Chapter 23 – Engine Mount Install

Chapter 23 – Engine Mount Install

24 March 2018 — Today I got to work on drilling the engine mount bolt holes.  I had an entire plan of drilling the engine mount with it off the extrusions, since I was thinking there wouldn’t be enough clearance for a drill to get a straight shot at drilling the bolt holes.  There may not be enough clearance for the bottom horizontal bolt holes, which are forward on the bottom, but for the top horizontal bolts (which are the aft positioned holes) there’s plenty of room.

Also, instead of messing around with some inherent induced error by measuring from F28 or the panel, I went straight to the tip of the extended pitot tube to measure the final position for the top engine mount cups to get them both at F.S. 134.2 AND equidistant from the very front tip of the plane [to be clear, I did FIRST confirm F.S. 134.2 from F28 since I needed a known F.S. to measure off of].  I’m fairly certain I’m off maybe 1/32″ at the most… maybe, maybe just a hair higher if we account for any flex and angle of the measuring tape, but definitely close enough that “these dogs will hunt!”

After drilling a very small pilot hole just enough to guide a larger bit, I switched to a long 1/8″ drill bit for the initial round, then stepped up a couple bit sizes each round.  Of course, going through 4130 took a bit for the initial hole, but went smoothly after that.

Here’s the break through on the right side.

And the left.

I then used a 0.25″ reamer, that actually measures out at about 0.246″ on the calipers. Perfect, I thought, but there was no resistance to the bolts when I slid them into the bolt holes.  Disappointing, but follows in line with what my buddy Dave Berenholtz experienced when he drilled his engine mount holes down in OZ (And here I just thought it was a hemispherical gravitational thing on his part . . . ha!)

Here’s the nicely aligned but not-as-tight-as-it-could-be bolt test fit in the upper right engine mount horizontal bolt hole.

And let’s not forget the left side. Same story.

I don’t have any pics of my next task, but with my top horizontal bolt holes drilled, and thus the top side of the engine mount configuration locked in, I spent a good half hour aligning the bottom engine mount tabs (using a squeeze-handle style clamp) so that the engine mount aligns leaning forward 2° at the top, which is the plans position.  Again, however, the plans was set up with a 118-125 HP O-235 motor in mind, while I’ll be pushing 180-190 HP.

However, after rereading Dave B’s account on setting his engine mount, I realized that I had misread what my fellow Long-EZ builder had ascertained about the translation of the 2° figure.  So, in the end, knowing that I wanted the aft side of my engine just a hair lower than that of an O-235 Long-EZ, I replaced the typical 1/4″ spacer at the top the engine mount when measuring for this 2° angle (derived during the build by setting the plans F.S. for the bottom mount at 134.45) with a drill bit 0.224″ in diameter.  This engine mount angle and alignment is of course checked by getting 90° on the level with the bottom against the engine mount and the spacer wedged in between the level and engine mount at top.

Once I dialed in my engine mount angle, I clamped the engine mount tubes to the lower engine mount extrusions.

I then started drilling the bottom left engine mount vertical bolt hole, which again, the aft bolt holes on the lower mounts are vertical.  I marked my hole from below, and again drilled just enough of a small starter hole to align the bit.  However, that experience alone told me there was no way I was going to drill a hole UP through 4130 for as long I would need to break through this thick steel tube.

So I carefully measured out the tube centerline and extrapolated all that data up to the top of the engine mount extrusion, and drilled from the top down.  Ahh, much easier!

I did use the reamer, not surprisingly with the same underwhelming results as I got on the top side bolt holes.

However, I decided to add a new twist (this is a pun . . . you’ll see!) to the lower left mount tube’s vertical bolt hole by getting the bolt hole just slightly off center.  The “twist” reference above is because the actual engine mount extrusion is slanted just a hair inboard at the top.

Thus, when I drilled straight down I was in fact relationally at an angle on the lower engine mount tube.  Not far enough off center to cause structural concern, especially with this super strong and rather forgiving 4130 steel, I just lose some major style and good craftsmanship points for this “infraction.”


