Norvel 061 Big Mig vs. COX Tee Dee 051

balogh Sat Mar 30, 2013 3:57 pm

I have been for long intrigued by the numerous reports circulating on the web that talk about the supremacy of Norvel engines over the COX brand. So I decided to buy a brand new Norvel 061 Big Míg R/C and temporarily retired my COX Tee Dee 051 (non-SPI, with muffler) in my Tucan R/C plane (wingspan 34”, weight 17,6 oz incl. 2 oz fuel)
I broke the new NV in as per the user’s manual and accumulated some 1,5 hours on it… by then it ran at stable, high speed. The Tee Dee had roughly 10 hours on it when the comparison took place.

Here is what I experienced:
• Engine noise: somewhat higher for the COX having a standard muffler (more efficient NV muffler)
• Castor splashed over the fuselage: less with the NV (better muffler fit around the exhaust and adjustable exhaust stub direction on the NV) The COX mufflers are good to look at, but are not quite so efficient
• Engine power: WAY HIGHER from the COX, despite the 20% more swept cylinder volume in the NV !!! The COX lifts the plane nose up vertically and loops it easily…the NV requires a steady acceleration in a dive before a full loop can be done.
• Plane speed: Way higher with the COX !!!
• Plane maneuverability: much better with the COX thanks to the higher engine power
• Fuel consumption: both engines run abt. 15 minutes on 2 oz fuel (50% methanol, 25/25% nitro and castor)
• R/C carb: the Norvel carb is excellent, assuring low and stable idle. The COX 051 in the comparison did not have an R/C carb. My experience with COX Tee Dee 050 R/C carburettors and Carno carbs both is not quite reassuring..maybe the standard COX glow head is not „hot” enough to sustain low and stable idle…a non-standard head with a hot glow plug may improve the COX idle I guess…I will try.
• Life expactancy: The NV sales guy wrote me the NV engines with the new, Revlite technology run about 18 hours (I have a pre-Revlite NV 049 with a manual that says: engine life no less than 6 hours….uhhhhh). The NV 061 Big Mig R/C in the comparison came with a very tight piston/cylinder fit and strong „pinch” at the top dead-end, but despite this, the brand new NV already had some cylinder blow-by even when cold and properly oiled. The compression in this NV when hot, is simply lost completely… you flip the propeller in the hot NV engine over with no compression resistance whatsoever. In contrast, the legendary millionth-of-an-inch COX precison really ensures that my several COX engines, some having more than 50 hours on them, all have original compression left after their long running history, and keep a resonable compression even when the engine is hot.
In summary: it was worth it…I will never abandon my COX engines for the NV brand.

Surfer_kris Sat Mar 30, 2013 4:05 pm

From my own experience, the Norvels are superior to cox engines. It sounds like there is something wrong with your Norvel engine, could you post some rpm numbers?

balogh Sat Mar 30, 2013 4:06 pm

Surfer_kris wrote:From my own experience, the Norvels are superior to cox engines. It sounds like there is something wrong with your Norvel engine, could you post some rpm numbers?

Will tach both of them tomorrow.

Surfer_kris Sat Mar 30, 2013 4:12 pm

Here are some numbers from my old Norvel .061RC (rev-lite) as a comparison (20% all castor, 10% Nitro, stock glow head and muffler);
Graupner 6x3; 18200rpm
Cox 5x4; 20500rpm
APC 5x3; 23500rpm

The Norvels also tend to be at their happiest when they rev above 20krpm.

balogh Sat Mar 30, 2013 4:16 pm

Surfer_kris wrote:Here are some numbers from my old Norvel .061RC (rev-lite) as a comparison (20% all castor, 10% Nitro, stock glow head and muffler);
Graupner 6x3; 18200rpm
Cox 5x4; 20500rpm
APC 5x3; 23500rpm

The Norvels also tend to be at their happiest when they rev above 20krpm.

Will tach both tomorrow...how about the compression in your Norvel? Mine is miserable...from the moment I took it from the box.

