Quote from: Dave Moritz on August 15, 2026, 06:01:04 PMHello All:


Back with a report. I put in a couple hours with diagnostics & attempts at running.

1) No leaks in tank or lines. Verified with serious bulb pressure tests in a quiet room.
2) With a full tank and ship at the level, I pulled the fuel line at the needle and could only get flow if I lowered it a half inch below needle.
3)The tank holds 1-3/4 ounce when full. It is plumbed with 1/8" pipes. No trouble getting it to fill completely.
4) When I installed the tank, it was a loose fit in the compartment. Loose enough so that I could pad it all around.
5) I did find that the needle was partially blocked, so cleared that out to great effect.

So, I attached an external 1-oz. uniflow tank with rubber bands. After many attempts to get the needle right for starting, I managed to get a run of less than a minute that left much fuel in the tank. I forgot to check if the exterior tank passed the flow test at the needle. I might try substituting a non-uniflow tank next if it doesn't.

I got a little burnt out, so that's where I left it. Will try again.

Dave Mo...

   After reading your last post a couple times, I and that you found the spray bar partially blocked, I would return there and recheck that. The  Norvel engines are different and can be finicky to get the run satisfactory, but I have never had trouble just getting them to run. Check the spray bar again and how it fits into the case and the venturi. The ones I have experience with have a special shaped flange on the nipple end of the spray bar so it only goes in one position and the hole in the spray bar lines up in the direction it needs to go. Check howo that is all lining up. The fact that you have had issues with two different tanks now makes me thing the engine is the culprit. If you have another needle valve, compare it to the one you are having problems with and see if length, taper and such is the same. As a last resort, if you can remove the tank from the airplane, pull the back end back off and see what the end of the pick up tube looks like. Keep at it!!
  Type at you later,
   Dan McEntee

I meant to come back to this one yesterday.

At this point I wouldn't blame the model's tank. I would encourage a good bit of bench running. I remember my Big Mig .074s were MUCH easier to start and much better (stable) runners after well over 60 minutes of running across many 1/2 ounce tanks. They were on a twin, so it felt like I was running these engines forever before I mounted them on the model.

I seem to remember a thread from several years ago that mentioned crank bearing tolerances can be a bit too tight on some of the NorVels...that is, beyond their normal, tight TDC pinch.

I think the find was running the engine to shut off and then probing the crankcase for excessive temps. The front of the case would exhibit higher temps than the rest of the case. The fix was to polish the crank a bit.

I think it was light finger pressure to probe the case.


Does this sound familiar?

Jim (and Dan):

I think we have an "a-ha" moment here! I too recall someone advising us to pull the crank and give it a good polishing, so good that the weight of the pin itself would float to the bottom when released (or something like that). Your suggestion, Jim, seems correct to me. Each time I ran the motor, it would bog down as if overheating in some fashion or other.

Polishing seems like an interesting winter-time project, and that'll be my plan assuming no other possibilities come to light here. As they say down under, "Good on you, Jim." And Dan, I picked up some pointers from your efforts at helping out.

Thanks a bunch, and I'll keep you all informed.

Dave...

As a follow-up, I hope to find the posting explaining how to polish the crankshaft. The trick will be how not to overdo it. If I recall, the grit was something in the thousands.

Dave Mo..

Mr. Dave
This should get you started. It is NOT an exhaustive list. Granted a thread is for the AP .061, but the premise is the same. Thank Mr. Larry Renger. The gist is to work the crank, not the case. Use sandpaper, not polishing paste.

https://stunthanger.com/smf/12-a-building/what-the-heck-is-'hypereutectic-alminal'/msg197537/?topicseen#msg197537

https://stunthanger.com/smf/12-a-building/cub-and-other-engine-hop-up/msg33594/?topicseen#msg33594

Check post #19 by Mr. Chuck Matheny here:

https://stunthanger.com/smf/12-a-building/norvel-061-big-mig-for-semi-serious-st/msg676990/?topicseen#msg676990

Check deep in post #5, Mr. Carl Cisneros:

https://stunthanger.com/smf/engine-set-up-tips/rpm's-okay-first-rookie-rebuild/msg476073/?topicseen#msg476073


https://stunthanger.com/smf/12-a-building/norvel-revlite/msg204561/?topicseen#msg204561



My "on-forum" search terms were "crank" and "polish," and set to display individual messages, not topics
There are other threads. I'm doing the copy/paste between tabs and rubbing my crossed eyes. Ouch!

