Older Norvel AME 061 running trouble

This one is running rich enough to 4stroke, and has a muffler with pressure tap. I don't think it's a fuel problem... But maybe. I'll give that a try.

I can touch the cylinder head after a run, but I cannot touch the crankcase nose without getting burned. The crankcase is heating from the bottom end up!

J

Right after the run, does it feel like its binding or stiffer than usual?. The over heated crankcase might be boiling the fuel off which might be causing the engine to lean out and quit. (Bandit)

Many of these engines were fit with a very tight crankcase clearance. It sounds to me that while the symptoms appear to be going rich, your crank is too tight in the case. I would dismantle the engine and chuck the crank up in a drill press and wrap some coarse emery cloth around the shaft while it's spinning. A bit of oil won't hurt during the process. Step down in finer and finer grits until you achieve a good shine and scratch free finish. I would especially pay particular attention up at the front of the shaft. Fold your sand paper or emery and polish out the radius where the crank web meets the shaft. Re assemble and try again. You might even have to lap the shaft into the case using Dupont #7 or a similar rubbing compound. Place some on the shaft and put the prop on it turning it for several revolutions. Wash all of this out with hot soapy water and dry well. Re oil and try the engine. Just be sure to wash all traces of compound from the case prior to running. A pipe cleaner followed by a good scrubbing of hot soapy water can rid the case otherwise it will bed itself in the case which is not good.

The AME also likes a bit less of prop load. I would downsize your prop and really allow things to wind up initially. I would keep the props in the 5" range until you get some more run time on it. Even smaller isn't going to harm anything. I run these on bladder pressure and my prop size is 3.5-4". Keep the pitch light like your doing. APC makes a 5x2 and a 5.5x2. Just keep the load light until you get the bugs worked out.

Yes, I agree to the above, the crank to case fit is simply too tight. A common issue but it is much easier to fix than a too loose fit (like on the AP wasp engines...)
Lap the crank to case, wash thoroughly, and run in on a 5x3 prop with plenty of castor in the fuel.

I agree with both Ken and Surfer_kris. While not common, tight fits did show up in the early NORVELs. Lapping and/or polishing can correct it, but go slowly. I would probably try polishing it first, starting with 400 grit and finishing up with 1000 grit. It will brighten up like a mirror. Run it again, checking for overheating the case.

It's a lot easier to take more off later than dealing with a loose fit.

Based on Ken's great advice I acquired a bunch of "polishing" items and agree that several different engine problems can be traced to tight fit in the P/C bore or the crank shaft to bearing/bushing fit.

His advice on emery paper is good--- but I had trouble finding differing "grits" so I went in search of alternatives

MicroMart is a great hobbyist resource

http://www.micromark.com/micro-mesh-finishing-kit,7601.html

Also I found that the Hobby Lobby carried Boy Scout pine wood derby car kits-- and some of the go fast items include a diamond paste to polish the Nail axles..... web searching for the diamond paste I found this stuff

http://www.dmtonlinestore.com/Dia-Paste-Diamond-Compound-P26C8.aspx

Again Ken's advice is perfect for what you are experiencing..... But if you want to make a small engine scream... Take it all the way to mirror finish smooth!

You may also want to try putting about four head shims in it.

chevyiron420 wrote:You may also want to try putting about four head shims in it.

Very good point, at least for the first couple of runs. My first Big Mig frustrated me so much, I put a Babe Bee head on it and it lit up much more easily. After some good hard runs, I put the Norvel head back on and it was an easy engine to use from then on.
Rusty

Great info guys! I'll give a lapping a try first (do least, then try more if needed), and I'll use a smaller prop, perhaps an old 6x3 cut to 4x3...

I'd love to hear her scream like she should!

J

You'll probably have to resist the urge to dive under the table when you crank it with a 4x3.

Before lapping to the case I would check that the crankshaft is not bent and that it does not have any rough spots or flat areas. Otherwise you might ruin a perfectly good crankcase.

George

Not much left to say other than that's what was wrong with mine went I took it apart really didn't look bad but, cleaned the crank up and the CC the next run proved it was the problem by running like the champ they are . I need to fit my with one of those smaller props and wind it up Eric

Jason, I was re reading your post when I noticed something you mentioned. You stated regardless of needle setting things are not working properly. You also mentioned the glued in carb body. I've had 2 distinct problems with old Norvel's. The needle is too coarse and has a very steep taper even for suction rendering a run that can go from very lean to too rich in a very small turn. The other problem is I had was the stock venturi assembly that developed air leaks from the glued in carb body. I used a small adjustable with the needle assembly removed and heated the case with a heat gun and wiggled until the venturi assembly came out. I then cleaned all the old glue off and reglued using J-B weld. Make sure your crank opening is closed doing this as you don't want any J-B weld in there. The needle issue was resolved by installing a Cox postage backplate needle. This is the 128 TPI. You can bush the hole in the stock Norvel carb body using 5/32" brass tubing. Make the tubing as wide as the assembly. In the middle of the tube file a flat until you break through. I then solder the spraybar into the 5/32" tube aligning the hole in the spraybar with the area I broke through when the flat was filed. Once soldered, this entire assembly can be JB welded into the Norvel aluminum body. You have a very good effective needle now which can be used with bladder pressure or suction. Ken

