I started up my new Evolution .61 on 5% nitro and ran it for a few minutes. The engine idles well but stumbles a bit toward full throttle. The engine manual recommends 10-15% nitro and adjusting the "Setright bar" for leaner mixture when rapid acceleration stumbles. Would the nitro content throw off the acceleration? Also, does it matter how much oil content is in the fuel? My LHS carries 15% nitro with 3 different oil percentages.

These engines take a little bit of running to finish breaking in. The liners are chrome and the ones I've seen have a tight pinch at the top, so they need a little running time. My advice would be to burn a couple of tanks of fuel on the ground, or on a test stand before final tuning and flying. I've only seen them run on 15% nitro.

Stumbling or dying could be a sign that your low speed needle valve is a little rich. Also, it is a good idea to replace the glow plug after you break an engine in. These engines don't require a whole lot of time doing that, but you may find that either a Saito SS plug or Towers plug will fix this symptom. The OS 8 plug is too cold for 3 other sizes of Evolution engines that I've seen. I have a friend who is using the SS plug in his .61 without any problems.

I make the first runs of an engine on a test stand.

I use old fuel to break an engine in. I put a little castor oil in the old fuel.

If the engine quits because of old fuel, its no big deal, You are not flying the plane. Just keep the igniter on the glow plug.

I don't pay much attention to the Nitro. I don't buy anything beyond the 10% to 20% range anyway.

Anything in the 10-15% nitro and 18-20% oil range will work fine...I've got 5 Evo engines and they all run great on either Powermaster or Omega fuel. I like the H9 Super Plug that comes with the engine or a "warm" long reach plug.

It does sound like it is rich through the transition...and you might need to re-set the "Set-Right" collar to allow you to lean the low speed some more? We usually just eliminate the collars because they get in the way and are a PIA.

One thing Dar and I agree on is to use a fuel with 25% oil for running in. I prefer all castor but so long as there's a good proportion of castor then that's fine too. I'm fussy about running in because I want my engines to have the longest life possible, they're not throw-away items to me. Nitro when running in is a waste of money but it doesn't take all that much fuel to run in an engine so I'd suggest getting a fuel with the lowest nitro content you can find and fly out whatever remains. If you make your own fuel like I do then just knock up a quart or so of zero nitro and 25% oil.

Hey Downunder, you agree with Dar?
I too use up to 30% oil for that first run. Color me oldfashioned because The extra oil is castor. I use up any old batch of fuel I have around in the process, since performance is yet to come.
When the engine limbers up my curiosity wins, and I put good fuel in, together with a new plug, and lean out the d*** thing to best rpm, just long enough to get a tach reading. When satisfied with the thereafters, I go fly it, dive to screaming rpm, fly and dive again.

Just one suggestion: When a chromed engine has a good pinch when cold, you should get it up to running temp (rich side of peak) as soon as possible. Running cold puts undue stress on the rotating parts. By quickly bringing it up to operating temp, the conrod, etc. will break-in smoother, with minimum wear. This will also slow down the wearing away of that pinch.

This is only valid for the first few minutes. After that, the rotating parts are worn in and it is what it is. Time to put it in a plane. I think most engines continue to break-in a bit for up to an hour of running time. After this time it should run stronger, smoother, and with better fuel economy than when first started. You might want to tweak some final carb adjustments at that time.

Of course this is only ONE way. There are others.

George

As a beginner you should use the 10 or 15% nitro. Makes engine tuning easier. Low nitro needs a leaner mixture so thats why the preset limit is not lean enough. I would add some oil for break in, but I don't think anything over 20 to 22% is necessary, unless you plan to keep that engine forever. My experiance is the first engines are never worn out, they get traded or crashed instead.

I found just the opposite. Running very rich and cold for 45 minutes the rod bush was polishing on the upper (load bearing) surface but the lower half still had all the original machining marks. The pinch (measured with a degree wheel) was also exactly the same as before I first started it. Just my observations .

When testing squeeking tight MVVS engines, I found it took very little heat to get the pinch out. This temperature is easily reached by an engine with rich needle settings. The pinch returns after about 5 minutes. I also do not see the need of lean running in for a true ABC engine.
For the record: MVVS uses a cylinder taper of 0.1mm (Novarossi uses 0.2mm)

Is that .1mm per meter?

No, over the total cylinder length.

I've noticed, on some engines, that the starting point of the pinch and the total amount of it can change just by holding the engine in your hand for a while, and letting your body heat soak in. (especially without a plug)

PĂ©,


The latest batches of MVVS ABC engines are CNC manufactured and are extremely uniform.

They do appear to have less pinch than some earlier engines... Some of those were almost impossible to hand-start.

It is likely that in new engines, the pinch will 'disappear' with a richer needle setting than was true of older MVVS engines, but I still don't subscribe to dumping so much fuel into the mixture that the engine will be run-in like a meehanite-steel P+L engine...

I never run any engine lean, just less rich and I always use 25% oil (castor added) for the break-in.

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I believe Brian and I agree on plenty of things, but you just don't read about them in the RCU engine fora...

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Back in the old days, when ABC was new and relatively rare, and before the manufacturers decreased the taper ratio by a good margin, running some ABC engines rich would break the crankpin. I've seen it myself, so I know that it did happen. Gradually, everyone making the engines (well, almost everyone) got their act together and backed off the pinch a bit, lessening the probability of suffering damage when ran rich. This is my theory and we are talking about averages over a large group of manufacturers and models.


Ed Cregger

I have a couple of early F-1 pylon engine piston / sleeve sets (K&B 6.5 and ST X40) that are so tight, that (when out of the engine, holding them in your hand) the piston will only go up to the bottom edge or mid way up the E. port before grabbing.
One ST X40 P/L I can only get the piston in half way or up to the wrist pin hole...the lower half of the skirt is hanging out the bottom of the sleeve. (that's the definition of "interference fit" aye!?)

I have measured for taper with a dial caliper, and get about half a thou...
(I'll admit that a dial caliper is perhaps not the most accurate, but it's all I have)

The right pinch is when the piston grabs just after closing the exhaust . (check with plug removed) Anything earlier will only increase friction without trapping more gasses. I like to take my diamond powder copper hone, and increase the piston play some more below the exhaust port edge, so in fact I have a two-taper bore. Power increase is significant in some cases.

@ Dar
Yes, MVVS did reduce pinch. Too many customers filed warranty claims, not knowing that the pinch is the benchmark of a good engine.
Early Irvines were so tight that they would ruin the connecting rod. Early MVVS were not far behind, but had much better rods.
I like to heat up new engines before the cold starts, until the fuel thinned oil film is capable of preventing piston grabbing. I never noticed any negative effect with 4-stroking running. When I stop an engine after a rich run, and check pinch, it is not there. It only returns when the engine gets quite cool again.