The Murphy Builders Site

Posted: **Sat Feb 18, 2012 2:01 pm**

G'day

I thought that I would like to share this with you.

My Rebel is fitted with a Rotax 100hp ULS engine, and it has been plagued
with a vibration in the 4000/5000 rpm range and it worsened after I fitted a
4-1 exhaust system. In fact it was vibrating so badly in that range that it
tore the rubber necks out of the airfilters.

No matter what I did I could not get the vibe out, and in desperation I
spoke to the local Rotax dealer who simply asked if I had an engine without
a clutch! I was not aware that a clutch in the gear box was needed, but he
said that they will now not supply a 100hp engine without one of them
fitted. We fitted a clutch ($1,200 Australian) and it has magically cured
the vibration. It now feels like a completely different engine and aircraft.

I know that a number of people are considering fitting a 100hp Rotax to
their Rebel and my piece of advice is to make sure it comes with a clutch.

Regards

Ian Donaldson

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Posted: **Sat Feb 18, 2012 2:01 pm**

----- Original Message -----
From: "Aurele Lavigne" <acerebel@ntl.sympatico.ca>
To: <rebel-builders@dcsol.com>
Sent: Sunday, October 16, 2005 11:37 PM
Subject: Re: Rotax 100 hp ULS

Ian, I only have the 80 hp and was considering the clutch. The vibrations
I
get are primarely at low rpm, start up and shut down and when I checked
with
a Rotax dealer, he indicated that the problem is most likely the carbs
were
out of synch. I don't have access to a pneumatic synch tool, but I did
have
them manually synched before.

He did indicate at that time that the 100hp comes with the clutch and
Rotech
Research in B.C. currently has reconditionned cluthes for $500 Cnd
available.

Havn't purchased one yet as I'm hoping to go to the 100hp in the not too
distant future.

Aurele
R063
----- Original Message -----
From: "IAN DONALDSON" <allsure@bigpond.net.au>
To: <rebel-builders@dcsol.com>
Sent: Sunday, October 16, 2005 2:18 AM
Subject: Rotax 100 hp ULS

G'day

I thought that I would like to share this with you.

My Rebel is fitted with a Rotax 100hp ULS engine, and it has been plagued
with a vibration in the 4000/5000 rpm range and it worsened after I
fitted
a
4-1 exhaust system. In fact it was vibrating so badly in that range that
it
tore the rubber necks out of the airfilters.

No matter what I did I could not get the vibe out, and in desperation I
spoke to the local Rotax dealer who simply asked if I had an engine
without
a clutch! I was not aware that a clutch in the gear box was needed, but
he
said that they will now not supply a 100hp engine without one of them
fitted. We fitted a clutch ($1,200 Australian) and it has magically cured
the vibration. It now feels like a completely different engine and
aircraft.

I know that a number of people are considering fitting a 100hp Rotax to
their Rebel and my piece of advice is to make sure it comes with a
clutch.

Regards

Ian Donaldson

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Posted: **Sat Feb 18, 2012 2:01 pm**

Hi Ian

Very interesting. I'm guessing there must be a rubber coupling or
dampening device of some kind that is part of the clutch. 4 cylinder 4
strokes actually have a slight torque reversal between each power
stroke. The torque from the engine actually goes slightly negative 8,000
times per minute at 4,000 rpm. That can be tough on a gearbox.

FWIW the Rebels that I've seen still all have those multiple pieces back
at the TS-1 location. Occasionally I see one that has replaced the
aluminum angle (the TS-3 bottom piece) with a steel angle. (I think
Angus had a crack appear in his alumium piece??) As long as there is no
up down or sideways free play, I think you are fine.

Ken

IAN DONALDSON wrote:

G'day

I thought that I would like to share this with you.

My Rebel is fitted with a Rotax 100hp ULS engine, and it has been plagued
with a vibration in the 4000/5000 rpm range and it worsened after I fitted a
4-1 exhaust system. In fact it was vibrating so badly in that range that it
tore the rubber necks out of the airfilters.

No matter what I did I could not get the vibe out, and in desperation I
spoke to the local Rotax dealer who simply asked if I had an engine without
a clutch! I was not aware that a clutch in the gear box was needed, but he
said that they will now not supply a 100hp engine without one of them
fitted. We fitted a clutch ($1,200 Australian) and it has magically cured
the vibration. It now feels like a completely different engine and aircraft.

I know that a number of people are considering fitting a 100hp Rotax to
their Rebel and my piece of advice is to make sure it comes with a clutch.