Surfer_kris Sat Mar 30, 2013 4:22 pm

Sounds like there is something wrong with yours. They are usually very tight, I wouldn't start a new one without heating it with a heating gun first. Even when well run in they will be tight and can throw a prop if you lean them out too much.

balogh Sat Mar 30, 2013 4:28 pm

Surfer_kris wrote:Sounds like there is something wrong with yours. They are usually very tight, I wouldn't start a new one without heating it with a heating gun first. Even when well run in they will be tight and can trow a prop if you lean them out too much.

It is still tight after some runtime in the air, with the pinch on the top dead and still being there. The cylinder/piston are said to be honed and this may explain to some eextent there is some blow-by when the piston has just closed the exhaust slot on its way up...but it keeps letting the compression out all the way up..has been like this from the very beginning...I have never experienced this with honed Tee Dee cylinder/piston units...fine compression, no blow-by..especially when the engine is hot, tolerances are less tight, castor is thinner, so compression, unless the piston/cylinder are made to the COX precison, is lost and power is gone.

Surfer_kris Sat Mar 30, 2013 4:34 pm

One shouldn't hone these cylinders, they are aluminium and just have a thin oxide layer that provides the hard cylinder surface. If you remove that layer you reach regular aluminium. Who made the honing?

There shouldn't be any blow by at any point on the travel up. On a cold engine they can even seize if turned over slowly through TDC without a glow plug in them.

balogh Sat Mar 30, 2013 4:36 pm

Surfer_kris wrote:One shouldn't hone these cylinders, they are aluminium and just have a thin oxide layer that provides the hard cylinder surface. If you remove that layer you reach regular aluminium. Who made the honing?

I was told by some Norvel users they are made like that...Mine came in factory-condition, with or without honing, no matter, but with a tight fit and cylinder blow-by when cold, zero compression when hot.

Surfer_kris Sat Mar 30, 2013 4:39 pm

That just doesn't sound right, I've certainly never had any Norvel engine like that.
Check the thread that "Rusty" made during his first encounter with Norvel engines, I'm pretty sure he had a very tight engine too.

Here is the looong thread started by RknRusty; running Norvels

**RknRusty** Sat Mar 30, 2013 6:46 pm

Wow, Balogh, that's not at all what I expected to read when I saw the thread title. I fly a Baby Flite Streak with a Tee Dee .051 and a 5.25x3 prop, un-muffled, and it travels at the top of my fun speed limit. I have another identical BFS with a Big Mig .061(both planes on pressure bladders and CL intakes), about an ounce lighter, muffled, and three head shims but I have to fly it with a 5.75x3 prop to tame it enough to keep it within my fun speed limit. Once I put a 5.25x3 on it and I honestly had bit off more than I could handle. The only thing that saved me was about 20 lazy 8s. These are Master Airscrew props, and both engines drink the same 23% nitromethane/20% castor fuel.

Also I guesstimate my Tee Dee runs about 2-2.5 minutes on 3/4oz of fuel, and the Big Mig sometimes makes me wonder if it's ever going to run out. Much more efficient.

I love my Tee Dee .051, by far the best fastest Cox I've ever run, but the Big Mig just radically blows the doors off of it. Just for the hell of it, one day I put an APC 5x2 on it on the test stand and it ran up 28.8K rpm. And I still consider this one new.

**RknRusty** Sat Mar 30, 2013 7:01 pm

Surfer_kris wrote:...Here is the looong thread started by RknRusty; running Norvels

Loooong is right. I feel like a real doofus after re-reading that. It's near the end of page 4 on my browser before I finally got it running.

Much of my problem was a leaky venturi gasket and a loose needle. I tried all sorts of silicon donuts to seal the venturi, and finally found that a ring of latex bladder tube(surgical tube) works perfectly. I change it every 40 or 50 flights in case it decays, but the old one always looks good. A starter spring makes it much easier too. I still use one.

andrew Sat Mar 30, 2013 7:32 pm

Your results are a little a little unusual. The NORVELs have been good performers, but will not turn up if over-propped. A 5x3, 5.25x3 are usually good fits. I replaced a BW with a Big Mig and had a significant step-up.

