The flying monkeys got me...

Helis and fixed wing

AMA 957918
IRCHA 4345
AMA Intro Pilot Instructor

Friday, November 25, 2016

A Bad Bulkhead and RCGF Spark Threads Strip Again

I ran the engine today with the 14x8x4 prop and it didn't come flying apart. It started and ran fine, but stalled in idle after a few moments. During that time the prop was fine, stable, and tracked perfectly without bowing, and no vibration. The second time it stalled at idle I could not restart it. I took it into the shop and I removed the spark plug to check the ignition and it sparked, but inconsistently. I decided to replace the Hall sensor and it fixed the spark problem. The Hall sensor frame had snapped and in repairing it it sat a bit higher than I think it should. I could not get the sensor head out of the case, so I had to replace the entire thing, and I just happen to have a couple.

I noticed that when I removed the spark from the RCGF 10cc engine, I noticed a "spring" in the hole. It took me a moment to realize that the spark hole threads had stripped. This has happened before as RCGF had a problem with the early engines they supposedly fixed where the threads were too soft or something and kept stripping easily. I replaced the spark and it threaded "finger tight". I tried turning it over and gas poured out... I could twist the plug with my fingers, it would "tighten" and then a half twist and it was loose again.

I ordered a new cylinder head. I hope these replacement heads have better threads.

When I noticed that the threads were stripped, I was concerned that some pieces fell into the cylinder head. I decided I needed to remove the entire cylinder head. Two of the screws came out easily, but two were blocked by the muffler header screws. One of them had stripped a while back... so I had to remove the entire engine to find a way to get the muffler off, and had to remove the prop. One thing leads to another...

I pulled one screw of the header easily, the other I could not get any purchase on. I twisted the muffler and it loosened. I managed to twist it and the screw got looser and looser, and eventually I could not turn it anymore. I grabbed it with a pair of needle nose pliers and managed to completely remove it! I got the cylinder head off and it was heavily carboned. The cylinder head was rough, like 60 grit. I used Gum-out and cleaned it all to nearly completely shiny. It took a few minutes to get the piston ring back into the cylinder head, but then it moved nicely. I used some WD40 to lubricate it. I put it all back together. That's when I tried to put the plug back in. 

Waiting for the new cylinder head. 

Earlier I kept hearing something rattling around and wondered if there was damage inside the frame where the fuse had been cracked. I opened the access panel I had made when I first built the plane, and found that the frame behind the firewall and in front of the gas tank was broken. I cut some ply into a U shape and divided it to get it in. Epoxied it. I added a couple of cross braces on the top, bottom and middle. This was easily done and came out perfect. This pic is before the crass braces. 

When the cylinder head is repaired, I hope to tune the engine for the new prop. Its very light. I have no idea if I will keep the 4 blade, it was more for fun than anything else. I wanted to check the static thrust, but the engine stopped working before I could.

So she sits on the bench. Hopefully the cylinder head will get here soon.

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