> > It is really hard to get a good handle on the compression
> > of a rotary engine as things happen too fast. The usual
> > way is to take the Shrader valve (tire valve) out of an
> > ordinary compression tester and watch it as the engine turns
> > over. You should get at least three pulses in a row all "about" the
> > same value. "About" is the problem. At 250 RPM the compression
> > should be 85 psi plus or minus 10 psi chamber to chamber.
> > It also varies with cranking RPM and altitude of the shop.
> > At 10,000 feet it is down to 57 psi. At sea level and 300
> > RPM it is up to 95 psi or so. At 200 RPM it is 73 psi or so.
> >
> > Mazda has a special device that shows the pressure in three windows.
> > Special tool 49 FO18 9A0 is it. I have never seen one.
> > A very very expensive tool. I have never seen or heard of
> > a rotary engine builder or re-builder that had one. They should have
> > them as that is a major issue with after market apex seals. Stock
seals
> > have a slight crown. You can see it when you put them belly to
> > belly. The after market ferrous apex seals I have seen so far have
> > no crown. This means you lose compression and power.
> >
> > This is another area where a PICAXE will help greatly.
> > You can use one of the analog to digital converters to
> > measure the compression with a Free Scale pressure sensor.
> > Say ten times a second. Send the data to a PC which is easy to do
> > with a PICAXE through the serial or USB port and you have an
> > under $75 rotary engine compression tester. Not counting the cost
> > of the PC but you already have one of those or you would not
> > be reading this.
> >
> > Paul Lamar ...No rotor no motor.
>
>
> When checking the compression on a Lycasaurus, A and P mechanics always
(or
> should) do a differential compression check using two pressure gages
every
> 100 hr and at annual inspections. Using a warm engine, each cylinder is
> checked individually with compressed air through a regulator set to 80
psi
> at TDC while the engine is immobilized. The greater the leak rate the
lower
> the pressure reading on the engine side of the regulator. A typical
reading
> may be 78/80. If the reading is too low, a little oil can be squirted
into
> the spark plug hole. If this method is applicable to rotary engines, a
big
> advantage is that the low compression rotor can easily be determined.
>
> Norm DeBoer
>
> That is a good idea Norm. In fact all three chambers on each rotor
> can be checked. Lock the e-shaft at Top Dead Center for each chamber
> and pressurize each chamber in turn. Note the rate of pressure leak
down.
> Six tests in total. Not only suspect rotors but individual leaking
> apex seals can be determined.
>
> Paul Lamar ...No rotor no motor.
Yes that is exactly right! Some one much smarter than me came up with
this
method of inspection long before I got my A & P. Each measurement is
recorded in the engine log book and when the readings start to go south,
it
is an advance warning of impending problems.
I did a Google before I posted the last and found some interesting info
from
operators using reciprosaurus engines:
http://www.napanet.net/~arbeau/swift/o3002.htm
There are others...
Developing a Standard Operating Procedure (SOP) for this method of
compression check for the Rotary Engine may be more acceptance criteria
for
some of the unconvinced...
Norm
Norm I am sure you have heard of the trick of taking the rocker arm
off and smacking the end of the exhaust valve stem with a hammer
to seat it better :)
Paul Lamar ...No rotor no motor.
It's called staking the valve :)
Norm
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