Hello Michael,
The Norvel engines like the 0.25 and the 0.15 are a special construction, of I believe, an aluminium piston and an aluminium cylinder coated with some dense aluminium oxide. They tend to be more like an AAC or ABC engine when it comes to running in. They have a tight fit at TDC and Norvel specifically state that they should NOT be turned over by hand when dry.
I would NEVER allow a  Norvel to be run in rich. They need to be got up to operating temperature as quickly as possible, otherwise you will damage the piston and coating. Running these engines in like an old iron piston / steel cylinder engine, ie very wet, will destroy the engine in short time. They should never be run rich. Let them run up to normal temperature, run maybe a tank or two through them and then go fly.
I think you have destroyed the engine, by running it way below operating temperature and the tight fit has ruined the piston / cylinder and probably has not done the con rod any good either. the only solution is to buy a new P/L set and just run it normally.
These are excellent engines when run correctly. I have two 15s which have maybe 500 hours on them. No sign of wear and easy starting too and very powerful.

Andrew.

             Michael, may I suggest that you look at the clamp ring holding in the head button. These are notorious for leaking. A simple water test can easily reveal your problem quickly. Just fill up a bowl with water and with the prop on, check your engine by immersing just the head upside down to the exhaust cutout in the bowl. Proceed to turn the engine over with a prop on and check for bubbles. Many times during run up you can also see it weeping. Having the proper pin spanner is a must to properly tighten and seal the head. Many have used high temp RTV in the threads to not only seal but prevent it from loosening. This generally happens upon start up or when the engine is still breaking in. I would also check to see how many head gaskets are there and remove one if possible. Placing the head button on a flat piece of glass and truing it up with some fine sandpaper and oil will also help as this will allow for a better seal. Check the backplate in the water while your at it as this can also cause weakness in compression. Also check the cylinder head bolts for tightness as leaks can form on the underside of the cylinder now that its been run in. Many times I remove the cylinder and lap the top of the case flat on a piece of glass as well until entirely flat. Make sure your properly install the base gasket as it has it's own orientation and must line up correctly on the top of the case.

As mentioned by the other posters, running these engines in rich is not a good practice. Your prop choice is rather much for this engine. Using a 8x4 allows the engine to run up with little load and prevents overheating. The needle valves of these engines are poorly designed and can be very responsible for air leaks. Placing a piece of fuel tubing tightly over the spraybar and up onto the needle can assist with any air leaks.  The Norvel has a very distinct pinch at TDC and running rich can quickly remove the fit due to galling and it's also very hard on the conrod. Let's just keep our fingers crossed here. The engine more than likely has more than one head gasket generally required to assist in break in and initial start up. Now that you have run time on the engine removing them certainly won't be an issue. Ken

Andrew,
Rusty,
Ken,

Thanks for the info.

Will check our for leaks.

T Michael Jennings   
Knoxville, TN