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RE: MT70CC TWIN - 8/30/2012 3:43 PM   
closetguy


 

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Status: offline 		it's amazing the demand for a good 60-70cc twin,even when they are out of production and parts are not around,guy's still will buy them.
good to hear you sold your engine it was a good deal,for someone.

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RE: MT70CC TWIN - 8/30/2012 5:39 PM   
Super08



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Status: offline 		Xoar 22x10 at 6100 is very poor performance. A DLE55 turns one at about 6800.

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RE: MT70CC TWIN - 8/30/2012 9:49 PM   
unit53


 

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Status: offline 		For what i paid,, to put this thing back together,,and to buy the carcass from someone who pretty much got burnt,,its  probably not a great value  only due to the brand,,,,but i am greatful to the seller,, this is why i ,elected to just tap out the stripped threads instead of investing time and money for helicoils,,or even using the prototype case i still have,because of work i havent attempted to start it up and still need to  finish setting it up to test,,,heck it  may blow the other cylinder off,,,im actually thinking it will be fine,,i also think  the ones doing low rpms may be one of those with dragging parts,or a combination of all the faults found on mt engines  my 70 standard plug engine does over 7k  with a 23x8 also running coleman pure white gas with none of that ethanol or octane thats designed for 4 stroke automobiles wil;l boost output and smell nice doing it.

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RE: MT70CC TWIN - 8/31/2012 2:04 AM   
Super08



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Status: offline 		That is more like what it should be turning. A 23x8 or a 22x10 have a similar load.

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RE: MT70CC TWIN - 8/31/2012 2:49 AM   
unit53


 

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Status: offline 		I also would speculate  that its possible the grade of fuel and altitude and not looking for peak rpms  on the ground,,even  restrictive fuel lines could  be causing the lower than expected rpms,, usually  modellers  flying twins,,will richen  to match  the  best setting on the weaker or slower engine ,,especially with glow engines ,,but if i had one doing several hundred  more than the other ,,i think ,i might  have the weak one checked ,,,and back to fuel ,,ive read a few say,,use good clean premium fuel,,,,,i suggest   regular non additive especially ethanol,,   or coleman fuel  ,,,,,good sized tight fuel connections and  a oversize filter if using one,,also many gassers get junk in the inner carb screen when breaking in,,and that alone can count for a few hundred rpms loss as well as plug type,, gap,,timing  even an inferior ignition battery will cause losses in rpms

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RE: MT70CC TWIN - 8/31/2012 3:06 PM   
capitalB


 

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Status: offline 		Mine has been flawless so-far. I got about 20-gallons through it. What the problem you have is a torquey engine that is not meant to spin the props at the speed of sound! WE have all met the guy with a O.S 160 that will only top-out about 9200rpms, constant complaining and telling everyone how big a piece of crap it is. It is a lot of fun for us he works for some big ass, enginern, company! (He runs a APC 10-6 from his trainer days, and says the math he does with the H.P. rating of the O.S, he should be getting 17000+, no tellin' him otherwise! Last thing on the MT-70, alot of them (50%?) had the reeds installed upside-down with sealing read valve ABOVE the stiffener reed. If your engine has this, correct it and bump timing up a few degrees at a time. you will be amazed at the improvements as this engine gets kinda scary-powerful. By-the-way I run only 23" or 24" props.. Sorry to have carried on so long, Brian

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RE: MT70CC TWIN - 8/31/2012 6:20 PM   
unit53


 

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Status: offline 		I agree with your assesment,,brian,,i cant think or speak for  the manufacturer,,and  dont know for sure but the engine was  targeted twards aerobatic flying,,and top end rpms  arent as important to me as accelleration midrange  transition starting and  realibility,,ill gladly trade a few hundred rpms ,,for  performance in the forementioned  aereas.

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RE: MT70CC TWIN - 8/31/2012 6:53 PM   
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Status: offline 		Interesting post Brian I did plan to check out the reed blocks when I rering both of them this winter. Frank the ring guy suggested I do this when I do the job for the same reason you stated. The ignition is 28 degrees BTC on both and I have heard of people going as far as 34 degrees to get more steam. Right now I can get about 6300 rpm if I really tweak the mixture, but with a big twin I really need reiability over a rip snorter. As previously stated they have been running good for a year and a half now with no indications of failure.l

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RE: MT70CC TWIN - 8/31/2012 8:59 PM   
capitalB


 

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Status: offline 		I checked my static timing today and I am about 33-34 degrees B.T.C. Make sure you listen for detonation, as of all the conditions out there that can affect max timing

