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Old 09-18-2017, 06:12 AM
jeffw@sc47's Avatar
jeffw@sc47 jeffw@sc47 is offline
Join Date: Aug 2014
Location: Simpsonville, SC (SC47)
Posts: 209
Default Lyc 390 Thunderbolt and cowling fit

RV14A, Lycoming IO-390 Thunderbolt

I spent the weekend trimming the top and bottom cowlings to fit to the fuselage. I trimmed to the scribe lines and they fit nicely at the forward fuselage cabin skins at the firewall.

The problem I have is that the forward face of the cowlings - right behind the spinner backplate both top and bottom, are pressed tightly against the spinner backplate.

There is supposed to be about a 3/16” clearance there.

This might require trimming the back edges of the cowlings another 3/16”, but that may cause other issues - so I am not going to do that without some clear direction form Van’s.

It might be something entirely different. I have gone back over propeller installation and everything seems per instructions.

Looking for any other RV14A builders who have fitted the cowlings to a 390 Thunderbolt?
Jeff Warren
Simpsonville, SC (SC47 - 10nm NW Triple Tree, SC00)
1946 Bellanca Cruisair 14-13-2 (72 YRS OLD 8/15/18)
RV14A (N14ZT), Ser#140195
Start 10/11/14
Dues paid 12/1/17 (USArmy 2/67-2/70)


Last edited by jeffw@sc47 : 09-18-2017 at 06:36 AM.
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Old 09-18-2017, 06:52 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 1,609

The scribe marks are there to get you in the ball park. Follow the plans and continue to fit the cowl.

Make sure you add the spacers and washers to the spinner backplate per the Hartzell install manual. These come in handy later if you want to do a minor adjustment to the spinner/cowl spacing.

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Old 09-18-2017, 07:04 AM
DanH's Avatar
DanH DanH is offline
Join Date: Oct 2005
Location: 08A
Posts: 7,800

What Carl said. The scribe lines mean nothing. Fit the cowl to the airplane.

This may help, or not:
Dan Horton
Barrett IO-390
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Old 09-18-2017, 10:06 AM
rvbuilder2002 rvbuilder2002 is offline
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 7,713

The scribe lines on the RV-14 cowl are accurate and valuable for saving a novice builder a bunch of time when starting the initial, trimming while doing a cowl installation.
They designed to trim the cowl enough that it can be fit into place, nested on the attache hinges and fitted behind the spinner, but not with the proper spinner gap. This is to allow for slight variations between each installation, trim error, etc.
If the builder follows the instructions, it will lead them through the process of initial trim to get the cowl quickly to a point it can be roughly fit in place, and then take measurements for the small amount of trimming required at the back to move it aft and achieve the proper spinner to cowl gap.

It is important to correctly position the rear spinner bulkhead on the prop hub and confirm that the bulkhead is flat and of equal distance to the ring gear support around its perimeter (detailed in the RV-14 spinner installation instructions).
Any opinions expressed in this message are my own and not necessarily those of my employer.

Scott McDaniels
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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