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Preventing rust in the Z's lower front fenders


inline6

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I've been thinking about how best to address one of the most common rust out areas on our cars, the bottom corner of the front fender.  There is a reinforcement panel which is crimped into the back edge of the fender, and where it twists at the bottom of the fender, it creates a trap for dirt and debris, which over time, collects in the bottom rear corner.  The debris which gets trapped here allows no air circulation so it holds moisture for extended periods of time, over and over again.  Eventually, bare metal gets exposed and rust starts.  

On my first 240Z, I bought brand new OEM fenders, and I sprayed epoxy primer inside this area along with paint.  That was in 1993.  Even though that car has seen relatively little weather (it has been stored in a garage for most of the years since), the lower corner of the passenger side fender started showing some raised bumps (indicating rust through from behind around 2011.  I also, unbolted the bottom of that cars fenders and blew out the debris and dirt a few times over the years with compressed air.  Still, these preventative efforts did not work.  With the 240Z I am restoring now, I want a better solution.

Initially, I thought I would address this problem area by cutting some oval vents to allow additional drainage from this corner, and additional air circulation for drying.  However, I think that would only be a slight improvement.  Instead, I now have in mind fabricating a small metal panel which will seal off this area completely, and therefore, not allowing any dirt or debris or moisture to collect in the corner at all.  Here is a cardboard mock up:  

IMG_20211106_174850.jpg  IMG_20211106_174920.jpg  IMG_20211106_174933.jpg

 

I will extend the actual metal piece I fabricate a little further down than this cardboard template, so that the gap is closed.  I may pop rivet this piece on using the little tabs.  Once secured, I will use seam sealer to seal all the gaps.  Of course, I now need to do something to seal up the oval holes that I cut into the reinforcement panel, or water and debris will enter there and I will still have the same problem for the bottom inch or so of the fender corner.
 

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Interesting.. (Also for  @Yarb)  Mine are a bit rusty in that area..  but as i learned to make some for my 280zx i think i can make also some for my 240z..  The problem there is that it's 2 layers of steel .. and thats aways going to be a rust problem..  maybe take some of the orignal inside layer out clean it completly and close it with some sealer?

Edited by dutchzcarguy
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I'd be very careful in trying to seal such an area.  If it is not 100% effective - to include preventing air in/exfiltration as it will carry water vapor which WILL condense inside that space at some point - then you'll be certain to seal IN water that makes its way inside. 

Perhaps cutting out that reinforcing panel altogether and applying modified design - one that is open and self-draining.  Sorry I can't be more specific about such a design.  I've given no thought to it as yet, but that same problem is headed right at me.  I have two new factory fenders to go on my car, and I am determined to prevent them from rusting.  I am also extremely reluctant to start cutting them up or modifying them in any way.  Right now it's an opportunity waiting for me  somewhere deep inside that tunnel, the light of which I am unable to see.

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Deep! LOL

That said, I think the worst option is spray coatings into this deep crevasse and hope for the best.  My fabricated parts will direct water away from this area and therefore, keep them dryer than they would be otherwise.  Additionally, I have coated these areas on more than one occasion with epoxy primer.  

Feeling good about it.  😎

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1 hour ago, ETI4K said:

I'd be very careful in trying to seal such an area.  If it is not 100% effective - to include preventing air in/exfiltration as it will carry water vapor which WILL condense inside that space at some point - then you'll be certain to seal IN water that makes its way inside. 

That was my thought too. I would think leaving a drain hole in the bottom would be enough to take care of that. The only concern then is stuff getting in through the drain hole in the bottom, which I don't think would be very easy, but I'm sure might still happen to a small degree. 

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8 hours ago, rturbo 930 said:

The only concern then is stuff getting in through the drain hole in the bottom, which I don't think would be very easy, but I'm sure might still happen to a small degree. 

Someone on this forum did an interesting modification to prevent water infiltration at the drain holes in the rocker panels.  A similar approach might work for a drain hole in the fender.

 

Rocker Drain Hole Cover.png

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36 minutes ago, Captain Obvious said:

Where do the cowl drains dump out?

Ehmm.. arn't those rubber pipes the extra airinlet's from those cold air inlets you can open from those pull-knobs... under the dash? (both sides.)

It was only last week i asked myself why are those openings even there in the cowl finisher?  (Air for inside is pulled through the inner fenders not the cowl.. (hope i say this right?) ) 

Edited by dutchzcarguy
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3 hours ago, ETI4K said:

Someone on this forum did an interesting modification to prevent water infiltration at the drain holes in the rocker panels.  A similar approach might work for a drain hole in the fender.

 

Rocker Drain Hole Cover.png

Yep, that was me also. 🙂

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10 hours ago, Captain Obvious said:

Dug up a pic courtesy of @jfa.series1

04.jpg

Actually, when looking at this picture, you see the black line going vertically just in front of the hinges?  The area that will be kept dry is to the left of that line, but entirely on the fender itself, not the car body.  When the fenders are re-attached to the car, I will use a new, closed cell foam weatherstrip in the location of that black line.  This will keep much of the water coming from the cowl drain from entering the bottom of the fender where the rear reinforcement panel is spot welded to the outer fender panel, but with that said, my modification will keep the lower backmost corner of the fender (area between the outer panel and the inside of the reinforcement panel) dry.  Cowl drain functionality will not be hampered.

