Revisited: Big Mig slows and dies after only a partial tankful

So you think that's fused aluminum we're looking at? It started this after my friend sporked it several times, so dirt was probably the offending insult to the parts. I'll try smoothing out the rough part of the case and give her a try. It might have a nose bleed, but that won't hurt it. I'll try it before I spend any money. Thanks,
Rusty

http://www.toadsrc.com/engines.htm

Good info mods / pics here on the crank shaft issue and fix..
Drag reduction on crank mod
NV mod
Venturi Intake mod
Piston mod
Crank fuel flow mod
With results.

There was a post of a new Big Mig the guy took the engine apart and solution / brushed cleaned everything prior to break in. A rather shocking photo of all the factory left over bits was at the bottom bowl he had used. Aluminum particles big enough to do the deed to the crank case and crank.

Yes could have been silica from the soil if the carb gulped in some terra firma.

Every Norvel I ever owned has been too tight. I wouldn't worry at all about having fuel spit out the front. My best runners wobble severely in the bore. My problem is the AME piston sleeve. The wrist pins keep sliding forward and jamming in the port of the liner. This just ruins the engine immediately. The Big Mig doesn't have this problem due to the smaller ports not being orientated in the path of the wrist pin which even if it does float and rub the sides of the liner, it won't jam in the port. I'm certainly more fond of the Big Mig due to the problems I've had with the AME .061. However, I was faster than the Cyclons and Foras when all of us were using rubber ducky props  at least for a season until it hand grenaded.

The picture your showing is exactly what I've been trying to convey. I don't think dirt had anything to do with your issues. If that was the situation every engine I own for combat would be destroyed. No flyers stuff engines into the ground like the abuse that a combat flyer provides.I bury these engines.  The 3 guys I fly with both fly with Larry Driskill and all of them have been monumental in seeing these engines into their top performance. Roy Glenn a good friend of Larry's is a engineer who has access to a Sunnen Honing machine. Roy has taken several of our cases and milled the deck as described in the article 1/2A provided and also honed the cases to loosen the fit.

I would chuck your crank in a drill press and using coarse emery wrap the cloth around the front of the crank and polish the marks out. Go to finer emery using a small 1/4" strip and polish the area needed. Afterwards, 3M Tri-Mite paper can be used in 400-600-800 with a bit of oil going over the entire crank.I use a mild  lapping compound (rottenstone and oil), but the article above suggested toothpaste and or Bon-Ami which I've used on piston liners. Mix it into a paste and work it in the case around and back and forth. Make sure you wash all of the parts in hot soapy water as this is a very good way to float out any debris which could be left in the material. Dry well and assemble oiling as you go along. Run the engine and try again. I've had to do this more than once to avoid the issues on the front of the crank like your depicting.  I also note the wear at the rear of the crank up against the web. I use a large countersink inside the case and I slightly chamfer the outer edges of the hole to lessen the drag against the inside radius of the crank web Ken

That's great news, thanks 1/2A Nut and Ken. Greenies to both of you.
I'll read that article and get this one running again. This one that Fit90 gave me is the only brand new Big Mig I've ever owned. And I have another one that I expect has been broken in but I've never cranked it. I'll go through it too before i use it. My third one, so far is running fine. It's on a Baby Steak with a Cox NV and I have actually tached it at over 28k with an APC prop. 5.5x2.5 maybe, but I forget. I'm going to have a new AME to play with in about a week.
Rusty

Dont forget to do this trick shown in the pic if you have the older pre revlite engines..

Thank you for the green badge of approval rare I ever get one always happy to share pics and info lol.

Rusty said ::: I have actually tached it at over 28k with an APC prop. 5.5x2.5 maybe, but I forget........... Man there is is something wrong with mine then I could only get 17K with a 6x4 prop , and it is broken in I am sure / I get time ill take that sucker apart and check for the listed problems . Glad you have this up . When we were building engines with galled aluminum to the geranial one of my old fart friends showed me something about removing the aluminum , take Muriatic Acid and brush on several times and it would EAT the stuff right off!! ( OF COARSE YOU WANT TO HAVE RUBBER GLOVES / PLASTIC CONTAINERS FOR IT TO SET IN, WATER FOR CLEANING AND BE OUTSIDE ) This is some pretty badass stuff if you have never used it . But I was amazed at how well it cleaned. Just my Eric ( sorry 1/2anut if I missed something )

