1QwkSport2.5r

I am breaking it in. I don't mess around when I break in lapped engines. I give it a good hour before I trust the engine. After half a gallon I'll have leaned it down to about 2000rpm rich of peak. Slow and steady wins the race. That's my motto.

earlwb

Cool, you had me a bit concerned there.
But yeah I do the same thing too.

1QwkSport2.5r

3rd run it ate the wristpin g-clip again. I have to take it apart and assess the damage. It might be okay.

edit: I pulled the engine apart and it indeed was the g-clip from one side of the piston that came through the transfer port and scored the cylinder. There are 4 or 5 knicks in the piston and the cylinder but since the engine hasnt been broke in all the way, there's a chance it might survive though I'm not sure for how long. I dont have any more spare g-clips so I'll have to get a hold of some and see if I can get one to stay in it this time. I dont think the clip was seated all the way into the bottom of the groove, perhaps a smaller diameter wire will work better.

Being that the wristpin is open to the transfers, I couldnt use a teflon pad in there like my buddy hoped I could do...

hsukaria

Ouch!!!

1QwkSport2.5r

Yes, indeed. This is the same thing that took out the original piston and liner. This new piston and liner still have a really snug fit; I wonder if through a slow break-in if it will still seal well and run good after all. I doubt it but who knows...

I'm really bummed.

earlwb

Aww man. Bummer. I think it'll be OK. Use more castor oil and it'll fill in the tiny scratch for you.

1QwkSport2.5r

The scratches arent real small, but the fit it still tight between the piston and liner so maybe if I can find a clip that fits without having to order online, I'll try running it again. The compression on this engine after the first run was insane. I backflip started it on the 2nd run. 3rd run needed the electric starter and I think that was karma kicking in.

Cougar429

My Feedback: (3)

Anyone fit a composite button in place of the clip on problem motors like that?

fujiman

My Feedback: (133)

fox use to sell a lapping and polishing compound to help re-fit or should i say help break in overly tite engines, seat rings, etc.. kind of like bonami polishing/cleaning powder. just don't remember their names and i don't know if they still sell them. you have to be very careful on how and hoe much you would use as i remember.

earlwb

I don't recommend using Fox Lustrox polishing compound as if you are inexperienced with it, you can wear out the engine almost immediately with the stuff. But it works pretty good for lapping valves in on a four stroke engine though. But still you have to be very careful only a little tiny bit will do.

1QwkSport2.5r

Well, I did some fiddling around and found a spring from a broken pen that fits the groove in the piston almost perfectly. I just made a "C" loop with maybe .25mm gap between the ends. Its not hardened spring steel, but it might do the trick. It fits better than the G-clip that broke.

There is no divider in the transfer port in the liner, otherwise I could use a teflon pad in there instead. So I may try it this way. I haven't much to lose at this point. The piston is pretty snug in the liner now... Should I lap it with a mild kitchen cleanser or something before trying to run it again? I have Bar Keepers Friend on-hand, but I dont know if thats too abrasive. Toothpaste is another one, but maybe not abrasive enough?

earlwb

I would say no. Just run it rich and have heat cycles where after you run it let it cool off before you run it again. It'll loosen up, but likely later rather than sooner.

1QwkSport2.5r

I put my homemade clip in and tried for about 5 minutes with a blade to get it out. It stayed in there, so I put it back together and I'll try running it again. I'll go at it like I was heating it up and cooling it off running rich. I'll post back with results.

There is some leakage in the scored area, but I'm sure it will run.

earlwb

The scratch will fill in some with castor oil varnish. So if it isn't too big it will more or less disappear to some extent. I have had engines before, when I lived in dusty Arizona, get pretty badly scratched up in the inside, but they would still run acceptably though. I don't think the power loss was too bad.

Sport_Pilot

Consider it a clearance groove!

hsukaria

The Power of Positive Thinking!!!

earlwb

I remembered that I had a similar situation when I replaced the bearings and piston ring in one of my old Hawk .60 engines a couple of years ago. I had discovered that the circlip had disappeared too. It apparently broke apart and the pieces left the engine however they could. But for some odd reason the cylinder wasn't scratched, but there were some dings and gouges in the aluminum here and there. But the cylinder was especially hardened on the inside to be very hard and long wearing though. So the circlip probably wasn't hard enough to damage the cylinder. Interestingly I flew this engine in a couple of airboats and on several airplanes. I never knew the circlip had come out all that time either. I retired the engine when the crankshaft bearings were going bad and getting loose. Since I had other .60 engines I had little motivation at the time to fix the engine.

I think the circlips broke and got sucked out into the intake passages and into the combustion chamber and on out the exhaust. But when it happened will be a mystery I as I used the engine for several years from around 1977 on through 1983. I am planning on putting it on something else one of these days too. I just haven't gotten around to it yet.

