Fitting and Gapping Doors

While pictures won’t likely do the volume of work justice, a lot of time and effort has gone into fitting the new doors to the Boss and getting the gaps tightened up just like we want them.  In fact, the pictures will look very similar to one another with the exception of the progressive details that emerge as our work progressed.

To date, we have about 75 hours invested in the overall door fitting process and the results are starting to show.  With known good hinges in place, the doors were each carefully adjusted to provide the best possible fit within the door opening in their “out-of-the-box” condition.  And while the doors are the best available on the market, like all reproduction sheet metal, they have plenty of little intricacies that prevent them from being a bolt-on operation.  However, after several hours of careful adjustment, the critical bottom and rear gaps were established and a baseline of measurements could be taken to determine how much work would be involved in perfecting the door gap at the b-pillar location.

Why are perfect fitting doors such a big deal?  Actually, the answer to this is kind of multi-faceted, but the big reasons are they look fantastic and they set the ground work for how the entire front end sheet metal fits on the car.  In vintage Mustangs, there are two extremely critical panels that dictate how the body panels “hang” on the car from the b-pillar forward.  Those panels are the rockers and the rear quarter panel assemblies.  These are what are often referred to as “anchor” panels and it is absolutely critical that these panels are properly positioned in the chassis (especially if they are being replaced) and that the doors are perfectly mated to them before any front end sheet metal is hung.  Since these “anchor” panels are bucked early in the chassis build-up and are very carefully positioned, they effectively determine how the rest of the car’s body fit will be from the b-pillar forward.  If the body gaps are sloppy here, you can expect the rest of the car to have similar fit and finish problems on almost all of the front body panels.  In other words, time spent getting door fit to be as perfect as possible will pay huge dividends later on as things like front fenders, hood and cowl fit come into play.

Once the doors were in their best possible fit condition, each gap was recorded in paint pen after careful measurement with a body gap gage.  I prefer to carefully “map” each door edge gap with yellow and green paint pen to show exactly what area of each gap has enough material to work with (marked in green) and what areas of the gap will require filling with weld metal (marked in yellow) to tighten things up and provide enough material to work with.  This allows for very precise addition of weld material to the gap for fitting without the need to weld the entire edge and is time well spent.

The target for the b-pillar gap on a “driven” show car is 4.5mm (just under 3/16”) and 6.0mm (just under ¼”) along the rocker and for a trailered “non-driven” show car is 3.2mm (1/8”) all around.  The slightly wider gaps on a “driven” car provide for an increase in operating clearance to help offset normal wear on the hinges and striker pins without smashing up the painted edges of the doors.

Now that the position of the doors was nailed down, each hinge was drilled for 1/8” reference pins.  These pins are simple 2-inch pieces of 1/8” steel rod that are used to perfectly align each door, time after time, as the gap and finish work are completed.  Small 1/8” holes are drilled through the hinge, a-pillar, and hinge mounting plate when the doors are bolted up in their perfect position so that the steel pins will snugly fit through these three components and establish perfect alignment among them no matter how many times the door is removed and reinstalled.  Once the hinges and a-pillars are pinned, the door is removed and the hinges flanges at the door are drilled and pinned in the same fashion.  Once this indexing work is complete, the door hinges can be safely removed knowing they can easily be reinstalled in their perfect position at any time required.

The first step in preparing the doors for gap welding is to carefully tack the door skin to the frame at several locations around the door.  This is critical to preventing the door skins from warping when the edges are welded since most replacement doors rely primarily on the hem around the door flange to secure the skin to the frame with only a token spot weld or two to keep them in position.  Even though you may only be welding the b-pillar edge of the door, it is essential that the door skin is tack welded around the entire edge to make sure things don’t crawl around.

Once the skin is tacked to the frame, work can begin on welding up the gap edge.  Here is where the “gap mapping” process starts to come into play by allowing the door edge to be welded only where material is needed.  This is also the time where a welder with very good low-end amperage control and performance is critical to a good outcome.  I am very happy with the performance of my Lincoln PowerMig 180C for this type of work as it has no problems doing this kind of precision welding.  Also, it’s worth mentioning that if you, the welder, are not very comfortable with precision, low amperage welding of a thing edge, then this may be a job best left to an experienced body sheet metal craftsman to complete.

