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Failed Mount Isolators

DanH

Legacy Member
Mentor
Engine seemed a bit shaky recently, so today the cowl came off for a look. Problem wasn't hard to find:

Slime1.jpg


The liquid was squeezing from an isolator:

Slime2.jpg


Bring out the wrenches...

Guts.jpg


These are the bottom isolators. Don't have the top pair out yet. Lord J9613-40, about 830 hours on a 390 with a BA Hartzell.

Looks like the choices are

Lord J9613-40
Lord J9613-49
VIP 50011-20 (=J9613-49)
VIP 50016-09 (acro)
Barry 94011-20 (std)
Barry 94016-08 (acro)

I think Vans is currently selling the VIP 50011-20, but they're not ID'd on the mothership website. What is different about the "acro" VIP 50016-09? Anybody tried the Barry isolators?
 
yes, but...

Sold the Barry parts for a while, but they seemed to go weak (540 ap) a bit faster than expected. Now suggesting the Lord 540/580 Acro mounts. I have no experience with the VIP parts, but I would start with the heavier parts.

I think the 540 parts will fit your setup if you want to try those - I might have a set here? I'll have a look if you want to try 'em.
 
Revenge of the Slobovians for that invasion yesterday!


The guy who sold me the O-360 that never made it into my -7 told me about fighting sagging isolators on an aerobatic biplane. Said that they finally cut some delrin bushings that matched the shape of the isolators, and they could barely tell the difference in vibration level.

But that's just something I heard...
:)

Thanks for coming over, and I hope we can visit Wetumpka sometime soon.

Charlie & Tupper
 
OK, that looks nasty. Pretty sure there are lots of those isolators out there on RVs (mine included), so what's the root cause here? Did you contact Lord to get any more info?

Definitely something to watch out for at each oil change/decowling. Thanks for posting this.
 
Graphic evidence why girls should avoid silicone implants!

Regarding mounts, ACS used to sell "Aerobatic mounts". Externally they looked the same but were firmer.
I tried a set on an 0-320. With the C- 177 /C-172 mounts that the builder had in my AC, I could watch the spinner rise and yaw as the G approached zero near the top of a loop.

The ACS "aerobatic" mounts did prevent the engine from moving as much with change in G loading, however they also transmitted slightly more vibration to the air frame. They are still in service 1700 at hours. YMMV
 
Yuck! E-yew!

I didn't know there was liquid in them. I suppose its like a spinal disc -- kind of like a jelly doughnut.

Supposedly the aerobatic mounts are a little stiffer, as others have said.
 
Dan,

I suggest you contact one of the engineers from Lord. I found her very responsive to a mount removal question we had.

Cynthia S. Reid, P.E. // Staff Engineer, Product Support Engineering
LORD Corporation
Telephone // 814-314-2957
Mobile // 814-392-6330
Fax // 814-860-3540

Erie Facility
2455 Robison Road West
Erie, Pa 16509-4675
 
Dan,

I suggest you contact one of the engineers from Lord. I found her very responsive to a mount removal question we had.

Cynthia S. Reid, P.E. // Staff Engineer, Product Support Engineering
LORD Corporation
Telephone // 814-314-2957
Mobile // 814-392-6330
Fax // 814-860-3540

Erie Facility
2455 Robison Road West
Erie, Pa 16509-4675

And please report back what you find out...specifically, the root cause of this failure.
 
I?ve had the same leaking lord mount on the RV-10 at about 900 hours. I replaced all of them. Not cheap.

Vic
 
Seen this issue before, Lord says no big deal. The fact that most other mounts don't even have this damper I can't imagine its that important, and not worth changing the mounts for.

The gel "footballs" appear to be viscous dampers, without any load capacity of their own. As such they would limit startup engine shake, largely a torsional reaction around the crank which displaces the mount in shear. They would also damp significant disturbance like roughness when finding the limits of lean mixture. They don't appear to do anything when the mount is loaded in tension or compression, and I doubt they have any effect in steady-state operation at small vibratory amplitudes.

The load carrying molded rubber assemblies have sagged in shear after 8 years/830 hours and probably exceed the limits published by Lord. I've spoken with a VIP representative and have some questions out with Lord; more later.
 
Just a data point.

Conical mount engines are magnitudes more rigidly attached to the airframe. Startup and low RPM idling are definitely not as smooth, but in cruise there's hardly any difference.

Seems to be a reasonable tradeoff. I've flown hundreds of hours in RVs with conical mount engines swinging Hartzells and found the vibration difference to be minor.

Many Continental-powered airplanes use conical mounts, and I don't find those airplanes to vibrate excessively either.

That said machining some adapters to use off-the-shelf isolators, such as the ones below, might be something worth looking into.

https://www.energysuspensionparts.com/9.4101

Not the right sizes but you get the idea.
 
