Coach screws securing engine mounts. Stainless or mild steel?

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fredrussell

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Currently replacing what I suspect are the original 33 year old (!) engine mounts on my boat. Yanmar recommend 6 year intervals so I’m only 27 years late on this.
They’re screwed into bearers with mild steel coach screws. Any reason not to replace with stainless screws? Can’t think why mild steel screws were used but thought I’d better check.
 
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fredrussell said:
Currently replacing what I suspect are the original 33 year old (!) engine mounts on my boat. Yanmar recommend 6 year intervals so I’m only 27 years late on this.
They’re screwed into bearers with mild steel coach screws. Any reason not to replace with stainless screws? Can’t think why mild steel screws were used but thought I’d better check.
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The engine mounts are made of mild steel (and rubber) so there's no advantage in using stainless steel holding down screws.
 
I used stainless because they were not expensive and readily available. The engine mounts are well painted whereas mild steel bolt heads are not so you may get unsightly rusting if you do get a leak.
 
One of my mounts is just below the end of the heat exchanger and despite care gets an occassional splash of salt water. Over 27 years that could build up to a problem! It might depend what they screw into and whether you judge they could rust. I used stainless when I replaced mine - cheap enough ordered online.
 
I fitted a new engine into my Stella 25 years ago and went to some trouble sourcing stainless coach screws. Neighbour had an identical engine fitted into an identical boat by a professional engineering firm. I noticed that they used mild steel coach screws. When I mentioned this, the engineer just shrugged and said it would "probably see us out".
Probably fair comment but I still think stainless is better.
 
fredrussell said:
Currently replacing what I suspect are the original 33 year old (!) engine mounts on my boat. Yanmar recommend 6 year intervals so I’m only 27 years late on this.
They’re screwed into bearers with mild steel coach screws. Any reason not to replace with stainless screws? Can’t think why mild steel screws were used but thought I’d better check.
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If the screws, like the mounts, are 33 years old. I don't see anything to worry about. :p
 
Has anyone asked why the ones that were taken out cannot be re-used?

The mild steel machine screws that I took out when I replaced the engine flexible mounts on my boat many years ago were very old, probably dating back to 1982 when a new BUKH engine was installed. They were, surprisingly, BSF threaded, which suggests the installing engineer used what he had handy.

They were in perfectly good condition, so I put them back; where they remain to this day.

Mild steel engine feet, mild steel engine bearers, mild steel screws. What's not to like?
 
Poignard said:
Has anyone asked why the ones that were taken out cannot be re-used?

The mild steel machine screws that I took out when I replaced the engine flexible mounts on my boat many years ago were very old, probably dating back to 1982 when a new BUKH engine was installed. They were, surprisingly, BSF threaded, which suggests the installing engineer used what he had handy.

They were in perfectly good condition, so I put them back; where they remain to this day.

Mild steel engine feet, mild steel engine bearers, mild steel screws. What's not to like?
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I assumed we were talking about coach screws, square or hex head with a tapered wood screw body to fix into a wooden engine bearer. Different thing to machine screw.
 
DanTribe said:
I assumed we were talking about coach screws, square or hex head with a tapered wood screw body to fix into a wooden engine bearer. Different thing to machine screw.
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Thank you, I know perfectly well what the difference between a machine screw and a coachscrew is.

Had my boat had mild steel coachscrews and not machine screws, and they were in good condition (as they may well have been if they were galvanised), I would have re-used them.

The same principle applies in either case: 'If it ain't broke, don't fix it'. or, to paraphrase that piece of sound advice, 'If it's re-usable, re-use it'!
 
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Well, easy decision in the end as one of the rusty screws has sheared on removal. Not a total tragedy- should get away with drilling new pilot hole a few mm over from (flush) sheared screw. I was lucky to get the others out as one or two the square heads had corroded and there was only just enough ‘meat’ left to get a 1/2” socket ext bar on.
 
fredrussell said:
Well, easy decision in the end as one of the rusty screws has sheared on removal. Not a total tragedy- should get away with drilling new pilot hole a few mm over from (flush) sheared screw. I was lucky to get the others out as one or two the square heads had corroded and there was only just enough ‘meat’ left to get a 1/2” socket ext bar on.
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I think that you have the answer to your original question now.(y)
 
penberth3 said:
Not really! 33 year old screw fastener fails on removal - so what? So the choice is plain steel with paint/grease, a galvanised option has appeared, or stainless. No definitive answer yet.
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That’s interesting. Which of those three options would you choose then?
 
Poignard said:
Has anyone asked why the ones that were taken out cannot be re-used?

The mild steel machine screws that I took out when I replaced the engine flexible mounts on my boat many years ago were very old, probably dating back to 1982 when a new BUKH engine was installed. They were, surprisingly, BSF threaded, which suggests the installing engineer used what he had handy.

They were in perfectly good condition, so I put them back; where they remain to this day.

Mild steel engine feet, mild steel engine bearers, mild steel screws. What's not to like?
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Mild steel, apparently.
 
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