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Anyone ever seen this?

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4'' ARM
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Chris, Kyle and Matt playing in the skinny water
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passtime & Chris
Hot Dogs - a cookin
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SAFARI RICK

Well-known member
Found this today when I was starting the boat to take it out.

IMG_00541.jpg
 
That don't look good--------------
Good thing that you caught it before you went out....
Did the boat have a new vibration when you come in the last time????
 
Safari, is that an allthread rod that is broken? If so, that stuff is too soft for a motor mount and this might be a blessing in diguise.
You need a Grade#8 bolt for that kind of a job.

Glad you found it though, man. It could have gotten bad ugly if you hadn't.

BF
 
I'm not going to try to be a showoff so take this for what its worth. I see a really weak mount to stand design there. I'd check the opposite side as well and see if its close to breaking or already broke too.

That rubber and cup washer above the two nuts should be resting on a flat plate (part of the motorstand) not a bolt and nuts. The stand should support the weight NOT the bolt or threaded rod. I'd say it needs a redesign.

If you repair it like it is it will break again likely in the same place or the opposite side.

Ditto what feather said about grade #8 and threaded rod. Get the right hardware in plce, then use castle nuts or deformed nuts under the plate portion of a redesigned stand. Castle nuts with a Cotta key is preferable but deformed nuts will hold. My opinion is that threaded rod is for hobyists not for this kind of application.

Scotty
 
Big Dittos, Whitebear .... there is too much movement in the way it's set-up now. The engine stand should be carrying not only the weight of the engine, but the torsional stresses too.
A bolt shouldn't be expected to do all of that.

BF
 
I have seen several engine stands with that style of all-thread adjustable motor mounts break just like that one did. A few ended up causing the back of the motor to lift and let the prop cut right into the cage, not a pretty sight. You need to use a good Grade 8 with a steel spacer cut to the length needed to hold the motor where you want it, leave the all-thread off. Here is a pic of another stand that makes me cringe when I look at it.
100_0199_Edit_1.jpg


Larry
 
90% of the aircraft motor stands around me only have one rear bolt and its a threaded rod. I have never seen one fail yet but it always creeped me out.
 
Checked into it and the allthread used was b-7 (think thats it) which is actually harder then a grade 8 bolt.(So I was told by the hardware guy) Both back supports were broken. Found that the front mount was a bit lose so the engine would actually roll forward about a 1/8-1/4 inch at high RPM'S. Only thing I can figure is that the rear mounts would flex a hair but after you bend something back and forth even if its only a hair it will brake. Welded them back on but at this point just hopeing that I have a fixed boat and not a death trap!
 
Safari, you don't want to weld those bolts ..... you need to replace them.
Welding could crystalize the metal on either side of the weld and set you up for disaster.

There are several very good fabricators on here (I'm NOT one) so do me a favor and don't run your boat until you hear from a couple of them.
If I'm wrong about this I'll be the first to apologize to you, but I think it would be the safe thing to do.

BF
 
I agree with big feather The cost for new bolts sure is a lot cheaper than a new boat. If you were to be lucky....
 
Im dead serious, those rear mounts need to be redesigned. Those metal cups under the rubber need to sit on the engine stand. What you described above will just break again. If I was back home I'd offer to show, help, or do it for ya, but can't do that from here.

Scotty
 
Whitebear is absolutely right about those rear mounts, Safari. There is just way too much torsional (turning) stress on those bolts. That set-up could hurt ya, buddy, and at the very least will eventually wreck your boat.

If you could see what's happening back there when you make a hard turn it would probably scare you to death. The only thing that has saved you so far is that the front mounts must be pretty strong. The rear engine stand needs to be extended all the way up to the engine mount cups. That's a half-day job for somebody that knows what he's doing.

BF
 
After thinking it over and taking a good second look I decided to cut out the old ones and start from scratch. Just too much rideing on that. Saftey is and always will ba a first for me with this boat. Thanks for all the input.
 
Good man!! That's what needs to be done. We won't worry about you now ...... :) .
You'll be amazed at how much better the boat handles after you get done too. You'll be rigidly connected to the rudders for the first time. It will turn sharper, and with less effort .... wait and see if it doesn't.

BF
 
Rick if ya would like I can draw up a design for ya. I'll do it in MS visio, if you don't have that I'll make it a .jpg picture. I wont put any dimensions on it so you can fit it to your boat as needed.

Scotty
 
Whitebear thanks for the offer but I have contacted the guy that made the rigging and stand and he is just as puzzled about what happened as me. He will be helping me to redo the mounts. He has made dozens of these and never had one fail, figures I'ld be the first. We have sumised that the mounts were to close together and that caused stress on them in an outward way. that in combination with the front mount being lose and causeing the motor to roll forward was the reason for the faliure. At least thats the best that we can come up with. The problem I'm haveing is that I need the rear mounts to be adjustable so I can pitch the rear of the motor. We will be changeing a couple of things so that the rear mounts won't be binding in anyway, just there to hold it in place.and redoing the front mounts to keep the motor from rolling forward at all, stiffing them up.
 
Rick I agree with Whitebear, the metal cups under the rubber should be supported buy something other than the adjustable nuts on the all-thread. The engine stand should support the weight and stress of the engine. If you need to change the pitch on the rear of the motor you can do it by changing the thickness of the rear rubber mounts. You can buy rubber mounts from diamondback that can be trimed down to fit your adjustment needs. They also come with thick washers if you need to adjust the other way. Bought some last week. $40 for 4 of them.
 
SAFARI - What is the motor that is on? GPU?

Larry - What is that set up on?

I would think it would be ok if solid steel spacers were placed around the outside of the bolts to keep them from having any flexing.

Lots of Lycomings have the single rear mount, with 4 front motor mounts. With that design I was alway told that if one of the front mounts is loose, then bad things happened.

Safari - Sounds like you might have had something similar happen.
 
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