Regards

Ian Donaldson

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Posted: **Sat Feb 18, 2012 2:01 pm**

Ian, I only have the 80 hp and was considering the clutch. The vibrations I
get are primarely at low rpm, start up and shut down and when I checked with
a Rotax dealer, he indicated that the problem is most likely the carbs were
out of synch. I don't have access to a pneumatic synch tool, but I did have
them manually synched before.

He did indicate at that time that the 100hp comes with the clutch and Rotech
Research in B.C. currently has reconditionned cluthes for $500 Cnd
available.

Havn't purchased one yet as I'm hoping to go to the 100hp in the not too
distant future.

Aurele
R063
----- Original Message -----
From: "IAN DONALDSON" <allsure@bigpond.net.au>
To: <rebel-builders@dcsol.com>
Sent: Sunday, October 16, 2005 2:18 AM
Subject: Rotax 100 hp ULS

G'day

I thought that I would like to share this with you.

My Rebel is fitted with a Rotax 100hp ULS engine, and it has been plagued
with a vibration in the 4000/5000 rpm range and it worsened after I fitted
a
4-1 exhaust system. In fact it was vibrating so badly in that range that
it
tore the rubber necks out of the airfilters.

No matter what I did I could not get the vibe out, and in desperation I
spoke to the local Rotax dealer who simply asked if I had an engine
without
a clutch! I was not aware that a clutch in the gear box was needed, but he
said that they will now not supply a 100hp engine without one of them
fitted. We fitted a clutch ($1,200 Australian) and it has magically cured
the vibration. It now feels like a completely different engine and
aircraft.

I know that a number of people are considering fitting a 100hp Rotax to
their Rebel and my piece of advice is to make sure it comes with a clutch.

Regards

Ian Donaldson

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Posted: **Sat Feb 18, 2012 2:01 pm**

Yes Ian...the 912ULS I installed in a Pegastol a few years ago was a freshly
reconditioned engine with only 25 hours on it as a purchaser returned to
Rotec on warrantee because of the vibration and they installed the slipper
clutch gear box and resold the engine to my customer. Very
smooth/quite...but he has thrown both carburetors out of their mounting
rubbers twice in 3 years...which rips the rubber flange they mount on
leaving you pretty much stranded (if not carrying some really good tape).
Luckily this only happens on start up or shut down and not in flight!

Wayne

----- Original Message -----
From: "Aurele Lavigne" <acerebel@ntl.sympatico.ca>
To: <rebel-builders@dcsol.com>
Sent: Sunday, October 16, 2005 9:37 AM
Subject: Re: Rotax 100 hp ULS

Ian, I only have the 80 hp and was considering the clutch. The vibrations

I

get are primarely at low rpm, start up and shut down and when I checked

with

a Rotax dealer, he indicated that the problem is most likely the carbs

were

out of synch. I don't have access to a pneumatic synch tool, but I did

have

them manually synched before.

He did indicate at that time that the 100hp comes with the clutch and

Rotech

Research in B.C. currently has reconditionned cluthes for $500 Cnd
available.

Havn't purchased one yet as I'm hoping to go to the 100hp in the not too
distant future.

Aurele
R063
----- Original Message -----
From: "IAN DONALDSON" <allsure@bigpond.net.au>
To: <rebel-builders@dcsol.com>
Sent: Sunday, October 16, 2005 2:18 AM
Subject: Rotax 100 hp ULS

G'day

I thought that I would like to share this with you.

My Rebel is fitted with a Rotax 100hp ULS engine, and it has been

plagued

with a vibration in the 4000/5000 rpm range and it worsened after I

fitted

a
4-1 exhaust system. In fact it was vibrating so badly in that range that
it
tore the rubber necks out of the airfilters.

No matter what I did I could not get the vibe out, and in desperation I
spoke to the local Rotax dealer who simply asked if I had an engine
without
a clutch! I was not aware that a clutch in the gear box was needed, but

he

said that they will now not supply a 100hp engine without one of them
fitted. We fitted a clutch ($1,200 Australian) and it has magically

cured

the vibration. It now feels like a completely different engine and
aircraft.

I know that a number of people are considering fitting a 100hp Rotax to
their Rebel and my piece of advice is to make sure it comes with a

clutch.

Regards

Ian Donaldson

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Posted: **Sat Feb 18, 2012 2:01 pm**

G'day Aurele

I was plagued with these vibrations not down low, but in the 4/5000 rev
range. The difference that the slipper clutch has made is truly remarkable.