Did you try a softer durometer than 85? What you observed was what I expected with large, machined polyurethane mounts.
 
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Yes I think there is more room for experimentation here, especially if we can talk Dan into doing it :).

I would love to have a $25.00 set of mounts that can be replaced every few years. $400+ is just getting out of hand.

These particular mounts are really the worst design of all isolators you see on GA airplanes, being hollow in the middle since they were originally designed to have the silicone-filled part. This makes them more sag-prone, and ultimately what caused this failure I suspect. In your case Mike since you did some simple lathe turning, this area was filled with 85 durometer polyurethane and that adds additional rigidity.

In my opinion, some machined cups to interface with smaller off-the-shelf polyurethane isolators probably would work very well.

I've had pretty good luck retrofitting poly mounts in cars.
 
If you want min vibrations go back with LORD.... Berry is cheaper and less engineered....

I have had the gel vibration dampers go 1000's of hours and keep on going. You have to
be careful not to pinch them or nick them with a tools. In fact I've never seen a Lord mount leak.
May be they had a bad batch?
 
I was flying (and maintaining) a buddy's Cardinal earlier in my flying days and discovered the silicone goop on the engine mount durring an oil change. These had a bunch of time on them without being disturbed. They were good one day; then not good the next.
 
I know the Lord are supposed to be the best, but I may eventually switch back to the VIP I purchased from Vans when building my airplane many years ago. I installed new Lord mounts a couple of years ago when I had to remove my engine for a repair. To be honest, I really haven't noticed any change in vibration levels. What I have noticed, is I think my engine is moving around more.

When I first got my airplane flying, I had to go with a shorter alternator belt because the pulley was rubbing on the cowl. That solved the problem. I have an IO-360 with a B&C alternator. Flew it for 10 years like that without any rubbing.

Now, since I reinstalled the engine with the Lord mounts a couple of years ago, the pulley is rubbing against the cowl again. I have already put a washer between the isolators and the engine on the bottom to correct for a little sagging, but the pulley is still rubbing. Granted, I'm doing a lot of aerobatics at higher g loading since starting this IAC competition stuff. But I've always done a lot of aerobatics and didn't have rubbing for the first 10 years. I may need to switch back to the VIP or find stiffer mounts designed for aerobatics.
 
Quick follow up...

The gel-filled inserts probably failed due to overload, a case of excessive deflection of the mounts due to load and age. Sag in shear allows the middle of the gel bag to get pinched against the ID of the inboard steel rings molded into the doughnuts, and when that happens, compression or tension displacement would tend to peel back the ends of the rubber bag.

I suspect the Lord J-9613-40 mounts seen here are just too soft for a 390 with a metal Hartzell on a sport plane, the result being a lot of sag in only 800 hours. Examine application listings which include Vans, and you'll see the same isolator spec'ed for a 320 with a Catto, and a 360 angle valve with a metal BA. The engine difference is as much as 50 lbs, and the prop difference might add 50 more. The prop center of mass is roughly 28 inches forward of a set of mounts spaced 10 vertically inches apart, so there is a force multiplier too.

The fun starts when trying to select an isolator with slightly increased capacity. None of the three aviation isolator manufacturers publish aviation mount catalogs with technical data, notably shear and compression ratings (lbs per inch). They do publish good data catalogs for hundreds and hundreds of industrial isolators, for every imaginable application except aviation mounts. Go figure.

Lord has the data, but the only way to get it is to identify a particular isolator part number, then ask someone in product support. They won't recommend a specific mount, but will shotgun a few suggestions and state the stiffness values when asked. There is no practical way for a customer to simply select an isolator from a list, based on engineering values.

Barry was somewhat less forthcoming than Lord. No catalog listing, just a "For what part number?" response.

For Vibration Isolation Products (VIP), aircraft isolators are a legacy product acquired when the current owners bought the company. There may be engineering data somewhere in the files, but no one seems to know where. Best they can do is cross reference Barry and Lord parts numbers, and of course they know they supply Vans with their part # 50011-20.

For now, what I've done is order a set of VIP 50016-08 isolators, which they identify as an aerobatic mount. "Aerobatic" means it has the same high stiffness rubber assembly on both sides of the mount ring. A standard mount (like the VIP 50011-20) is a stiff assembly paired with a soft assembly. Using two stiff assemblies means the mount has a higher shear rating (the sum of the two), and the same compression rating as the standard isolator when either inverted or upright. The higher shear rating should help limit torsional engine movement at startup, i.e. less cowl banging, as well as offer more sag resistance. The downside will probably be more vibes in the cabin. We'll see...more later.
 
A ton of good info, thanks for sharing it.

When I bought my FFW kit, it came with VIP mount. I returned those and got Lord mostly based on pervious info shared that Lord mounts are the best. I guess we will see how long these will last on my IO-390.
 
