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Merco 61 Twin Plug Strip Down


Andy J
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On 02/01/2022 at 10:56, Engine Doctor said:

Hi Andy. Sorry missed that you had fitted a sealed bearing. Bearings g fit will only seal if its leaking around the outer race. 

Try the crankshaft in the bare case and check play in the case behind the front race. If this is excessive you can shrink the case to a snug fit around the shaft but you will need a lathe to make the tool. If play in too bad then only real solution is fit a bush or replacement. 

Good luck with renovation.

Took the engine apart yesterday and applied some lock-tight to the engine case and then reassembled the crank.  Engine seemed to draw fuel a bit easier when primed but still stops when the glow plug is removed.

Wondering if the caster oil based fuel has gone off as its possibly 5 to 7 years old.

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Yes do have plenty of synthetic oil based fuels purchased for my RCV engines but was recommended by my LMS to use the caster oil fuel when I first started playing around with the Merco 61. Perhaps he had a lot of old stock in his shop which nobody else would purchase! Did not know any better at the time as I was flying electric models then.  Did not give the fuel any thought as should have known better after spending weeks last summer cleaning up another old Merco of its burnt on residue.

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3 hours ago, Andy Joyce said:

Took the engine apart yesterday and applied some lock-tight to the engine case and then reassembled the crank.  Engine seemed to draw fuel a bit easier when primed but still stops when the glow plug is removed.

Wondering if the caster oil based fuel has gone off as its possibly 5 to 7 years old.

Andy, I had similar problems starting an engine a couple of months ago.  One of our members brought out his 'witches brew' for priming which had some petrol in it.  It certainly made the difference.  Merco instructions used to advise adding 5% petrol in normal 80/20 methanol/castor mix.

With regard to the age of fuel, the stuff I am using at the moment, I bought at a Sandown Show in 2003 (I wrote the date on the bottle at the time).  It works fine other than that particular occasion so I'm pretty sure the fuel is ok.  This one was a new unopened gallon of Southern Modelcraft Double Lube Hi with 5% nitro that had been stored in the dark since bought.
 

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Had another play today with the engine after blowing through the carb and changing the tank fuel line to a larger internal bore pipe. End result is the same with the engine stopping once the glow plug is removed.

The engine still needs to be primed through the exhaust port to start, so assume there is some form of pressure leak in the crank case which prevents fuel getting to the piston when turned over by hand.

Piston is I assume correctly orientated with the hole on its side facing towards the intake side of the crank case (if that makes sense). This places the protruding upper part on the top of the piston furthest away from the exhaust. Internal sleeve  ports appear in line with the exhaust so at BDC of the crank the top of the piston can be seen in the exhaust port.

 

 

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2 hours ago, Andy Joyce said:

after blowing through the carb

 

A preliminary tune can be achieved in both the high and low needle Andy

Is this what you did, barrel fully open, turn high needle steadily in and out until it just blows freely

Barrel to idle, blow until you just hear the hiss on opening the low needle.

 

This should have worked. The motor would be very near tuned and not rich.

If the motor is still too rich it could be flooding the plugs out.

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Denis, I never got to the position of achieving a preliminary tune. After allowing the motor to warm up for about 15 secs at a mid throttle setting removing the glow causes the motor to stop. Tried screwing in the needle to lean the mixture but the end result is the same. One thing I did note is that when screwing in the needle with the engine running that it seemed to have little effect on the revs.  Little reluctant to use full throttle at the moment as the engine had a new ring fitted so was trying to bed that in first. Will try letting it run for several minutes with the glow attached before attempting a tune at full throttle to see if that works.

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We are on cross purposes Andy.

The " blow tune " is powered by your breath .

No fuel to motor, no glow driver on the glow

 

You blow down a spare piece of tube and tune the high and low needle to a hiss noise that is heard.I

You screw in to stop the hiss

And screw out to just that point that the hiss is heard.

It works

 

This process just gives your carb a chance to deliver fuel.

 

Next is your pressure leak, and on your two stroke this can be anywhere from a pressure leaking tank, the fuel tubes, the motor back plate, the carb ' O " ring not pressed down upon the throat, the back plate gasket, the front bearing, crack in crankcase.

Rule out each one

 

Edited by Denis Watkins
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Well if I had, its been wrong ever since I owned the engine. Was second hand when I purchased it 50 odd years ago.

 

Tried again this afternoon to get it started but apart from the odd ignition could not get it to run. Double checked the glow and it certainly lights up so will proceed to try my starter next time I try to get it running.

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4 hours ago, Engine Doctor said:

Hi Andy. When you start the engine are you adjusting the mixture while the battery is connected?   ie adjusting it until the engine will run properly at WOT?

. Don't worry about the ring for a short test run but keep it just on the rich side. Does it still spit fuel out anywhere ?

