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Roger Lee

Why we should replace engine isolators

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The engine rubber isolators should get changed with the Rotax 5 year rubber replacement. These rubber engine isolators are under constant pressure and stress just sitting 24/7. They get cracked not only from stress, but from the heat in the cowl and the two rear isolators often crack when there is an exhaust leak because the exhaust gas blows right on these, especially the #3 exhaust. (common for bottom right side) With the engine pressure these get crushed and will allow engine sag in its mount. There are 16 of the isolators and we can only physically see the ones on the outside. This is another good argument to remove the engine during the Rotax rubber replacement. Rubber dries out with time and you can not access this damage. Changing these engine mounts is very easy and not time consuming with the engine off. It's a good argument for pay a little now or twice as much later because they will need to be done, so you might as well do it while the engine is exposed. Here are a couple of pictures of crushed isolators and this is the norm in a 5 year engine. I will get some shots of some cracked ones up here soon.

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gisurvey   

Hello,

 

I'm preparing to change the mounts in the next few months for my CTLS 2008.

Visually, I'm counting 4 bolts x 2 rubber isolators for each one (one in front and one in back), total 8. Where is my mistake, there are 2 on each side front/back of the bolts?

 

Thanks,

Alec

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Hi Alec,

 

The CTSW has 16 engine isolators that are totally different from the CTLS which only has 8. You'll have to get the FD isolators or from Rotax. The FD ones are $5 cheaper each. Total price for the LS isolators is $280. So far the LS isolators don't seem to be suffering the deterioration rate that the SW ones are.

 

 

While we are on the subject. I have found a very big help in longevity if you put some fire sleeve material around the bottom right isolator to protect it from exhaust heat. This one gets a lot more heat from the exhaust and causes early cracking. I think I would do the same with the LS isolator on that right bottom side too.

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Marco01   

Hello Roger: I'm just replacing mine on my 2007 Ctsw: they are far worse than the one shows, so, I will post some pictures as soon as they are all dismounted. Consequences were high vibrations, + Engine axis with negative degrees...

Again, thanks for,your very welcome informations...

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Hi Marc,

 

Glad it's working out. Like I have been trying to relay to everyone you can't see on the inside. No X-ray eyes for the engine mounts or the interior of the hose. Like the oceans of the world we are only the 20% land above that water and the rest lies below. We might see 20%-40% on an inspection, it's the other 60%-80% you can't see that worries me.

 

I have been slacking off.

As I find more trashed mounts and hose I'll post more pics, especially of the areas you can't see or inspect.

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Marco01   

Hi Roger,

 

Job is finaly done: as you mentionned, removing the insulators was a surprise to found out how they were in a bad shape.

I have attached the pictures with 2 of them: less + worth damaged ones.

 

Engine angle improved by 2°, plus less vibrations on cruise...

 

Thanks again for your support and advices...

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Hi Marco,

 

 

Nice pictures.

Glad it worked out well. I have been trying to tell everyone things like these can't be done on just a condition inspection because you just can't see on the inside and have no way of knowing. The only way to inspect these would be to pull them all out and look at them, but then you might as well replace them especially once you see them. Vibration and engine angle are truly affected. Hoses many times are the same way, we can only see the outside and not under any fire sleeve.

 

 

Note:

 

Here is a tip for you and others. The bottom right engine isolator takes a lot more heat than the other three sets because of the muffler heat. Wrap this one engine isolator with a piece of fire sleeve to help insulate it and it won't crack and fail before the others. For many people this is the isolator that will crack and smash earlier than the rest.

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gisurvey   

Hello Roger,

No, are new - I wish to be in so good shape after 500h :)

Pictures are only for info, showing the differencies LS vs SW. I'll post pictures of used mounts after replacement.

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It is my understanding that the lower right isolator located closest to exhaust will exhibit damage first.  When should an isolator in that position with edge cracking like in Roger's picture 6 (see first post in this thread) be replaced?  (...and yes, I know, replace the whole set of 16 at the same time.)  Immediately?  At the next annual condition inspection?  At the next five-year rubber hose/etc. change?  

 

Thanks in advance...

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Superficial cracks around the outside edges are from the #3 exhaust heat. Wrapping that engine mount on the outside will help stop that. That said the superficial cracking is not a problem unless it proceeds deep into the mount. You should replace all rubber engine mounts at the 5 year rubber replacement time frame. This way you should not have to worry. If you fail to do it then you will have to pay someone all over again to remove the engine a second time because those mounts won't make ten years.

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My isolators look like this pic:

 

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Roger found the issue when helping with my exhaust problem last year.  I've scheduled this year to have Roger do my 5-year hose change a year early, so that I can get these changed as well.  There were also some incorrect hoses used in the hose change that was done when I bought the plane, but I didn't know any better then.  So between the hoses and the isolators (which don't look like they were changes with the hoses), an early change out seems prudent.

