I had already thought of checking to see if I had the engine mount the right way.I did.So this morning I called a few hobby shops and finally found one that had a TT YS metal fan in stock and got them to measure it for my.Assuming they measured correctly there is no real difference between the two.The guy at the hobby shop said they were the same just one was threaded for the YS engines.
So this left me with either buying a new YS fan which I had serious doubts would solve the problem or finding another fix for the problem.
My choices were:
1--File the engine mounting holes in the frame.I did not like the idea of doing this as there is not much material below the bottom holes to work with.Also it would have to be done very carefully so as not to make it hard to align the engine later.
2--Have some material machined on the fan hub where the clutch mounts.Once again it would need to be done carefully so as not to mess up the way the clutch sits.
3--Remove some of the front crankcase material that sticks out passed the front bearing.There is about 3/16" if crankcase sticking out beyond the front bearing.So much so I needed to use two .040" washers and a .010" washer to get the fan to clear the crankcase front by .030".
I decided to go with option #3.I disassebled the engine and removed a 1/16" of the crankcase front.I used some thin pinstrip tape to make a even line all around the crankcase front 1/16" back from the front edge and used a razor saw to slice a thin disc of material off.With carefull cutting and a little touch up with a file the crankcase looks like it did before the cut.
After cleaning up the crank case I reassembled the engine and installed the fan using one .040" washer.One was still needed so the fan would clear the crankcase front by about .035".A test fit in the frames showed the engine mount holes lined up now and that the clutch was no longer bottoming out in the clutch bell.I figure the top of the clutch has about .015 cleareance from the c-clip on the start shaft.I should also mention I had to drill a little material ( .040" ) out of the fan from the back side of the threads.The YS61ST1 has a very short threaded section and the fan was running up against the nonthreaded section below the threades before it was tight.Removing the .040" solved this.
I guess some may say there may have been a better way of solving the problem but after studing it for a few hours and looking at all the options I could not see one.After all there are not to many areas where the extra little bit needed to get the engine mount holes to line up could have been gained.In all once I decided what I was going to do it took me about 2 hours of carefull work and the problem was solved.
In case any one wonders why I was using the OS fan it was because I bought the heli new and never assembled from another modeller and he was originally going to use an OS engine.I already had the YS61 and knew the the threads in the fan for the OS were not that far off from the 8mm threads the YS engines use.To be honest rethreading the fan was a piece of cake compared to the fix I had to do to get the engine mount holes to line up.
Now I can finish assembling the heli.