Please forgive me for not doing the whole copy/paste of all of the relevant hits. I'm keeping an eye on this one!

You have to decide if you are changing the fit of the bearing, or are cleaning up the crank surfaces.

To clean up the surfaces, I polish the cranks on plain-bearing engines with SemiChrome polish (Happich) or Flitz. They perform about the same. If you are using a drill press, then get a stick with a good flat surface and "charge" it with the polish and use the stick to get where you want to go. The polishing removes very, very little material when used on steel. So you are cleaning off tarnish (or rust if the engine was REALLY neglected) and the peaks left behind by machining processes that probably should have been smoother. Using rags for polishing on any powered equipment (drill press) is asking for trouble. You can do it until there is a mistake and the rag gets caught. Human reactions are nowhere near fast enough to avoid that carnage. If you insist, try taking a jersey material like a T-shirt and cutting a 1/4" wide strip around 8" long. Charge the strip in the middle with SemiChrome and then hold one end with one hand (index finger and thumb) and the other end with the other hand. Yes, it will roll up when you pull on it. That's not a problem--it is just how the stuff is woven. The little strip gives you control, and it avoids most (not all) of the risk of wadding up the whole project--and your hands--in the drill press.

I always polish the crank and run it again to see if the problem was the tarnish and manufacturing peaks, first. If that fixes it, then I'm done and did not do extra work with sandpaper to "prematurely wear it out."

Larry Renger was specifically checking shaft roundness using his "pinch" technique. With the tools available at Cox, he was able to convince himself that his polishing technique was maintaining roundness. That is important. But roundness isn't the only issue. The whole length of the journal should remain constant diameter to achieve a constant fit. If you have a more aggressive metal removal scheme than just the SemiChrome polish (ie. sandpaper) it is more difficult to work the length of the shaft equally. Nothing shocking about that logic. Keep in mind that one person's "gentle rework" with sandpaper may be very different from another person's that results in the removal of .005".

If you are trying to change the fit of the bearing, since you don't know (or state) the actual clearance fit you are trying to achieve, and since most people are not going to have inspection equipment anywhere near accurate enough to measure the bore properly, we are stuck using a "feel" criteria. All I can suggest is go slow, expect lots of iterations, or be sure to have a lot of spare parts. If it ran at all before, then you probably don't want to remove more than .001" if that much.... Before I even took it apart, I would probably try running some all-synthetic fuel thru it just to see if the crank and/or piston was all varnished up. A Cox engine will behave like your description. So will a Fox .35.

https://happich.de/en/products/simichrome-polish


https://www.walmart.com/ip/Simichrome-390050-All-Metal-Polish-Tube-1-76-oz/5229982330?wmlspartner=wlpa&selectedSellerId=101017072&adid=22222222222000000000&wmlspartner=wmtlabs&wl0=e&wl1=o&wl2=c&wl3=10352200394&wl4=pla-1103028060075:aud-821217196&wl5=79192&wl6=&wl7=&wl10=Walmart&wl11=Online&wl12=5229982330_10001036451&wl14=happich%20simichrome%20polish&veh=sem&gclid=36c068e0173c11269edf026811f7385d&gclsrc=3p.ds&msclkid=36c068e0173c11269edf026811f7385d

Man alive, you guys - ask here and ye shall most certainly receive! Jim, your Cyclops work beats my double eye approach by a long shot. Great search results and much to digest there from some guys really in the know.

Dave: I'm inclined to use your less aggressive Simichrome approach. The tolerances inherent in Larry Renger's skill level are well beyond my "shade tree mechanic" aptitude and tool selection. Appreciate your mention of the drill press caution. This hobby can be hard on the fingers and hands and we can't be too careful.

Much obliged to both you gents!

Dave Mo...

PS: I'll mix up a trial batch fuel sans castor oil and see if that makes any difference.
D...