25 March 2018 — In the movie So I Married an Axe Murderer, Mike Myers has a line where his character states to Nancy Travis that he believes that “all Scottish food is based on a dare.” Well, sometimes I feel that way about building Long-EZs: that all majorly important steps are based on huge dares, fraught with the exacting fear that if you screw it up… well, really bad stuff awaits.  Like major rebuilds or just parting with a lot of money to fix it.

The biggest two build dares that come to mind involve drilling: First, drilling the wing bolts through the CS Spar into the wings has got to be the biggest right of passage on a Long-EZ build… simply crazy.  Second, is drilling the engine mount bolts into what is supposed to be 5/8″ engine mount tubes (I just extrapolated this info from a conversation I had with Dave B!) whereupon mine are actually 9/16″ in diameter… let me tell ya, in this situation that extra 1/16″ might as well be an added meter on the target!

Ok, here’s another odd statement that is probably rarely heard: So I fixed my “loose” bolt hole drilling problem by swapping out my REAMER for just a standard 1/4″ DRILL BIT. Crazy? Yes. True? You betcha!

When I drilled out the vertical bolt hole in the lower right engine mount I used a 1/4″ drill bit for the final 1/4″ hole.  The fit was way better than the 1/4″ reamer since it took a bit of finagling to get the bolt to go into the hole.  Woo-hoo!

I then drilled the horizontal bolt hole in the lower left engine mount to finish off that position.

I again calculated the midpoint of the engine mount tube and the 3/16″ thick engine mount extrusion and drilled from the outboard side in.  It worked a treat!

I then had 5 of the 8 bolt holes drilled . . . nearly 2/3rds of the way finished!

As with an alternating clamping process of attaching something into place that has a lot bolts or screws, my next engine mount tube to be completed with the drilling of the second bolt hole (forward/vertical here) was the top right position. Clearly on this one I was able to drill straight into the engine mount tube itself.

I then jumped back down to the lower right engine mount to drill the forward side horizontal bolt hole.  I started with a 1/8″ starter hole as shown below.

And ended up with a 1/4″ bolt mounting hole.  Again, after the initial go with just using the 1/4″ drill bit, the reamer went back on the shelf…. the 1/4″ drill bit simply did the job in stellar fashion.

Here we have the finished engine mount bolt holes on the right side:

Of course finishing off drilling the lower right engine mount bolt holes meant that both lower engine mount bolt holes were completed.

Yes, not a great pic, but the best I have for viewing the fitted temp bolts on the lower engine mounts.

I then finished the engine mount installation by drilling the vertical bolt hole on the upper left engine mount tube.  Both this bolt hole and the horizontal took significantly longer with quite a bit more effort than any of the others, because remember in this position the engine mount extrusion is 4130 steel (which may help explain why it’s so much narrower than the other engine mount extrusions).

Here’s a shot of the top engine mounts with the bolt holes all drilled.

I then double-checked my slightly modified angle and, again, using a 0.224″ spacer (drill bit) vs the plans 1/4″ (0.25″) spacer, I was at exactly 90° [Note that although the board is in place on the engine mount, I am measuring the angle with my contact points for the level and spacer positioned on the board as if there was no board present].

Bam Baby!  90° on the nose . . . now that’s the money shot!

Here I will regale you with a plethora of officially installed engine mount pics!


2 April 2018 — Today I did a quick test install of the engine mount on the firewall to ensure my efforts were all for a good cause!  Actually, the quick test fit came after a half hour of me chamfering all the engine mount bolt holes on the firewall extrusions, then taking a file to the engine mount to clean up the rough edges on the bolt holes.

The engine mount fit well, although I noticed that the lower right engine mount stub was gapped vertically with the lower right extrusion about 0.030″, and the left the same at about 0.020″.  I think there’s enough flex in all this that they can be cinched up fine without any undo stress, but it is interesting how these things appear after the fact.

Here’s a shot of the left and right side test-fitted engine mount.


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