How I fixed my rear motor mount

                                    Last update:  5/4/2019 

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Important Note

I originally posted this article on 6/1/15. This method of  fixing the rear motor mount worked OK for ~3 years.  After that  the shudder when starting to move from a stop got worse and worse even though the filler caulking I used appeared to be holding up OK.

Luckily a member of the insightcentral.net form, eq1, came up with a much quicker repair and did a series of tests to reduce the NVH for the rear mount that is easy to make, works great and should last much longer than my (as it turned out) 'band aid' fix.  His fix uses two GMC rear axle bump stops and two washers. You will need a source of heat to remove the old flexible mount from the housing but other than that the actual process to modify the mount is straight forward.  I did find having a lathe, a drill press and a "flame wrench" (oxygen-acetylene torch) helped to make the task easier.

I modified my rear mount according to his instructions and can report that it works great. Clutch shudder is gone, no vibration of any sort, it just works the way a motor mount should work.

You can find his detailed post (with pictures) here.  

 I will leave my original article [below] for the Background and other information that may help people to understand what happens when the OEM rear motor mount "comes from together" (the legs tear loose!).
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Background


Many first generation Honda Insights suffer from a broken rear motor mount.  This causes various affects while driving the car.  In my case the clutch release at slow speeds was somewhat harsh with chattering.  This was particularly noticeable in reverse.  I also had the affect that when letting off on the gas pedal that the engine had quit running completely and would suddenly kick back in with a lurch with a little increase in throttle.

The three cylinder 4 cycle engines tend to be fairly vibration prone beasts at low or idle RPMs.  While Honda did wonders using the IMA system to tame down most of the idle vibration, the system depends upon the special motor mounts to be in good condition to complete the vibration suppression.   The rear motor mount in particular is an important part of reducing noise, vibration, and harshness (NVH).  If any part of the system is not in good shape the NVH will suffer. Forget about polyurethane.  It is much too stiff to use as an Insight motor mount replacement.

The rear motor mount is quite special in that it is not like normal motor mounts which are basically a rubbery blob that has a central metal sleeve that the mounting bolt goes through.  The Insight rear mount looks like this.  Notice that large portions of the area is open and not solid like typical motor mounts.  

REAR MOUNT


My apologies to the poster of this picture. I found it on a Google image search and it appears to be in the public domain. Google has also posted some of my pictures and I guess that's the price we all pay for a free to use search engine etc.  And Google sometimes puts a link to our websites.

The two red lines are where the typical mount may be torn loose from the outside of the metal circle part of the mount.  Sometimes only one "leg" will be torn loose rather than both of them.  Notice that the top rubber part above the metal sleeve is NOT connected to the outside portion of the black flexible material.  This allows the motor to rock back and forth  in normal operation.  When the flexible legs of the mount are broken the motor is free to move around way too much.  Unfortunately I didn't take any pictures of what I did but I have a lot of commentary of how you can fix your mount.

The Honda engineers did a lot of design work on the motor mounts for the G1 Insight.  Like the rest of the car, the motor mounts were designed to work as a team. Each of the three mounts (two on either side near the upper part of the engine and the rear mount) have small, added metal weights on them to tune the system to allow smooth idle etc.  The rear mount has a ~2.5" diameter by ~3/4" thick cast iron "washer" that is mounted on the long bolt that goes through the center of the sleeve.

If you pack the mount with stuff or caulking material that doesn't match the original vibration frequency of the OEM mount and you will throw the tuned motor mount system out of balance. The result is severe vibration at or just above the  900 rpm idling rpm. This will be especially noticeable with the A/C ON when the engine is idling at 900 rpm.  As it is right now I have my engine idling at 1100 RPM which is just above the A/C induced vibration at idle.
 


What has been tried to repair a broken rear mount

People on the  http://www.insightcentral.net/forums/1st-generation-honda-insight-forum/ have tried to repair broken mounts by filling the open spaces with various caulking compounds (typically in 10.+ oz tubes), various strips of foam, rubber, pieces of fan belts etc.  In most case they have reported that the material is just too stiff and the NVH has gone out the roof.  Vibration at idling speeds is particularly bad.  Some people report that the resonances of the engine cause the windshield mirror to vibrate so badly that it is unusable.  Basically the stiff material used has thrown the tuned motor mount system out of it's normally tuned range.  And the floor of the car is very good at accentuating the vibration of the engine if things aren't perfect..



My thoughts of what needed to be done and what I did after fixing the rear motor mount

Filling the entire open area of the mount is the first thing that seems to be a natural thing to do.  The problem in doing that is the natural flexibility and the tuned frequency range of the stock mount would be changed unless a material was selected that would have the same characteristics as the original mount had.  Considering the test equipment that the Honda engineers have and what we have to work with, it doesn't seem possible to DIY fix a rear motor mount.  Not knowing specifications of the original material makes the repair job even worse.

After reading the comments of other people on the forum I reasoned that a rather flexible material would be needed. And even if it was much softer than the original mount material it might still work since all the open areas of the mount were going to be filled.  By overlapping the filler to the edge of the outer metal part of the mount I hoped that would hold the material in place.  I've been using my new mount since 1 Jan 2015 and it is holding up fine.

