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Old 22 March 2018, 05:23   #1
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Lower unit bolts

Maybe a stupid question so apologies! however are the bolts holding the lower unit on just straightforward marine grade stainless?

My Towatsoo lower unit was held on with x4 metric sized bolt heads and x2 imperial (weird) and all were showing signs of being rounded by previous attempts (not me!) to remove so I was planning to replace them all with A4 grade stainless bolts but just wanted to check in case? TIA
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Old 22 March 2018, 07:16   #2
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replace with the correct bolts Matt, sounds like someones been using open ended spanners or a crap make hence different bolts originals damaged too much. problem is imperial might have damaged the thread on the metric insert but that can be replaced.
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Old 22 March 2018, 07:51   #3
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Possibly a different hardness to a standard a4 or a2 stainless bolt there pretty soft so its possible the manufacturers used a special to hold a critical component
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Old 22 March 2018, 15:56   #4
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hi guys ive just brought a4 marine stainless steel bolts, would you recommend to use another type ? i only got them as i thought they would be the best for marine environment
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Old 22 March 2018, 18:31   #5
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Check the hardness marks on the head of the origionals and get the same grade if you can.
Stainless bolts are often much weaker than a high tensile carbon steel bolt
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Old 23 March 2018, 04:46   #6
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for a lower unit surely they cant be made from anything over than stainless?
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Old 23 March 2018, 05:38   #7
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Quote:
Originally Posted by mattwarner View Post
for a lower unit surely they cant be made from anything over than stainless?
Different manufacturers use different methods of corrosion resistance. Yamaha bolts are fully magnetic indicating high tensile steel,suzuki and mercury are none magnetic suggesting stainless but there are differing grades of stainless to achieve different hardnesses, standard 316 or 304 are both soft in comparison to hts
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