Although you indicated that it was a new engine, is it the AAN or Revlite model. The Revlite will have fairly large cylinder fins, be black in color and have holes in the fins for the cylinder mounting screws.

Check to ensure that the coverplate is tight and not leaking and that the glowhead gasket is seated, the gasket edges are not rolled and that there are no leaks around the glowplug.

andrew

**RknRusty** Sat Mar 30, 2013 8:05 pm

Yeah, what Andrew said.
I've never felt a loss of compression on a hot engine. The pinch is relieved, but it still pops over TDC with authority.

balogh Sun Mar 31, 2013 2:24 am

andrew wrote:Your results are a little a little unusual. The NORVELs have been good performers, but will not turn up if over-propped. A 5x3, 5.25x3 are usually good fits. I replaced a BW with a Big Mig and had a significant step-up.

Although you indicated that it was a new engine, is it the AAN or Revlite model. The Revlite will have fairly large cylinder fins, be black in color and have holes in the fins for the cylinder mounting screws.

Check to ensure that the coverplate is tight and not leaking and that the glowhead gasket is seated, the gasket edges are not rolled and that there are no leaks around the glowplug.

andrew

Thanks for the comments. This is definitely a Revlite model (or at least was sold by Norvel USA like one) with the fins having the holes for the bolts holding the cylinder down to the crankcase, and has no leakage problem at any of the places you all mentioned. When the piston travels up you simply hear through the muffler outlet stub the air leaking between the piston and cylinder...sorry for the blasphemy on NV but for me COXtill remains the etalon of precision.

I made it damn sure that no fouling should get into the engine to prevent unwanted piston/cylinder wear, but the blow-by was there from the very beginning, no matter how tight the engine fit was.

I also bought a spare cylinder/piston combo and it is the same loose fit at the bottom part of the compression and gets suddenly at the top. Truly, I do not understand the concept...loose fitting with low compression then a helluva big resistance at the top for a short piston travel only.....where is the thermal and mechanical efficiency that the NV website talks about? As at least my example shows, not in this NV engine.

**RknRusty** Sun Mar 31, 2013 5:26 am

When the sun comes up I'm going to go to the shop and listen for leakdown through the exhaust port. Maybe NV had a bad run. Hardly anyone posts on the NVengines.com forum. I think I might have more posts than the administrator. But I would suggest posting of your findings there.

Surfer_kris Sun Mar 31, 2013 5:26 am

It is a tapered bore, just like in ABC engines. The idea is that when the engine gets hot, the top of cylinder expands more and pinch at TDC is then just right, while the lower part is still a little loser to reduce friction. One therefore have to heat the cylinder before the first start, so that the piston is not worn into a too small shape (by hitting a cold and too narrow top part).

If you have blow by in a brand new engine there is something wrong, but it sounds like something went wrong during the brake-in and you now have a too loose piston.

balogh Sun Mar 31, 2013 6:15 am

RknRusty wrote:When the sun comes up I'm going to go to the shop and listen for leakdown through the exhaust port. Maybe NV had a bad run. Hardly anyone posts on the NVengines.com forum. I think I might have more posts than the administrator. But I would suggest posting of your findings there.

Will appreciate your feedback on the leak-through in your NV. I use COX after run oil (the blue oil Bernie sells) to lubricate the engines after each day of run. This is thick enough to prevent any blow-by in any of my old COX engines, but is not for the new NV that lets air escape all the way the piston moves up....again, the blowby was there before the first break-in run, on the brand new engine....the same loose fit in the spare piston/cylinder combo that I have in the box, so I do not suppose this was a bad run at Norvel...these engines are simply as it is.

balogh Sun Mar 31, 2013 6:23 am

Surfer_kris wrote:It is a tapered bore, just like in ABC engines. The idea is that when the engine gets hot, the top of cylinder expands more and pinch at TDC is then just right, while the lower part is still a little loser to reduce friction. One therefore have to heat the cylinder before the first start, so that the piston is not worn into a too small shape (by hitting a cold and too narrow top part).

