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Post  RknRusty Sat Oct 25, 2014 11:33 pm

I had a thread on this last december, but the best suggestion I had, which came from Ken must've been in a PM because there's no sign of what I was to investigate. Kris did mention it, but in the context of a new engine. The "it" was the possibility of too much crankshaft friction. Well tonight I finally took it apart to see what's up. The front end of the crank tube inside the case looks like crap, very scratchy. The crank also has marks on it. Ken suggested maybe it had aluminum fused to it. I can't see anything that just jumps out and says Bingo, but it definitely could use some serious polishing. So I'm going to post the best pictures I could manage and then discuss my options.

Here's the crankcase markings just to establish the generation of manufacture. It has a 10 instead of .061 on the side and the Cyrilic AM... the last character is a delta that looks like an A.
Revisited: Big Mig slows and dies after only a partial tankful WP_20141025_034_zps5d4cae64

The piston and liner are in great shape and still has a very tight pinch right at the very top. No wear marks at all in the liner or on the piston.

Here is the crank. Click the link for a very large picture with the best detail. Then click the magnifying glass icon with the + in it.
https://s166.photobucket.com/user/rknrusty/media/Airplanes/WP_20141025_029_zps52d9314a.jpg.html

Here is the same pic sized for the forum. But you can't see much.
Revisited: Big Mig slows and dies after only a partial tankful WP_20141025_029_zps52d9314a

Same thing for the crankcase. The link tells the better story.
https://s166.photobucket.com/user/rknrusty/media/Airplanes/WP_20141025_032_zpsbee363b3.jpg.html

And the smaller sized pic.
Revisited: Big Mig slows and dies after only a partial tankful WP_20141025_032_zpsbee363b3

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

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Post  1/2A Nut Sun Oct 26, 2014 12:59 am

I would just lap polish the crank and grove the front of the crank to hold oil releave some drag.


Noted info:
When we started using AMEs they would often seem to go lean soon after launch. But when you picked up the plane (after the engine died from the seemingly over lean condition) the bladder fed needle would still be putting out fuel at the normal rate. But the engine would be very hot - just like you would expect from a lean run.

After it cooled you could fire it up and the needle setting would seem fine, even though you had not changed the needle. Launch again and you would again get the few good seconds of run and then . . . lean again.

In spite of "clever, sought by the babes, and talented too", I was slow to solve the problem. The engines usually got better after a whole bunch of tries and flights, if you stuck with it. Then I realized that the engines were overheating from the bottom end vice from being too lean. The shafts were fitted too tight in the crankcases and when the engine began to warm up the clearance decreased and friction increased causing more heating and it was all downhill until the shaft seized in the case. I finally figured it out when I checked out a shaft and found aluminum on it where it had galled in the case.

I cleaned off the aluminum, lapped the shaft in the case with Bon Ami and oil and viola! Problem solved.

The next step was to put a shaft in the lathe and use emery cloth, followed by 400, 800, and 1200 wet / dry paper with oil to remove a tiny amount of material from the center portion of the shaft. The surface of the shaft behind the port opening and the front 3/16" was left alone. This reduced drag between the case and shaft, but left the front and rear bearing surfaces untouched.

And so . . . especially with plain bearing engines, it may well be that a careful fitting followed by an equally careful bench break-in to the point where you are sure the engine will hold a good, top end needle without overheating and stalling is good practice and will help prevent unwanted dead stick landings. If the engine does not hold a setting on the bench, it probably will not be any better in the air.

Revisited: Big Mig slows and dies after only a partial tankful Crank10
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Post  RknRusty Sun Oct 26, 2014 1:08 am

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,
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Post  1/2A Nut Sun Oct 26, 2014 2:03 am

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.

Revisited: Big Mig slows and dies after only a partial tankful Half_a10


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Post  1/2A Nut Sun Oct 26, 2014 2:14 am

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.
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Post  Ken Cook Sun Oct 26, 2014 6:18 am

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
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Post  RknRusty Sun Oct 26, 2014 10:13 am

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.
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Post  1/2A Nut Sun Oct 26, 2014 10:36 am

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.

Revisited: Big Mig slows and dies after only a partial tankful Half_a11
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Post  getback Sun Oct 26, 2014 10:39 am

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 Two Cents Eric Very Happy ( sorry 1/2anut if I missed something )
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Post  RknRusty Sun Oct 26, 2014 11:52 am

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.
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Post  Ken Cook Sun Oct 26, 2014 3:30 pm

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
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Post  1/2A Nut Sun Oct 26, 2014 3:56 pm

Yes right on or even a * should be the end all for any concerns of migration. Popcorn
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Post  Ken Cook Sun Oct 26, 2014 5:08 pm

Now if I can only keep the rods from breaking. Still working on that problem. Ken
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Post  balogh Sun Oct 26, 2014 7:04 pm

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.
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Post  RknRusty Sun Oct 26, 2014 10:22 pm

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.
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Post  Surfer_kris Mon Oct 27, 2014 3:38 am

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.
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Post  balogh Mon Oct 27, 2014 5:30 am

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....
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Post  Surfer_kris Mon Oct 27, 2014 5:32 am

@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)


Last edited by Surfer_kris on Mon Oct 27, 2014 5:36 am; edited 1 time in total
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Post  balogh Mon Oct 27, 2014 5:35 am

@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!!!
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