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Fuel tank leak or possible overfilling?

crabandy

Well Known Member
Wings are the last thing to inspect for my 3 month long condition inspection, plane has been easy it’s the twins and rest of life that makes a couple hours of free time hard.
Popped the wings root fairings off and noticed the blue staining right away, I built the tanks in 05-06 with 9 years and 600 hours leak free. Also found a little blue streaking staining on the outside of the inner wing inspection plate, the spar area inside was clean. Fuel tank Inspection cover, fuel and vent line all 100% clean. Blue staining was kinda dry and powdery.
Initially thought I’ve got a leak and need to pull the tank, but after looking closer I’m Starting to wonder if it wasn’t fuel spillage from overfilling the tank. Flew to VA first part of Oct, FS via fuel truck was the only option and he was going to wait a couple hours until the next arrival to fill up both at the same time. 99% of the time I’m fueling or assisting the fuel guy and this time I wasn’t. I made sure he was aware of the fuel caps and the last couple gallons go real slow.
After fueling it did sit in the remnants of “IAN” for a couple days before flying home. Since then it’s been undergoing my record breaking longest condition inspection ever.
I’m thinking clean the stains, fly a few hours and reinspect. Thoughts?
 

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No harm in cleaning and checking again but I have a hard time to see this from overfilling the tank. How did the fuel travel all the way to the wing root are and only seeing the die at that place.
Cleaning and rechecking will confirm what you have.
 
Hmm seems like a funny confined location for blue dye from over-filling the tank. Can you get a borescope in to have a look around the tank baffle seams and rivets?
 
In my experience the blue dye doesn't generally show up from one-time events such as spills or a few drops that don't continue. Whereas a steady drip from a quick drain will do so.
 
Looks like classic tank leaks. Looks like it’s been seeping for a while.
Only way to assess how bad is to remove the tank for a good look.
I see leaks in the inboard lower corner, small leak by the second nutplate forward of the spar, third rivet on lower inner tank rib, & the one that would concern me most is the wet stain you found under the spar at the bottom wing inspection cover.
Repair process is described on multiple threads on VAF,
 
Rechecked today, definitely fuel tank leaking. Made it almost 20 years without leaking.

Hey Andy,
I hear there is a product I think they call Slosh.. Ha! I built my tanks about 10 years ago - only flying for 2 years and I hate the thought of finding a leak. So much so I have a wing kit and Im going to build another set of tanks so I could just swap them out!

Good luck on the repair. I hear they are not that fun.
 
I have repaired/fixed several leaks on a 1998 vintage -6.
Once you to commit to fixing it and remove the tanks, it is not that bad.
Most leaks are at the business end and somewhat accessible, after installing a access plate.
 
I actually had an A&P just recommend using slosh, just like they do on the Cherokees……..
I think my only decision now is to fly most of the fuel out of the tank and then pull it or just drain it.
 
I actually had an A&P just recommend using slosh, just like they do on the Cherokees……..
I think my only decision now is to fly most of the fuel out of the tank and then pull it or just drain it.

I cant believe people are still recommending slosh. I only saw it once on a plane and it did not look like any kind of fun removing it. I have read several different repair tips with people putting something on the leaking rivets and using a vacuum? I hope when you pull the tank it will be easy to find the leak.

Good luck with the repair.
 
Searched and found the Green Loctite 290 threads on VAF and seems like a viable solution for rivets, not sure about seams. I’m thinking the lower corner is leaking in addition to a rivet or 2, also some leaking from the mid-rear baffle. I’m going to attempt to snake my WIFI scope behind the tank and see what I can see tomorrow.
 
Andy & all others discussing slosh,

Read Vans SB 11-9-13 before sloshing your tanks. It's been done before and the sealant flakes off becoming a contaminant.

I agree with the post that a one time fuel spill is not likely to cause the amount of stain pictured. This is a classic pattern for leaks at the aft bulkhead of the fuel tank. Seen it a number of times doing CIs, repaired it almost as many.

Its is not that difficult to remove the tank, de-rivet the bulkhead, clean and reseal the tank. It is also an opportunity to fix weeping rivets.

