Guys,
I recently (like Saturday) had my engine bind up and loose power after flying one normal flight. This is the Fox 35 in my El Diablo that I have been flying for about 7 months. The engine has a tongue muffler and I have been running fuel with 26% castor 3% syn and 5% nitro. Because of the tongue muffler I run a light load 9x6 old Top Flite prop at about 9650 rpm release. The motor has run very nice with a classic 4-2-4 break.

This past weekend we finally got a decent day and I was hoping to get some good practice in before KOI. The first flight was normal and I got the cob webs out of the pilot. The engine had a slight crackle to it (has done this since the first flight), I had a K&B long idle bar plug which is one of the hottest. I had done some research and found that the Fox RC long idle bars is suppose to be a medium heat plug, so I thought I would give this a try to pull back the timing a bit. Once fueled I went to start and it popped back, loosened the prop. When I when to start again it was very tight near the top. I pulled it through a few times and it seemed to loosen, so we fired it off. Power was way down but steady. Next flight I went in on the needle 1/4 turn and the flight was flyable but soft, the engine was steady with no crackle. When I went to fly again the engine was tight again and I decided I needed to look inside.

Once on the bench I removed the plug and slowly turned over the engine as I removed the bolts thinking that maybe something caused the case to twist and cause the bind. None of the bolts caused anything and the bind was still there. I pulled the head and saw the vanish. I thought the 3% synth would keep it clean, it didn't. I'm going to go to the 50/50 mix going forward.

Has anyone used a few tanks of high syn oil fuel to clean out varnish? How well did it work?

Best,   DennisT

Hi

You can use 25 to 28& oil fuel with 1/2 castor, That is the blend I used in my FOX 35s, and I have many hundreds of runs on them, They are still in very good shape and most are 1970 model 35s. They are in much better condition than ones I used all castor fuel in, and they still have good fits in the bushing, rod, and P/S

Randy

if the tongue Muff is too resrtctive it will cause the engine to carbon up more quickly

Dennis,

I use diamond paste only for lapping steel parts, like shaft/bearing fit and wristpin/conrod pin polishing. Please do yourself a favour and never use diamond paste for piston lapping. It tends to get embedded into aluminium and cast iron and never come out. We lap pistons only in extreme situations, normally we just cut them in final shape&diameter with a good lathe and diamond cutter.
If you have to lap, then you'd better use fine carborundum or aluminium oxide.

For cleaning carbon buildup, paint polishing compound works well. I use Farecla C4 or C3.

Lauri

Thanks for the input, I understand both points. For me I have used the fine grade Scotch Brite and diamond lap approach for a long time and have not had anything wear our because of it. I first read about this in something that GMA wrote 30+ year ago. If anyone tries this you need to go slow and check often to only get the varnish off not try to polish the metal (this would wear stuff out). I would say if in double don't try this on your best/favorite engine the first time, use Randy's approach.

Best,          DennisT