If you have blow by in a brand new engine there is something wrong, but it sounds like something went wrong during the brake-in and you now have a too loose piston.

The blow-by was there right when I took it out from the box...then I added COX after run oil into the cylinder and carb....the blowby was still there...I followed the Norvel break-in instructions....poured some oil into the cylinder and carb then turned the engine without the head on it with an electric starter for some time...then started up and let it run rich for many minutes...then let it peak out....the pinch is still there when cold, as is the blowby...I can only hope the castor shellac will deposit in the micro scratches of the cylinder and piston thus improving the compression over time.

balogh Sun Mar 31, 2013 6:29 am

RknRusty wrote:Wow, Balogh, that's not at all what I expected to read when I saw the thread title. I fly a Baby Flite Streak with a Tee Dee .051 and a 5.25x3 prop, un-muffled, and it travels at the top of my fun speed limit. I have another identical BFS with a Big Mig .061(both planes on pressure bladders and CL intakes), about an ounce lighter, muffled, and three head shims but I have to fly it with a 5.75x3 prop to tame it enough to keep it within my fun speed limit. Once I put a 5.25x3 on it and I honestly had bit off more than I could handle. The only thing that saved me was about 20 lazy 8s. These are Master Airscrew props, and both engines drink the same 23% nitromethane/20% castor fuel.

Also I guesstimate my Tee Dee runs about 2-2.5 minutes on 3/4oz of fuel, and the Big Mig sometimes makes me wonder if it's ever going to run out. Much more efficient.

I love my Tee Dee .051, by far the best fastest Cox I've ever run, but the Big Mig just radically blows the doors off of it. Just for the hell of it, one day I put an APC 5x2 on it on the test stand and it ran up 28.8K rpm. And I still consider this one new.

I will try with more shims...I currently have 2 but reducing the compression with additional shims will not help that compression is practically already zero when the engine is hot...I do not think I have a premature ignition problem (to be cured with shims )here that leads to low engine speed...that would also result in overheated engine which is not the case here.

Surfer_kris Sun Mar 31, 2013 7:31 am

balogh wrote:
The blow-by was there right when I took it out from the box...then I added COX after run oil into the cylinder and carb....the blowby was still there...I followed the Norvel break-in instructions....poured some oil into the cylinder and carb then turned the engine without the head on it with an electric starter for some time...then started up and let it run rich for many minutes...then let it peak out....the pinch is still there when cold, as is the blowby...I can only hope the castor shellac will deposit in the micro scratches of the cylinder and piston thus improving the compression over time.

I never understood that part of the Break-in instructions, it is completely counter effective, I don't know who came up with those...

By turning the engine over, cold and without a plug, one will just jam the piston into the pinch at TDC and wear it out prematurely. The way to brake in tight engines is to preheat the cylinder to reliev the pinch and then fire them up, that keeps the cylinder hot and all parts can be gently mated.

Surfer_kris Sun Mar 31, 2013 7:50 am

I only have one of the latest versions, i.e. from NV rather than Norvel, and it might not be very tight just when the exhaust port closes, but it shouldn't leak and it it should have a tight pinch at TDC.

It might be worth taking the backplate off your engine and check for a bent conrod, electric starters can have that effect on engines and it will reduce the compression ratio.

Surfer_kris Sun Mar 31, 2013 8:57 am

Okey, I've now had a closer look at the latest NV engine, and there seems to be some differences. The .061RC that I have from NV does not have any SPI and the piston does not travel as far up the bore as the older ones did (they also had SPI though). So there seems like they have indeed changed things under the NV brand. Not sure where exactly the difference is, they might simply have raised the cylinder a little.

Once all the snow is gone here I'll make a few bench runs with the NV (I only have the one) and compare it to the earlier Norvel engines (I have several of those).

andrew Sun Mar 31, 2013 9:14 am

Surfer_kris wrote:
balogh wrote:
...I followed the Norvel break-in instructions....poured some oil into the cylinder and carb then turned the engine without the head on it with an electric starter for some time...then started up and let it run rich for many minutes...