Ken posted a great topic on this method some time ago.... here

https://www.coxengineforum.com/t2949-fine-thread-needle-on-norvel-s-and-similar-engines?highlight=Norvel

Interesting... Haven't addressed this yet, spent the weekend working on my Cox Sandblaster, and watching it spin about on the icy driveway... Too windy to fly what I wanted!

Soon, soon!

J

Spent a bit of time the last few evenings inside this engine. I don't know that I was clear initially, this is an RC version. An early short-case RC AME, with the Norvel logo cast in the side.

In tearing it down, untouched since our last bout a couple years ago, I made some discoveries and observations.

1. The oil near the front of the crank was burnt black and hard. The rest of the engine's oil was clear and still liquid, except some residues in the muffler. I think this leads credence to the theory that the real problem is in the crank journals.

2. I've got a good number of sleeve bearing motors. This is the ONLY one I have (other than, perhaps my Big Mig, but I didn't tear it down as it's mounted on its plane) that doesn't feature an oil slot cut in the top of the "thrust bearing" area where the crank web spins. My OS 25 has it, my Cox TD has it, my Cox Reedies have it.

3. Unlike the TD crank, there is no separation of the crank into discrete front and rear journals, with a relieved section between them. On the TD, this functions to reduce bearing drag and as an oil reservoir for the journals.

Now, I think I understand what's happening. When it's running, assuming there's a tractor prop on the engine, the crank web is pulled forward into contact with the crankcase, where it functions as a thrust bearing. Since this surface is very smooth, it seals pretty well. No oil can flow from the crankcase to the journals this way. That leaves only whatever oil can leave the intake at the rotary valve to lube the bearings. The intake is typically under vacuum, and unlikely to deliver much oil to the crank journals, whose other ends are either at ambient pressure (front) or elevated average pressure (rear).

On a TD or similar engine with an oil path in the thrust bearing, you have a average high pressure area (crankcase pressure averages a psi or two) with a lube path to the crank journals. Some of the fluids in the crankcase WILL be blown to the bearings. And thus they're lubed.

I tested the fit of my crank to case, and found it to be quite snug, but free running. There is small detectable play, but far less than, say, a Bee. It has clearance (at least at room temp). Clearance should only increase as the engine heats up, unless all the heat's going to the crank.

So, last night I used a jeweler's file to make an oil path as described above. Took about 5 minutes, excepting assembly/disassembly. I'll try it when next I can (received 8" more snow last night, that's 24" this week). This seemed a smaller intervention than lapping the case, which I can still do should this not do the job.

J

JasonB wrote:
2.  I've got a good number of sleeve bearing motors.  This is the ONLY one I have (other than, perhaps my Big Mig, but I didn't tear it down as it's mounted on its plane) that doesn't feature an oil slot cut in the top of the "thrust bearing" area where the crank web spins.  My OS 25 has it, my Cox TD has it, my Cox Reedies have it.  

Now, I think I understand what's happening.  When it's running, assuming there's a tractor prop on the engine, the crank web is pulled forward into contact with the crankcase, where it functions as a thrust bearing.  Since this surface is very smooth, it seals pretty well.  No oil can flow from the crankcase to the journals this way.  That leaves only whatever oil can leave the intake at the rotary valve to lube the bearings.  The intake is typically under vacuum, and unlikely to deliver much oil to the crank journals, whose other ends are either at ambient pressure (front) or elevated average pressure (rear).

On a TD or similar engine with an oil path in the thrust bearing, you have a average high pressure area (crankcase pressure averages a psi or two) with a lube path to the crank journals.  Some of the fluids in the crankcase WILL be blown to the bearings.  And thus they're lubed.

It is sort of the right track but doesn't quite make sense, to me...

When the intake is closed you have an overpressure in the crankcase and lube can be pushed forward around the crank opening (facing downwards). Some engines have a lube channel spiral starting right at the crank window and continuing forward. This actually makes more sense than having a grove in the bearing surface at the top where there is never any over pressure.

You can quite easily make a relief area on the crank, similar to the TD, it doesn't have to be very deep at all.

Thanks for those thoughts, Kris. You're correct, of course on the lube thru the window... Seems so bloody obvious once pointed out.