You can follow the rest of the progression of this work done to the fenders in my restoration thread if you are interested.  The link is in my signature.

Edited by inline6
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1 hour ago, dutchzcarguy said:

Ehmm.. arn't those rubber pipes the extra airinlet's from those cold air inlets you can open from those pull-knobs... under the dash? (both sides.)

It was only last week i asked myself why are those openings even there in the cowl finisher?  (Air for inside is pulled through the inner fenders not the cowl.. (hope i say this right?) ) 

Cold air for the vents comes from the front ahead of the rad support. Those rubber tubes are for the cowl drains, here is a good discussion on the subject. See post #6 by @Terrapin Z.

 

Edited by CanTechZ
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32 minutes ago, ETI4K said:

I love the idea so I had snagged a pic with the intention of doing similarly on mine.

Sorry I couldn't properly attribute it to you.

Not a thing I care about - just decided to point out that it was me. 🙂

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Perhaps, instead of fighting Mother Nature, you let her work for you?  Attach hoses to those cowl drains and terminate them in the area of your concern.  Then, when it rains, that water will work to flush out whatever crud that may have accumulated in the lower fender.  You could also periodically pull your cowl and then flood the drains with a garden hose to flush out gunk and follow up with a blast of compressed air.

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Not a bad idea in concept, but the I think the problem is that the rear fender reinforcement panel, specifically because of how the shape of it twists at the bottom where it is then spot welded to the outer fender panel - it makes a "wedge" area which literally traps debris.  Sure, the water (gravity fed) will flush the area if you route the drain to this location, but I don't think it is accurate that it will flush out all of the debris.  Depending on the shape of the debris, it can get stuck in a way such that it will not get flushed out.  Also, focusing the drain from the cowl area, in addition to flushing with water, will add a new source of debris.  Anything that finds its way past the cowl panel vents in the top of the car will work its way to the cowl drain holes.  Think propeller seeds... or pine straw, for example.  Debris that doesn't flush out holds onto water every time it rains... thunderstorms... or possibly even sprinkles... or the car is washed, etc.  Thinking about it, I am now of the opinion that the main contributor of that debris in the first place is the cowl drain.

Edited by inline6
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Maybe I did this too many years ago to actually remember doing it, but my cowl has black fiberglass glued to its underside that prevents any large items (and skeeters) from entry.  I guess that I roughed up the surface and used epoxy to hold the screening pieces in place.

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Anything functional that comes out of this discussion will be of interest to me next year (or maybe the year after to be realistic)! The driver's side is identical. It really seems like a monumentally bad design to me! Hey, how about we funnel water and cowl debris into an enclosed, invisible area between two tight-fitting pieces of lightly rust-proofed metal?!

 

 

20211109_202312_HDR.jpg

20211109_202524_HDR.jpg

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I know!  And, all the time and money that has gone into repairing and then painting 💰💰💰💰💰 on everyone's Z before us... and possibly will go into every one after us!  I mean, I REALLY don't want to have this area rust out again on my restored Z after I spend 2000-3000 hours and tens of thousands of dollars on it.  Just not an option.

For what it is worth, I considered removing the lowest 4-6 inches of the reinforcement panel, in order to remove this "trap", but there is one of two bolts which secures the lower fender here, and without it, the shape of the outer panel will be altered, and unsupported.

Edited by inline6
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Personally I would clean that area as thoroughly as possible and make sure the weep area was clear. Then I would pour rust modifier in-between the panels, letting it soak all surfaces and seep into the pinched seam and drain out the weep hole. Once that was complete, I would do the same thing with POR-15 making sure it coated all surfaces and sealed the pinch seams - again draining out the weep hole but making sure it stays open.

 Weep holes and drains are an incredibly important part of managing moisture and I would never eliminate or purposefully block them. 

(My son thinks you should separate the two pieces at the rear of the fender, then do the above, then put them back together using seam sealer. Probably involves a little cutting and welding... Important part of that is sealing both surfaces in there and keeping the weep hole open. POR-15 is stupidly effective.)

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Since that area would likely flex on a regular basis, would you be confident the POR-15 would flex with it and remain adhered to the surfaces?  I've used similar products and they are extremely hard - which always raises a flag because with hardness, often comes brittleness.  I've never evaluated any of them on that basis so I am curious what you think.

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Following up on ETI4K's observation, if I were going to go that route, I'd consider using a vinyl plastisol to seal the area.  That's the stuff you dip you tool handles into in order to give you a non-slip surface.

The vinyl formulation is heavily plasticized and exceedingly flexible.  However, it's thermal expansion values are a lot larger than those for steel so it is possible that it might pull away from the metal surface were they both to get very cold.

A flexible polyurethane coating (NOT POR-15 as it is crosslinked to provide chemical resistance) material might work as well; but I'd make sure it was based upon MDI isocyanate and not TDI so you get the greatest flexibility.

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Our experience with POR-15 is that it adheres ridiculously well with metal surfaces when it's applied as they instruct. It was developed to adhere and encapsulate rusty surfaces in a marine environment. They have several products for conversion and encapsulation you might want to look at. We've used it on Z car floors, under cowls and fenders, in wheel wells, and in the area that you're trying to protect as well. But, keep in mind that we're in Arizona so, not a lot of wet here... POR-15 is UV light sensitive but in the areas I've talked about it doesn't require a protective top-coat.

 

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