Merco .61???

LAST EDITED ON Oct-22-03 AT 04:50 PM (CDT)
 
Hello Gang!,

' just got delivery of an Old Merco .61 single glow plug (cast iron, baffled, ringed R/C version)in near mint condition.

Anyone have any info on these old puppies? Fuel to use, Power output, Venturi size? I've got ST 60 NVAs for it.

I Figure it will go on a Sig Magnum.

As always any and all input is greatly appreciated!

Many Thanks and Nitro Fumes!........Hib

Yo, Hib, congrats!! <-- me, green with jealousy...

Tim

I've just measured a venturi from a Merco 61SS which we put out a few years ago. The venturi measures 0.284 and the spraybar hole measures 0.165.
As a matter of interest, what is the spigot dia. of your venturi? Earlier Mercos had 3/8", a later one measures 0.4275. This came in the search for more power for the radio boys.

If anyone is keen I can look out for these motors at swap meets here. Price would be $66 + post. Let me know and I can make a "waiting" list.

Mr. John Wright is the "MERCO MAN"

Yes, I have a lot of experience with Merco's. A .300 venturi with a ST spray bar (.155) is a good starting point. Should take about 6 oz of 10% nitro, 20%oil. Frank Williams cautioned me about using more oil because the Merco runs cool and can "flame out". I had that happen when I used 24%oil. A 13-5 or 6, 2 blade wood is also a good starting point.
The stock Merco will be a nice docile 4-2-4 stunt engine but only modest power. For more power take the engine apart, take the bearings out and "square off" the round intake hole in the case. This gives more intake area without altering the intake timing. I usually square only the bottom of the intake hole where it mates with the shaft. The top is left round to hold the venturi insert. This is a very difficult proceedure that I have done with a hand file.
Notice the construction of the Merco. It has a conventional sleeve but the case is two piece. A lower part holding the crank and bearings, and an upper part which is just alum fins. I have shaved .007 off one set of fins to lower both exhaust and intake timing. Another set of fins I shave .018 but no experience yet on that. And .018 will freeport the piston, so you need to have a new, longer piston made. Not for the faint of heart.
Beyond that I had some of mine bored out to about .63 or .64 cid. The power is definitely improved with this mod. I run a 12.5-5.5 3 blade Mejilik prop on that one.
By the way, I prefer the early (60's) light weight crankcase casting, but if you have the later, heavier case, you can shave some weight off with a hand file if your careful. Or your can interchange shafts, pistons and sleeves on either the light or heavy cases.
Let us know how yours works.

Interesting. I didn't know Tomas made Stunt size props (just RC giant scale sized stuff, other than the Russian Combat and Racing stuff).

When Tom Dixon was importing these in the mid 80's he ran them on 23% 50/50 lube. The power was supposed to be comparable to the Tigre 60.

Too bad you don't have the control line version from the early 90's which were based on the work of Scott Bair designed for high torque and large props. They had a plug in the rear slanted backwards.

I have 2 of the 61 rear plug Mercos
Ran them on 25% all castor 12-6 bolly ,5% nitro as delivered
from merco for control line use.
In 64oz. magnum
Set up was better than I was.

Dale Barry has a Merco in his Icarius ; Flies it at contests likes it as a back up to his nats contenting planes.

Excellent info!...many, many thanks!

Mine has a quite large case port(spigot?)at the shaft port best I can read with a caliper is .409".

John O., thanks for all the specifics... are you running 20% all castor? Does the .007" shave off the bottom, no doubt, give enough increase in power that it's worth the effort...also, what does it do to the 4-2-4 break? I like a good old classic definate (hard) break both up and down.

The intake "squaring" reminds me of the trend 30 years ago of needle filing the venturies of Fox 36x(s) till they we paper thin to get max induction. It might be a good mod for flying here at 5600'msl.

If Tom Dixon was the importer I'll bet he's a good source for venturies, as he probably has a few of these motors around... I'll give him a call.

Once again thanks to all of you!

Cyber Information and Nitro Fumes!........Hib

Hib,

You might also talk to Dave Royer. He has the sweetest running Merco .61 on a very large Super Chief. I love the sound of that engine and it is a very cool plane.

To answer a few more questions.
I use 10% castor and 10% klotz oil. All castor would eventually gum up the ring but 15% castor and 5% Klotz would probably work.

I shaved .007 off the bottom of the fins because the threads for the headbolts are on the top. This fin shaving doesn't increase the power, it just lowers the rpm where you get the power. I run about 7800 rpm with a 13-6 wood 2 blade, 8400 with a 12.5-5.5 Mejilik 3 blade.

I'll give credit to a 1956 MAN article by the late George Mohr. He modified the intake of a Fox 29 stunt for team racing. He also chopped the sleeve but I don't recommend that. I followed the similar proceedure for the Merco 61. I also tried it in a Fox 35 but have yet to see any significant benefit.

