Aluminum Hood Fit & Finish

[TrueFaith]

I noticed on picking up my Altima Coupe at the dealer 2 months ago that the hood had gaps, especially at the front, that seemed to exceed the standard for most Japanese-designed cars. It was pretty noticeable, but not enough of a problem that I cared to comment on it to the salesman. Now that I've seen pics of other new Coupes on the forum, I see that the problem was not restricted to my Altima. With fit and finish so precise on the rest of the car, I can only imagine it must have something to do with the aluminum hood. Has anyone else noticed this overlap and gap compared to the tolerences on the rest of the vehicle? Is this normal for aluminum hoods?

[adidas2go]

They are all built like that, even the sedans. I wouldn't worry about it You aren't gonna find anything else that fits better, than a product from Nissan

[jaxCoupe08]

Get a bodyshop to put it on and they will find ways to adjust it to fit perfectly.

[motaman]

I wouldn't take it anywhere to have it adjusted to fit 'perfectly'; it already does. The larger gap is to allow for the increased expansion of the aluminum hood. Give the engineers some credit here.

The coefficient of thermal expansion for aluminum is roughly twice that of steel. This means the aluminum expands roughly twice as much as steel, all other things being equal (part size and temperature difference).

I am an engineer; I design machines and tooling that use steel and aluminum components together in moving assemblies. I have to deal with this all the time. If anyone is interested, the coefficients of thermal expansion that I use for the grades I work with are:

Steel: 6.36 x10^ -6 in/in/°F Alum: 12.7x10^ -6 in/in/°F

Your average body shop guy is probably not going to know that. I occasionally get second-guessed by the guys in our tool shop - they 'fix' something where they think that I have allowed too much clearance. Then it comes back into the shop because the mechanism starts binding at process temperature.

-Mike

[adidas2go]

Very knowledgeable post. Thanks for that valuable insight!

[mcheddadi]

you have a bright future here

[GryStrm]

I am an engineer; I design machines and .....

..i too am an engineer.....and i have a hammer and strike block that says ur wrong!>.......if it dont fit give it a hit!....

[motaman]

....if it dont fit give it a hit!....

Let's not forget rule #1 of engineering: Don't talk about the real methods

Our co-workers and bosses are supposed to think it's complicated!!

[maxentropy]

Let's not forget rule #1 of engineering: Don't talk about the real methods

Our co-workers and bosses are supposed to think it's complicated!!

[TrueFaith]

Thanks for the detailed explanation, Motaman. That's why forums like this are so valuable. Now I don't have to lose sleep wondering why everything else on my Coupe except the hood fits so perfectly. I really thought it might be a quality control thing after seeing other's hoods. Now I know it is, but in a good way.

[vballer22]

Thanks for the detailed explanation, Motaman. That's why forums like this are so valuable. Now I don't have to lose sleep wondering why everything else on my Coupe except the hood fits so perfectly. I really thought it might be a quality control thing after seeing other's hoods. Now I know it is, but in a good way.

Okay, the coefficients and variables make sense to me, but Im not sure thats what the engineers had in mind. Remember we share the same hood with the sedan, and no other body panel. This is to save costs at the expense of a tiny little bit of quality. Also, the hood doesnt expand more than maybe .001" when at the hottest temperature. I live in AZ, and here recently it's been 113 degrees. driving my car for four hours the other day in traffic with a hot engine, the hood had no visible expansion at all. the same gaps were still there. I know what you're talking about when you mentioned the expansion. SR-71's are built so loosely that they lose 80% of their fuel during takeoff due to leaky fuel tanks, then after refueling they fly at cruising speed, which heats up the body so much that all the gaps are filled and fuel no longer leaks. Also, the concorde was builtso that at mach 2 the friction and heat on the skin actually expands the length of the plane 6 inches. I guess Im just saying it's a cost saving method, not an engineered variable.

[vballer22]

And I almost forgot; If the hood expanded any more than 0.1" the multi layer, metallic paint would crack and have spiderwebs.

[ultima67]

if you are talking about gaps where the hood meets the front bumper, you can adjust it. when you pop the hood the rubber stoppers that are on the hood actually screw in. Give em a couple turns to the right, shut the hood.

my hood looked like it had a bigger gap on the passenger side so i asked the body guy at the dealership this is what he told me and what do ya know he was good for something!

[mikegtr06]

oohh awesome i didnt know that, ill give that a try.

(make a write up on it. )

[mcheddadi]

oohh awesome i didnt know that, ill give that a try.

(make a write up on it. )

a write up for that?!

imagine two piece of rubber than move up and down by being screwed or unscrewed and there's your write up lol

[mikegtr06]

makin write up.....

[mikegtr06]

http://forums.altimas.org/zerothread/350832

heres the link

[dangeris]

..... Also, the concorde was builtso that at mach 2 the friction and heat on the skin actually expands the length of the plane 6 inches.....

C'mon now guys...lets try to keep this forum clean!

Good information though! I'm an engineer too but a network engineer...This... Steel: 6.36 x10^ -6 in/in/°F Alum: 12.7x10^ -6 in/in/°F.... means absolutely nothing to me but I'm sure I can talk about it and impress the ladies with it. My luck though, the girl I'd talk to would be a structural engineer

[spockrock]

engineers in the US, still use imperial measurements??? I remember hating to do calculations in imperial or converting between imperial to SI, no offense but join the rest of the world and go SI. There are no logical steps between units of measurements in imperial.

Also hi fellow engineers.

[vballer22]

C'mon now guys...lets try to keep this forum clean!

Good information though! I'm an engineer too but a network engineer...This... Steel: 6.36 x10^ -6 in/in/°F Alum: 12.7x10^ -6 in/in/°F.... means absolutely nothing to me but I'm sure I can talk about it and impress the ladies with it. My luck though, the girl I'd talk to would be a structural engineer

Hahah nice one dangeris. Btw the sr-71 expanded up to ten inches at altitude

Anyways, Im not an engineer, but I do have my pilots license and I've spent years and years around aircraft. I know way more about pratt and whitney engines than nissan ones!