Hmm..., I just finished a short run of the Norvel with synthetic only in the fuel mix (30-20); it again bogged down. I noticed that the cylinder was way too hot to touch after the short (10 seconds) run. The crank bearing, not hot at all. Not sure what to think other than I might have goofed up the break-in routine in that I used castor in the fuel at that time. I'll read up on what Jim's links above might suggest about a cylinder or piston problem.

Dave Mo...

Curly Moe,

Not sure you can blame yourself for a break-in procedure using castor as a cause of the problem. If you didn't blow the rod out or break the crank, then the worst the all-castor might do is varnish up the cylinder or the journal bearing. If the journal was not getting smoking hot, I wouldn't expect varnish. If you were able to run a fair amount of all-synthetic thru the engine, then that would also remove much of the varnish. So I don't see any reason to think that you goofed up much.

Not sure if you can see the piston very well, but I think it is time to take a very close look. In the best-fitted engines the OD of the piston at the top gets shiny when running in. It is the "wear band." The rest of the piston should have more clearance. You can get this if you taper the bore of the cylinder and use a "straight" piston. This is best case. Note that the head of the piston runs the hottest, and it expands the most. This effect is really minimized with the hypereutectoid aluminum piston material--but it is still there--probably about half. (Varies with alloy.) If the barrel and skirt of the piston have shiny spots BELOW THE WEAR BAND one option is to get out your 1500-grit paper glued to a very flat substrate and start lapping the piston by hand. (You can use a 1/4" wide strip of .062 aluminum cut like a popsicle stick, for example.) If you see sleeks on the piston, polish those to. But never the wear band. This is an extremely iterative process but it acknowledges the actual parts and the actual fitup, not a bunch of measurements. There was a pretty good writeup about the technique by Glen Lee(?) years ago in the magazine (probably pre-Model Aviation?) called "Tiger Tuning.)  As I recall, he was hand-fitting a SuperTigre .15 for a scale racer. But the techniques listed might be used if you really have too tight a piston fit and continued running won't loosen it up.

One of the problems with plating is controlling the thickness. Plating a bore with chrome you have to deal with the "throw" of the anode. With anodizing it is not a simple matter of a time-function to buildup. Anodize actually goes into the metal, converting it as you go to something akin chemically to sapphire--some kind of Al2-O3 base compound plus whatever "magic" that this particular engine maker decided on. And sapphire is dang hard. Which makes break-in dang hard if the fit is even just a bit too tight.

If you wanted to lap the bore, then you would need to make a tapered brass lap. You never use the piston. The best lap would be adjustable diameter. You start small, charge the lap and start to gently work the bore in a back-and-forth-while-round-and-round motion. Put a handle on the bottom of the lap to make this easy. The lap needs to be near-perfect shape because the bore won't end up any better than the lap. I've done crude versions of this on engines that were donated to me because they were "dogs." In some cases, the liner was buckled from mishandling and all I had to do was "bump out" the defect--usually near a port. Often because someone used the screwdriver-in-the-exhaust-port trick to try to jack out the stuck liner. These engines usually have the pliers marks on the liner flange, too. I have a Brian Gardener P/L set that I bought from someone here in the states that has the bottom of the liner pushed in from being dropped. I haven't messed with it yet because I didn't need it, but it is going to need some help.

If nothing on your engine is broken yet, you are doing ok. You just have a little farther to go. I'd look at the piston next to try to understand the wear pattern.

Good Luck!

The Divot

Yup! Inspect the top end. I remember my NorVel .074s being absolute beasts in the early runs. They were well-behaved after quite a long break-in.

I'm curious, so I may have missed this one:

How many head gaskets?

Can you try a Cox "normal-compression" glow head (same threads)?

Are you running the engine rich, or leaned out to max rpm? Or, somewhere just fat (rich) off of the lean run?

Ah, ask and I shall receive!

To the Hullmeister: a capital suggestion on the wear band. Also am glad to hear that I've not likely deep-sized this engine yet.

Jim: One standard head gasket. Yes, I ran it some time ago with the Cox head and it did all right. You might have a point on needle stinginess. This mill is such a beast to clear out when flooded, so I might be erring too much on the side of caution.

Will return here with results.

The not so curly Moe...

Advertise Here