----- Original Message -----

From: Tracy Crook

To: Rotary motors in aircraft

Sent: Monday, March 10, 2008 8:46 AM

Subject: [FlyRotary] Re: Unusual Noise in Engine

Noises are really difficult to describe in words so this is just a shot in the dark.

 

You might be hearing the sound of the tension bolts suddenly releasing residual torsional tension from the overhaul.  The threads will sometimes suddenly overcome their starting friction and spin (just a partial turn ) until the residual tension is relieved.  On a freshly overhauled engine I noticed this on cool down after a run.  In a car with a good muffler you might gear it while it's running while warming up.   This noise sounds like a sharp metalic tick, very similar to engine 'ping' from detonation. It also is the same sound as a Rotax cylinder stud makes when it breaks.

If this is what it is, it eventually stops when all the bolts are 'relieved'.  I then continued to fly that engine for 856 hours.  If this occasional tick doesn't stop, after a dozen or so engine runs, this isn't it.  Don't be in too big a hurry to tear the engine down until you are sure there is a real problem.

 

Tracy

 

On Mon, Mar 10, 2008 at 3:16 AM, Tom-Lynn Koftinoff <tomk@telus.net> wrote:

I am testing an '88, 13B, non turbo engine that I rebuilt according to Tracy Crook's manual (Aviator's Guide to Mazda Rotary Conversions).  I did the rebuild, many years ago, before Tracy sold his rebuild kits, and it's my first rotary that I rebuilt.   I purchased my rebuild kit from Dave Atkins.    I am running it with Tracy's EC2 (purchased in '02), and I wired the harness as per his plans.  I fabricated my own intake manifold.  Presently, the motor is installed in an '86 Mazda RX-7 car.  I am using the transmission (i.e., most of the drivetrain) from the car, to put a load on the engine (i.e., wheels are off the ground).   The fuel pump, fuel tank, battery, tach, coolant temp gauge, exhaust, starter, is, stock, from the car.   I have an external oil pressure gauge, oil temp. gauge, ammeter, voltmeter, vacuum gauge, air/fuel gauge, circuit breakers, and toggle switches.  I didn't want to spend any more money  (i.e., purchasing Tracy's RD-1B, EM3, prop. etc.)    on the engine until I knew the engine was running adequately, and, therefore, I am using the car as the test bed.   The engine starts fairly easy up here in B.C., Canada, on cold winter days, and I have been running it, off and on, since late spring of '07.   One of the problems/issues I am trying to deal with is a random, intermittent noise from the engine, when the engine is running cold.   The noise sounds like a coin on edge being tapped against some metal, such as a fender of a car.   After the engine warms up, and I run it up to 3000 - 6000 RPMs I don't hear the noise.   The engine hasn't used any oil, and I have run approximately 40 gallons of gas through it.   At very high RMPs (5000 to 6000) I have placed the transmission into neutral because I have been concerned about damaging the transmission/drive train.   As a result of running the engine with no load (i.e., transmission in neutral) on it, at high RPM's, my plugs have fouled and stopped working or produced a weak spark.   Tracy has warned me that his EC2 was designed to run with a propeller load, and my plugs will foul, if I don't run it with a load.   My question is regarding the noise that I hear.  Has anyone experienced such a noise?  I have noticed the engine missing sporadically at low RPM's with a load on it, and the fuel/air mixture gauge showing five to six LEDS.   Can a miss, detonation, bad timing, fouled plug(s) etc cause such a noise?  My timing is very close to 23 degrees BTDC.   When I turn the engine over manually (i.e., with socket and ratchet) the engine feels like it has good compression, and doesn't make any strange noises, such as, anything broken or loose inside.    I may tear the engine apart to inspect the inside, later this year.  

 

Thanks,

 

 

Tom