The edge welding is rather tedious work and essentially consists of about a million small tack welds that eventually connect to form a continuous bead along the door edge.  In fact, once all the “dots” are connected, the weld has the appearance of a single weld bead along the edge.  This technique requires a very steady and well braced hand and involves skipping around the edge for each series of welds and cooling each weld stitch completely with copious amounts of compressed air before moving on to the next weld location.  Eventually, the edge welds will be complete with a very small Heat Affected Zone (HAZ) and virtually no warping in the panel.

With the edges welded up where necessary, the doors are reinstalled on the car using the alignment pins to locate the hinges precisely and the door is checked for fit.  With all reference dimensions verified and the door fit confirmed, the edges are very carefully ground to the exact 4.5mm gap, starting at the top and working to the bottom, and always checking the work with the body gap measuring tool to ensure not too much metal is removed.  The idea is to keep the edge as flat and perpendicular to the outside body surface so that when the final edge rolling is done, the gap will be crisp and look exactly like a factory rolled door edge.

Once the gaps are defined along the edge, the inner and outer edge surfaces can be carefully ground and smoothed of all weld over run and the entire surface metal finished.  At this point, I leave the doors mounted in their ideal positions to allow me to perform any additional work I need to before stripping the door skin surface in preparation for filling and blocking.  This will allow me to carefully refine the door gap edges and character lines with the door in the perfect position.  Once this is done, I can take the doors off to allow the larger scale blocking work to continue in a more convenient position.

That’s it for this month’s update!  Stay connected with us on Facebook at Instagram for up-to-the-minute updates on the work we’re doing!  In the meantime, we’ll be moving along toward at mounting our unique outside mirrors to these doors and all of the little intricacies involved in the process.  Should be fun!

Fitting new doors starts by getting the out-of-the-box door to fit in the opening as perfectly as possible.  This keeps any corrective measures minimal and allows the gaps to be established with much less work.

 

Generally, on "driven" cars, the rocker gap is slightly larger than the end gaps.

  

Here, the driver door b-pillar gap is "mapped" using green and yellow paint marker.  The green areas have enough material to work with to get the gap perfected and the yellow areas will require welding to add enough material to tighten up the gap.

 

The passenger door b-pillar gap has been mapped in this photo and will require a fair bit of material addition to tighten things up.

 

This photo shows a nifty trick I use to keep the doors exactly matched to the car so they can be removed and reinstalled without loosing all of the careful adjustments that made them fit.  These 1/8" alignment pins fit snugly into holes drilled through each hinge, A-pillar post and bolt plate to ensure perfect alignment of all mounting components.

 

Here is the lower hinge with two alignment pins in place.  this is just about the only location these pins can occupy on the lower hinges due to the torsion spring location.

 

Here you can see the alignment holes drilled through the upper door hinge into the door shell for location.  A mating hole is located adjacent to the lower mounting bolt on this flange as well.

 

Here is a look at the lower door hinge flange at the door shell with a similar locating hole.

 

When reinstalling the door, the alignment pins are used to precisely align the hinges and bolt plates.

 

Before the door skin can be tacked to the door frame, the EDP primer must be removed from the hemmed flange around the entire door.

 

Small tack welds are position at about 6-inch intervals around the door skin hem to anchor it securely to the door frame for support.

This close-up of the tack welds shows how intentionally small these welds are kept to minimize distortion.

Once completed, all of the tacks are ground to the same height as the flange material and brushed clean.

Once the door is finished and primed, these hems will be seam sealed and the tacks will be completely invisible.

Once the door edge welding begins, it is important to weld short sections at a time and cool each one completely before moving on.  These welds must be staggered by several inches to minimize distortion and heat build-up in the panel.

The edge welds are basically made up of a series of sport welds linked together.  When done correctly, the weld actually looks like a very uniform, nicely formed and continuous bead when completed.

Here is the driver door edge fully welded up.  Notice the very small heat affected zone (HAZ) surrounding the weld bead and the uniform bead appearance.

A quick pass over the outer surface to remove the high spots along the weld bead is all that is required before reinstalling the door.

With the edge fully dressed and the gaps at a perfect 4.5mm, the driver door is done.

A closer look at the gap shows how nice and consistent the fit is after fitting.

Passenger door after final grinding and finishing.

A close up of the passenger door gap.  A thin skim of filler to tidy things up and this will look outstanding!