For a venturi, I cut a piece from 5/16 brass tube. Then I drill and tap 10-32 into one side and thread an Enya 60 R/C angled spray spigot into the side. You can adjust the spigot in or out as need be for different field altitudes. Also, the needle is outboard, and I don't burn my fingers on the muffler.

Hope this helps. Happy Landings

Some time back I got a Merco from the 'bay.

Ad claimed it was set up for stunt 'by an expert'.

All I know about it is in the photos below.

Can anyone tell me anything else?

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Would this benefit from a Supertigre NVA, or is it best left alone?

At one point I did a weight/displacement comparison of all the engines I had at the time. This was either the heaviest or second heaviest of the lot.

My plan is to install it in a Super Chief.

Dave R's Super Chief was originally powered with the Merco .49. That engine wore out and was replaced with the .61. He claims it to be too much power for the plane, but having seen it fly at 70',it seems to be a great flyer. I love this plane for it's simple elegance, ease of constuction, and the way it flys. I had one framed up and when the earthquake hit Olympia, WA four of my projects were crushed. It took a lot of wind out of my sails. The plane is close to being repaired and will hit the circles this next season. Jim J

What I actually meant to communicate was that the .49 was more than adequate power for my rendition of the big Chief with 715 sq. in wing at 56 oz. and that a .61 was not really needed. Too much power? I think not! I have a drawer full of Mercos, including N.I.B. .49s set up for stunt. There are no plans to put any of them in the Super Chief! The .49 worked beautifully but the .61 is almost a half ounce lighter and I definitely like the extra umph(technical term). As many have said, power is addictive.

Jim, glad to hear you're going to finish your Super Chief. It's a great way to sample the bigger ships with minimal investment and is quite capable. I love to have experts take a flight on mine and then watch the giant grin they get on their faces. I'm sure you'll like it a lot. Feel free to inquire further into my experience with this ship if you like.

Dave,

As I noted, I love this plane. It presents very well in the air, though you try to scare the snot out of me with it on occasion. I may hit you up for the plans.

Hiyer Cyber Flyer. I am gradually accumulating info on the Merco engines, and anyone with definitive details of the various Marks etc. is most welcome to get in touch with me.
Among what I have ascertained so far is that the first Merco 61 was a small case variant, and had the same mounting holes as the ST61. I believe ST were chasing some of the Merco market! The Mk2 Merco 61 was still on the small case, and had the twin plug head. Your engine has the large case, so it must be Mk3 or later. It also has the integral steel cylinder/fins combined, and I think this will fix it as soon as I find out which model this is. I suspect it may be a Mk4. Is it a conventional ring, (one or two?) or a Dykes ring? That would fix it further.
For how far I've got with all this see under Merco on Dave Day's site, < www.iroquois.free-online.co.uk >.

Thanks for the info.

My engine has one ring, roughly 1/16th thick, just a shade less than that distance below the top of the piston. Hope that helps.

I was wondering if the twin plug head was an aftermarket add-on. I gather you are saying it was a factory option. The exaust openings in the liner are smaller than the exhaust port in the case and are positioned up towards the top of the cylinder. Is that normal?

Not having any Mercos to compare with (not ever having seen another Merco), I can't say what kind of case it is. But from the heft of it, I'd say it is a heavier rather than lighter case.

As an aside, when I got the engine it spun freely, no play whatsoever. I don't get that this engine has been run much, if anything more than a test after assembly. I filled the venturi full of After Run oil and flipped it around a bunch of times to work the oil everywhere. Then I wrapped it in Kling-wrap, a couple of sheets of paper towel and finally some bubble wrap to store it until I got a plane to put it in.

When I took it out of the box to check it for this thread, I noticed that there is an odd little rumbling when you turn the crank by hand. It's as if there are a bunch of detents that it is turning over. The shaft does not turn smoothly, rather ripples over a bunch of little stops. I'm wondering if the After Run oil dried up in the ball bearings and is just presenting a little stiction that will go away when I put some fuel through the engine and break it in, or if the bearings have somehow rusted or worse.

Any thoughts?

I also note that I can turn the engine through compression with my thumb and fingers on the back of the prop drive shroud, something I can't do on, say, my SuperTigre .60's. Is this a symptom that the ring is not seated? Could that be because it has not broken in yet? Or is this a bad thing, indicating the engine is weak? The cylinder walls and piston that I can see through the exhaust port are all clean and shiny with a thin film of After Run oil on them.

The .61 in my Super Chief did the same thing when I got it used 7 or 8 years ago. It's still going strong. When some fuel gets sloshed around in those bearings they'll most likely free right up. Mine did.

The picture of that twin plug Merco is one of the later, heavier cases. I think the twin plug is factory, not after market. Also, the dark fins are probably the steel fin model, very heavy. If you have any others, you can swap parts and come out with one good stunt engine, and one "R/C" engine.

