Norvel .074 Turbo head
 

I finally managed to acquire a turbo head for a Norvel .074. Not just the insert, but a complete one-piece thread-in head. Genuine glow inserts are getting harder to come by and more expensive as time goes on, but I love flying these little engines. In my area, O.S. turbo plugs are very easy to come by. Problem is, I don't have a clue where to start as far as heat-range is concerned. My "1/2A fuel" of choice is Wildcat 30% Heli spiked with 6oz./gal. of Sig castor. My prop of choice is the APC 7x3. Any suggestions?

The heat range is not very critical in my experience. I have used both P3 and P6 with 10% nitro and the P6 seemed a little better.

Thanks, Mr Cox. Did one seem better than the other for idling?

I thought the P3 would idle a little better but in practice I didn't notice much difference. This could be related to the fact that there is no low-end adjustment though, so when the top-end is set well the idle will be whatever you get. The P3 will need a richer top end so the idle will then be richer too, and the engine cools down during idling.

For flying, anything around 5000rpm is low enough. If you want better you will need to add an adjustable airbleed. There is not so much space but AndyW knows how to do it and he was kind enough to make one for me. I haven't thanked him enough for that I think.

Here is a little movie to show what can be done with the .074 engine. For a low idle, go to about 1:05 where I'm lowering the idle setting on the radio. This engine is inverted and fully cowled, running the stock glow plug and 10% nitro (and 20% all castor). Without an adjustable airbleed it would not have been running this well.

http://www.youtube.com/watch?v=trSCx-6zlAo

Any link to were you found that Turbo head adapter for that Norvel .074? Even NV doesn't carry spares for the .074! They just have the adapter for regular short plug:
http://www.nvengines.com/index.php?o...id=6&Itemid=65

Found it on *bay. It was a package deal with a Mecoa 1/4-32 glow plug adaptor insert. The Mecoa adaptors work, but cost you 1500-2000 rpm. I gave away the two I bought a couple of years ago. I bought some .074 parts from NVEngines about 3 years ago and they were fine. Kinda wish I'd ordered a bunch to put away for a rainy day.

Jon Valentine used to make some, I think that's where I got mine from...

If you have access to a lathe you can quite easily make your own heads, AndyW, or was it Japanman (?), has shown how to do it with simple tools.

merlin glowplug company is your go to source for the norvel and cox engines..they boost rpm, and are a great value...http://www.merlinglowplugs.com/Aircraft.html this link has the norvel with clamp ring listed for very reasonable prices....

Mine was said to be a Valentine head, but the package wasn't marked. Merlin only makes inserts for the .049 and .061 Norvels. (They are interchangeable) NOT for the .074, however.

Yes, Merlin doesn't make any for the Norvel .074, as far as I know.

Mecoa are listing some on their website for the .074 (proper inserts not "conversions"), but I haven't tried these myself.

http://www.rcuniverse.com/forum/1-2-...ml#post4533758

For all Cox engines AND Norvels, .049, .06 and .074

About throttling. There are only two engines that I've ever encountered that had perfect throttling without the need for an adjustable airbleed. The OS .10 and the Norvel .074.

Mr Cox seemed to get one that was the exception and I was more than happy to fix his up with an adjustable airbleed.

But all of mine have throttled perfectly, as is.

The trick is this. The .074 has a very broad, high end needle valve setting. You can dial it in perfectly and that's that. However, dial it in some more, and nothing much happens. It takes a half turn or so, of the needle before the engine shows signs of going lean.

That feature allows you to dial in your bottom end.

First, get it going JUST lean at the top end. Throttle back and let it idle and it'll either sag a bit or quit altogether. Start it up again and dial the top end a bit more. Throttle back and see what you get. Repeat the process until it idles forever and cracking the throttle open produces almost instant power with little smoke or fuss. All of mine function this way, can't imagine why Mr Cox's doesn't but we DO know that it isn't something that he's doing wrong, we went through that exercise at the time.

Lots of nitro always helps throttling, I never run anything less than 25%.

An overcompressed engine can suffer from going rich on idle even with an adjustable, low speed mixture feature. Adding a gasket or two under the head can help.

My .074 runs like a top, and idles better than any other small motor I have. I have noticed that the high speed needle setting is very broad like you have said. This is a great characteristic. It does make me feel as if there could be some room to open up the carb for more performance. I won't do this because it runs just great as is, and I wouldn't want to ruin it. I have been making a bunch of turbo heads lately, and use a 1/4" centre drill because it has a 60 degree taper on it. My lathe (Hardinge chucker) is adjustable for the center size to get the .284" hole size needed. This solves the hassle of making a proper size form tool. I haven't done a head for the .074 yet because my plug is still fine. (touch wood) I'll try to remember what you said about being overcompressed and the rich idle. That would explain some things I have had problems with over the years.

The Norvel .074 is one of those rare, virtually perfect devices that come along, usually by accident. I have no idea why it works the way it does but over the years, I've found that port timing, compression ratio, glow plug heat range, nitro content all play a role.

