68-72 acceptable alignment of front bumper, guards, and grills- photos

[Mark E.]

How precisely should the front bumper, bumper guards, and grills align to be considered within factory specs? I didn’t see any tolerances in the AIM or service manual. I'm thinking specifically about 70-72, but this probably also applies to 68-69.

And for NCRS judging, how badly can these parts be aligned without penalty?

I may be getting too obsessive about this issue on my 1970, so I thought I would ask this group of maybe even more obsessive Corvette people.


My situation:For reference:

• First photo: My car (green)
• Second photo: Car (red) from 1970 brochure showing good alignment but with small gaps between the grills and guards. Confirmation that these gaps are ok?
• Third photo: 1971 car with Duntov from "Car and Driver" road test showing very poor grill alignment. What's up with that? You'd think press cars would be perfect.

Thanks for your input. No comment is too anal or fussy!

[Bill C.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

Here is my old 72.



it was a 48k mile car with one owner before me.
Here it is before I restored it


hope it helps.

[Edward J.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

Mark, the gaps are normal, Just about every 70-72 has some sort of alignment problem, I like many have done the same as you have done many hrs. spent for alignment of the three pieces. and my 72 is a no hit front end.

[Mark E.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

Thanks Edward. You have a beautiful 72. Your photobucket link has shots of the chassis and interior... but not the exterior. Any photos of the front you can share?

[Edward J.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

Have you checked Patrick H. he has a photo gallery of his bowtie 72. many question have been answered by taking a look at them for me at least, and many others.

[Mark E.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

So there aren't any factory tolerances specified for the fit of these pieces?

And how mis-aligned can they be without a deduction for condition during judging? Is this a subjective item?

[Mark E.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

So there aren't any factory tolerances specified for the fit of these pieces?

And how mis-aligned can they be without a deduction for condition during judging? Is this a subjective item?

Any insights about this?

For judging, maybe it comes down to assessing if the car was repaired poorly in the field (a deduction for condition), or if the panels are aligned as they came from the factory- (no deduction regardless of how poor the fitment)??

[Pat M.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

Mark, my 70's front grilles have slightly unequal gaps like in Bill's first photo, and they even stick out slightly so that the dark gray paint on the grilles do not perfectly line up with the dark paint on the bumperettes. My relative bumper placement is also similar to the above photos, and not perfect. At a National I was told this was just right.

I took that to mean there are no specific alignments and that slight misalignment of these pieces was normal, although I was not specifically told that.

For whatever that's worth. Good luck.

[Edward J.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

Mark, John Ballard is the 70/72 exterior judge He seems to be at most of the NCRS regional and nationals and he seems to be pretty fair with his standards of judging. He has his areas that he is a expert on and paint is that area. panel fit and alignment are generally small deductions, I would think from looking at you front pic of the grills they should fly by without a problem.

[Monte M.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

Mike,
Depending on how in depth you want to get, there is another way. Your car looks very similar to mine before my adjustments. My passenger side bumpertte seeded to be twisted a bit. I ended up having to grind 2/3 of the bottom weld out. It was a bear because it was almost impossible to get a cut off wheel inside the hooped part to cut.

Between a small cutting wheel and a plasma cutter we got it to break free enough to be able to bend it a bit and re-weld. Of course, this meant re-chroming them. I was going to do that anyway. If I was not going to re-chrome them I would have made shims that were different depths on either side like I had to do on a 69 I had years ago.

Basically, what I did was leave the bolts a bit loose. Then pull the bumperette into the place where it looked best. at that point it was all about figuring out how to shim it in that location. On the bottom bolt the inside of the bolt had far more shims than the outside did. Once I had the bumperette shimmed where I wanted it, I pulled it back apart and welded all the shims together and then trimmed them so they would not stick out from behind the bumperette.

Bottom line is, leave it loose enough to move it where it looks best. If you have to oval the mounting hole just a bit, so be it. Once you have it where you like it best, make shims to hold it in that location.

