Moki/Mark G140RC rod failure

dieselcrazy

Well-Known Member
Here is the response that I got from Moki Motors. At the time of the response they did not know of the mixing of the two oils. What my concern is the 95 octane gas. I'm just running premium gas which here is 91 octane. Does 4 octane make that much difference in these little engines?

For certain, the 91 octane gasoline is posing a problem (in Europe the minimum is 95 octane), and will lead to pre-ignition, i.e. knocking and can cause a failure of the needle bearing. As stated in the instructions, the engine has been designed for 1:25 mixture (4% oil). Once run in, depending on the quality of the oil, and the running circumstances (load, temperature) the oil content can be lowered to 3%, but in this case you should closely observe engine temperature. staying with 4% means staying on the safe side. I can’t judge the quality of Morgan’s Cool Power, as this oil is not marketed in Europe – just make sure, it is really designed for gasoline engines! It is very unusual to have one oil for both fuels, as usually the ones that blend well with gasoline won’t blend with methanol and vice-versa – and Morgan claims its oil can serve both.
As far as the ignition timing is concerned: if you use the factory-supplied ignition, sensor and prop hub there is nothing you could do wrong. The only thing you can measure as a hobbyist is the static ignition timing, i.e. how many degrees before TDC does the magnet pass under the sensor. The 15° you measured are OK. The ignition itself (the CDI) will dynamically adjust the ignition timing based on a pre-programmed curve, firing late at low revs (easier start, no risk of kicking back), and advancing the ignition at higher revs. There is a little adjustment bandwidth by moving the sensor back and forth a little bit, this is to optimize engine behavior, but is not large enough to cause serious pre-ignition with knocking.
 
if i remember right in Europe they use the RON (research octane number ) and we use RON plus MON ( motor octane number ) divided by 2 to get the AKI (antiknock index ) , take their octane number and multiply it by 0.95 = AKI,,(98 RON Octane( Europe measure) x 0.95 = 93.1 AKI Octane (US measure) )
 

Tired Old Man

Staff member
That is correct. The difference between European and American premium grade gasoline is negligible. The problem here comes from mixing oils. There are many cases where a particular oil will not remain in solution with gasoline and others where two oils will form a barrier that prohibits mixing. Similar to water and oil where one or the other globs up depending on the quantities involved. The gas is not a part of the problem.
 

red7fifty

BadAss Member
TOM (Pat), what is your opinion on a BME .90 (SuperTiger on Gas with needle bearing Rod) on Redline 40:1 mix?
 

Tired Old Man

Staff member
40-1 is a little thin for an engine that turns really high RPM. 32-1 would be my minimum but I would be watching the color of the piston skirt to see if more might not be better. If the skirt starts going black from cooked on carbon I'd increase the oil even more. The BME 90 is a pretty good little engine.
 

dieselcrazy

Well-Known Member
UPDATE:
I purchase another rod and crankshaft from the left over stock that Hobby People had. Rebuilt the engine and six months later and about two gallons of fuel I noticed the what I thought the rod feeling a little slop in it. I pulled the front crankcase and sure enough the rod pin started showing signs of ware.

I contacted Moki again since this was twice now. I guess Moki has a new owner. After they requested a picture of the side of the crankcase he confirmed that the 2011 production 1.4 gas engine had a crankshaft pin issue. What the crude, it would have been nice if the other owner would have told me that. Said he was sending me another crankshaft but not sure about the rod. When I ask about the rod he didn't reply back, that was a couple of weeks ago and waiting.
 

dieselcrazy

Well-Known Member
Update, after a few additional emails and being patient Moki did send me a new rod and crankshaft. The new crankshaft has a pressed in hardened pin. Engine is now rebuilt but haven't ran it yet.
 

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red7fifty

BadAss Member
Wow, that took a WHILE to get sorted out!
Note to self.....that is the reason RC Flyers have Multiple Airplanes in the Hangar....Spares!
 
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