The Ponz

I purchased a new Evolution 35 Gas engine a little more than a year ago.

I broke the engine in as instructed using synthetic oil. The engine would run at full throttle for about 45 seconds and then fade out.

I decided to run the engine extremely rich and try flying it. Out of four flights, I had two dead stick landings.

I took the engine off the plane and removed the muffler. In inspecting the piston through the exhaust port, I noticed scoring on the piston. I then removed the cylinder head, where I found scoring on the cylinder wall, piston and ring.

Horizon Hobbies fixed the engine under warrentee and I am very satisfied with their work.

I would like to hear anyones experiences with these engines good or bad and any advice in breaking this engine in, ex. Lawn Boy oil vs synthetic oil.

The engine flew my 1/4 scale GeeBee very well until the engine quit, sadly GeeBee R2's don't land very well dead stick.

Ben

pe reivers

This engine normally is a zero defect in mechanical sense.
What oil did you use, kind of gas, and oil mix ratio?
What prop?
How was your engine cooled? Details please, not just a statement that it was well cooled.

The Ponz

Thanks for your interest.

I used Amsoil Denominator synthetic oil, mixed at the recommended 30 to 1 with 87 octane gasoline. I used APC props 20x8, 19x8 and 18x8 along with the inverted muffler that can be purchased with the engine. I I flew the plane successfully twice with the 18X8 prop and with the fuel mixture set extremely rich. At this setting if would not come onto the two cycle sound until at full throttle for a few seconds.

As far as the cooling issue, the engine was broken in without the large GeeBee cowl. The cowl was installed for the four flights. As you can imagine, I have wondered if the engine over heated which then caused the scoring problem along with the engine quitting. The cowl has a plastic radial installed with the plastic in front of the inverted Evolution engine cylinder removed to allow cooling. There should be enough air exiting the cowl to allow sufficient cooling.

The purpose of this thread is not question the quality and usefulness of this engine, but to make sure I can avoid the problem of the engine quitting prematurely.

Was the scoring on the piston and cyinder wall cause by not breaking the engine correctly, running the engine too lean, or simply overheating? Who can be sure, but since the engine has now been restored to an almost new condition, I would like to do my best to make sure the problem doesn't happen again.

As I stated in my initial post, I followed the user guide in the breakin process, but I could never get the engine to run at full throttle for the maximum time of one minute as recommended, after about 30 to 45 seconds the engine would fade out and quit. To get the engine to stay running I had to run it extremely rich.

I am now in the process of repairing the 1/4 scale GeeBee and when completed I would like nothing more than to fly this plane with this terrific engine.

Sincerely,

Ben

pe reivers

The first thing that comes to mind is the fuel octane. The 35 needs leadfree premium 91 PON or better (NO AVGAS!). 87 is just not good enoughunless you place two extra shims under the head. This explains the inability to keep sustained power on. You also may have your mixture too lean, but with too low octane these problems blanket each other. You need to check your plug to get the needle settings right.
In a large radial cowl, guiding the cooling air alongside the cylinder is very important, and so is creating a low pressure air exit at the cowl rear edge. The plastic radial cutout can be OK, IF the openeing is very close to the cylinder. Better would be with the cylinder IN the cutout. If the cylinder is a way back from the cutout, air guiding towards the cylinder is needed.

The Ponz

Thanks very much for your advice on the octane rating. I will definately use 91 octane from now on.

I believe the air flow over the engines is sufficient, but I will monitor this in the future.

Thanks again for answering my posts, it just show how helpful the internet can be for the customer and the manufacturer.


Ben

pe reivers

For correct understanding, I am not the manufacturer.