The engine used to clank and rattle around a lot on start up and when
stopping, but that has gone. There is no more noise at all!

I never let carby sync worry me too much. I just do what they say in the
Rotax manual and get the carbs as closely mechanically balanced as I can.
The engine idles fine so I must have them OK and of course most of the
running is done with the throttles well open and it does not seem to make
all that much difference. I have used vacuum gauges to balance them and not
noticed any difference.

I am really happy with the way the rebel performs with the 100 hp engine. If
I was doing it over again I would make or alter the engine mount so that I
could use the factory airbox. I think that if you put in the 100 hp engine
the performance difference would amaze.

And thanks again for the assistance with the muffler design, The muffler has
about 25 hours on it and not a sign of cracking. The 4-1 did make a
difference to the performance and it has a nice throaty exhaust sound!

Regards

Ian Donaldson

Ian, I only have the 80 hp and was considering the clutch. The vibrations
I
get are primarily at low rpm, start up and shut down and when I checked
with
a Rotax dealer, he indicated that the problem is most likely the carbs
were
out of synch. I don't have access to a pneumatic synch tool, but I did
have
them manually synched before.

He did indicate at that time that the 100hp comes with the clutch and
Rotech
Research in B.C. currently has reconditioned clutches for $500 Cnd
available.

Haven't purchased one yet as I'm hoping to go to the 100hp in the not too
distant future.

Aurele
R063
----- Original Message -----
From: "IAN DONALDSON" <allsure@bigpond.net.au>
To: <rebel-builders@dcsol.com>
Sent: Sunday, October 16, 2005 2:18 AM
Subject: Rotax 100 hp ULS

G'day

I thought that I would like to share this with you.

My Rebel is fitted with a Rotax 100hp ULS engine, and it has been plagued
with a vibration in the 4000/5000 rpm range and it worsened after I
fitted
a
4-1 exhaust system. In fact it was vibrating so badly in that range that
it
tore the rubber necks out of the airfilters.

No matter what I did I could not get the vibe out, and in desperation I
spoke to the local Rotax dealer who simply asked if I had an engine
without
a clutch! I was not aware that a clutch in the gear box was needed, but
he
said that they will now not supply a 100hp engine without one of them
fitted. We fitted a clutch ($1,200 Australian) and it has magically cured
the vibration. It now feels like a completely different engine and
aircraft.

I know that a number of people are considering fitting a 100hp Rotax to
their Rebel and my piece of advice is to make sure it comes with a
clutch.

Regards

Ian Donaldson

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Posted: **Sat Feb 18, 2012 2:01 pm**

G'day Ken

The gear box is a very simple step down using two gears, and behind that is
a "sprag" clutch arrangement. This is what causes the Rotax rattle
particularly on shutdown. The "clutch" appears to be a plate at the rear of
the box that dampens the action of the "sprag" clutch. I have read the
manual, but it still remains a mystery as to how it all works!

regards

Ian Donaldson

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Posted: **Sat Feb 18, 2012 2:01 pm**

Hi Ian

Remember that I don't know much about rotax engines in particular.
However sprag clutches work at low engine speed and specifically during
start and shutdown to allow the prop to freewheel forward during that
negative torque pulse between each piston ignition or powerstroke. That
eliminates torsional harmonic resonances that can be quite destructive.
I can't imagine many situations where it would be wise to choose not to
have one on a rotax unless there have been maintanance problems with it.
At least one other manufacturer does have a bit of a nightmare situation
with them (my opinion) but that's not applicable to rotax at all from
what I've heard.

At high speed, the sprag generally doesn't do anything which is a good
thing. However the most common method of moderating high speed torsional
vibrations is with a rubber or spring drive plate similar to what you'd
find in a car clutch plate for a manual transmission. You can design to
avoid these but in both cases it is important to respect any propellor
size/moment of inertia limits specified by the manufacturer as you are
dealing with a tuned spring system. Operation outside those parameters
is somewhat akin to bringing an expensive crystal a wine glass to the
opera...

Ken

IAN DONALDSON wrote:

G'day Ken

The gear box is a very simple step down using two gears, and behind that is
a "sprag" clutch arrangement. This is what causes the Rotax rattle
particularly on shutdown. The "clutch" appears to be a plate at the rear of
the box that dampens the action of the "sprag" clutch. I have read the
manual, but it still remains a mystery as to how it all works!

regards

Ian Donaldson

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Posted: **Sat Feb 18, 2012 2:01 pm**

G'day Ken

That is interesting! Unfortunately I am not an engineer, but I have just a
enough understanding to keep me out of trouble.