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RE: MT70CC TWIN - 8/31/2012 9:23 PM   
unit53


 

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Status: offline 		 also try to avoid  high octane and  ethanol fuels,,ive been educated on using  octane,, yes it prevents detonation,,,pre ignition,,,but in our little low compression two strokes, lees agressive timing will prevent detonation.we are all aware of squeezing every  last  bit of power can  damage an allready less than perfect engine and the trade off is bigger displacement with the weight gain .or spending 3 times as much for a mintor high quality engine,, a little attention to things like  cleaning up rough casting in the cylinder ports when  re ringing may  help  performance as well

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RE: MT70CC TWIN - 8/31/2012 10:37 PM   
capitalB


 

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Status: offline 		There is a big difference between pre-ignition and detonation. Pre-ignition is just that...the spark plug fires way too soon after B.D.C, causing the rapidly expanding fuel charge to reach its maximum P.S.I. before the piston reaches T.D.C. Engine mechanical related detonation can be caused by many things, such as too much compression, port timing issues, hot spots in the cylinder and to much load (Bigger prop then it was rated to turn.) Now this is the part that I spent my 2-cts discussing. High octane does NOT mean more energy content, or power output. In fact in most of engines not designed for it (probably 95%.) I don't care if is 2 or 4 stoke, in a car, boat, motorcycle, big, small, Asian or American. I find it odd that people will spend up to 40 cents more for "premium" gas, when the car they are putting it in will have less power, and lower gas mileage. It's says Premium, so it MUST be better! Back in the early day of getting my degree, One of my profs. had a very interesting way of demonstrating this on a special engine that turned very slowly with a clear plexiglass cylinder. He would run the engine with the room lights on, so we could all HEAR the sound of detonation, then he turned off the lights and all of the questions that we had and did not at the time were answered instantly.You can win any discussion on premium fuel this way: Octane is the rating which the fuel will self ignite (think diesel) So engines with high cylinder pressures, such as turbos and compression ratios of over approx. 10.5-1, high octane fuel is need to control the maximum cylinder pressure that it can take be for lighting up on its own without and ignition source (spark plug.)
So where in I going with all of this? Octane additives can be thought of as candle wax added to slow the burn rate and raise the maximum cylinder pressure before it burns on it's own. Now you can see why in MOST engines you loose power as the don't need, or want octane higher then a true 87! Sorry to get carried away, but I love to hear myself talk!! Brian

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RE: MT70CC TWIN - 8/31/2012 11:33 PM   
unit53


 

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Status: offline 		 agreed,, octane is a long chained alkyloid that  slows or retards COMBUSTION and  is supposed to help prevent detonation
+due to exactly what was mentioned,,i found out by being corrected a while back,,and from my broither who actually designs and operates hydrocracker units

< Message edited by unit53 -- 9/1/2012 10:54 AM >

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RE: MT70CC TWIN - 9/2/2012 1:40 AM   
unit53


 

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Status: offline 		Well i have come to the conclusion  that either the previous owner got a double whammy ,,because after  starting this thing up ,,discovered  the  engine way out of balance with a bent  crank or output  shaft,,from what i was told the engine had never been in a plane,,and  either it got damaged in shipping,or sold defective,,and i am a personal witness to this condition coming from mt,, the 57 i had was rediculously out of center ,,the box i recieved  was in perfect condition,,and would have expected a  big old gash or smash mark to justify that this occured  when sent to me,,,Now my options would be to use the prototype case ,,which i dont trust,,or to see if valleyview has parts ,,i do not think i can scavenge parts from the proto case because i was told the crank is different.I also cannot say for sure  even a real unbalanced engine would  have popped the cylinder,,and could have added or hastened   the  failure but  still believe  crappy assembly and  machine work was the main cause ,If I had have gotten screwed that badly ,,plane crazee,s complaints would have been considered rather mild in comparison to ,what i would have said...

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RE: MT70CC TWIN - 9/2/2012 2:49 AM   
capitalB


 

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Status: offline 		Amen! WE should all be ashamed just to save a buck or two. I have hear that if US citizens would pay just 1-2% more, the Chinese could not compete. I for one am sick of buying a product that used to last a lifetime and get handed down, now to last a yr or less just to buy a new one and "Throw-away" the old one. If the parts available at all, they cost more than the unit new. I am sure you all know about the brand name game they play......"Sorry no parts available, no sell anymore. Tractor supply had my exact compressor for sale (different color and name) bragging about it's great warranty. So I took the serial# and model # down .and called the warranty line. I never got thru to any human, but I was told by a strong Indian voice the the model was too new or obsolete, no warranty, no parts! Just like all those cheap dirt-bike, scooter, go carts ect., no parts, BUT, Honda OEM parts fit perfectly. The Chinese, like the Russians, have no problem copying and producing other peoples engineering. Soon China will have to normalize it's currency to the standards of all other nations and then, BOOM, GAME-OVER!

