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Old 16-12-2020, 10:33   #1
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Raising Motor Mount Height Perkins 4-108

I have removed the propeller shaft for replacement. Have found that the engine is sitting somewhere around a 1/2 inch to low. The engine mounts that are installed look to be about 4.5 inches from the base where they sit on the engine bed to the top of the adjustment bolt. The engine is adjusted as high as possible. So the question is whether there is a suitable motor mount that has a height of say 5.5inches? Allowing for the engine to sit higher. Which seems like the easiest thing although there is a question in my mind about stresses on a higher mount....Or whether I should create a spacer between the engine bed and mount. The engine bed appears to be steel. Would that also be recommended material by everyone?
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Old 16-12-2020, 11:51   #2
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Re: Raising Motor Mount Height Perkins 4-108

Add the spacer unless the mounts are worn out.
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Old 16-12-2020, 12:00   #3
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Re: Raising Motor Mount Height Perkins 4-108

Well the mounts are most certainly worn out. They are definitely over 20 years old. Do you think they would drop 1/2 an inch? Seems like to much.
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Old 16-12-2020, 12:17   #4
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Re: Raising Motor Mount Height Perkins 4-108

Yes on the spacer make them steal and por-15 them. 2 dots of 4200 or similar under plate slows corrosion from vibration. dont slot the holes in the plates. make them big enough for the foot to move from slot end to slot end. Also the most important thing is the shaft sits true in the shaft log when doing the alignment. So think concentric at the front of the log and back of log. I make doughnuts out of wood with hole saws split them like a shaft zinc. this goes around the shaft and slide into the log from both directions.. this holds the shaft centered while doing the alignment. I did installation and alignments for years seemed to work the best. funny...my boat had a strut that needed to be rebedded to point straight to the shaft log. I only knew this because i couldn't get both doughnuts in. I think it was out of whack from the factory...chewed cutlesses quick...
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Old 16-12-2020, 12:17   #5
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Re: Raising Motor Mount Height Perkins 4-108

Are you seeing any extra vibration w/the engine or are you guessing the mounts are worn out due to age?
These look like the mounts you would need.


Here is another CF thread on replacing mounts on your motor for earlier this year.
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Old 16-12-2020, 12:57   #6
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Re: Raising Motor Mount Height Perkins 4-108

I am guessing they are worn out, just based on age. Seems if I have to put a spacer under them, good time to replace them.
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Old 16-12-2020, 13:45   #7
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Re: Raising Motor Mount Height Perkins 4-108

Squarepeg go to my blog http://choate-40.blogspot.com/2013_08_01_archive.html?m=1

Go to the motor install section. This may give you some ideas. My adjustment plates are 1/2 thick. As for the mounts they should be replaced ever 5 years due to erosion of the rubber. Depends on the exposure to environments too.
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Old 16-12-2020, 16:11   #8
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Re: Raising Motor Mount Height Perkins 4-108

If you are correct ????? Install new mounts and remeasure. If you still think it's too low you can jack the engine and shim at that point.

I recently went through the same issue and found that the starboard forward mount needed a 1/2' shim. The difference in noise and lower vibration was amazing altho it did not seem bad until I made the change.
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Old 17-12-2020, 13:11   #9
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Re: Raising Motor Mount Height Perkins 4-108

Consider making the spacers 3/4 or 1 inch thick so the threaded rod on each mount is not at the end of its travel.
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Old 17-12-2020, 13:28   #10
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Re: Raising Motor Mount Height Perkins 4-108

Are you sure the engine is on the same plane as the shaft? You need to know that first.
In other words: the back isn't adjusted low and the front high?
Just a thought.
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Old 17-12-2020, 14:08   #11
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Re: Raising Motor Mount Height Perkins 4-108

My understanding is you should aim for lower part of engine mount post. looks like you need new mounts AND a spacer. Otherwise you're introducing a potential for a lot of sideways torque which puts a lot if force on the whole drivetrain.
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