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Post  JPvelo Wed May 01, 2013 8:16 pm

Does a norvel .061 have the same mounting lugs as a tee dee .049/.051? Can the norvel be bolted right in where a tee dee once sat?

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Post  Ken Cook Wed May 01, 2013 8:24 pm

Jim, the Norvel does have the same bolt pattern as the Cox. Problem is, the lengths of the case are all different. So assuming it's the same length, you may have to chamfer the beam due to the case itself being slightly wider. I usually shave the beams on a 45 deg angle for about 1/16" to clear the radius of the Norvel case. The bolt holes work fine however. Ken
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Post  JPvelo Wed May 01, 2013 8:28 pm

Cool, thank you.
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Post  RknRusty Wed May 01, 2013 10:32 pm

If you use a starter spring as I do, you also may have to carve a relief for it. After the engine is bolted in place, I usually secure the spring to the bottom beam with a zip tie to help hold it in place. If you do a perfect carving job that may not be necessary.

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Post  balogh Tue May 14, 2013 2:20 pm

@JPvelo wrote:Does a norvel .061 have the same mounting lugs as a tee dee .049/.051? Can the norvel be bolted right in where a tee dee once sat?

Jim

I would never place a Norvel where once a COX sat. Despite the positive postings on Norvel engines I have had very discouraging experience with this Big Mig Russian crap...no compression even when new...the only good thing about a Norvel is the RC carb....providing you can start the engine at all to benefit from the RC carb.
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Post  Jason_WI Tue May 14, 2013 4:31 pm

The couple of Norvel engnes I have that are new have tons of pinch at TDC and would require heating with a heat gun to get started. Are you talking about the recent stuff from NV Engines or the old stock?
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Post  Cribbs74 Tue May 14, 2013 4:43 pm

I had one of the old stock ones and it was a bear to start. It had a good pinch though. The starting issues is what turned me off of them. I do think they are good engines though once broken in. They are just not for me. Small Cox Logo
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Post  RknRusty Tue May 14, 2013 6:42 pm

I'm a wuss. I use springs to start mine. They are all first spin crankers, and scary fast. I don't know what Balogh got but he definitely didn't like it. Pinch but no compression as I recall from his thread a couple of months ago.

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Post  anm2 Tue May 14, 2013 6:59 pm

I have run two norvel engines. One was a Big Mig with a pressure tank. It started and ran with ease. Because of the way it was set up, it is one of the smoothest engines I have ever owned. I also have a norvel that came to me in a bubble pack. It isn't quite as good as the boxed one. I think it was purchased from Mecoa when they were dumping the last of the lot they had, but I can't be sure. Anyway, I struggled to get it started, but once I figured out the needle position it ran without a problem. We will see. The trouble with some of the foreign engines is quality control. Sometimes it is hit or miss. I would generally say that the Norvel is pretty good. I have a Brodak Mk I that I can't get to run at all. I honestly don't think you can beat a Cox engine for pure utility, ease of use, and fun. You can still pick up a brand new Tee Dee for around $60. I think that is a bargain. It may be a 50 year old design, but it worked, and worked well. They are kind of like the B-52. They will still be flying a hundred years after they were first made.
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Post  RknRusty Tue May 14, 2013 8:19 pm

I agree, the Tee Dee is a most elegant design, the art of simplicity and completely dependable.

The only problem I have with Big Migs is the venturis can leak and if not sealed properly, will cause rough underpowered performance. My brand new one was like that and it gave me fits at first. After fixing that, it's as dependable and easy as a Tee Dee, with the exception that I still need a starter spring. The main reason for that is, with pressure bladders, if I accidentally flood it, it's harder to burn off a flood without the help of the spring. And I love the fact that the .061 has so much power in reserve that I can run it muffled and still use a 5.5" prop. Or even an APC 6x2 if I want to fly fast on short(35') lines.

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Post  andrew Tue May 14, 2013 9:14 pm

@cribbs74 wrote:I had one of the old stock ones and it was a bear to start. It had a good pinch though. The starting issues is what turned me off of them. I do think they are good engines though once broken in. They are just not for me. Small Cox Logo

They certainly can be aggravating on starting for the first time. I'm convinced that's why the later instructions recommend cold flipping or running cold with a starter. Also, unlike COX engines that are ready to go after 3 or 4 rich runs, the NORVELs can take a long time to eventually break-in. I confess, with the chance of being strung up here, that I really like the NORVELs. But, you really have to have a lot of patience when dealing with new engines.
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Post  RknRusty Tue May 14, 2013 9:22 pm

I'd love to know what's wrong with Balogh's. I wish he was here in the States, maybe we could be of more hands on help.

