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Author Topic: Sheared Motor Mount Bolt  (Read 4021 times)

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scgunner

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Sheared Motor Mount Bolt
« on: July 27, 2021, 07:00:29 AM »

On a sail trip to Catalina island an interesting, or alarming, thing happened, while charging the batteries with motor I noticed on the front right motor mount the front bolt bouncing around in the slot. I pulled it out and saw it was sheared in half, I checked the other seven, which were fine. That's a pretty beefy bolt, I've no idea what could cause that.                                                                                                                                                 
                                                                                                                                                                                                        I'm just wondering if anyone has had a similar experience. If so how did you proceed with the fix.
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Kevin Quistberg                                                 Top Gun 1987 Mk 1 Hull #273

glennd3

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Re: Sheared Motor Mount Bolt
« Reply #1 on: July 27, 2021, 01:40:48 PM »

Kevin I have not had it happen to me but I have been researching replacing my mounts on this site and broken and stripped bolts have been discussed at some length. I would search this site with motor mounts being the topic. Broken bolts have been repaired.
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Glenn Davis
Knot Yet
1990 Catalina 34 Mk 1.5
Hull 1053
TR/WK
M25XP
Patapsco River
Chesapeake Bay Maryland

Jim Hardesty

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Re: Sheared Motor Mount Bolt
« Reply #2 on: July 27, 2021, 01:51:24 PM »

Kevin,
My previous boat had a broken motor mount bolts.  Looked like it had been that way for a while.  I replaced them all, used the boat a lot for 5 seasons and never had another problem with motor mounts.   Think it's just something to fix and keep check-on.
Jim
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Jim Hardesty
2001 MKII hull #1570 M35BC  "Shamrock"
sailing Lake Erie
from Commodore Perry Yacht Club
Erie, PA

Ron Hill

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Re: Sheared Motor Mount Bolt
« Reply #3 on: July 27, 2021, 02:45:00 PM »

Guys : Those engine bolts are tough, but they do break!!  If you make a slippage mark on the nut you'll probably help you spot that "something is happening"

I have slippage marks on all of the visible nuts on that engine!!  I have two bottles of fingernail polish onboard a red and a white - just to make slippage marks!!

A thought
« Last Edit: July 27, 2021, 02:55:08 PM by Ron Hill »
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Ron, Apache #788

ewengstrom

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Re: Sheared Motor Mount Bolt
« Reply #4 on: July 28, 2021, 05:50:23 AM »

I pulled the motor on Ohana over the winter of 2019 for heavy maintenance and found that very same bolt had sheared off well inside the engine bed itself.
I thought about just angling the new bolt down next to the broken piece inside the engine bed but felt it would be better to remove that broken piece so the new bolt wouldn't be torqued in at an odd angle and possibly shear off again.
To get to the broken bolt end I used a dremel tool to widen the hole somewhat and then used an "easy out" to extract the roughly 1.5" broken piece inside the mount.
I now had a bolt hole that was far too big for a new bolt....so to fix this issue I used a chisel and squared the hole off and then carefully fit a piece of mahogany to it and imbedded the whole piece in epoxy. Once dried I was able to drill out the hole again for the new bolt.
I do periodically check to be sure all the bolts for the engine mounts are still tight and have not had any issues with this repair.
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Eric Wengstrom
s/v Ohana
Colonial Beach, Virginia
1988 Catalina 34 MKI SR/WK
Hull #564
Universal M25XP
Rocna 15

scgunner

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Re: Sheared Motor Mount Bolt
« Reply #5 on: July 28, 2021, 07:42:12 AM »

Jim,

My broken bolt also looks like it may have been that way for awhile, can't say for sure since it looked OK when the motor wasn't running, it's with the motor running it was apparent. How did you extract the broken bolt(s)?

Eric,                                                                                                                                                                                       
                                                                                                                                                                                             Interesting you sheared the same bolt out of the eight. I'll probably replace the motor mounts since they are the originals. Maybe I should have replaced them sooner but they all looked good and I don't recall ever seeing anything on motor mount replacement interval.
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Kevin Quistberg                                                 Top Gun 1987 Mk 1 Hull #273

ewengstrom

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Re: Sheared Motor Mount Bolt
« Reply #6 on: July 28, 2021, 08:23:43 AM »

Found this pic I took when I finally removed the broken bolt. I believe it was originally 4" when it was in one piece.
I'm not exactly sure of the recommended replacement interval of our motor mounts but if they are original, it's probably time.
I went with Vetus K 75 mounts all the way around and have been very happy with them. The vibration transmitted thru the engine beds has been much reduced.
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Eric Wengstrom
s/v Ohana
Colonial Beach, Virginia
1988 Catalina 34 MKI SR/WK
Hull #564
Universal M25XP
Rocna 15

lazybone

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Re: Sheared Motor Mount Bolt
« Reply #7 on: July 28, 2021, 04:03:15 PM »

