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Old 06-06-2016, 04:33 PM   #1
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Bent engine mount bolts

Anybody ever see this before? I was taking some measurements while planning to possibly change out engine mounts and discovered that the bolts on the rear mounts are bent. Someone told me that is what can happen on a hard grounding. The PO did ground hard enough to bend shafts twice. Maybe that's it. I don't appear to have alignment problems. The front mounts are not bent. They have been that way for at least six years and about 1200 hrs.
Dave
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Old 06-06-2016, 04:39 PM   #2
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Goes to show you...less than perfect can easily go unnoticed...and also may never cause further damage.

Yes a hard grounding might bend them, but you can bend shafts without displacing the engine that much also.

The forward engine mounts on my assistance boat would rotate all the time from trying to unground boats...they were a mother to keep tight and probably rotated rather than bend the bolts.

I have seen bolts almost pulled from the rubberized material on other style isolators...but not bolts on that kind bent that way....seems easy enough to do once past the design limits.
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Old 06-06-2016, 04:45 PM   #3
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Maybe it's the picture, but the engine mount in the lower pic seems to be way out (not parallel ) to the engine bed. Don't know how much out of parallel is allowed, but that seems like a lot.

Ted
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Old 06-06-2016, 04:51 PM   #4
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Maybe it's the picture, but the engine mount in the lower pic seems to be way out (not parallel ) to the engine bed. Don't know how much out of parallel is allowed, but that seems like a lot.

Ted
Ted, I noticed that too...but everything is so disturbed, I couldn't tell what was still in place and aligned or not....the metal cap is really cocked...one end near the top of the nuts, the other end way down...so I wasn't sure what to even say.....
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Old 06-06-2016, 05:03 PM   #5
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If I were redoing the mounts, I would redo the bed plate so that the plate and the motor mounts were parallel. Second, the motor mounts should be close to the top of the isolators. This can easily be accomplished by shimming up the isolators with .25 to .5" plates between the isolators and the bed plates, then through bolt them in place.

Ted
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Old 06-06-2016, 05:08 PM   #6
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Maybe it's the picture, but the engine mount in the lower pic seems to be way out (not parallel ) to the engine bed. Don't know how much out of parallel is allowed, but that seems like a lot.

Ted
I dont know enough about mounts and alignment. Your point is what had me concerned. I would think that the base and the mount off the engine should be parallel, they are not. I wanted to make this a DIY job but now I am afraid it could turn into a big project that requires modifications and a big drain on my wallet.
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Old 06-06-2016, 05:11 PM   #7
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Originally Posted by O C Diver View Post
If I were redoing the mounts, I would redo the bed plate so that the plate and the motor mounts were parallel. Second, the motor mounts should be close to the top of the isolators. This can easily be accomplished by shimming up the isolators with .25 to .5" plates between the isolators and the bed plates, then through bolt them in place.

Ted
Darn, that is were I thought this was going. Time to break out the wallet again.
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Old 06-06-2016, 05:29 PM   #8
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Don't make a snap decision....

If the engine has felt fine...take a quick alignment check to see where you are.

The engine mounts and stringer plates should be parallel...but a tad off isn't a huge deal on low power, low speed boats.

I have run a few where the engines were hard mounted...so as long as the engine can be aligned well enough....all is not lost.

It's DIY....at least up to the point where it isnt.......but you won't really screw things up worse than they have been if you take your time and pay attention....
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Old 06-06-2016, 05:52 PM   #9
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Dave,

This isn't going to be bad (for my wallet anyway ). Building shim plates to level the surface isn't real difficult. Visualize two .375" shim plate that are slightly larger than the foot print of the isolator. The 2 plates are stacked and touch at one end. At the other end a piece of square stock .375" is inserted between the two plates. The two plates are welded together at the ends forming a wedge. That wedge becomes your shim and corrects the excessive angle. The wedge can either be welded to the bedding plate or you can drill holes though it to utilize the isolator mounting bolts. Obviously the plate thickness and elevation would need to be calculated, but fabricating a pair of these should be relatively easy for a metal fabricator.

Ted
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Old 06-06-2016, 09:21 PM   #10
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Those are Cushyfloat mounts by Trelleborge. The mounts take thrust and technically the engine bracket should be on the adjuster and the entire mount shimmed until the bracket is engaged and the mount square and evenly loaded. The adjuster should be in the middle of its range after the mount has had a day or two to settle under load and gross alignment should be done with shims leaving fine alignment for the adjuster.