My preference is to use a Dykes ring piston taken from a steelfin engine, put it into an early light case, along with the sleeve and separate alum fins of the early engine. I have found that the Dykes rings gives a tad more power. Then put the compression ring piston in the steelfin sleeve in the heavy case. Use the light case for stunt and sell the heavy one!

John Wright's wheeze of putting a dykes ring in an early light case 61 sounds absolutely great. This will have good stunt timing and good power characteristics. Just didn't think of it myself. I now have to look out for a dykes ring Merco at a swap meet!
I do have an original machined sand cast Mk1 case, and intend to build it into an engine some time. John's trick will be very hard to resist, but I suppose it really should use parts as original.

Have done a little more digging. The single ring Merco 61 and 49 also came about in seeking more power (less ring drag) for the radio boys. When we put the 61SS into production, the one with the single rear plug, the other partner allowed me all the other mods for stunt, but insisted on reverting to 2 rings, "the stunt boys definitely prefer two rings. They like the extra compression". But ST's get some super comp with their single ring?
I think Cyber's illustrated may be a Mk.3. Doesn't it look great? Looks as if it's possibly not been mounted. With the all steel fins/cylinder it probably is the heaviest Merco 61 of all. The twin plug head is a follow on from the small case Mk2, and I'm suspecting the dykes ring engine will prove to be the Mk4. The twin plug was standard on the Mk2. I think the lumpy bearings will prove to be congealed oil, I have experienced this a couple of times. But will do no harm just to check for rust
Another changeover for the benefit of the radio guys was the increase in exhaust timing and port size. I've done some measuring today. The original Mk.1 and 2 had 0.186 square ports. The larger ones were enlarged to 0.215.
Of course, parts of most mks. are interchangeable, but I do have an old large case engine with the small ports.

Another hint for Merco 61, or any engine with two rings.
When installing new rings, just replace the top one. Clean the grove for the lower one but leave the old ring in. It won't have as much friction as a new one. And the new top ring will be enough to get top performance from the engine.

The posts above don't make me feel too good about this engine. The good news is that it is very near new. If it's been mounted, I can's see any marks.

But I gather I have the heavy case, the steel fins, the small exhaust ports and the single ring piston least perferred for Stunt. Well, at least it has a nice teflon venturi.

I got curious and decided to see how chunky this big Merco iron really was.

I weighed one of my Tom Lay ST V.60's and found it to be 11.915 oz. I weighed a second one just to compare and it came in at 12.290, although that included a very short exhaust extension for a muffler.

Then the mystery Merco went on the scales.

Turns out it, too is 12.290 oz.

Exactly the same as the heavier of my Tigres.

Which makes me feel better.

A magnet will tell you if the fins are steel. But at 12.29 oz they are probably alum. As for the crank case, it would easy enough to cut and file some of the weight off, without altering the internals. My lightest Merco 61 is 320 gm, no venturi. My lightest ST 60 is also about 320 gm. Sorry, I can't find my calculator to do the conversion.
From the sound of things, I think you got yourself a good stunt engine.

I've gotten to the point that I don't even think twice when it comes time to find some information of any form--I just go to Google, knowing that (a) if it exists, someone, somewhere has put up a web page about it and (b) Mr. Google knows where all the web pages are. You really only need one bookmark any more.

Unit conversion is a simple thing to do, so there must be some javascript out there for an interface to the forumla,

Thus, a search for "conversion grams ounces" on Google leads me to this tasty site:

http://www.gourmetsleuth.com/gram_calc.htm

320 grams turns out to equal 11.24 ounces.

In your terms, John, my lighter Supertigre weighs 339.22 grams.

The heavier Supertigre and the mystery Merco weigh 349.896 grams.

All of that from the same browser that brings you the Stuka Stunt Forum.

On more truffle of information is that my heavy Merco weighs 29.896 grams, or 1.05 ounces, more than your lightest Merco.

An ounce here, an ounce there--as the man said--sooner or later it adds up to real weight.

I'm thinking I'll just build a stock CLC Super Chief kit as light as I can, maybe put on a set of Carbon Fiber gear instead of the metal ones and go flying.

I got the Merco because a lot of stories claimed it was a good stunt engine and I suspect putting it in a Super Chief will result in more airplane than I know how to fly.

Cyber, I notice something I omitted every time I look at these sites. Your query re. turning by finger probably indicates the motor is not run in, and therefor the ring is not bedded in yet. A period of alternate lean 4 stroking and pinching the fuel line to get bursts of rich two stroking, will probably result in good compression.
One thing which has been mentioned before concerniong weight is the way we strive for the lightest motor possible, then suddenly heavy 4-strokes arrive and we can accommodate them! Whatever your Merco weighs it should make a fine stunt engine.