Hi

I've just bought a new ThunderTiger GP42 glow engine. I installed straight on the plane and setup according to the instructions on the manual.

In the first flight, it was setup to very rich operation. However, after 6 to 7 flights, the engine began to loose compression. When it is cool, the compression is normal. But when is operated for a while (rich), the compression is bad... feel as if there is little resistance when flipping the propeller!

When consulted, the salesman said that the piston has to be replaced! It costs more than half the price of a new engine! It would be better to purchase a new one instead.

Any tips to solving this problem?

Thanks for any help.

Not sure what the problem is! Definitely not normal having to replace the piston/liner after 6 or 7 flights. Who made that determination, you or the salesman? Do you fly where there is alot of dirt on the runway? One of the first things lots of flyers do to a new engine is remove the backplate and inspect for any metal shavings from the machining process. Although not so much anymore with the newer technologies in machine equipment, it can still happen. Doesn't take much to score a liner.
How is the engine running? Can you tune and fly it at all_bob

Klgan,

Try to get it replaced under warranty.

When you get the new engine (providing it is the same engine, or another ABC/ABN type), break it in as described here:

http://www.rcuniverse.com/showthread...59&forumid=145

Disregard the bashing at the end of the thread.


If your replacement is a ringed engine, break it in very rich, four-cycling for the first 2-4 tanks.

DON'T BREAK AN ENGINE IN ON A PLANE. A FEW BENCH/TEST STAND RUNS HAVE CAUSED NO HARM TO ANYONE YET.

Sincerely,,

Hi

Thanks for the prompt reply. Yes, the engine is still running... but there is little resistance when flipping the propeller when starting the engine.

As the compression is low, it is a little hard to start the engine after the each flight. It has to be left to cool down before the subsequent flight.

The flying field is on an open space of red earth... very dusty under dry and hot day.

The salesman recommended for the piston to be replaced. However, due to the high cost, I refused.... may consider a new one instead ... not another ThunderTiger!

Thanks again.

Klgan,

ABC/ABN engines, which have been run-in too rich sometimes suffer from reduced hot compression.

Try to feel, with the glow plug and the backplate removed; to cancel out upper and lower compression forces, if you can feel any resistance to turning the engine at TDC (the piston at the very top of the stroke). There should be at least a light "pinch".
If no pinch is evident, your engine is not in good condition.

It can be your break-in technique (too rich), or abrasion from the sand and dust, but abrasive condition damages, usually cannot be felt after less than two hours of running time.

Your warranty must be applicable here and you shouldn't have to pay for piston/cylinder replacement, unless TT can prove you are to blame.

Most engines have better compression when cold, but can still be started, even by flipping, despite the lower hot compression.

If you can start your engine when hot, you can keep using it.

TT has been known to sell the piston/cylinder set just shy of a new engine's price...

Sincerely,