CASTOR

I AM WORKING ON A G.P. EXTRA 300 ARF. THE ENGINE IS MOUNTED AND SEAMS TO BE 3/16" TO THE LEFT OF CENTER (VIEWED FROM THE PILOT SEAT) THE THRUST ANGLE OF THE FIRE WALL IS TO THE RIGHT. WHEN I PUT THE COWL ON THE ALIGHNMENT IS OBVIOUSLY CROOKED. SHOULD I TRY A DIFFERENT ENGINE MOUNT?, RE-MOUNT THE EXISTING?, OR JUST ALIGN THE COWL WITH THE FUSELAGE & ENJOY HAVING THE ENGINE OFF-CENTER?


P.S. THE ENGINE IS A GMS-76

DGrant

My Feedback: (4)

Was there any changes made to position of mount on firewall? Or....is your distance from firewall to thrust-washer correct?

Obviously something is off. When doing engine overkills such as this one, one must be careful to get dimensions correct. At least as much as possible. If you already know it's going to be off, that's where major planning comes in.
I'm just wondering though...what was changed when you were setting up for the .76.

I might venture a guess here though...the engine was long, so it was put as far back on the mount as possible, and that's where it's at. .... If this is the case...the mount needs to move on the firewall to obtain center for crankshaft to plane.

Next scenario....engine fit well, measurement for firewall to thrust-washer was perfect....in which case again the mount might have to be moved to get the crank centered for plane.

Actually the most obvious would be the engine position is to far out from the firewall which in turn puts the crankshaft off center to the right side.....how am I doin?

I hope I'm making this understandable. The measurement for your thrustline of the engine(firewall to thrust-washer) is there to get the crank in the correct position for the finished plane. If it's measured correctly it won't matter what engine you use, it comes out the same. IF your engine is to large, or long, and that measurement has to change to accomodate, then something else has to as well to keep the geometry the same for the finished plane.

I don't think it's critical to how the plane will fly, at least on that small of a plane. The offset for torque is not changed, although it did put the crank in a different position. This is one to put to test though, as it will change the thrustline slightly, putting the thrust further right.

Double check your measurement....thrust-line to firewall...see if that is off from what the book calls for, and if so...how much?

As for the mount being off center of the firewall 3/16" to the left...this is to compensate for your firewall being actually angled, so when you install your engine your crank ends up in the center. I really hope I didn't confuse you....some dimensions are very important to the finished plane though....If I'm way off here...my apologies...I tried... Good luck with your plane though.

TerrellFlyer

THE plane is factory set up for right thrust, the firewall is offset as the engine mount ,the engine will angle to the right ,but the prop shaft and spinner lines up with the center of the cowling open,plane needs this thrust to fly correctly.
Have a goodun,John.

MinnFlyer

My Feedback: (4)

Terrell is right, don't change anything. That's how it should be.

tinman

My Feedback: (13)

when the cowl is on in proper position the centerline of the crank at the prop seat should be at the center of the cowl when it exits the cowl. if you have to move yur mount right or left then thats what ya have to do....we had a similar event like this a while back i remember and the person had the engine mounted sideways and on the wrong side of the mount! the underside of some mounts have a slight taper and if this is what you did and yur motor is mounted sideways (glow out the side)it would appear as you say. ...its possible...let us know how it turns out for ya...

DGrant

My Feedback: (4)

These are all correct, and possible answers to the problem. I think the bottom line is though, that the dimension from the firewall to the engine thrust washer has to be what manufacturer calls for. If this is followed and done, your engine/crank will be centered, hence, the cowling would end up where it should.

Picturing this in my head here....if your crankshaft/cowling are to far right, your enginethrust/washer was to far forward.

And....as Terrell pointed out...don't change the angle of thrust..it is what it is, straight from factory.

tinman

My Feedback: (13)

he says its to the left....i will wager its mounted sideways and it is mounted on wrong side of the mount. alot of mounts are 1/4 off center if ya put motor on wrong side of mount......arrrgh we have to know now...ya have to reply!

TerrellFlyer

the mount is to the left side of the firewall and the firewall has right thrust,if the mount wasn't on the left the prop shaft would'n come out the center of the cowl.put the cowl on screw it on, and go fly the----thing.
Have a goodun,John.

CASTOR

HEY THANKS FOR ALL THE HELP! KEEP WATCHING I'M GOING TO TRY AND POST A PICTURE LATER.

THEN DISTANCE TO THE THRUST WASHER IS AS RECOMENDED IN THE ADDENDUM TO THE INSTRUCTIONS PROVIDED IN THE KIT 4 7/8" INSTEAD OF 5 1/8" WITCH WOULD CAUSE IT TO BE TO THE LEFT A-LITTLE BUT THATS WERE IT SAY'S IT SHOULD BE.

I'M PRETTY SHURE THE ENGINE IS MOUNTED ON THE CORRECT SIDE OF THE ENGINE MOUNT ( IT DOSE'NT MAKE SENCE HAVING IT THE OTHER WAY)

ALSO THERE HAS BEEN NO MODIFICATION TO THE FIRE-WALL...THE ENGINE BOLTED UP PERFECT EXCEPT FOR THE ALIGHNMENT TO THE COWL.


THANKS FOR THE HELP!! I CANT WAIT TO FIGURE THIS THING OUT ...

CASTOR

here is the picture the total distance is 5.1" and the center is 2.4-"

CASTOR

HELLO!

WELL I BOUGHT A DIFFERENT ENGINE MOUNT AND RE-MOUNTED THE ENGINE (PERFECT COWL ALIGNMENT NOW)

I NEVER REALLY FIGURED OUT WHY THE ORIGINAL WAS SO FAR OFF AFTER EXTESIVE MEASURING WITH CALIPERS!

I HOPE TO BE FLYING SOON I PUT MY LAST PLANE IN THE DIRT AND WANTED AN ARF SO I COULD GET BACK IN THE AIR. THIS MOTOR MOUNT THING DELAYED ME THIS WEEKEND MAYBEE BETER LUCK NEXT WEEKEND.


THANKS FOR ALL THE HELP,

DESPERATE