 

Just FYI, the incorrect hoses used where the coolant lines, which are 3/4" (0.75") automotive hoses.  The correct hoses are 17mm (0.66") wrapped wall hose.  The hoses have worked fine, but early on I had  tiny coolant leaks due to the hose being slightly oversized.  I double clamped everything and got the leaks stopped, but didn't know why they leaked at all until Roger explained it to me.

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Runtoeat   

Hi Roger.  There's been a lot of water under the bridge since most of us did our rubber changes 5 years ago. When I did my change in 2011, I was told I MUST use high pressure fuel injector fuel line in 1/4" and 5/16".  I bloodied my finger tips pushing this hose over the nipples.  Then Gates Barricade hose was recommended..  As I understand now the best hose to use is standard bulk rubber fuel line. My understanding is the radiator hose is 17mm which is European DIN hose and the only place to obtain this is from LEAF because they have purchased this from overseas in bulk rolls?  The oil hose is standard Gates but I don't recall the size for this.  It would be super helpful if we had a list of fuel, water and oil hose sizes and a sources for these and approximate lengths required for CTSW and CTLS.  I can think of no other person who would be more qualified to provide this than you and wonder if you might find the time to do this?

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... I bloodied my finger tips pushing this hose over the nipples.  Then Gates Barricade hose was recommended...

 

Rubber fuel line and barbed fittings are not compatible, that is Gate's policy that they plaster everywhere.  The action of pushing the hose over the sharp barbs will shave even Gates Barricade smooth on the inside creating rubber debris in your fuel system.  I had an aborted take off at South Lake Tahoe due to rubber debris from Gate's Barricade forced over my barbed fittings.

 

 

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You are correct about Gate's stance, but most of the light aircraft industry worldwide uses them. There are alternatives, but that would require a lot of changing on most our aircraft and approvals from the MFG's. 

This is why caution from a mechanic that knows those risk and what causes them is important. Just because you can cut a hose off and forcibly shove another on doesn't make for a sound practice.

Sloppy sterile practices makes for carb debris.

It's the details that make a difference as a mechanic. The 5th grader next door can shove a hose on, use the wrong clamps, use the wrong hose, over clamp the hose and then write in the logbook all is well.

You shouldn't have to FORCE the hose over the fitting if the correct hose is used. Forcing shears off the inner liner. This is why I use the practices I use today. I was a live and learn in the earlier years.

 

Even when all is done as clean as possible and with great care debris can still happen. Best to check the carb bowls after about 1-2 hrs.  If its many hours down the road it may be because someone over tightened a clamp and cut into the barbs or you may be getting degradation. 

 

 

Unfortunately it isn't a perfect world. Not for light aircraft or larger GA aircraft.

 

 

Question:

Why do you think many Mfg's of light aircraft choose brass barbed fittings?

 I think I know the answer, but I'm not sure.

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Answer:  there is no good reason for the barbed fittings.  compatible beaded fittings are called for and are no big deal to use instead.

 

How many hoses with barbed fittings are there?  A few?  Multiply by 2 and that's how many fittings are wrong, you could switch the fittings or you could switch the fuel lines but it is an airplane, compatibility here is a no-brainier.

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Anticept   

Use a mild soap and water and wet the inside of the hose and on the fitting before installing. It's sort of the "anti-seize" for hoses.

 

Barbed fittings? Probably because it's readily available and actually provides a more reliable seal against leakage when properly installed. The problem here is they are meant to be a permanent installation fitting. I prefer the beaded fittings as they are designed for removability.

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Use a mild soap and water and wet the inside of the hose and on the fitting before installing. It's sort of the "anti-seize" for hoses.

 

Barbed fittings? Probably because it's readily available and actually provides a more reliable seal against leakage when properly installed. The problem here is they are meant to be a permanent installation fitting. I prefer the beaded fittings as they are designed for removability.

 

It's worse than that (meant to be permanent).  The barbs are meant to puncture and penetrate and the rubber hose is only 'fuel proof' on the inside lining.  Once that lining is breached than the additional layers are subject to fuel saturation when they were not meant to be.  In addition to that barbed fittings shave debris off of rubber hose and contaminate the fuel system.

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Anticept   

They are not supposed to puncture the rubber lines. If it does, then it's an improper mix of inflexible rubber and fittings. Barbed fittings are meant to be used with very soft, flexible hose, including rubber hosing. An improper mix of hose and fitting is what is leading to our problems.

 

The fact we use clamps with them aggravates the problem.

 

See https://www.bnl.gov/esh/shsd/PDF/Compressed_gas/BarbedFittings-Introduction.pdf

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I know they are used, but if you look close enough like with a microscope you can see why they are called barb.  They have many barbs meant to puncture, its unavoidable and it contaminates the hose.

 

http://blog.hemmings.com/index.php/2014/12/05/tech-101-fuel-line-hose-what-you-should-and-should-not-use/

 

'Nylon tubing uses barbed fittings that are inserted into the tubing, and the connection is then heated to shrink the tubing around the fitting.'

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Barbed fittings are for nylon hose where the punctures work and don't damage the hose and beaded fitting work with rubber fuel line and don't pucture.

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