GR7Racer

Ok, I'm stumped and need some help.

I've got an Evolution 26 in a H9 Mustang that has over 100 flights on it. Engine has run like a top and has plenty of power for the airplane with an APC 16x8. It's got an Evolution wraparound muffler and I've been using about 5oz of oil per gallon (twentysomething : 1 ratio)

About 2 months ago after over 100 great flights on it with no problems, it flames out on takeoff....but that's not my problem.

I proceed to check the fuel system out completely, and ended up rebuilding the tank to make sure there were no problems. I also cleaned out the carb and double checked the fuel passages and gaskets/diaphram. I had to change the spark plug because the other one broke off. I don't know what the gap is set to. I put it back together, and now it runs like a top again.....but......and here's where I'm stumped....it now seems to get hot after a few minutes in the air and starts surging/quitting. I proceed to rebuild the carb with all new gaskets/diaphrams, and even a new thermal spacer between the carb mount adapter and the carb body. Still the same problem. I can richen it up and make it slobbering rich and fly it around and it still gets hot. I don't think the engine is seizing up, I think the carb is just getting so hot that the fuel/gas is starting to boil. When I land, I can't even touch the carb it is so hot.

What would make this engine start acting like this after so many troublefree flights. Again, it runs perfectly for the first few minutes while it's cool, then the heat starts to soak into the carb and it goes south. Cooling air opening for the engine is right in front of the carb and it blasts right on it before it gets to the cylinder, then the muffler. Could a bearing be going away and causing the excess heat? The engine feels beautiful when you turn it over and will do a nearly impossible tick over idle when cool. Could an improper gap on the sparkplug cause excess heat? Maybe a bad batch of gas?

Anybody have any ideas? I've even replaced the ignition to eliminate that possibility.

Help!
KMac

w8ye

My Feedback: (16)

Sounds as though you have advanced your timing too far?

GR7Racer

I don't think the timing is adjustable. The hall effect pickup is mounted to the side of the crankcase and cannot be slid or rotated at all. The ignition unit is just a black box with wires coming out of it with no adjustment either that I am aware. If I'm wrong, I'd certainly like to hear how this can be adjusted.

K

w8ye

My Feedback: (16)

There's two different program selectable spark advance curves. Unless you are running a tuned pipe, the switch on the ignition module should be set to the short curve?

GR7Racer

Thanks, I'll take a look, but I don't think my unit has a switch on it. Are we talking an actual physical switch, a set of jumpers, or some sort of programming mode that you enter?

I'm using the stock ignition that comes with the engine....this one.

http://www.horizonhobby.com/Products...odID=EVO3314LB

Thx
K

w8ye

My Feedback: (16)

It is on the end of the module with the little wires. There's a shorting plug. But it is unlikely you have changed it.


If you study how the carb works, you will discover the low speed screw has a big effect on the mid rpms as well as the low speed. You may have the low speed mixture needle in too far?

Lnewqban

Oil it has plenty, since the recommended mix is 1:40.

Is the thermal grade of the new spark plug similar to the old plug?
Might it be too hot for that engine?

Besides checking the timing, as recommended by w8ye, I suggest inspecting the exhaust port, and also the muffler, for any obstructing buildup.
For that, you will need to disconnect the muffler.
Excess or less than ideal type of oil can lead to those buildups, which restrain the proper ventilation of the hot exhaust gases.

Regards!

the Wasp

My Feedback: (1)

gap is .024"

Jim

GR7Racer

Thanks for the ideas everybody. I'll check this stuff out and report back.

