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e2vdavidb

Moster 185 Exhaust bracket Failure

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Hi, not sure why but I have now had this exhaust bracket fail 2 x in under 21 hours of use, actual engine hours. (MP162 btacket)
I´m super careful about engine warm up so am at a loss.
Both brackets have exactly same failure.
Moster 185 plus 002280 about 3 years old but not used so much.
Is there an alternate or workaround?
Thinking of putting a rubber bush between exhaust and bracket but maybe that will make it worse.
Drawing shows rubber washer between the bracket tangs and I assume this is correct.
I do note that in each case the rubber insulation strip between bracket and exhaust slips very quickly and bunches at the bolt.
Any other observations?
Dave

Moster1.JPG

IMG_4004.JPG

IMG_4005.JPG

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Dave i think you'll find M141 is a solid spacer not rubber and is or was yours mounted with washers and spacer as in your above picture?.

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Hi

The M141 part was ordered and delivered from Italy Fly Products and was a stiff rubber in the 1st unit and the new part.

M143 is a stainless washer though.

In both instances it was the location where it was direct metal to metal, clamp to exhaust and maybe there is some resonance causing micro fractures.

I have ordered all parts new again but also a M8 rubber isolation bush to decouple the direct exhaust vibration from the clamp.

As the exhaust bush is at 20 hours I´ll replace at the same time with the new 50 hour bush.

I´ll post pics to show the bush fit if it looks like the alignment is good.

Dave

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New bracket arrived, I tried to add a rubber bush but spacing is all wrong so I have to use the factory setup.

I hope I get more than 10 hours from these, its getting expensive!

image1.jpeg

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Looking at the drawing, I am assuming it breaks the tab that sits against the bracket....?
If your not a million miles away from Accrington Lanc's... ill weld those back together for you so you can experiment with your setup knowing you have a couple spares.
I could maybe add a web on one side of one of them to see if transferring the stress to the other side of the knee onto the larger radius prevents any further breaks.
One way or another, you have to move that stress point away from the center of that slot.

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On ‎08‎/‎06‎/‎2019 at 15:46, e2vdavidb said:

Thinking of putting a rubber bush between exhaust and bracket but maybe that will make it worse.

Just re-read this.... a rubber would very likely spread the focus of that stress point, I cant see it making things worse.
Like asquaddie alludes to, the problem looks to be a highly focused stress point.

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Chaps thanks for feedback, and Mark thanks for the welding offer but I´m based in Munich Germany.

I did order and have received a new part plus a spare and today had a message from Vittorazi saying I could warranty the bracket.

The manual has no torque figure but I´m not gorillering it down.

As I now have a collection of the inner rubber bushes I will add one to the inside where it is indeed braking.

My suspicion is that the direct metal to metal is causing local micro fractures.

The big issue is they it seems to be a 10 hour event and I was more concerned about it failing and going through the prop.

I think I will also wire on the new bracket to be sure.

I will see if I can persuade one of the chaps in my office to do a stress analysis on the design as is daily business for designs, although our electronics packages never see the 2-stroke vibration in reality (I hope).

I did note that the rubber band around the bracket had a tendency to ´walk´ to the stress and failure point but could be some resonance issue.

 Dave

 

 

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No worries.
10hrs is abnormally bad so a bit of tinkering ought to get you much better numbers than that... wiring is a good idea (ask me how I know :) )
I'm 90% sure your man in stress analysis will have some good pointers with just a glance at the design.

I'm guessing the rubber band movement will be an artifact of the need for a lose (ish) fit... a great many exhausts have springs, rubber mounts and lose fits to allow enough movement to prevent focused stress points that will fail in short order... once one joint fails, the next stiffest joint will fail.

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