I wrote this for someone who had the very same question about different motor installations, but it is pretty generic....

- Quoted post for installing engine into Pitts Biplane -

Using a ruler mark the vertical and horizontal center points lines.

This will be where the engine camshaft at the tip ( by the prop washer ) should be aligned to.

Now mount the engine on the engine mount temporarily ( I use clamps ) at the correct distance. I put both of the mount "arms" pointing up on a table, and then clamp the engine to the arms at the correct height. BE SURE that the engine is perfectly "square" with the base ( table top ) and sides ( arms )... use a "T" square to get things right. Adjust the engine position until it is perfect.
( at this point you also want to make your engine bolt marks so you can drill these out later ).

Hold the fuselage with the nose pointed straight up. I clamp mine to a table to make it immobile.

Put the engine on the firewall, and center the shaft with your marks. Sight down from "above".

Because of built in right thrust you'll note that the base of the engine will be ofset about 1/4" or less from the marks you made while the camshaft is centered.

Use a Great Planes Center Hole finder to mark the positions for the blind nuts, using the engine mount holes as a guide.

Even if things are not PERFECT most engine mounts have ovoid holes permiting some final adjustments.

Drill out your holes using increasing sized bits, to avoid fracturing the wood. PRESS LIGHTLY as you drill, let the drill do the work.

Test fit the blind nuts to see if the hole is of the right side. If so remove the blind nuts and apply thin CA to harden the holes and surrounding area. Let dry.

Install the blind nuts and "pull" them into the wood using a washer ( sometimes I also add a few nuts ) and a cap screw of the appropriate size. Be sure that the blind nut is almost flush with the wood and it's teeth have dug in.

Affix your engine mount and engine then do the "cardboard" trick to determine where cowling holes and openings will be required.

Have fun.


- Post for gasser YAK below

It sounds like this is a bit new to you....



Re: Standoffs

Temporarily mount the engine & muffler using standoffs you may have around, so that you get ample clearance for the carb, etc.

Put the prop on it and check that the C.G. is about where recommended. ( you'll want it a bit forward of the recommended anyway ).

With everything else in place see how far off the C.G. is. If the plane requires seemingly a LOT of nose weight, move the engine forward by increasing the standoff length.

It is NOT unusual to have to go beyond 3" for the standoffs, but if you do have to go that far, it is better to build a "U" shaped block that goes on the mounting box between SHORTER standoffs and the box. That way there is less of a lateral torsional force applied to the standoffs.

Once you have things "good enough" ( it does NOT have to be exact at this point ), remove the muffler and if possible install the cowl to measure the distance required and the centering, then mark where you'll be placing the cowl mounting holes.

If because of clearance issues you cannot put the cowl over the engine, mark the centerpoint of the driveshaft, where the prop driver ends. Make the marks on the mounting box. You'll be sighting down the cowl to the "X" you make to line things up...

This will be where the cowl will need to align once mounted.

Also measure the distance from both the firewall to the prop driver, ( and add about 1/4" or so ) and again from the engine box to the prop driver, so you know where to place the cowl...

You may also want to use the cardboard/paper trick to delimit where you'll need to make the first cuts in the cowl to position it with the engine in place.

Remove the engine, and put the cowl back aligning it to the marks you made and at the distance you've measured. Also mark where the cuts will be by transferring them from the cardboard/paper...

Remember it does NOT have to be exact yet. Do not put the cowl mounting holes in at this time.

Start cutting the cutouts in the cowl, but do not make them to their final size. You can always remove more material later... adding material back is obviously VERY difficult....


Put the engine back on at the proper distance, and check to see if any additional material needs to be remove from the cutouts... don't worry about the muffler cutouts yet.


Once you can get the cowl over the engine, put the cowl loosely in place, put the spinner basplate on and prop, prop nut etc.

Center the cowl under the spinner baseplate ( leaving enough clearance ) and then TAPE the cowl to the fuselage in this position.

NOW drill the mounting hole locations, right through the cowl to the wood below.

You can take it from there.


Re: Spinner

Spinner selection is completely up to you. (Hint: True Turn does a NICE job custom cutting spinners for your engine and prop for you ).

Check out pictures of other RC Yaks to see what the relative proportion is of spinner versus cowl front.

You'll not that space is left on the Yak for airflow around the spinner. Things don't have to be exact though you want it to look OK.

I always play this by ear and choose a spinner that seems to fit appropriately...

When in doubt, make a cardboard circle to see how things will look, and position it in front of the cowl...

Once you have a size that looks OK to you, measure the circle and find a spinner that is close.