K

ggroyal1

I have both MVVS and the Evolution 26cc engines. On break-in I used Mobil 1 racing 2T fully synthetic oil at 30:1 for the first two gallons and 40:1 after break-in. MVVS and Evolution support says you must use fully synthetic. I have a tuned pipe on the Evolution and a Pitts on the MVVS. The timing was set by a shorting plug that plugs into the ignition for each setup. I have the Evolution in a H9 Sundowner and the temp is about 180F on the ground at full rpm. The MVVS is not in a plane yet, but on the test bench, it is almost exactly the same as the Evolution. I would run it at max rpm and check the temp, if it is in the high 200 or more, I would send it to Horizon for them to check. I sent my Evolution 26 in because it leaked out the front bearing, they repaired it and even paid the shipping both ways. It does not leak now.

pe reivers

The carb getting hot, with all else the same as before indicates crankshaft rubbing in the front bushing. This can be due to lack of cooling, or crankshaft/bearing combo out of whack. Did you get a prop strike? I suspect either a bent shaft or worn front bearing.
BTW proper plug gap is 0.020 - 0.024 " Too small a gap may also cause hot running.

GR7Racer

Thanks again everybody for the ideas...I'm heading out to the shop to investigate.

Pe....I did have a prop strike. I have a 5" spinner on the airplane, and when I observe it on the ground running, it appears to be running very true. I know this is probably not a good indicator for a small misalignment. I'll take a crack at disassembling the engine again. I tried once before but the steel liner wouldn't budge out of the case. Ended up cutting a couple of glow plug washers in two trying to lift it out. I'll try to soak some penetrating oil in there, or maybe heat the case some. Once I do that, I'm hoping the crank will slide back through the case, or is that a press fit that will need some mechanical force? Getting new bearings shouldn't be hard, I'm just wondering if I have what I need to get the old ones out and the new ones in.

I did notice that the piston will rotate a small amount back and forth with the engine assembled. When I had the backplate off, I cold see that this was play between the needle bearings on the rod and the crank pin. Is this normal?

By the way Pe, I just ordered a carb for my MVVS 35 cc from you. Looking forward to getting that and getting it going again too!

K

ggroyal1

Heat it, the liner will pop right out.

pe reivers

so will the bearings, if you keep the crankshaft in for added bearing alignment. You can heat until oil starts to smoke without fear for overheating. Use a heat gun, or boiling oil to heat the parts (beware: fire hazard).

samp

I agree with Pe. A damaged front bearing would certainly cause the overheating symptoms you describe. A technique I recently learned for removing sleeves is to carefully heat the cylinder ( from the outside) with a propane torch of the type used for soldering copper plumbing pipes. The cylinder being an aluminum alloy will expand more than the steel sleeve allowing the sleeve to loosen so it can easily be pulled out. Don't use any presses, pullers, or heavy mechanical force or you could ruin the engine. Add a little heat, try the sleeve, and repeat until it loosens.

Amazing how a bad bearing won't show up until a combination of time and high rpm have worked on it. I recently went through a similar scenario with a 35cc.

GR7Racer

Ok, here's the details on what I've found so far.

Ignition....no timing adjustment that I can find anywhere. If it's there, it's inside the case and I haven't opened it, so I guess I haven't changed it.

Spark plug gap.... .024

Spark plug type....CM6, just like the one that I replaced.

I did heat the case with a torch like recommended here, and the cylinder easily came out. The crank slid out with zero effort.

I chucked up the crank in an old lathe that I have with the jaws just aft of the threads, and mounted a dial indicator in the tool holder and read just in front of the crank disk. It showed .004 runout, but I think that's all in the lathe as I can rotate the crank in the chuck and move the high spot around on the crank and the amount of runout never changes...so I think the crank is straight.

The bearings look and feel fine, but I did find a lot of dark paste on the outside of the front seal of the front bearing. I'm wondering if I have just cooked out all of the grease/lubricant in the sealed nose bearing? Should I just pop both of them out and change them or is there a way to evaluate them? The sealed nose bearing feels very free, but not sloppy.

I'm thinking the main bearing is fine. It feels good and there is no discoloration from high temps on it.

Thanks again for the help!!!

What do you guys think?