I never understood that part of the Break-in instructions, it is completely counter effective, I don't know who came up with those...

NORVEL's heritage came from the competitive 1/2A pylon and C/L combat market where the flyers understood engines. When the engines became widely available to the public, I think difficulties arose because folks had a hard time getting the engines to run, mainly due to the cold TDC pinch. I'm convinced the break-in instructions were written to make the engines more "user friendly", not because it was the best approach for the engine and longevity.

For many of us that have run NORVELs for some time, I think the general consensus of opinion is:

1) Don't follow the cold run-in instructions --- removing the cold pinch means a sloppy fit at running temperature.
2) Start these engines hot. My initial starting accessories are fuel, battery, heat gun, patience. I use a 6x3 (6x2 if I have one) at first just because I think it gives a bit more flywheel effect.
3) As soon as the engine starts, get it up to temperature immediately. I've used a baffle to block the airflow to the cylinder to quickly warm it up.
4) Run the engine in 2-cycle ---- it can be a rich 2-cycle, but don't run it in a 4-cycle mode. Keep it hot.
5) As soon as the engine will run continuously, I usually drop to a 5x3 or 5.25x3. I like the COX rubber ducky or a MA 6x3 cut to a 5x3. I tend to shy away from APC on break-in just because I've got a limited number of fingers.

Checking for a bent conrod is a good idea. NORVELs will run with bent rods, but performance will be way down. You might also want to drop to a single shim.

balogh Sun Mar 31, 2013 12:41 pm

andrew wrote:
Surfer_kris wrote:
balogh wrote:
...I followed the Norvel break-in instructions....poured some oil into the cylinder and carb then turned the engine without the head on it with an electric starter for some time...then started up and let it run rich for many minutes...

I never understood that part of the Break-in instructions, it is completely counter effective, I don't know who came up with those...

NORVEL's heritage came from the competitive 1/2A pylon and C/L combat market where the flyers understood engines. When the engines became widely available to the public, I think difficulties arose because folks had a hard time getting the engines to run, mainly due to the cold TDC pinch. I'm convinced the break-in instructions were written to make the engines more "user friendly", not because it was the best approach for the engine and longevity.

For many of us that have run NORVELs for some time, I think the general consensus of opinion is:

1) Don't follow the cold run-in instructions --- removing the cold pinch means a sloppy fit at running temperature.
2) Start these engines hot. My initial starting accessories are fuel, battery, heat gun, patience. I use a 6x3 (6x2 if I have one) at first just because I think it gives a bit more flywheel effect.
3) As soon as the engine starts, get it up to temperature immediately. I've used a baffle to block the airflow to the cylinder to quickly warm it up.
4) Run the engine in 2-cycle ---- it can be a rich 2-cycle, but don't run it in a 4-cycle mode. Keep it hot.
5) As soon as the engine will run continuously, I usually drop to a 5x3 or 5.25x3. I like the COX rubber ducky or a MA 6x3 cut to a 5x3. I tend to shy away from APC on break-in just because I've got a limited number of fingers.

Checking for a bent conrod is a good idea. NORVELs will run with bent rods, but performance will be way down. You might also want to drop to a single shim.

Thanks for the useful information. The conrod is OK, it has not been bent. What makes me believe the NV concept is a loose fit is that the brand-new piston/cylinder combo I purchased from NV a month or so ago is the same sloppy fit up to about 3/4 piston upward travel when the pinch cuts in as with the new NV. Meaning, that the blow-by is inherently there in the design and pinch only adds to the power loss at least until the engine has run long enough to remove much of the pinch. I am not saying all NV engines are like this but the one with the spare cyclinder/piston combo are doomed to low performance.

In addition I have alo checked the R/C carb and it opens wide at full throttle hence the weak power is clearly thr result of loose fit/blowby.

I am eagerly waiting for Rusty's feedback from his shop as for the blowby of his NV...

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