My guess is someone over-tightened the thing and snapped it.
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Ciao tutti


S/V LAZYBONES  #677

Jon W

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Re: Sheared Motor Mount Bolt
« Reply #8 on: July 28, 2021, 06:37:35 PM »

Eric, do the bolt holes of the Vetus k75 mount line up with the bolt holes on the original mount?
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Jon W.
s/v Della Jean
Hull #493, 1987 MK 1, M25XP, Std Rig
San Diego, Ca

ewengstrom

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Re: Sheared Motor Mount Bolt
« Reply #9 on: July 29, 2021, 04:26:45 AM »

The difference did not require any new holes to be drilled (or moved). It was VERY slight and many others have made the switch to these mounts with no problems. I'm quite sure I got the size and type from other posts on this forum too....I definitely didn't reinvent the wheel.
I also have no clue as to why these bolts break, they are set into a wood base so I'd suspect that if you over tighten them they would simply strip out the hole, I'm leaning more toward the conclusion that they are old, they've vibrated (sometimes violently) for many years and the constant cycling just wore them out. In the end I did replace all the bolts, not just the broken bolt.
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Eric Wengstrom
s/v Ohana
Colonial Beach, Virginia
1988 Catalina 34 MKI SR/WK
Hull #564
Universal M25XP
Rocna 15

scgunner

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Re: Sheared Motor Mount Bolt
« Reply #10 on: July 30, 2021, 07:14:20 AM »

Lazybones,

It's unlikely you could snap a S/S bolt, especially one that beefy, by screwing it into fiberglass reinforced wood, more likely you'd strip out the mount. In any case the mounting bolts on mine were never torqued.

Eric,

I'll probably do what you did and replace the mounts with the K75s.
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Kevin Quistberg                                                 Top Gun 1987 Mk 1 Hull #273

lazybone

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Re: Sheared Motor Mount Bolt
« Reply #11 on: July 30, 2021, 05:47:46 PM »

Itís just as hard to imagine that lag being sheared horizontally by the engine. 
The p.o. Might have substituted a longer lag in the same hole because it was stripped.  Soft Chineseium galvanized lag in an unpiloted piece of oak. 
My stringhy noodle arms could do it easy.  Is there any of it left in the hole
« Last Edit: July 30, 2021, 05:50:00 PM by lazybone »
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Ciao tutti


S/V LAZYBONES  #677

scgunner

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Re: Sheared Motor Mount Bolt
« Reply #12 on: July 31, 2021, 09:29:24 AM »

I don't see what's so hard to imagine, a bolt torqued down under vibration for 1800+ hrs over the course of 35 years. I bought the boat from the original owner who owned it for about 14 months with about 50 hrs on the motor, essentially a new boat. I doubt the original owner did anything to the motor since it hadn't even reached it's first service interval, certainly not over torquing the motor mount bolts. Since then I know the only thing I've done is to occasionally put a wrench on them to check for tightness.

I agree with you on the poor quality of imported Chinese hardware, it's everywhere in Marine West stores, I avoid it at all costs. However back in the mid '80s the Chinese really weren't as yet importing their inferior products, if the bolts were imported it was most likely from Mexico.
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Kevin Quistberg                                                 Top Gun 1987 Mk 1 Hull #273

scgunner

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Re: Sheared Motor Mount Bolt
« Reply #13 on: August 21, 2021, 08:14:04 AM »

Just an update, in case anyone's interested. I got the motor mount out but I had to take off the mounting bracket on the motor to do it as the two as frozen together. Separating the two of them is my next project. The bad news is the other bolt is also sheared.

Eric,

My base looks like yours except my motor is still in place, which will make bolt end extraction extremely difficult if not impossible. I think what I'll do is reinstall the motor mount turned slightly, drill pilot holes along side the original holes in a solid part of the base. That's the plan, we'll see how it goes.
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Kevin Quistberg                                                 Top Gun 1987 Mk 1 Hull #273

scgunner

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Re: Sheared Motor Mount Bolt
« Reply #14 on: August 24, 2021, 07:13:56 AM »

Well I have to say this repair went surprisingly well. By turning the motor mount about 30 degrees I was able to drill new holes in the base and install new bolts. With everything in place I ran up the motor, in and out of gear, and everything looks good. Hopefully I'll get another 35 years out of the new bolts.
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Kevin Quistberg                                                 Top Gun 1987 Mk 1 Hull #273
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