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Post  balogh Wed May 15, 2013 12:46 am

@RknRusty wrote:I'd love to know what's wrong with Balogh's. I wish he was here in the States, maybe we could be of more hands on help.

Thanks Rusty,

although I will be travelling in Seattle and Calgary on business in late May I do not think I could have any more help than what this forum can provide.

Once again, my apologies to the Norvel fans who may find my comments on the Norvel quality blasphemous, but I experienced what I wrote in my posting a few weeks ago: a brand new, out-of the box NV 061 Big Mig with RC carb, with a tight TDC pintch, but with practically zero compression when out of the box. Same thing with the spare cylinder/piston combo that I also purchased from Norvel USA...

The observation: hard to start because of poor compression, way lower power than any of my old COX TD 049 or 050 or 051 stuff with 10-s and 10-s of hours of reliable and powerful run on them, having practically original compression with only mimiumum blow-by that engines with steel cylinders (COX: yes, NV: no) tend to cure themselves by the castor varnish building up on the cylinder wall and making up for any occassional cylinder wear..

Engines tend to lose compression when hot (COX included) because of the different thermal expansion of the piston and cylinder that will leave a bit wider gap between the piston and cylinder and thus more gas will escape. In addition, the castor that seals the gap between the cylinder and piston loses viscosity when hot and is blown away by compression easier than when cold, thus allowing route for the gas to escape.

You may say that the high velocity of the piston when the engine runs does not leave too much time for the gasses to escape, so what?

I would say in the Norvel this is comparable to a case that some of you may have experienced, when the glow head of a COX gets untight when hot and the engine loses power rapidly in a mid-air situation. The problem with my NV is that it never has the power it is supposed to have as it has already very low compression when cold, let alone when hot.

Those of you with some gas-dynamics and thermodynamics education may know that the loss of compression in an engine like COX or NV depends only on the time the gasses have to escape (i.e. the engine revolution cycle length) and on the gap between the piston and cylinder through which gasses escape. The pressure inside/outside the cylinder does not matter above a certain ratio. If the channel through which the gasses escape do not have a cross-section variation similar to a Laval nozzle (which the channel i.e. the micro-gap between the cylinder and piston in an engine does not have), then once the pressure ratio inside/outside the cylinder is higher than about 2 for air-based gasses (meaning 2 bars inside and 1 bar atmospheric outside) the speed of gasses will reach that of the sound in the channel, and unless a Laval orifice geometry is there, they wont accelerate at higher pressure ratio i.e. even if the pressure inside the cylinder is higher than 2 bars (it is around 40-50 bars when the fuel mixture explodes in the cylinder). Meaning that the only thing at the end which matters in an engine for loss of compression is the speed of the piston (the length of the period the cylinder is pressurized at or above the ratio of 2) and the cross section of the gap.

All I am saying is the lousier the fit between the piston and cylinder, the higher the loss of compression and power in the engine. NV-s with aluminum-based cylinder and piston do not allow the build-up of varnish to plug the gap of wear or lousy manufacturing accuracy. COX with steel cylinder will build up the sealing varnish and this will compensate engine wear to some extent and greatly elongate the lifetime of a COX.

Sorry if I was too academic, but it does not help the fact that I contacted the NV USA sales organization for help, who cooled me down that NV very seldom have acknowledged warranty claims in its history, but if I want I can courier my engine to St Petersburg Russia to an address that I could simly not google on the net. Then I was advised to hand-deliver the engine from Budapest Hungary where I live to St Petersburg Russia to make sure it will hit the address. Needless to say the NV is still sitting boxed in my cupboard, waiting for some business travelers on my company to head for St Petersburg.

So much about my experience with NV. I hope this partly technical explanation will will clarify I have no historical bias with products of a country that occupied my country after WW2 till the Iron Curtain fell, but simply the quality difference between a 50 years old COX and a present-day NV is so striking that not too much remains to explain here.

Good luck with your Norvels, I will never abandon COX for any other brand.
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Post  Surfer_kris Wed May 15, 2013 1:47 am

I only have one of the latest NV engines and it is not as good as the older "true" Norvel engines are. It seems they haven't yet managed to duplicate the piston and cylinder matching that they are famous for.

Try to get one of the original Norvel engines and you'll understand why they are so much better than cox engines. I have indeed swapped out a few cox engines for Norvels in a few planes, just for testing, and there is no way I would go back...