Not at all sure if its still leaking fuel from the front bearing as could not get the engine to run long enough. As for adjusting the needle certainly it would have been with the glow connected as it does not run without.

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Piston crown deflector on engines left looking from the rear. Head fitted so deflector will "fit" in groove in head.

 

The holes in the piston skirt align with holes in cylinder sleeve.

 

Exhaust ports in cylinder sleeve "higher" than main transfer ports, which is deflector side of engine.

 

You have checked glow plug in an other engine and/or fitted/tried a new plug ?

 

Catalytic action between glow plug element ( platinum ) and methanol.

 

Idle bar plug ?

 

What fuel are you using ?

Edited by Rich Griff
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Yes did try a new plug Rich but no idea of its ID as it came out of a batch I spares I picked up as part of a another item purchase. The other plug of the pair fitted to the head is the original one I have had in the engine since I last used the engine in anger many years ago but it does still glow when power is applied.  Neither plug has an idle bar.

 

First fuel I used was Model Technics GX-5 which I think is caster oil based. Second fuel was Model Technics Tech Power 10.

 

Believe I have the internal piston sleeve positioned correctly with the exhaust cut outs higher than the intake but will double check once again.

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33 minutes ago, Andy Joyce said:

Yes did try a new plug Rich but no idea of its ID as it came out of a batch I spares I picked up as part of a another item purchase. The other plug of the pair fitted to the head is the original one I have had in the engine since I last used the engine in anger many years ago but it does still glow when power is applied.  Neither plug has an idle bar.

 

First fuel I used was Model Technics GX-5 which I think is caster oil based. Second fuel was Model Technics Tech Power 10.

 

Believe I have the internal piston sleeve positioned correctly with the exhaust cut outs higher than the intake but will double check once again.

Surely the exhaust port should be higher than the transfer (intake) port. Just remove the silencer off & have a look. If the cylinder sleeve is the wrong way round the top part of crankcase exhaust outlet will be obscured. 

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Any white deposits on/in the glow element ?

 

Glow plugs may glow when battery powered, but refused to run the engine when the battery is disconnected.

 

I have a Cox td 09 with a glowing glow plug which the engine will start with, and run, but remove the battery power and it dies. New glow plug and she runs with the battery disconnected.

 

There is a visible white deposit in the element coil of the bad plug.

 

That Cox glow head will be converted to the removable glow plug type. Had to alter an 049 head to accommodate a removable glow plug over 30 years ago due to necessity.

 

Dans model supplies only does Cox 049 parts sadly. Mecoa in USA do lots of Cox stuff but are UK unfriendly.

 

Exmodelengines and Cox international are more UK friendly but don't have everything I want for the TD09.

 

In the merco, check the cylinder sleeve orientation, info in above reply and parts picture.

 

Try a NEW glow plug, Enya no.3 perhaps, mt still do glow plugs ?

Edited by Rich Griff
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Well by chance I had an Enya 3 plug, so fitted that and changed back to the original fuel I purchased quite some years ago.

 

After several attempts to start it using my starter, finally got her running again and even managed to remove the glow this time.  Engine still leaks slightly from the front bearing so don't think I can do much about that but at least its running now and I was able to tune for max revs.

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  • 3 weeks later...

Andy, all this talk of twin plug Mercos inspired me to have a look at the twin plug 61 I picked up many years ago.  It was minus the carb,  the backplate screws and one cylinder head screw.  It was seized solid, and had clearly had some sort of grips on the prop driver at some time.  At least there are no signs of crash damage though, and both glowplugs work.

It took a number of attempts with lots of heat from the hot air gun, some automatic transmission fluid and glow fuel to get things to start moving, but eventually they did.
The next step will be to get it apart for thorough cleaning and in all probability, bearing replacement.  When I eventually was able to remove the backplate, the inside was reminiscent of opening a very old tin of golden syrup.  I'm guessing this engine has seen an awful lot of castor oil!

Questions I'm hoping you may be able to answer are:

  1. What threads is this engine likely to use?  I've tried what I think are M3 and 6BA, but neither seem to want to go in.  The only review which mentions these threads is the one on the late Premier-made Merco 61 which were M3, but I guess by the time they were made, older sizes of production taps may have been getting expensive or difficult to obain.
  2. What grade of bearings do you use?  The Sceptreflight review of the Mk1 says the original used an FBC (UK) 1/2x1 1/8 x 1/4 rear bearing and a Fafnir (UK) 8x22x7mm front one.  What would be appropriate bearings without going overboard on quality or price?
  3. Can you tell from the pictures which Mark mine is?  I'm guessing a Mk2 or a Mk3?
  4. How interchangable are the carburettors between the various Marks?  I'm likely to a have a Merco carb somewhere, but before I go rummaging it would be nice to know.

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Edited by Robin Colbourne
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