For now, what I've done is order a set of VIP 50016-08 isolators, which they identify as an aerobatic mount. "Aerobatic" means it has the same high stiffness rubber assembly on both sides of the mount ring. A standard mount (like the VIP 50011-20) is a stiff assembly paired with a soft assembly. Using two stiff assemblies means the mount has a higher shear rating (the sum of the two), and the same compression rating as the standard isolator when either inverted or upright. The higher shear rating should help limit torsional engine movement at startup, i.e. less cowl banging, as well as offer more sag resistance. The downside will probably be more vibes in the cabin. We'll see...more later.

I have the same setup on my Rocket and even though its sat for a long time (too long) it hasn't sagged one bit.

One thing a Lord engineer told a me a few years ago was to immediately rub the rubber mounts with silicone grease upon receipt to inhibit the natural aging of rubber.
 
Not

On the -10, all of the isolators are the same...

Van's part number EA DYNA VI I(O)-540 is $125 EACH.

There is a new part number through Lord, and the new version costs around $250 EACH.

I called Lord to see why the new ones were double the price and the guy I talked to was, well, shocked to hear that. Apparently, the difference is in the silicone damping material.

FYI
 
Previously..

For now, what I've done is order a set of VIP 50016-08 isolators, which they identify as an aerobatic mount. "Aerobatic" means it has the same high stiffness rubber assembly on both sides of the mount ring. A standard mount (like the VIP 50011-20) is a stiff assembly paired with a soft assembly. Using two stiff assemblies means the mount has a higher shear rating (the sum of the two), and the same compression rating as the standard isolator when either inverted or upright. The higher shear rating should help limit torsional engine movement at startup, i.e. less cowl banging, as well as offer more sag resistance. The downside will probably be more vibes in the cabin. We'll see...more later.

Ok, the 50016-08 acro mounts are now installed, and I got an opportunity to get in three hours today over to Baton Rouge and back.

Initial impression: Vibration transmission is acceptable, but different. Previously it was smoothest around 2400~2450. Now it's glass smooth at 2700, acceptable at 2450, and shakes the glareshield at 2350 and below.

There are two possible explanations, maybe more. It was dynamically balanced recently, but the Lord mounts were sagging enough to have internal contact, so that may have skewed the balance process. It feels like it needs balancing, but I know that human perception is a very poor gauge. The other possibility is perhaps more likely. Short version is that I've raised the system's natural frequency, so it's now closer to the disturbing frequency, increasing transmissibility. Isolation gets better as the ratio of Fd/Fn is increased, and I've decreased the ratio.

I'll get another balance and we'll see. More later.

Fit: The VIP acro isolator set (50016-08) is simply two compression assemblies, each 1.11" thick. The standard isolator set (50011-20) currently sold by Vans and others is a 1.37" thick softer assembly, combined with one 1.11" compression assembly. We normally put the thicker soft mount on the forward side of the upper dynafocal rings, so replacing it with a thinner hard mount requires inserting a spacer about 1/4" thick. You can do it with big washers, or machine some from aluminum. Without them, the spinner will be a 1/2" or more too high if you're replacing standard isolators.

This is a Lord drawing, with VIP dimensions noted:

Mount%20Dimensions.jpg


Spacers:

Spacers.jpg


BTW, a few of the VIP mounts had some excess rubber in the center of the big molded-in steel end plate. The center spacer tube (not shown) is tensioned against the end plate, so this excess rubber should be removed. No big deal, 30 seconds with a pocket knife.

Excess%20Rubber.jpg
 
BTW, a few of the VIP mounts had some excess rubber in the center of the big molded-in steel end plate. The center spacer tube (not shown) is tensioned against the end plate, so this excess rubber should be removed. No big deal, 30 seconds with a pocket knife.

Excess%20Rubber.jpg

I kinda disagree with it being no big deal...that speaks to poor QC to me.
 
Tough crowd. We trim and deburr RV parts, don't we?

Yep. I just don't like getting parts that *should* be cleanly manufactured and QC'd that aren't. Makes me wonder what else they didn't do correctly. Especially in a relatively expensive part for what it is.

I used Lord mounts with the inner isolator part, and have experienced no problems...but I'd really like to know for sure what the root cause of the failures of those gel-filled things is.
 
I used Lord mounts with the inner isolator part, and have experienced no problems...but I'd really like to know for sure what the root cause of the failures of those gel-filled things is.

When the inner spacers pinch the gel bag against the inside of the isolator rings, the ends of the bag will be peeled back if the engine moves in the mounts. If I had to pick (caution, opinion), I'd say they sagged enough to pinch the bags due to a combination of four factors.

