have a 1994 Johnson 15hp that I am rebuilding the upper motor mount system.
The original system is no longer available and junk anyway.

The original design used 1/4"x20 (about 2.5 inches long) from inside the exhaust housing to the threaded steering bracket.
Both ends are exposed to salt water and they used stainless.

My concern is the stress on a stainless bolt with my new design that will have less dampening factors than the original design and I am worried about stainless breaking as the originals did anyway.

Could I use a higher grade (non-stainless) bolt instead?
Something not as brittle as stainless that will hold up in the salt conditions?
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Old 31-12-2010, 05:28   #2
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Why not consider using 3/8" 316 Stainless Bolts - doubt that a 15hp engine is going to break those.

McMaster-Carr
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Old 31-12-2010, 05:31   #3
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Carr mcmaster also has what they call an ultra bolt grade 9 and coated as not to rust, Allen head check it out
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Old 31-12-2010, 05:50   #4
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Quote:
Originally Posted by Laidback View Post
Why not consider using 3/8" 316 Stainless Bolts - doubt that a 15hp engine is going to break those.

McMaster-Carr
the threads in the steering bracket are 1/4x20.
there is not enough wall space for me to drill the threads to that size.
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Old 31-12-2010, 05:58   #5
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A higher grade galvanized bolt may be the ticket.
I need it done today so Napa or West Marine will have to do.

What grade is stainless?
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Old 31-12-2010, 06:02   #6
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When forced to use steel bolts I have had decent results coating the whole bolt with a brush on gasket sealer Most likey the factory bolts were steel on that motor SS bolts are grade 5 or so
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Old 31-12-2010, 06:44   #7
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See the Bolt Grade Markings and Strength Chart
Hex Bolt Identification Guide - Engineers Edge
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Old 31-12-2010, 12:20   #8
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Thanks All,

Your advice helped alot and my project is complete and I feel very satisfied with the results.

Cheers
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