Uncowled, the CHT will be about 140C with needle setting slightly rich and temperate climate (20C)
The difference of 120C with the outside air will remain the same, so adjust for your climate as appropriate.

Thank you, Pe. I suspect the CHT to be around there. Outside temp runs around 95deg F (35d C) this time in Houston, TX. Delta temp plus 95d F would put me right at 311d F (155d C). That is HOT. I will take a temp measurement to confirm this.

As a side note, of all engines I have ever owned the MVVS 26 has the SMOOTHEST feel when turning the crank over . It is so smooth it feels slippery with no audible bearing noise.

Gas engines do run hot. That is why appropriate cooling air management is so important.
see http://naca.larc.nasa.gov/reports/1941/naca-report-719/

The MVVS 26 + pipe = one potent and sweet combo. I put in 3 flights today and am completely satisfied. I ran one tank yesterday in my backyard to tune it. It is as reliable, smooth and powerful as my OS 1.60 (muffler). My other gassers are shakers. The MVVS 26 being purpose-built, really shines.

absofrikinlutely -

Pe,

I was out flying my F90 with MVVS 26 on pipe last night. This is my second F90. Two club members were so impressed by the performance that they wanted to know everything about the engine. I started telling them about the engine then noticed that there was about 1/32" of axial play. This was right after I have landed and brought the plane back to the pit.

I could grab the prop, pull back and forth and hear/see the shaft move in and out. Is this normal? After it has cooled down, the movement was reduced significantly - still a tiny bit though. Thank you for your answer.

A slight axial play in the cold engine is normal. (0.3mm max) This always is less than it seems to be. Did you measure, or eyeball the 1/32 when hot? Is the engine still running in?

Hi Pe,

I eyeballed it - totally uncalibrated eyeballs. Yes, the engine is still running (breaking) in. It is turning faster than when brand new, i.e. was 8.3k on APC 18X6. I have not tached it since. It pulls my 11lb F90 effortlessly and accelerates vertically.

I too have a newer setup F90 with Evolution 26 and pipe. After landing the head temp was 250F at 78F ambient temp. The play "eyeballed" was more than a 1/16 on an inch while still hot. It too had very little play after cooling. Running 18 X 6 wood prop. I have less than a quart of fuel through it with Mobile1 synth. 2 stroke oil. Is this normal? Should I be worried? The motor sounds great but I am concerned that this motor has that much movement on the crank when at operating temperature. Please, any input is greatly appreaciated.

-Dan

Axial play in this engine -is to me -just fine .
there should however, be no axial or radial play in the front bearing or in the front bearing to case.
Many believe there should be no fore /aft play in an engine.
This is wrong
The crankshaft -being steel grows lengthwise less than the case grows -due to heat .
For years, we deliberately added a shim behind the front bearing, IF NEEDED, to allow a clearance behind the rear bearing (we essentially moved the crank back inside the rear bearing)
There eliminated danger of the front and rear bearing fighting against each other .
The front bearing takes the END load --the rear bearing takes the rotating load
The end load is not shared between the bearings
This will probably draw some firm opposition as to how the bearings share loads
So be it.

Thank you for you answer, Dick. The steel crank is very beefy and the aluminum case is light - ratio wise when compared to say OS 160. I could see how this produces more axial play considering how hot this gasser operates to the glow OS.

Hi!
Your correct about the bearings!

Regards!
Jan K

That is caused by detonation.

Nikasil is the highest quality cylinder lining avaliabe.

Thanks for the input Dick. I rechecked the play when warm (still un-calibrated eyeball but paid closer attention) and it is actually more like 1/32 of an inch movement. At this point I will just watch it for any change and continue flying and breaking it in. The steel header and aluminum pipe get upgraded to CF pipe and aluminum exhaust header on Thursday if Big Brown is delivering as scheduled That should drop almost a half pound! I hope to see it in the flight characteristics for slow speed flight. It is great as it is but a slower stall speed would be great for playing down low.

I don't believe the MVVS/ Evolution 26 and 35 have a Nikasil cylinder liner, I know for a "fact" that their cylinder liners are ground (NOT honed !!) "unless they have been changed since I have bought mine", so for that I don't believe they are flashed with Nikasil, nickel or chrome (yet I guess they could), I'm betting they have a hard chrome steel liner, well that's what it looks like,,,,


I don't think you hurt it with the Lawnboy but you should switch to synthetic !! and mixing it NO thinner than 40 to 1 is what the factory recommend's unless they have changed it again..


coronabob ,, 1 reason your motor is running so hot is the octane rating your using, a small motor does not need as much octane as a large motor does, yes the MVVS/ Evolution 26 and 35 do have higher compression than some other motors, but still the 26 is a small motor, try a rating around 88 or 89..

Jim

Reporting back on my MVVS 26, the axial play became worse and I could hear slapping sound when toggling the prop back and forth. This was after 1.5 gallons. The engine continued to operate but I started loosing the top end. By the end of the 2nd gallon, the axial play was very severe.

I pulled the back plate and found that the crank pin has worn down to 2/3 of its original OD. There was quite a bit of metal particles in the crankcase. I contacted MVVS and sent the engine back for repair. I followed their shipping instruction to a T and sent it off for about $16 USPS.

I got the engine back in about 2.5 weeks. The factory replaced all internal components: piston, cylinder, crank. They did not touch the outside.

I have installed it on my new Balsa Nova 120 and flown 5 times. The engine no longer shows axial play as it did the first time around by about this time. It runs very strong - better than 8,600 on 18X6W APC. The BN 120 is so easy to hover compared to the F90, Aeroworks 80" profile Extra, Mayhem 90, DP Ulti 120, etc. that I have. It accelerates out of the hover. My BN 120 weighs in at 11lbs 2oz. Flies like a pattern plane w/3D thrown in.

I believe the original crank was not heat treated by accident at the factory. If it does not seem right, it probably isn't.

When the engine is up to running temp, being able to slide the crankshaft back and forth a bit (fore and aft) is the perfect set up. That way the bearings are not in tension and stressed in the case.

Radial play, side play, is a different matter.