The first two are pretty common. #1 is calendar age, about ten years since hung, and eight flying. That's probably beyond the manufacturer's suggested replacement interval. Shame on me.

Second is supporting an IO-390, heaviest of the 4 cyl models, with a metal Hartzell. There is a very large difference between this combination and an 0-320 with a Catto, yet it's the same isolator part number. Seems logical that big motors will need new isolators at shorter intervals.

Loading is a little less predictable. This one sees 3.5G on an irregular basis. Some RVs never pull G, some acro on every flight.

The unusual factor is heat. I operate with lower cowl temperatures which are somewhat higher than average.
 
Just one other data point (therefore anecdotal). I just pulled an engine - Superior XP400 - from an RV14A for the Superior recall. One of my 4 mounts had failed with the other 3 in excellent condition. Time in service is 21 months and 380 hours - mostly cruising but some mild acro. The failure was eccentricity of the stiff discs with a ruptured gel donut. While it looked like it could have been an installation error where one of the interior tabs on the disc snagged/pinched the membrane on the donut, I now believe because of the eccentricity and this discussion that it is a similar failure mode to what Dan has described. These 390/400 engines can move a lot, and can shake pretty violently at start/shutdown.
 
Example of the eccentricity due to sag. You can see how there is very little room remaining for the center spacer and gel bag, and the raised ribs can't help:

Eccentric%20800w.jpg


Thickness of this bottom compression element is way down too, about 0.86" rather than the original 1.115"~1.085" spec range.

Thickness.jpg
 
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The rest of the story. Previously I wrote:

Ok, the 50016-08 acro mounts are now installed, and I got an opportunity to get in three hours today over to Baton Rouge and back.

Initial impression: Vibration transmission is acceptable, but different. Previously it was smoothest around 2400~2450. Now it's glass smooth at 2700, acceptable at 2450, and shakes the glareshield at 2350 and below.

There are two possible explanations, maybe more. It was dynamically balanced recently, but the Lord mounts were sagging enough to have internal contact, so that may have skewed the balance process. It feels like it needs balancing, but I know that human perception is a very poor gauge. The other possibility is perhaps more likely. Short version is that I've raised the system's natural frequency, so it's now closer to the disturbing frequency, increasing transmissibility. Isolation gets better as the ratio of Fd/Fn is increased, and I've decreased the ratio.

I'll get another balance and we'll see. More later.

The answer seems to be ....both.

With the VIP acro mounts, the airframe shake below 2400 felt like an out of balance prop. Vic had done a dynamic balance not long ago, before I discovered dripping silicone, and realized how far gone my Lord mounts really were. With new VIP acro mounts installed, we were both curious about how failed Lord mounts might affect the dynamic balance process. If one or more gel bags and center spacers were against the inner steel ring, would it skew the dynamic balance results?

Answer...apparently yes. I flew over to Fresh Fried Chicken where Vic and I repeated the balance done just a few months ago. Getting down to 0.01 required the removal of a #10 screw, washer, and compact nut installed when we balanced with bad mounts. IPS immediately dropped below 0.04 (or maybe it was 0.03). A washer or two in the right place dropped it to 0.01. The lesson, now learned, is obvious; check your mounts before balance.

However, when flying home, there was no significant difference in cockpit feel. Pulling the prop to down to around 2300 would still make my sunglasses dance. Ok, fine. If it ain't balance, it must be resonance.

As previously noted, the VIP acro mounts are simply two thin isolators and a slightly different internal bushing length. I called VIP, and they were willing to sell me the thick isolators and the correct bushings, since I already had plenty of thin isolators. The resulting thick-thin set is exactly what you would get from Vans or Aircraft Spruce. Blocked out the day Saturday and got 'em in there.

Drum roll please; a short test flight yesterday confirmed the return of good vibes. It's been a long time since I had new Lord mounts, so a direct comparison is hard to judge. There is no objectionable behavior with the VIP mounts; I can pull RPM down with fairly high MP and the previous large amplitude shake is gone. I did notice one difference between the VIP and Lord mounts. With the Lords, I recall pulling 3G would cause a noticeable change in engine sound and feel. There does not seem to be any change with the VIP mounts. I assume G would push the Lord gel bags into contact with the rings. I do not know how long ago I noticed the sound change with G; could be after they had sagged a little.

I'll fly the new isolators a while and eyeball them for sag. Given this is a return to the "one size fits all" isolator set, I'm interested to see if the large engine actually does shorten isolator life. Seems logical that a 320 would not load the isolators as much as a 390.

For those who wish to know more, there is a nice tutorial regarding isolation and transmissibility in the Lord isolator catalog:

https://www.lord.com/sites/default/files/compressed_PC6116_AerospaceandDefenseIsolatorCatalog.pdf
 
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great info

Thanks Dan - this is great info. I learned a lot, and I suspect many others did too.
 
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