As I said I don't really understand how the clutch assembly works, but the
difference it made was amazing. When I bought my engine the clutch was
available but the dealer said that it was not needed. Five years later he
has changed his mind!

. You can design to avoid these but in both cases it is important to
respect any propeller
size/moment of inertia limits specified by the manufacturer as you are
dealing with a tuned spring system. Operation outside those parameters
is somewhat akin to bringing an expensive crystal a wine glass to the
opera...

That is an interesting concept! I once tried to work out the limit imposed
by the manufacturer but gave up. If my math was correct I would have to use
a toothpick on the engine. I chose a Warp Drive composite, put it on and
stopped worrying. If anything goes wrong I will be the first to know! There
are some certified planes/engines here that use a great chunk of wood as a
prop and if that does not break a gearbox then my prop won't. ( I hope).

regards

Ian Donaldson

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Posted: **Sat Feb 18, 2012 2:01 pm**

Ian, glad to hear the exhaust is working fine.
As for the clutch, did you install it yourself and is it a big job??? If
possible, could you send me pics directly and any installation instructions
if that's possible. I may look at byuing one for my 80 hp, even if I do
upgrade to 100 hp down the road.

Regarding the airbox, I had one made from a plan I got from Rotax and only
needs the butterfly linkake to complete. You could probably buy the original
and modify/ extend each extrimity to accomodate the reversed intakes on the
Rebel, as you know.A buddy just purchased a Rebel with 100hp and has the
factory airbox, so I will ask for pics so we can see what they did to modify
for a fit???

Aurele

----- Original Message -----
From: "IAN DONALDSON" <allsure@bigpond.net.au>
To: <rebel-builders@dcsol.com>
Sent: Monday, October 17, 2005 2:29 AM
Subject: Re: Rotax 100 hp ULS

G'day Aurele

I was plagued with these vibrations not down low, but in the 4/5000 rev
range. The difference that the slipper clutch has made is truly
remarkable.

The engine used to clank and rattle around a lot on start up and when
stopping, but that has gone. There is no more noise at all!

I never let carby sync worry me too much. I just do what they say in the
Rotax manual and get the carbs as closely mechanically balanced as I can.
The engine idles fine so I must have them OK and of course most of the
running is done with the throttles well open and it does not seem to make
all that much difference. I have used vacuum gauges to balance them and
not
noticed any difference.

I am really happy with the way the rebel performs with the 100 hp engine.
If
I was doing it over again I would make or alter the engine mount so that I
could use the factory airbox. I think that if you put in the 100 hp engine
the performance difference would amaze.

And thanks again for the assistance with the muffler design, The muffler
has
about 25 hours on it and not a sign of cracking. The 4-1 did make a
difference to the performance and it has a nice throaty exhaust sound!

Regards

Ian Donaldson

Ian, I only have the 80 hp and was considering the clutch. The vibrations
I
get are primarily at low rpm, start up and shut down and when I checked
with
a Rotax dealer, he indicated that the problem is most likely the carbs
were
out of synch. I don't have access to a pneumatic synch tool, but I did
have
them manually synched before.

He did indicate at that time that the 100hp comes with the clutch and
Rotech
Research in B.C. currently has reconditioned clutches for $500 Cnd
available.

Haven't purchased one yet as I'm hoping to go to the 100hp in the not too
distant future.

Aurele
R063
----- Original Message -----
From: "IAN DONALDSON" <allsure@bigpond.net.au>
To: <rebel-builders@dcsol.com>
Sent: Sunday, October 16, 2005 2:18 AM
Subject: Rotax 100 hp ULS

G'day

I thought that I would like to share this with you.

My Rebel is fitted with a Rotax 100hp ULS engine, and it has been
plagued
with a vibration in the 4000/5000 rpm range and it worsened after I
fitted
a
4-1 exhaust system. In fact it was vibrating so badly in that range that
it
tore the rubber necks out of the airfilters.

No matter what I did I could not get the vibe out, and in desperation I
spoke to the local Rotax dealer who simply asked if I had an engine
without
a clutch! I was not aware that a clutch in the gear box was needed, but
he
said that they will now not supply a 100hp engine without one of them
fitted. We fitted a clutch ($1,200 Australian) and it has magically
cured
the vibration. It now feels like a completely different engine and
aircraft.

I know that a number of people are considering fitting a 100hp Rotax to
their Rebel and my piece of advice is to make sure it comes with a
clutch.

Regards

Ian Donaldson

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