Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Exhaust flexible rubber test

2026-07-14


Rubber flexible mounts for the M3W muffler

I heard - driving in the Pyrenees - a strange metal sound in my Starboard side Muffler.
I was worrying that parts of the muffler were inside broken.

Back home I took away the Krazy Horse muffler with the attached pipes and checked it thoroughly.
I had ideas of making a muffler myself after asking Krazy Horse if they possibly had the whole thing for sale. The very friendly help told me : “No they did not at this moment”.

I read several articles for making a separate Muffler, but more noise seems to be the result, and my nice trike makes noise more than enough.
The TM-articles are about an ‘open’ Muffler – see f.i. ( Magnaflow ) #442461 - and I found that mine KZ-Muffler was blocked at the end.
I do not understand why at the end, because in my opinion when you make those blocking devices in the beginning of the muffler it would really better help. As is done with several motorbikes.
The device has holes in a smaller inside pipe which forces the exhaust-gasses to swirl and so the sound will be better damped in the muffler, which is the purpose of a muffler. When blocked at the end – it seems to me - you will not have that air-turbulence effect so much for the full length of the muffler.
As an example for such a device see the following picture.
One without and one with a filter , all to create air-turbulence in the muffler.





But this issue is for a time I have to renew the muffler.

Broken rubbers.
The noise was not the Muffler but two rotten flexible support under the muffler, which attaches the muffler to the M3W.
I suppose looking at the History of my M3W they are maximum around 6 years old.

 
I found at “garage56” new flexibles for € 47,23, for a set of four.
Because – from my experience - most UK companies do not feel any obligation to withdraw the VAT ( they are obliged to do this ). It costs them too much time ?
Sending and import taxes to Europe will raise this product for EU citizens probably to € 85,- before getting it in Europe.
That means € 21 apiece.

So I looked around to other possibilities and found
On Amazon 2 different kits I both bought.

A. DIABOLO DESIGN ( as is the type I have and Garage 56 is offering )
“GREENSTAR - Silent Block Diabolo Model - Ø 40 mm - Length 30 mm - M8 thread length 22.5 mm - Vibration absorption “
€ 3 x 4 = € 12 incl. sending and free returning.

B. “4 x Rubber Can Holders M8-40mm x 30mm Anti Vibration Isolator Mounts Air Compressor Pump Damper Cylindrical Male I Male (Thread M8 x 23mm I - 40mm D x 30mm H)”
for € 30, so € 7,5 a piece incl. sending and free returning .
These are not diabolos so they are less flexible and are not advertised for exhausts.

I also found the Bosal RTN4 255-336 as mentioned in Ian Bratt’s fantastic list, but these have different shapes than the round rubbers of the diabolo types. Flat and with the bolts not in line with each other.
The Bosal RTN4 255-333 instead is the diabolo type.
Average price on internet of this one is around € 3,50 ( exclusive sending costs).

I bought a set of A. as it was advertised for exhaust pipes and a set of the fully round ones B., not advertised for exhaust pipes.

Which one is good?

Exhaust pipes at these supports can get a maximum heat of 200 degr C, that is the officially agreed norm. I measure that the Cylinder head temperature nearly never comes above 220 degr. C either.

So I have put A. and B. and the old one ( C. ) in the oven for an hour at 200 degr. C to see what happened.

The results are interesting.
C. The original one, was slightly broken but after this hour totally gone.
A. Looked still intact but smoked a little bit - Horrible smell - A not so healthy test.
B. Looked perfect and did not smell at all.

Seeing the result of C. I got the idea to do a stress test.
Stress test was making one end of the metal tread longer so I could bow to all sites to an angle of at least 60 degr.

Ad C. The stress result for C. was not anymore necessary, the result would be clear : Ashes to Ashes!

Ad A. The stress result for the official exhaust diabolo A. was surprising.
On the one not in the oven I could do all stress-tests.
But the one which had been heated for an hour you clearly could see the rubber was slightly damaged
by the heat.
 
Ad B. The stress result for the not exhaust flexible B. was also surprising.
On the one not in the oven I could do all stress-test
And the one which had been heated you absolutely could not see any damage at the rubber.
Stressing it to 60 degr. was not more difficult and took not more power than with the diabolo one A..

My humble conclusion : “Do not believe advertisements”.

I choose for the ordinary round ones - B. - because they are in all conditions the most strong examples. And exactually the muffler is fully vertical mounted so there is no angle to correct for the flexible. And there was no real extra power used compared with A. in the stress test to create an angle.
A little bit more expensive than the exhaust diabolos.

As a typical Dutchman I cannot throw away € 12,- for nothing so I will use the diabolo styles first, but keep a sharp Eye on them.

Always best to replace the exhaust flex bobbins with stainless type. The factory ones can rust badly leaving the bond to rubber parting.

The one's from the Alternative Parts List (Renault Traffic, Master, Espace RTN4 255-336. M8) are well proven to last 10s of thousands of miles and around 4-5 years. They are readily available at around £2 each.

You will need to trim the threaded part as they are too long for the exhaust bracket but this only takes a few seconds with a hacksaw.

Hi RichardV6

I am afraid that's not a good idea.

Stainless steel and aluminium hate each others present.
Stainless eats the Aluminium fast.
Cause : Electrolyse. Especially at this point where you have very often water.

A former owner of my M3W used SS refits to connect the body to the frame.
All aluminium is damaged around the refits. You can see the paint 'bubbling'.

So always use the galvanised bobbins and not the SS ones. Zinc - Galvanise material - is nearer to aluminium in the periodic table.
Even Tefgel will not help here connecting surface is too big.

Herrie - the stainless steel rivets were installed by the MMC dealer when the body was replaced.

The Renault Traffic, Master, Espace RTN4 255-336. M8 exhaust bobbins work fine and as Chris states they last for tens of 1000's of miles and are cheap and easy to source.

See you in Grindelwald?

For a long time, I’ve been using 8mm washers with a small outer diameter to adjust the exhaust pipe's height and balance its weight across the two rubber mounts; this also helps slightly reduce heat transfer. While it is possible to make thermal spacers to prevent heat transfer, they aren't really necessary. I’m still using the rear mounts from when the chassis was replaced at the factory in 2015; the front ones—replaced with mounts from a classic Mini—are about 5 or 6 years old and still in good condition. I once bought some blue silicone mounts that came apart when bent by hand, so they went straight in the trash without ever being installed. Normally, all TWs have the bodywork riveted to the chassis using 5mm stainless steel rivets (18mm long) with a synthetic fiber washer.
For the best performance and simplicity regarding the exhaust, the best approach is to have two 2.5-inch stainless steel pipes slightly bent and fit them with two TVR Cerbera track-day silencers. I’ve been running the unrestricted Morgan exhausts for five years now; they are a bit louder than the stock ones, but the performance is so good that you wouldn't want to put the originals back on—though there are likely still some left at the factory.

I first tested the silicone rubber mounts on the original exhaust, then on my homemade exhaust :





Then I completely removed the Rubber Mounts :

Will be interesting to see the long term impact on the alloy body without rubber in the mounts.

Plus the risk of additional heat transfer & cooked paint

I found these in the US that look like what you mentioned above a "B.".

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