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MVVS 77 issues

Old 05-20-2022, 06:31 PM
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GoNavy
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Default MVVS 77 issues

I'm looking for help to diagnose, and then solve, two issues with my MVVS 77.
Have been breaking in a brand new MVVS 77, on test stand, test stand screwed tightly to solid deck, zero nitromethane, just 20% castor and methanol. Jtec pitts muffler.
Have run it with an 1, OS#8 plug, 2.the plug supplied with the engine and 3. the plug supplied with a differrent MVVS 77 I had. Now have run 1/3 of a gallon thru engine. Running to full throttle awhile, than down to reliable idle, then repeat. Reliable idle now about 2400 rpm, with little exhaust smoke; smokes up a cloud from about 6K to WOT, about 10K. Running APC 13 x 6, balanced to a fair thee well, tip to tip and across the hub.
Fuel line pinching indicates low needle is spot on, and high end is still a few clicks rich. Idle to WOT quite smooth, only slight hesitations. Generally smooth running EXCEPT around 2,800 rpm where it vibrates big time.
It displays the same strong vibrating with all three plugs, and with a 13 x 8 Zinger Pro, 12 x 6 Zinger Pro and 13 x 6 Zinger.
I can think of no other glow engine I have used that displays such serious vibration. I do hear what sounds like possible pre-ignition.
Oh, the weather has been between 60 and 75 degrees F, 50 -70% humidity, 1,500 feet ASL.
Hope there is a fix, thanks.
Old 05-21-2022, 03:54 AM
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1200SportsterRider
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The go to prop for the MVVS 77 is a 14 x 7, it is a torquer and will idle at 1,000 rpm when so equipped. I had an MVVS 61/LS, not officially called a long stroke but was one. I tried a 12 x 5 Grey Graupner, it shook a Bruce Tharpe Venture 60 like a rag doll. A 13 x 6 cured all of that.
Old 05-21-2022, 09:37 AM
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GoNavy
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Interesting... was the engine vibration spread out over a wide range of rpms, or did it occur only at one engine speed?
I dug through my 14 -16 inch prop box, but no 14 x7 so will order one.
The long stroke was the reason I wanted to try this engine. The MVVS instructions recommends 13 x 7, 13 x 9 or 14 x 7 but adds "(Use
lighter propellers with standard silencers so that the engine will be able to reach at least the RpM listed above.)" The minimum rpm is 10,000.
I won"t mind turning less than 10K if it solves the vibration.
Old 05-21-2022, 10:42 AM
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look at it this way, the Europeans love torque, while the Asians love High RPMs. I learned that from the Japanese and European dirt bikes of the 70s.
many people use 13 inch props on their OS 60s, so I can understand how the MVVS 77 would like a 14 inch prop. needless to say, that you may say your 77 is in the 80 size category.

I would love to have a MVVS 77, but I allready have more engines than I will fly.

Jim

Last edited by the Wasp; 05-21-2022 at 10:45 AM.
Old 05-22-2022, 12:08 PM
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jaka54
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Hi!
I have run several MVVS .90 engines , but no .77 and I have not experienced anything that you have described. All my MVVS .90 engines have run good with very easy starting , throttling and setting with no excessiv vibration at any rpm.
I have run them on both 20/80 fuel (castor oil) and on 15% syntetic (Motul "Micro") 5% nitro and 80% methanol, all with the same good behavior.
Glow plugs have been MVVS 5 (Which is a Nova Rossi plug) OS 8 and Enya 3.
Props have been small up to very large APC props (11x9, 12,7, 13x5, 13x6, 14x5W, 15x4W , 16x4W and 17x4W) all with the same good running characteristics.
Silencer used has been the new MVVS alu silencer.
I would recommend not using the small j'tec pitts style silencer as it has a too small volume that robs the engine of power.and could perhaps make carb setting more difficult.
My MVVS engines have all been equipped with the "new" MVVS 8mm carb that has a black high speed needle and a tapered idle needle. The old carb had a blunt idle needle and was a little more sensitive to set and gave a more "direct" throttle response (which is not as desirable).


Old 05-26-2022, 02:47 PM
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GoNavy
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Originally Posted by 1200SportsterRider
The go to prop for the MVVS 77 is a 14 x 7, it is a torquer and will idle at 1,000 rpm when so equipped. I had an MVVS 61/LS, not officially called a long stroke but was one. I tried a 12 x 5 Grey Graupner, it shook a Bruce Tharpe Venture 60 like a rag doll. A 13 x 6 cured all of that.
SportsterRider, I think you are on to something.........
I was still waiting for my 14 x 7 to arrive, so I did some prop load factors (14 x 14 x 7 = 1372 and 15 x 15 x 6 = 1350) and so I balanced a 15 x 6 and put it on the engine this afternoon, 53 F, high humidity. Same fuel, plug etc as before. That serious vibration around 2800 rpm was greatly reduced. While impossible to document, it seemed the vibration, tho reduced, was still there...you could feel it while siting behind the engine on the deck (to which the test stand was attached).
,
Reliable idle 2100 rpm. I did not try to find the top end though had it up to 7300
.
But I was reminded of what Ice said to Maverick after they had taken care of the Libyan Migs and returned to the carrier: "Maverick........you'r STILL dangerous"
I began flying glow engines in 1954, and I have never experienced the kind of vibration as demonstrated by this engine. I am lerry of this engine, it is "still dangerous", and absent finding a fix,
I will put something which runs normally in my brand new Dalotel.

Last edited by GoNavy; 05-26-2022 at 02:49 PM. Reason: grammar

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