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RE: MT70CC TWIN - 9/2/2012 3:21 AM   
unit53


 

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Status: offline 		 i think this is how the  dealers got screwed,,  they would buy a pallet of engines,,then wind up dissasembling  half of them,,for  repairs, because they didnt get many spare parts to start off,and all their spare time is spent correcting defects,,,i read in f.g. forum and this was tommys post ,on how he was going to personally reject any defective parts  assemble and test every engine before shipping  and fully cooperate with and support his dealers,,and all this was said after  several pleas to do just that ,,and this was before the 70 was even  put on the market,,,as  of this current date absolutely nothing has happened ,,even worse  mr. shen has seemed to have dissapeared...and has made people associated with him  ashamed to speak up...sad commentary here...

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RE: MT70CC TWIN - 9/4/2012 2:11 AM   
unit53


 

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Status: offline 		Today i found time to tinker,, when i discovered the bent crank ,i had to decide whether i wanted to  see if a crank was available,,what i decided to do was seperate the front and back case  flanges on the prototype case ,,which leaked like a sieve and i had given up on,,coated all mating surfaces with rtv and let set ,,i also filled in this weird  spot that tommy had filled with a silicone  piece with jb weld and   shaped to look like it was made into the engine,,,instead of using the studs and nuts tommy suggested,,i found socket head  allen bolts and had to grind the heads to allow clearance against the cylinders,and found lock washers to fit,,i carefully assembled using  used gaskets and sealer on the cylinders ,,made a  reed block gasket and used blue locktite on all bolts ,,cleaned up the plugs  installed and the same with the sensor for timing ,i found this setup  nice and smooth and not draggy ,,so i mounted the thing and  to my surprise ,it didnt run too bad considering i still need to final set the timing and and carb  which may have stiff parts due to additive type fuel and sitting up,,i used my rcexl tach and saw 7.6 k this is with a vess 22a  open exhaust  setup,,i will be using a 23 to 24  prop once in satisfied ,,,,i think i know how the crank got bent ,,,this is my best guess ,,,the previous owner got so frustrated ,,he unbolted the junk from his test bench and threw it in the corner.......i bet if he reads this post  hes grinning and saying thats exactly what happened...so   far no case leaks runs reasonably good ,,, not draggy ,,compression seens reasonable ,, rings need to set,,,even the one plug i pulled  had a nice tan look,,will be using safety wire over the plug caps ,,one popped off and the engine continued to run on one plug,,we all know what that would have done to my radio,in the air.maybe i will  see if anyone else  has a 70 they have given up on,,i dont know if my concience would allow me to fix then and sell on ebay ,,but they will be ok for personal use.

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RE: MT70CC TWIN - 9/7/2012 8:30 AM   
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Status: offline 		I think deep down, you love MT engines

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RE: MT70CC TWIN - 9/7/2012 12:16 PM   
closetguy


 

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Status: offline 		no he just refuses to give up.

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RE: MT70CC TWIN - 9/7/2012 6:29 PM   
unit53


 

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Status: offline 		Let me speak for myself here,,, im definitely  not in love with  mt engines,,,its more like regret ,,not with the engine,,but in how  it never  panned out  as far as a company ,,,,but there may be a surprise on the horizon,,,we all know whan the engines are  good   thats just what they are,,,,,,,and when bad and no support  and the manufacturer dosent listen to his dealers or customers,,we all are  aware of that outcome....yes i could   put  my remaining mt  products in the scrap pile ,,but   i currently have 2 great running 70 s that  suit my  flying style and needs ,,and im going to keep em running ,,more will be revealed in regards to  revival of this engine line,, from  who assembles how they are assembled  who sell s them and how the end user gets treated,,and   a certain individual  wont have anything to do with this as not to interfere with anything besides the actual design and nothing else. bottom line ,,ive given up one the guy who put them out but not the engined i own,,and as far as the enigines ,,,yes id like to see them  introduced correctly and done right..otherwise when my  junk gets crashed or  worn out ,,that will be the end 


< Message edited by unit53 -- 9/7/2012 7:07 PM >

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RE: MT70CC TWIN - 9/7/2012 6:55 PM   
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quote:

ORIGINAL: capitalB

There is a big difference between pre-ignition and detonation. Pre-ignition is just that...the spark plug fires way too soon after B.D.C, causing the rapidly expanding fuel charge to reach its maximum P.S.I. before the piston reaches T.D.C. Engine mechanical related detonation can be caused by many things, such as too much compression, port timing issues, hot spots in the cylinder and to much load (Bigger prop then it was rated to turn.) Now this is the part that I spent my 2-cts discussing. High octane does NOT mean more energy content, or power output. In fact in most of engines not designed for it (probably 95%.) I don't care if is 2 or 4 stoke, in a car, boat, motorcycle, big, small, Asian or American. I find it odd that people will spend up to 40 cents more for ''premium'' gas, when the car they are putting it in will have less power, and lower gas mileage. It's says Premium, so it MUST be better! Back in the early day of getting my degree, One of my profs. had a very interesting way of demonstrating this on a special engine that turned very slowly with a clear plexiglass cylinder. He would run the engine with the room lights on, so we could all HEAR the sound of detonation, then he turned off the lights and all of the questions that we had and did not at the time were answered instantly.You can win any discussion on premium fuel this way: Octane is the rating which the fuel will self ignite (think diesel) So engines with high cylinder pressures, such as turbos and compression ratios of over approx. 10.5-1, high octane fuel is need to control the maximum cylinder pressure that it can take be for lighting up on its own without and ignition source (spark plug.)
So where in I going with all of this? Octane additives can be thought of as candle wax added to slow the burn rate and raise the maximum cylinder pressure before it burns on it's own. Now you can see why in MOST engines you loose power as the don't need, or want octane higher then a true 87! Sorry to get carried away, but I love to hear myself talk!! Brian



+1
So many people think if they run 110 race gas that their engine will run better. i think all new car/truck engines have knock sensors to prevent this and some may retard timing some but the power difference is very little from 92-95 pump gas. I think all the car MFG's work for the oil companys lol because they say only run premium fuel. heck even lawn mowers and weed wackers with 7-1 computed ratios.

If you have low compression 11.5-1 or less and running high octane fuel you will lose power in the long run as carbon will build up faster in the exhuast ports or so i have read. In my quad i run 13-1 computed compression ratio. i run 92 pump gas. the piston is over 4" in Dia. since pistons of this cant burn the fuel in the chamber fast enough at high rpm I run three spark plugs per cylinder. i do this to burn all the fuel and reduce the negative torque... making more power. :-)

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RE: MT70CC TWIN - 9/7/2012 7:34 PM   
unit53


 

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Status: offline 		 I had to laugh at one review on the hk site ,,where this guy was so happy with how his new  hobby king engine ran with 20 to 1  oil to fuel rtatio and using the  best premium grade fuel ,,he claimed the high octane  really made his engine run well...i can bet if he used  the correct oil to correct fuel he may have,,,,,,,,passed out from the thrust ,if  what he had impressed him.in the first place.

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RE: MT70CC TWIN - 9/7/2012 8:26 PM   
capitalB


 

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Status: offline 		You both are 100% correct. I can't even get my family and friends to believe it..Don't get a oil thread started (YIKES!), but, all synthetic oil should be mixed at the ratio it was made for. (kinda like laundry detergent concentration) they all ain't the same. In all my years racing M.X. I used Bell-Ray at 70-1, never had a oil issue and could run all year on one plug. One time I had my girlfriend, get gas for me, and it ended up a 40-1ish. I fouled a plug in 2 laps (practice thank God!)

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RE: MT70CC TWIN - 9/7/2012 9:52 PM   
unit53


 

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Status: offline 		allmost the same analogy could be used for engines,,,,,the 2 stroke  engine isnt a new invention,,nor is the concept of quality or customer satisfaction,,just follow the dierections,but dont change whats proven to work,just do it right,,i read a post from someone who bought a plane from craigslist and got mad at the manufacturer when  it fell apart,,apparently  someone didnt follow instructions,,,but blamed the wrong people for his loss.when we make mistakes we are better off  owning our shortcomings and learning from them




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RE: MT70CC TWIN - 9/8/2012 12:05 AM   
capitalB


 

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Status: offline 		I have always laughed inside at the 40yr old CEO can't tune a engine with 3 moving parts. He looks down at the 22yr old auto-tech, who deals with more technology on a daily basis, then the Space-Shuttle techs (Trust me I know some of them) Not to mention the 22 tr old British Kid, who, under the Blitz, can keep a Rolls-Royce V-16 running happily..

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RE: MT70CC TWIN - 10/24/2012 12:57 PM   
capitalB


 

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Status: offline 		I need both bearings, gaskets and cir-clips for the pistons. Any suggestions, Brian

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