The Norvel are easier to set up and run smoother for the whole tank. They also love to rev, and will run all day well above 20krpm. The fact that you can replace a cox .049 with a Norvel .061 without any increase in weight, helps of coarse.
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Post  balogh Wed May 15, 2013 2:23 am

@Surfer_kris wrote:I only have one of the latest NV engines and it is not as good as the older "true" Norvel engines are. It seems they haven't yet managed to duplicate the piston and cylinder matching that they are famous for.

Try to get one of the original Norvel engines and you'll understand why they are so much better than cox engines. I have indeed swapped out a few cox engines for Norvels in a few planes, just for testing, and there is no way I would go back...

The Norvel are easier to set up and run smoother for the whole tank. They also love to rev, and will run all day well above 20krpm. The fact that you can replace a cox .049 with a Norvel .061 without any increase in weight, helps of coarse.

Thnaks,

you may be right, I also have an older NV049 from ebay, made somewhen in the mid 1990-s and while I have not started it yet, it seems to have a better compression tha the 061 I bought brand-new this year.

Given these engines were made in the past by a Russian defense industry workshop with probably very high discipline and quality standards, and nowadays NV maybe only one of the standard eastern-European/Russian factories of not quite high quality, I am not surprised at all.

But it does not help the fact that I can dump my new 061 with all spares worth north of 90 bucks because the duplicated cylinder-piston matching is only the thing of the past and my engine is the crap of the present.
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Post  RknRusty Wed May 15, 2013 10:48 am

Okay, Balogh, you have a convincing argument for the condition of this engine. I don't know much about thermo/fluid/gas dynamics, as my field was electronics, but I understand what I'm reading about it. If you would indulge me one last time, I promise to quit worrying about it. And that would be to re-check and make sure sure sure, the venturi or carb is not leaking air where it inserts into the receptacle on the nose of the crankcase.
I know that has nothing to do with compression, but... just a last K.I.S. thought.

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Post  balogh Wed May 15, 2013 1:32 pm

@RknRusty wrote:Okay, Balogh, you have a convincing argument for the condition of this engine. I don't know much about thermo/fluid/gas dynamics, as my field was electronics, but I understand what I'm reading about it. If you would indulge me one last time, I promise to quit worrying about it. And that would be to re-check and make sure sure sure, the venturi or carb is not leaking air where it inserts into the receptacle on the nose of the crankcase.
I know that has nothing to do with compression, but... just a last K.I.S. thought.

Rusty


ZThanks Rusty,

I have already gone through those venturi leak check exercises (perfect seal) and head shim reductions. This latter helped my squeeze some more power out of the NV with only 1 shim left there.

But the essence of high pwer/efficiency from an internal combustion engine is to have most of the combustion gas work to drive the piston and not to escape with useless blow-by (poor compression), and this is particularly true with an engine of very tight TDC pintch that uselessly dissipates mechanically the useful energy of expanding gases.

The TDC pintch is supposed to ensure that even when the cylinder top where the most intense combustion occurs expands thermally more than the bottom when hot, the fit between the piston and cylinder remains normal. But if this pintch is restricted to the last 5% or so piston travel before the TDC (=Norvel design), it is worth nothing as 95% of the piston travel is with slack fit where most of the gasses will escape.

To the contrary, a tapered bore cylinder ensures that a longer section of the piston travel will occur with a better fit with the cylinder even when hot, thus the amount of gasses escaping is much less.

Anyways this is just the opinion of a humble mechanical engineer who has got nothing to do with engine design but you will appreciate a discrete pintch cannot be so efficient to retain hot-engine compression as a tapered bore design (COX Tee Dee)

Unfortunately the real experience supports the above theory quite well - at least in my case.Hope to not have written nonsense in my Hunglish
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Post  RknRusty Wed May 15, 2013 2:43 pm

Your Hunglish is better than many who's first language is English. I appreciate your detailed analysis and have no doubt that it is accurate. I am just disappointed to hear of the poor performance. I can't stand a machine that isn't right. Thank goodness for Tee Dees.
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Post  gcb Wed May 15, 2013 10:04 pm

@balogh wrote: ...Given these engines were made in the past by a Russian defense industry workshop with probably very high discipline and quality standards, and nowadays NV maybe only one of the standard eastern-European/Russian factories of not quite high quality, I am not surprised at all.

The owner of Northern Velocity (NORVEL) before SIG visited the factory. Apparently part of the responsibility for high quality was the group of women who did the assembly.

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