K

ggroyal1

I replaced one of my 26cc engines with a dual seal front ceramic bearing and because I had it apart, I replaced the rear bearing with a very high quality ceramic bearing.
I use a shorting plug to change the timing.

ggroyal1

I would like to add a comment about Evolution/MVVS gas engine timing. I have been able to change the timing on every engine for the last three years. My last engine would not let me change the timing. After many attempts, I contacted Horizon support about my timing problem. They called me back a day later and told me that you could no longer change the timing and it was not needed any more. They could not or would not answer why the directions still show how to change the timing and why do they still provide the shorting tool and the engine still comes with two magnets for the pick up.. The engine runs so good the way it is, I decided to drop the whole matter. If I ever changed to a tuned pipe, I guess I would be out of luck.

Tired Old Man

My Feedback: (1)

Might want to reduce the gap on that CM-6. The wider the gap the harder it is on the ignition coil. Lots of resistance. .018 to .020 should work well for you.

GR7Racer

Thanks again everybody for the ideas...

I popped the seals off the ends of the nose bearing and there's no grease in there at all. The bearing seems smooth. Is there a visual indication that will point to a bad bearing? Discoloration from heat?

I'll knock the gap down on that plug to about .020....thanks for that advice.

KMac

pe reivers

That is a sign of the front bearing outer ring spinning in the crankcase. The fit gets loose if the engine runs too hot. Once at that point, the tight tolerance between crankshaft and crancshaft bore is exceeded and the shaft rubs in the bore causing extra friction, extra heat, extra friction, etc..

To check this, watch for rub marks on the shaft.

todo:
- replace the front bearing, and use loctite 648 to fit it in thecrankcase.
- fit the crankshaft in the case, then chuck the shaft front in the lathe and while holding the crankcase, check for wobble. Tap-tap with plastic mallet until running true. If lathe/chuck is old, you may need to make a true bore first that will hold the shaft front end, or use a 4-chuck.
- Check engine cooling. Is the liner straw - blue colored? it should not be!

GR7Racer

Pe...

The front bearing was pretty snug in the case when I popped it out. I had to heat the case and tap it from the back with a long socket wrench extension. The inside of the bearing seat on the case did have some black residue, as did the outside race of the bearing. After cleaning the residue out of the seat on the case, the surface there doesn't really show and signs of the bearing rotating, but the surface is slightly pitted.

The crank has a shiny spot about 1/4 of the circumference of the shaft in the area where it sits in the bearing, and the bearing has a similar sized area of discoloration. To me, this doesn't look like a wear area though, more like a chemical (fuel?) laying in there and etching the metal. Both areas have an irregular shape and no directional abrasions.

Does the absence of grease in the bearing mean anything, or is that just normal?

The crank/bearing alignment method that you suggested sounds a little out of my league. I only have a three jaw chuck, and I'm not sure I can make a true bore...I'm not sure what a true bore is!... I'm assuming it is a threaded sleeve that will go over the threads and allow me to chuck that end of the crank in the lathe.

I have't removed the main bearing yet, Could I use it and the crank to align the new front bearing when I install it? Then after the nose bearing is in, remove the main bearing and replace it?

Lastly, the Loctite 648 that you mention, will it allow me to remove the bearing in the future if I need to do this again?

Again, thanks for you help.

KMac

pe reivers

The front bearing is a double lip seal bearing, there should be grease in it, unless the seal has failed.
The shaft is a good tool for guiding the new bearing in.
Loctite 648 is a high temperature retention glue. If you want the parts to assemble at lower temperatures you should use Loctite 641.
Speaking of temperature: what did your liner look like? (color)

A true bore in an old lathe can be made easily:
chuck some scrap metal in the 3-jaw and drill undersize for the front of the crankshaft.
Now bore it out, so the shaft is a snug fit. The bore is now true with the lathe spindle.
Assemble the shaft in the housing, and use some locktite to fit the shaft front end into the bored hole you just made. If you now rotate the chuck whilst holding the crankcase, there should be no wobble at all. If there is wobble or run-out, the shaft front part is bent, and should be straightened, or the shaft needs to be replaced.

GR7Racer

Thanks again Pe, and everybody else too!

I've got some bearings on order, and I'll update this when the engine is reassembled and tested.

KennyMac