After I repaired and installed my fixed mount I found that the NVH was far more than I wanted to put up with but I decided to give it a try anyway to see if the material would even stay in the mount and not fall out.  After about two weeks it seemed that the NVH was much reduced and only a big problem was at engine rpms below ~1000 rpm when starting or when the engine was under a load at low rpms as when you have the A/C running.  Less than 900 rpm can also occur when you let the clutch out and especially just when the engine starts after autostop between 500(?) rpm and the 900 rpm idle..

I realized that the tuning of the motor mount system was close but still too firm after my first attempt.  After studying which way the torque of the engine might be producing the most NVH I decided to cut away some of the filler material between the original legs under the metal sleeve to slightly change the resonant frequency of the caulking I used in the mount.

I cut out a 1/2" wide block of filler from the original outer edge of the black material upward to the black material that is coated on the center metal sleeve. The cut out block goes through the mount from one side to the other. See the picture above. The green outline area is the where the plug of filler was removed.

I would strongly suggest that when you apply the filler material that instead of cutting out the plug later, you make a form (maybe with a round piece of 1/2" diameter material). Perhaps some soft compressible foam would work.

Cutting the plug out greatly reduced the start up vibration and all but eliminated the AC being ON at an idle in Auto mode with the idle set to 1000 rpm.



OK, so what caulking did I use that worked?  And how did I position the metal sleeve so I could put the mount back on the car?

GE 100% Silicone caulking from Home Depot is my secret ingredient.  One 10 oz tube ought to be enough to do three mounts.

First clean the flexible part of the mount so there is no dirt or oil on it.  Allow it to dry and then proceed.

It's important that the metal sleeve be positioned in the mount so you can get the fixed mount back into the car.  My mount had one leg torn completely free and luckily the other one was hanging on by a thin strip of the original (black) material.  I was able to use the broken leg and the other one that had a thin sliver of rubber attaching it to the mount to determine where the sleeve was located when mounted on the car.  It seemed that it wasn't exactly in the center of the large metal part of the mount.

I carefully measured what it would take to center the sleeve side to side relation to the large aluminum part of the mount.  I found that to center the sleeve side to side in the mount would require the sleeve to extend 0.690" on either side of the larger aluminum part of the mount. In other words when the sleeve is centered in relation to the large part of the mount it extends 0.690" outward on either side of the large part.

I wanted to be able to lay the mount horizontally down on the surface of my drill press table while putting the Silicone in the mount gaps. To do that  I took two 0.75" thick metal spacers and placed them at either end of the large aluminum part of the mount and laid the mount on the spacers so the sleeve was vertical.  I then slipped a 0.060" thick aluminum spacer between the sleeve and the drill press table. That lifted the sleeve UP 0.060" and it was centered on the large part of them mount.  ( 0.750" - 0.060" = 0.690")

I used two large "C" clamps to hold the 3/4" spaced mount to the table, carefully centered the center sleeve as best I could and stacked some steel pieces of metal on top of the sleeve to hold it in place.

Hint:  Put a piece of wax paper on the metal table before you clamp the mount to the table.  That way if you squirt filler around it won't mess up your table.

Don't forget to put your 1/2" wide hole making form in the gap between the sleeve and the outer edge of the mount before applying any caulk.  It's OK if it sticks out of the mount on either side.




Now the correct way to apply the Silicone    (Do NOT put it all in there at one time!)

Like most caulking compounds you should not apply too think a layer at a time.  Typically a 3/16" to 1/4" thick bead is as much as you should do at a time and allow 24 hours for it to cure thoroughly before applying the next layer.  As you can see repairing a motor mount  isn't going to be a one day affair.  It took me about 5 days to do the filling and curing.

My method was to apply a first thin layer in the open areas 1/2 way inside the mount.  This layer is the base so you can later apply additional layers on either side of the center at the same time.  You can basically do the job in 1/2 the time as compared to starting at one side and working your way out and then turning the mount over to do the other side..

In other words if you were to look at the mount down the length of the large metal part you want the first thin layer to be in the middle of the mount like the filling of a sandwich.  If possible don't make this layer real thick at all. It's more important to get the Silicone in there and not move the center sleeve while doing it.  Allow 24 hours for the layer to cure.  Once it has cured the sleeve will be held in place for the rest of the layers but you still want to clamp and put weights on the sleeve to make sure everything stays in alignment after you turn the mount over to apply more caulking to both sides.

After 24 hours apply another 1/4" or thinner layer to each side of the center layer and re-clamp the mount to the table and stack the weights on the center sleeve. As you apply each layer of filler try to not have any air trapped in the silicone. If you see any air bubbles in the silicone just poke them out with a tooth pick or something sharp. I found it best to not try to move the silicone around once it is in place. It isn't fluid enough to flow smoothly and just piles up in lumps.

Wait 24 hours for the new layers to cure and repeat until the mount is filled to the top edge of the larger metal part of the mount. The silicone sticks very well to the original flexible part of the mount and it does seem to be staying attached after several months of using the repaired mount.

If you used some straws or something to make the gap in the filler you can cut them off even with the outside of the mount or carefully collapse them and remove them from the filler.

That's it .................. enjoy!

NOTE:  I still have some vibration with the A/C ON and a very short amount when I am first starting the engine after autostop.  I am thinking that it might help if I were to also cut a small amount of the filler over the top of the sleeve but I haven't tried that yet.


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