Best of luck. If you have any questions, let me know and I can send you some pictures of how I did it.

[Mark E.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

Monte,

Thank you for sharing your expertise and tips for aligning the bumper. It sounds like you needed to adjust the bumper guards (bumperettes) forward and/or aft. My guards and grills are aligned ok forward/aft; I have a gap between the guards and grills that's about 3/16".

From the replies, it sounds like this should be ok.

But I'm still unclear if there's specific NCRS judging criteria for alignment of these pieces- or panel and trim fitment in general. I'm thinking there's a lot of leeway about this since factory quality can be poor, and the focus with judging is more about originality.

[Monte M.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

Mark,
The location of the "bumper guards" was actually not too bad when I started the initial alignment. I got them to fit pretty good with the exception of the gap between the guards and the grill. I shimmed a little here and there to try to get them closer. I had done this on at least a half a dozen cars before and eventually got them in a location that was acceptable.

Until I ran across the car I was speaking about earlier. After many ties and failures of getting them to fit right is when I went to the extreme of relocating the actual mounting plates on the back of the bumper guards.

It really came down to holding the guards where I wanted them. I could alter the car, or I could alter the guards. After measuring the car and determining it was all in pretty good alignment, I decided to alter the guards.

Again, I never removed the mounting surface from the guard. I just loosened enough of the welds to be able to bend them enough to move the guard closer to the grill. After a few creative shims and a few minor pulls on the mounting surface of the guards they came within an 1/8" of the grills and were in alignment, vertical, and side to side.

Again, I started out holding the guards where they would end up ideally and then did what it took to make them end up there. I actually turned out to be quite a bit of work, but the guards fit better on that car than any of the other many early C3's I had ever owned.

I was just an idea that worked for me, ON THAT CAR. I was a bit extreme because that kind of alteration should NOT be needed to make them fit. That being said, we all know that it only takes a minor alteration (wreck) to shift these front pieces of fiberglass around. Especially if the person doing the repair is not a seasoned Corvette repair person.

I have seen new fenders put on cars that look great. When they attempt to put the hood on it no longer fits and they have to shave 1/4" off the leading edge on one side of the hood to make the gap correct. This is due to the person doing the repair measured the location of the fender instead of having the hood on the car while locating the fender. You get a very different result from the two different ways of aligning the fender before attaching it.

Have you double checked if there has ever been any kind of repair on the grill portion of the car?

Best of luck with resolving the alignment issue. I am sure there are other members that have ideas how to resolve your issue too.

Monte

[Bill C.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

I think the most important thing is to get the bumper to fit properly to the nose and brackets.

then get the bumper guards and grills to sit as nicely as possible.
The gaps between the pieces are maybe 1/8 to 1/4 depending on figment issues.


If it all looks good as a whole assembly then I would not see any issues from a judging stand point.

fwiw.
These suckers were flying down the line and the assembly guys had a small amount of allotted time to get those pieces on and looking okay.
I sincerely doubt anyone went around with a ruler and checked.

My two cents.

Bill

[Terry M.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

So there aren't any factory tolerances specified for the fit of these pieces?

And how mis-aligned can they be without a deduction for condition during judging? Is this a subjective item?

Mark,

Have you looked in the 1970 AIM? If there are any tolerances that is where I would expect to find them enumerated.

1970 at Lake of the Ozarks.JPG
My 1970.

[Patrick B.]

Re: 68-72 acceptable alignment of front bumper, guards, and grills- photos

Here are some closeups of my 70 LT1 bumper fit. All of the bumpers, grills etc are original and the car is unhit. Yes, the parking lamp lenses are 1971 because I think the amber lenses look good. I think this is an example of typical factory fit. I always thought it looked pretty good and symmetric. I bought a new GM front bumper in the 80's, but it didn't fit right so I put the original bumper back on despite a few scratches.