stunthanger.com
Engine basics => Engine set up tips => Topic started by: Dennis Toth on July 27, 2019, 11:40:12 AM
-
Guys,
I have been using JB Weld to fill part of the bypass on my Fox 35 in stead of the stick. On of the engines seem to be running a little off and I'm wondering if I mite have gone a bit to far. I would say I filled about half the depth of the bypass, if this to much? What would be a symptom of going to far with this?
Best, DennisT
-
If you block it completely it might not run . VD~
There must be a happy medium ? Youd think a bigger heavier plane'd require more area , a smaller lighter less .
Theres some ' cas speed / Charge Density - ram effect going on in there .
Seen the vertical / perpendicular to cylinder 1/8 wide hardwood channel devider trick .
Maybe better than just bogging the outer face .
-
Guys,
I have been using JB Weld to fill part of the bypass on my Fox 35 in stead of the stick. On of the engines seem to be running a little off and I'm wondering if I mite have gone a bit to far. I would say I filled about half the depth of the bypass, if this to much? What would be a symptom of going to far with this?
Half sounds about right. That should have more-or-less no affect on the performance aside from the burp. My bypass is *much smaller* than half, if anything it picked up a bit of power.
If the bypass is too small, you would probably expect the peak RPM to be reduced.
There are plenty of other ways to cause it to lose power or run strangely afterward. In addition to the plethora of conventional Fox issues (like uneven tightening of the head screws, etc), if your "stuffing" isn't done just right, and the JB Weld is sticking out from the rest of the bore, it could distort the cylinder. Things like that. But just plain old taking it apart and putting it back could have caused it.
Brett
-
I had such great success getting my McCoy Red Head Lightning Bot 35 to run a 4 2 4 break on a Ringmaster using a 4oz clunk tank that I wanted to see if I could get the Fox 35 to do the same. I spent a lot of time the end of last year with the Fox 35 Stunt and tried the popsicle stick one time, JB weld in the port another time with no luck. The problem I was having is that the engine kept on running away into a 2 stroke half way through the flight. I tried all caster 10N 28 oil fuel, 10N 25 oil fuel, and Power Master GMA 10N 22oil fuel, same problem every time, and using the same tank I used with the McCoy 35. I removed the JB weld and put the case back to stock and flew the Ringmaster but now I had the Fox Burp on outside loops. I was ready to pull the Fox for good, but tried it one more time using a larger .156 spray bar and bingo, no more burp! I also can use any of the 3 fuels I tried before. Fox .35 venture is .270 and the stock spray bar is .130 and that makes a large area for a slow running engine. I also added one extra head gasket because the engine was breaking hard into a 2 stroke from a 4 stroke. The best prop I found to use is a Bolly Clubman 10.5x5. Good luck with setup and let us know how you make out.
Al
.
-
Did you have to drill out the existing hole to accommodate the .156 spray bar? Also, what manufacturers spray bar and needle did you use?
Thanks,
George Albo
-
George,
I have used Randy Smith's PA-Fox NVA with very good results. It matches the original Fox NVA with the turned down center and give a very good seal and setting. I don't know if anyone else does the center reduction, many guys use the old ST NVA.
Best, DennisT
-
Mid-sixties Fox .35, piston and cylinder lapped together. internals de-burred. Exterior de-burred and polished. I used a 3/16" wide spruce "stick" that was fitted to the case and cylinder. Stock NVA. This combo was used on a 38 ounce El Diablo (Thanks Walter!) with good results. Same lap times upright and inverted, didn't really have a hard break . I run an APC 10-4.5 prop trued and balanced. This was an awesome set-up until somewhere around 200 flights. The engine wouldn't "needle". I tried several things to rectify the problem. I disassembled the engine and found that the stick had wore and tilted diagonally across the bypass. Ugh.!!
-
John,
This is interesting that the stick moving caused needle issues. Did you put in a new stick and did that solve the needle issue? Has it happened after that first time (maybe the stick wasn't fit tight in the bypass)?
I have just set up motor for my Ringmaster. I had at one time used JB Weld in the bypass, but have not decided that the stick in the bypass might be more reliable. I had one case that I did the JP Weld and had it fail and fall out. I assume I did not get it completely degreased before applying the JP Well. The stick approach has been used by many people and if you used the measurements in the attach diagram it only takes about 15 mins to make and install once the motor is apart. I bench ran the motor today and it was very solid. One thing I did with this motor was to make sure the sleeve fit smoothly into the case. I had to clean up the case near the bottom just as it slid pass the exhaust port. The fit is such that you can push the sleeve down and pull it out with a little effort not lose enough to just slid straight in. The motor ran great, ready to install in the ship and fly.
Best, DennisT