I gave'er a run this evening. Hooked up on my 1/2a test stand, with a 2oz Sullivan tank, burning Omega 15% with a bit of extra castor. I made 2 run attempts.

First, with the Norvel glowhead'n'clamp, 3 head gaskets to lower the compression some. Started reasonably easily, and after a bit I came to a mixture setting on the rich side of the 2cycle band. As long as glow was maintained, it ran quite well. Removing glow resulted in a sag starting about 4-5 seconds later, though after a minute or so, it was able to hold itself for 2 or 3 minutes. Any throttling snuffed it, unless glow was applied. Still, better than I'd previously achieved. Needling is very touchy (a fine thread woudl be nice!), mostly though because the needle's on the moving part of the carb, part of the barrel.. And there's always play. On shutdown, smoke rose from the muffler. The ccase was about 50C, the cylinder fin area about 75-80C, and the muff 160C read by IR thermometer.

Anyway, suspecting glow head issues, I switched to a Galbraith +Nelson HD plug. On removing the Norvel head, I found it and the piston head covered with carbon particles and brown residue... Far more than one would expect from 1oz of fuel burnt. I mention it in case it's relevant. The head of my Big Mig is nearly mint clean by comparison, just a slight yellow staining in the "corners", despite dozens of flights.

Installed the Nelson combo, again with 3 head gaskets. It seemed a bit more powerful in this config (no RPM's taken, as I'm under fluorescent lights), but if anything less stable. It ran as long as 30 seconds between bouts of slowly loosing RPM (regained instantly if glow was reapplied), and would quit if left alone. Mixture was stable at between 2-4 break and peak, well in the happy range. Changing the mixture had no effect on reliability. After the run, the Galbraith head was also carbon coated.

It is NOT suffering from crank seizure, I"m now sure. The crank still turns freely immediately after it quits, and glow wouldn't revive it if that was the trouble.

Is it, perhaps, overcompressed? I'll try with 4 or 5 gaskets tomorrow... Hard to troubleshoot here after 7.... Kids sleepin', ya know.

J

Jason, I never use more than two gaskets with a Nelson head combo. I don't know what thickness shims your using however. I have high doubts that your over compressed. Signs of a over compressed engine is usually a very sand blasted pitted looking combustion chamber. In addition to that, it usually takes the plug clean out by essentially ripping the coil out of the plug. What I do recognize is your fuel. AME engines want more nitro than your offering and the fact your using even more oil is also throwing a red flag. While others will comment on their fuel I will tell you I use 35% minimum in the AME engines and as much as 60%. My oil content is anywhere from 18% -20%. Norvel fuel was 18%. This doesn't mean that a engine won't run on a lesser nitro fuel, but it certainly sounds like your in need of a hotter plug or more nitro. A Nelson head can start running real rough if the plug is cooling off which certainly sounds like it from the symptoms your explaining. What Nelson plugs are you using? Does you plug have the notches on the edges of the flats?

Jason, I am not a galbreath head expert, but have been experimenting with one on a mark XIII wen mac. It seems to me that the plug is relativly cold and requires a high compression ratio to keep it lit. If so it may be a bad set up to add shims to. Ken get me straight here if i'm wrong!
On my project, my compression ratio is higher than stock, but a little lower than doug designed the head for. I can only get a two cycle run with the wire connected. If I remove the wire it shuts off. It will continue to run however if I leave it four stroking. My plug has a groove around the hex. I think I need the hotter plug to try, but cant find one or afford it.
Phil

It sounds like you have the colder HD Nelson plug, try the hotter ones instead (no groves on the hex part).

Merlin makes Nelson style plugs too, they are no more expensive than other plugs as I remember it...

I do have Nelson HD and Hot plugs available.

This weekend, I'll make attempts with both plugs and I'll vary the compression ratio between 1 and 5 shims (all standard .005 cox shims).

This engine was given to me by a fellow club member some years ago when he couldn't make it run well either. I monkey with it on occasion, trying "this and that". I know I've attempted to run this engine before with 1 and 2 shims, using known good Norvel glowheads and Nelsons, but it's been some time. I'll keep trying.

Nothing seems to be mechanically wrong. There a nice little pinch at TDC, and when it DOES run, it sounds nice enough. One day it and I will come to an understanding

J

I do have Nelson HD and Hot plugs available.

This weekend, I'll make attempts with both plugs and I'll vary the compression ratio between 1 and 5 shims (all standard .005 cox shims).

This engine was given to me by a fellow club member some years ago when he couldn't make it run well either.  I monkey with it on occasion, trying "this and that".  I know I've attempted to run this engine before with 1 and 2 shims, using known good Norvel glowheads and Nelsons, but it's been some time.  I'll keep trying.

Nothing seems to be mechanically wrong.  There a nice little pinch at TDC, and when it DOES run, it sounds nice enough.  One day it and I will come to an understanding

J