The entire thrust of the propeller pushes the engine through the engine mounts on through the stringers to move the whole boat. That's a lot of force to be pushing on a 20mm stud on a bracket an inch above the mount. It also cantilevers the force to push down on the front of the mount using the stud as a lever.

On the base near one of the two bolt holes there will be a number indicating the shore or durometer of the mounts rubber. It will be a 2 digit number from 40 to 75 in increments of 5.

A very popular and reasonably priced mount, you should be able to find for less than $200 each if you want to replace. Studs and Adjusters are available separately too.

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Old 06-07-2016, 10:07 AM   #11
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Dave, While it's not my preference, you can make those wedge blocks out of hard wood. My boatyard does motor installs on wood work boats. The engine beds and shim blocks are all wood. Seem to remember that you like to make saw dust.

Ted
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Old 06-07-2016, 11:53 AM   #12
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Quote:
Originally Posted by Keysdisease;
On the base near one of the two bolt holes there will be a number indicating the shore or durometer of the mounts rubber. It will be a 2 digit number from 40 to 75 in increments of 5.
A very interesting and informative read, Keys, thank you.

Does the higher number indicate an increase or decrease in hardness? Secondly how is the right durometer selected?
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Old 06-07-2016, 12:04 PM   #13
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Marine Engines : Drive System Alignment by David Pascoe, Marine Surveyor
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Old 06-07-2016, 12:07 PM   #14
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A very interesting and informative read, Keys, thank you.

Does the higher number indicate an increase or decrease in hardness? Secondly how is the right durometer selected?
http://www.missionsupplyonline.com/p...yfloat_eng.pdf
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Old 06-07-2016, 12:27 PM   #15
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About 15 years ago, I replaced 8 mounts, typical donut mount.

Dual Flex Engine Mounts | Bushings Inc
Bought direct from the manufacturer.

I drilled out the holes, so went from 5/8 studs to 3/4 studs.

I had read negative stories of these donut style mounts collapsing, (online Pascoe article showing wimpy mounts holding a heavy motor) so I figured go up a size. Have not had any troubles with them moving, cocking over, collapsing under the weight. Each mount has to support about 300 pounds. Mine are single, painted black, not the dual mount.

Maybe with a heavy powerful diesel engine they are bad. These do come in various sizes.
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Old 06-07-2016, 12:36 PM   #16
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The durometer is selected based on the load per mount. On metalastic sp?? website there are charts showing model, durometer and load lines. Motor and gear about 1500lb, so about 375 per mount. If mounts were not spec'd out right, it would shake the boat at 600rpm idle. If no shake, they were spec'd "good enough".

With these types of mounts, it is not critical that the base surface be exactly perpendicular to the stud axis. In photos it does not look too far off to me, but hard to tell.

I'd just replace the bent studs and set alignment.
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Old 06-07-2016, 12:40 PM   #17
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Nice link Capt. Bill. Higher number means can take higher load. (higher means harder, but) Given the correct loading a soft or a hard mount of the same type can provide the same isolation. Its more important to get the "right" mount, than a soft one.

In the selection chart that Capt. Bill provides in his link it's important to use the *M-Max column, (thrust taking) and choose a mount that will be loaded to about 70-80% of its max capacity and will provide 3-4mm static deflection. This will give good performance with a good safety margin. There are calculations to "dial in" a better selection, but you need a lot of data to do it correctly.

Non thrust taking applications like generators use the M-Max column.



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Old 06-07-2016, 12:53 PM   #18
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Need to convert to Kg, not Lbs.

So convert 1500lb to 680Kg divide by 4 = 170kg per mount. Looking at the chart a 17-1609-65 will provide 3.5mm static deflection under that load and be very comfortable with a *M-Max for that mount at 210Kg.

The chart is a guideline, if the mounts front to back aren't approx. equally loaded, maybe because of the gear, than some more guidance would be in order.




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Motor and gear about 1500lb, so about 375 per mount. .
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Old 06-07-2016, 03:02 PM   #19
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Thanks Bill, that info is very helpful.
Dave
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Old 06-07-2016, 03:14 PM   #20
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Thanks Bill, that info is very helpful.
Dave
I agree, great thread.
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