You can see where the circlip on the wristpin had come out and gouged a chunk of the piston out in this pic. I replaced the circlip, but I think the varnish on castor oil residue was holding the wrist pin in better that the circlips could. I am concerned about the little circlips though as a few of them broke when I was inserting them into the piston/groove. So it was probably better to have not bothered putting in a new retaining circlip in there.




Some divots on the head too.


Looks like matching divots on then piston crown too

hsukaria

Earl,
Would you leave the dings as they are or would you polish them off when you rebuild?

earlwb

I left them alone. I figured if I messed with them it might lower the compression ratio.

1QwkSport2.5r

Well, I got about 1 minute out of it before the new clip broke. Made another one from a different spring and got more time from it. 3oz of fuel worth. It loosened up a little, so it may live still yet. I think I'll go find a snap ring and be done with it. The scoring goes from the top of the piston to about 3/4 down. The liner scraches are shorter. I don't think this liner is hardened. I scraped the dings in the transfer port with a utility knife.

The broken clips are happening in the rear transfer port. The scratches are horrible but it still runs. I'm quite surprised.

1QwkSport2.5r

It survived another run.. I made a video of it this time. It took some time to get the carb just right so it would start reliably, but I think I have it in the ballpark. I left the glow on it for a couple runs so it would stay running better while the piston and liner loosened up a little from the last mishap. Without glow at its current mixture setting is running about 7200rpm or so. I have my fingers crossed that it stays alive, I'd like to see what it can do later on.

Fuel is 5% nitro 25% castor, no synthetic. Glow plug is McCoy MC59 hot, prop is a 9x6 APC. About 55°F air temp.

http://youtu.be/Mw_AJXbtopc

hsukaria

I am trying to upload some picture of my Fox(y) 74 Eagle IV mounted on my new plane. I hope I get this right.

Well, I'll be dipped... I got it right the first time!

Anyway, this is an older Eagle IV with a high compression head. New bearings and piston ring, new TN carb. Runs great on the ground, but stalls in the air. You can see that it has overheated some by the discoloration on the head and castor blotches. The muffler is an MVVS Quiet Muffler from Pe Reivers Model Engines. It is very lightweight and quiet, but the exhaust stinger does not rotate, the 2 pieces are riveted and sealed to each other.

This weekend, weather permitting, I will run it with 5% nitro instead of 15%. Tune it per instructions I got from Earl and Konrad, and hope for no more stalls. The engine still feels tight when rotating it by hand. So, even though I ran almost a gallon through it, I still need to run it extra rich on low nitro.

DougB1

My Feedback: (11)

I have a brand new still in the box with all paperwork a Fox 74 that is several years old that I will never use ( went to almost all gas ) Anyone have an idea what it is worth so I can put it on RCU to sell.
Thanks
DougB1

hsukaria

You can box it up and send to my address!!!

But seriously, Fox sells it for $121 if you send in a junk engine as a trade.

earlwb

It is hard to say if the varnish on the head came from overheating as the carb tends to spit a lot of fuel out of it too. Plus the angle of the engine tends to have oil and fuel accumulate on the head too. I would order a new head button to get the lower compression so you can run higher nitro percentages in the fuel. Fox tended to make the engines with a lot of compression there for a while. So FAI or 5% was about all that the engines would run with. Sometimes even that was a little too much with 5%. The engine may be picky with the high compression. it may also be it needs a long break in and is running too lean in the air as the fuel tank empties. You could try adjusting the engine on the ground with 1/4 tank of fuel, then fill it up for the flight. But let the engine run more on the rich side. The setting for the needle where you can run a whole tank through it on the ground with the nose a little high is probably about what it ought to be set to for flying. So it may need to be pretty rich depending on how tight the engine is. of course then you have to decide if it is too rich to fly Ok or not.

You can also try flying the plane without the cowl on, just in case it was experiencing a cooling issue too. I tend to maiden planes without the cowl on anyway and also to ensure everything is Ok before putting on the cowl. I have accumulated extra brand new cowls over the years from failed maiden flights too. But sometimes I have had bad landings after a maiden and then the cowl doesn't get scratched up on me.

Now years ago I had a Goldberg Ultimate Bipe. Nothing I could do stopped the engine from stalling out if I did a roll with the plane. It flew loops, inverted, and so on just fine. A sloooow roll or a slooow four point was Ok too. But a faster roll or four point would cause the engine to quit. I tried different engines, even different brands to no avail. I changed the fuel tank several times, even tried a uniflow tank too. Last I tried a fuel pump and it still did it. I eventually gave up on it and sold the plane to someone else who thought he knew what the problem was. Sure enough he had the same issue too. The Ultimate bipes are like the space shuttle when they are dead stick, they are coming down fast.