Eric, 17k is about right for a 6x4 prop. 6x4 is way too much prop for that engine. You'll probably be lucky to break 20k with a 6x3 in anything besides APC. APCs always give you a false sense of superiority when taching. For CL, mine is is not happy with any bigger than a Master airscrew 5.5x3. That's my main 40' line prop. Next time I crank it with that one I'l tach it and see what I get. I usually don't mess with taching except when playing in the shop.
Rusty

The factory staking on the wrist pin doesn't keep the pin in. I've had them fail about 6 times now. I can get a better count by counting all the screwed up cylinders on my bench. In addition, I would stake in a X rather than one single horizontal staking. I made a fixture to hold the piston to avoid making it of round. Ken

Yes right on or even a * should be the end all for any concerns of migration.

Now if I can only keep the rods from breaking. Still working on that problem. Ken

Without trying to be cynical, the experiments you have taken to complete the manufacturing process of the sh...tty NV engines reminds me of the good ole days in communism when the limited makes of cars available in Eastern Europe included the Dacia from Roumania, a French Renault licence-made sh..t, that, when you were honored to receive after 5 years waiting in a queue, had to disassemble at home and work on it for days if not weeks before you could call it an autoimobile...

Good luck with your NV-s (= No Value), I stay with my over-abused COX engines. My experience with Eastern-European scrap, be it Roumanian or Russian, will never change before I die.

Andras, I know, as I mentioned in my first post, of your bad experiences. But mine have all run like giant killers with this being my first failure. I'm sticking with them until they do to me what they did to you. Then the two of us can have a beer and commiserate.
Rusty

It seems like NV might have had a problem in reproducing the revlite cylinders. I have one of the newer ones and it is much looser than the old stock. With the old ones being a little on the tight side, the newer ones are now a little too loose. The one I have is fine right at TDC but the tapering seems too begin too high up in the cylinder, thereby not giving much too seal against at the height of the exhaust port.

The older ones are the opposite, they were almost too tight. One has to be very careful with the running in of the engine, and always pre-heat the cylinder. Once they are fully run in they are great though.

The pre-revlite ones are perhaps better actually, they are more traditional in their construction, are easier to run-in, and they give a similar power. Plus, they are more compact with the smaller cylinder and head fins.

Thanks Kris, your answer alleviates my sould about the negative things I have written about NV engines. My experienceis roughly the same. I have an older NV which I have never started yet, and the revlite-version that is not only loose but lousy as well. In my perception the loose piston-cylinder fit with this new engine is far beyond my acceptance, not simply because of my opposite experience with excellently fit COX engines, but because the loose fit in a new engine will become even looser when you run it, and at the end - within a short time - the engine becomes totally paralised.

No wonder that the Manual of the older NV engine says the lifetime of the engine is more than 6 (!!!) hours. My gosh, a COX TD051 with 100+ hours runtime in my RC Tucan plane is laughing its head off....

RknRusty wrote:
New crankcase from NV Engines, $22.99. New Crankshaft $24.99. New Big Mig, $74.99. After seeing the trouble Andras Balogh had I'm hesitant to buy an NV engine. I wonder if a new crankcase and polishing the old crankshaft would restore this engine to its previous performance. Any opinions?
Rusty

Just polish and lap the two surfaces, that should be enough I think, it doesn't look too severe in the images to me.

If that doesn't work, then a new case and crank from NV should solve it. I have only have one of the later production engines from NV, and I have not found any real problems with the case and crank. The top of the case seemed a little too high in combination with the new cylinder, but with an older cylinder it now works fine.

Just remembered one more thing, the "new" engine came with a plug that looked like the older cold ones.
(they are recognized by a smaller outer diameter towards the clamp, and a flat top on the center electrode)

RknRusty wrote:Andras, I know, as I mentioned in my first post, of your bad experiences. But mine have all run like giant killers with this being my first failure. I'm sticking with them until they do to me what they did to you. Then the two of us can have a beer and commiserate.
Rusty

Rusty,

thanks, I am glad that you have had the good experience with NV-s, but it looks like (see the posting of Surfer Kris) the later versions with the revlite coating are often inferior. At least his and my (bitter) experience tells that.

About the beer, yes, we can/should have that and try to find an opportunity earlier than your disappointment with NV comes!!!