“Basics of Basics” Trial fitting parts
By Brian Martin
There are few procedures that give you more ‘Bang for your buck” than trial fitting parts. Sounds simple, just common sense. However, it is something that comes with very hard-learned lessons. Even after doing this work for over twenty-five years, I still forget once and a while. When I do, there is a good chance I will pay for it dearly.
Like the fabricators motto “If you don’t have a pile of rejects in the trash, you aren’t doing good work”, the time spent on trial fitting is VERY good time spent.
This trial fitting should include nearly every single part of the car.
When installing a weld on part such as a quarter, trial fitting ALL the adjacent panels is not just something you “should” do, you MUST do it. The decklid, door, rear bumper, window mouldings, etc., should ALL installed and fit well BEFORE your welding is done. At this time a little minor tuning can turn an “OK” job into an outstanding one. You may even find the need to serious adjustment.
Trial fitting is not holding the part up and saying, “yep it fits”. We are talking FULLY bolting the part on. If this is a moving part such as a door or deck lid, the latch should be installed, hinges FULLY bolted on and adjusted. The rubber seals and bumpers should be installed as well. On an older car this is not so easy because many are glued in, but SOMETHING has to be done to insure the part will fit properly when the rubber is installed later.
If you can’t install the rubber at that time at least spend some time looking at where the rubber fits to for a proper gap. For instance, while fitting a decklid to your new quarter (or the other way around, it makes no difference) get in the trunk and close the lid. Inspect around the channel where the rubber fits. Be sure it is a uniform distance ALL the way around. You can usually find the correct distance right where the hinges are. If the panel fits correctly on the outside then that gap for the rubber is usually going to be correct. If you feel for some reason that there is damage to that area, you need to spend some time there. If you feel the car has been hit on the side pillar post (if you were fitting the door) you really need insure that the door fits properly and that you KNOW what that rubber gap should be. This gap is usually a uniform distance all the way around, be sure of it. When you are doing a door, you always have the other side to check to guidance remember. When installing a quarter, rear panel, upper panel, this is very critical. You don’t want to find out later that your gap is too small, the lid won’t close properly or sticks up. You don’t want to find out the gap is too large, the rubber may not seal and the trunk leaks water. A little minor shifting of parts prior to welding could take care of it.
You want ALL gaps perfect PRIOR to welding (a little tack here or there may be needed for fitting the parts) there is NOTHING that will tell you this other than FULLY mounting the adjacent parts.
When doing any plastic filler work (“bondo”) or straightening metal you need to trail fit the mouldings, trim and adjacent parts as well. This is VERY important with parts like fender extensions. I don’t care if they are new/used or the even the same ones you took off the car, AWAYS trial fit them. Don’t leave you new repro parts in the package to install them after paint, you WILL be sorry.
Prior to paint or even primer you can “tweak” these mouldings against the body. After paint, it is much harder because you can scratch it. If there is plastic filler work or metal being straightened this is VERY important. After you have drilled holes for mouldings (Basics of Basics-Templates) bolt the mouldings on for fit.
The cars weight should be on the “wheels” when making these panel adjustments. NEVER fit panels while the car is on jack stands on the frame or on a rotisserie for something like that. You can have the car on jack stands but be sure they are under the rear axle and front control arms to “replicate” the forces of the car on it’s wheels. I don’t even like the under the control arms at all, I put the car on it’s front wheels. The weight transfer is not the same in the middle of the control arms as it is at the point where the tire hits the ground.
I can not stress this enough; trial-fitting parts is not because you are a newbe or something. Every experienced body man does it everyday to some degree. Trial fitting is done throughout the entire repair of the car. Nothing could be worse than getting your car back from the painter only to find parts don’t fit!
Just yesterday I was working on 2002 Honda CR-V with a little dent on the quarter right at the edge by the rear gate. I had finished the plastic filler work and was ready to send it to the paint department. I went ahead and installed the new decklid just to be sure it was right, even though this was a very minor repair that should easily be fine. I found out I was a little on the filler work. Now, it wasn’t the end of the world and could have even stayed that way. But with literally only a few minutes, it was perfect. On a very large job lately I found the need to pull the car back up on the frame rack for a little minor repair to where the rubber fits or the door would have been MUCH too tight. Just this little fine-tuning made a world of difference to how the door fit.
The moral of the story is don’t ever “assume” your parts are going to fit. I don’t give a darn if they are new, repro, NOS, original, it really doesn’t matter, they MUST be trial fit.
The final assembly of your car should be fun, and relaxing. It is the best part of the whole project. Don’t make it a nightmare, don’t let someone rush you during the earlier phases of the project. Right from the very beginning you are laying the foundation for the finished project. Take the time to do it right.
If you trial fit the parts properly you will never know the pain