You can bore out the throttle barrel a shade and get a few more revs without hurting throttling. Don't use a drill bit, that barrel is some pretty hard steel. I use a round, diamond file and work it in from both sides by hand. This minimizes burs all around but even then, you need to dress off the burrs that DO form very carefully. Use the fingernail test.

On this one, http://www.youtube.com/watch?v=7lM9fbsPaBA I used a throttle made by GS for their ball bearinged, Cyclon clone. Superbly made with a considerably larger bore in the barrel. In this case, it DID need an adjustable airbleed. I put a GS pipe on it and got some pretty good numbers. Soon as I can, it'll be permanently installed on my Tsunami that came out a tad heavy. Can't fly this one in the park, need much more room.

Back to the stock, .074, LiteMachines had Norvel make them a special, .074 and the appealing feature was brass bushings at both ends of the crank. The LM heli uses an exhaust throttle and it's very efficient. So I got me a few when they were being sold off for 25 dollars and proceeded to add a throttle. I used the GS throttle mentioned and it had an adjustable airbleed. Despite that, the idle isn't as good as the original and acceleration isn't up to par. I used all the tricks I know to improve things to no good effect.

On the LM .074, the crank is shorter and the intake is rounder and not as oblong as the original. I haven't bothered to check the port timing though, that may be a factor. Which only illustrates again that the original, Norvel .074 is unique and a true gem in the world of small engines.

That .074 plugs are no longer available from Norvel is a bad sign that currently, it seems, Norvel is just selling off stock and will one day be gone. Sure glad I have their entire engine line including a half dozen .06s and .074s

I've been picking up all the reasonably priced .049 to .074 Norvel stuff whenever I see them. Could only find one .074. Got to make a bunch of planes soon? Maybe I should get off this computer sometime.

The .074's do seem to be harder to find than their smaller counterparts, at least N.I.B., since I've always been a little skittish about buying used ones.http://www.rcuniverse.com/forum/atta...mentid=1977248

I was lucky, mine was NIB, and at a swap meet. One of my new .06's doesn't idle really at all, but one of my used ones does quite well. Nice little plane for the .074 there.

I have 5 .074's that I fly, plus 2 that are still new. Some idle a bit better than others, but all of them do quite well. The only problem I've had was after not flying one of them for awhile, I took it out to fly and it seemed down on power. After several flights that day I took it home and gave it a close look. Turns out, the rod was bent pretty badly. I must have hydrauliced it without realizing it at some point. After a new rod from NV Engines, it's a great-running engine again. Now I'm very careful about clearing the cylinder before hitting it with the starter. I have a couple of the Norvel-marked starters that Sig used to sell. Even though I use them exclusively on the Norvels they apparently have enough oomph to trash a rod. Beware!

There is no need for any electric starters on these engines...

A spring starter is nice to have though as it gives a little more snap than I can manage with my fingers. On the Super Chipmunk above I have springstarter inside the cowl, works very well.

I like APC props and I like my fingers even more. I'll continue to use a starter.

You just need to deburr the trailing edge a little, it is only a glow engine so the compression ratio should not be very high. So unless you flood it, there shouldn't really be any problem.

The latest MAS props are even worse in terms of a sharp trailing edge from the mould...

I'm sure you are right, Mr Cox, but my days of sticking my fingers in little props are well behind me. The MAS props I've had were ALWAYS bad that way. Larger CDI gassers are the only thing I "flip" anymore. Has anyone tried the .074 glow head from Mecoa? Would be nice if they were a viable replacement for my dwindling supply of original Norvel heads.

I bought the MECOA 1/4-32 standard plug adapter for my Norvel .074. With a K&B 1L non idle bar plug. The adapter was machined so the K&B plug sits flush with the top of the combustion chamber. The difference was only a 950 rpm loss over the factory Norvel plug. I just tested them yesterday. Idle, transition and top end were good.

Around 1000rpm less sounds like the typical loss problem with regular plugs then...
What prop was that on?

Whether the problem is due to the threads, poor plug length matching, too low compression ratio, or a combination of them all, doesn't matter so much. There is no reason to just throw away all that power.

I think it has to do with the thread losses. I played a fair bit with an ASP .15, and it was fairly highly compressed with the stock head as it was blowing plugs fairly regularly. I made up a new turbo head and it went around 2400 rpm better. I used the same radius cutter to remove material from the stock head, as the turbo head. They both are pretty much the same compression ratio and shape, so I figure it is the way the plug seals. I got slightly less gains in the LA .10 and .15, as well as the Norvel .15. I chalk that up to the original company spending the research time to perfect the stock head. There was still a gain however, just not 2400 rpm. I think if there was a huge gain, that they would have gone to a turbo or equal button like the Fora or more high performance motors. Still, if you can not get the turbo heads, some high temp grease, or silicone may help marginally if put on the 1/4 - 32 threads. You have to remember the seal is not only the thread itself, but the sloppy fitted washer, and the undercut of the plug's thread too. Henry Nelson used the taper type plugs even on his larger .40 motors. Every little gain makes a difference. When there are many small things, it shows up in spades. The cost of the plugs is not an issue, as they cost the same as a regular plug. A Nelson plug, or a Merlin Turbo plug are only $5.