_BOON_

Hi all,

I am learning to fly choppers right now.
The engine I have os the OS50 SXH.
It has had about 3-4 tanks of juice through it now with needle valve open 2 turns with an extra 2 turns as per the intructions for breaking in.
Today I turned the valve back in 1 turn and started hovering. All fine for a while then the engine stopped after about 5-10mins.
Couldn't get going again - noticed I could turn the fan and starting cone on the Moskito sport with not much resistance at all.

Came home.
Pulled out glow plug, it is dead.
The engine is not as stiff as it was when new I have noticed.
Is this just a broken in engine feel?

Now my question is :

1 Is my engine broken now
2 Is it just the glow plug (havent got one to try as of yet)
3 If it is broken, can I replace the piston ring and all will be OK

I got my fingers crossed for your replies

Regards

1 worried man

downunder-RCU

Ooooooo...Boon....a ringed engine takes a LONG time to run in properly at a slobbering rich setting. The fact that your plug is dead isn't surprising either. Unless you flushed the engine out first you're likely to have had a bit of swarf inside and the running in process can send tiny particles of aluminium through the engine. The tiniest bit will kill a glow plug. Always run in an engine with the oldest plug you've got, just in case.

You may have cooked the ring but I'd try running it in more on the bench and see how it goes. If you're using one of the imported Yank fuels it may not have enough oil in it. It probably doesn't even have any castor in it

_BOON_

Hi downunder,

I pulled the engine down and it has a 1.5mm hole in the top of the piston which is at the bottom of a small concavity about .5cm round.
There is no mark on the pug side of the casing to indicate something banging on it.
could it be a faulty piston?

This is my problem I guess, what would have caused this?

have ordered a new piston and ring everything else looks ok.

boon

nozzles

Perhaps I can add a question too. I am in a similar position to Boon, but with an engine that does not turn over when I try to start it. The starter wand just rotates in its housing, causing a horrendous squeel, and getting very hot, very quickly. If I take the plug out, it turns over just fine, obviously spitting fuel everywhere. Might there be some sort of hydraulic lock, or vapour lock? The engine ran fine for about 3 or 4 bench starts, but now I am out of ideas. The manual doesn't shed any light on this problem.

Bax

My Feedback: (11)

If there's a small crater in the center of the piston top, right under the glow plug, and the piston is holed, it indicates that detonation has been taking place. This creates a local hot spot and the aluminum of the piston slowly vaporizes away. A lot of that vaporized aluminum precipitates back onto the piston towards the rim and makes the top of the piston become "grainy".

Detonation can happen if the engine is run too lean or too hot. Also, an engine over-compressed for the amount of nitro in the fuel will cause detonation, a badly-tuned exhaust system, a too-hot glow plug for the nitro being used...all can cause detonation.

If your piston's top is crushed, did you use a piston-locking tool to keep the engine from turning over when you installed the flywheel? That type of locking tool puts tremendous strain on the piston and can weaken it enough so that it fails at a later time. A crankshaft lock should be used. O.S. makes such tools in different sizes for the different engines.