A thin good quality putty knife works very well to separate pro-sealed joints. Take your time.

PM me if you want more info.
 
Went back out today and no new fuel or blue, seems it just weeps sometimes. Weird. Tank has been full for almost 3 months and still is.
Also got the WIFI scope behind the tank and it also seems to show some blue staining along the bottom rear baffle, again not so fresh.
 

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Drained the fuel and pulled the tank. I didn’t know about wiring service loops when I installed the tank/fuel sending unit and had to snip the wires, flop tube on this tank. Took me 4 hours plodding along to drain and remove the tank.
 

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Appears to be 2 separate leaks on the lower rear baffle.
 

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The leaks on the tanks seem to be in the same area I placed the pad of my aircraft jacks (boat jacks.) I tried 2 different spots along the main spar/tanks for jacking the airplane off the ground, I centered the pad on the spar but I’m guessing there was enough pressure on the rear tank baffle to create a leak. DOH!
If that’s the case my other tank is most likely leaking or about to start leaking as well.
 

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I pressurized the tank slightly with a balloon on the vent line and sprayed the blue stained areas on the rear baffle with soapy water. Weird, No bubbling from the rivets shop or factory side nor baffle. I’ld really like to verify the leaks….
 

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I pressurized the tank slightly with a balloon on the vent line and sprayed the blue stained areas on the rear baffle with soapy water. Weird, No bubbling from the rivets shop or factory side nor baffle. I’ld really like to verify the leaks….

I’ve heard of tanks that pass the soap bubble and air or water tests, yet still leak with fuel.. I would look into getting the Vans Repair kit, or making your own.. basically you fly cut 5 inch holes in the rear baffle, and make oversized plates to seal and pop rivet back on.
 
I’ve heard of tanks that pass the soap bubble and air or water tests, yet still leak with fuel.. I would look into getting the Vans Repair kit, or making your own.. basically you fly cut 5 inch holes in the rear baffle, and make oversized plates to seal and pop rivet back on.

Thx Tom, I’ve already looked at the vans repair kits. The staining looked like it bordered several of the ribs, if I’m needing to open up 4 bays wondering if it might be better to just remove the rear baffle. If it’s 2 bays only the repair kits make more sense.
Also what about prosealing over the outside of the rivets/baffle edge.
I wonder what kind of pressure the tanks are seeing in flight through the vent?
 
Lower baffle fay seal..

Id bet a dollar your baffle is leaking at the lower edge. The baffle is the leak point on 95% of all leaks...I've fixed a bunch. When the baffle is installed, its a goop and close event with no way to perform a proper fillet like the other areas. Yours looks like a classic case. Since yours isnt painted, removing the baffle may be your best bet, otherwise you will need to put the access hole in each bay, clean and reseal the rear baffle. make sure you "butter" both the baffle and the tank skin/rib ends with sealant for the best chance to have a good seal. I am currently doing a set of -4 tanks that were leaking bad but had nice paint we didn't want to drill through. Opted to do the access holes and not remove the baffles. Theses tanks were "sloshed" and flaking badly..he was lucky to not have engine out. Avoid slosh at ALL costs. The slosh had to be removed by careful stripping and cleaning, and I will be starting the reseal and close over the next few days. I have attached a couple pics of the leak and the repair access. The tanks are now internally cleaned, but I don't have a picture of them.
 

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Thx Tom, I’ve already looked at the vans repair kits. The staining looked like it bordered several of the ribs, if I’m needing to open up 4 bays wondering if it might be better to just remove the rear baffle. If it’s 2 bays only the repair kits make more sense.
Also what about prosealing over the outside of the rivets/baffle edge.
I wonder what kind of pressure the tanks are seeing in flight through the vent?

I think you will probably need the access holes in the back anyway, in order to remove the baffle. This is because the baffle needs to be separated from the ribs by inserting a sharp paint scraper or similar to cut the sealant in the joints. That was my experience recently when taking the backs off my tanks for a complete clean and re-seal. I wouldn't have been able to get the back off without having the access holes to work through.

I also think that you should be able to re-seal your baffle seams just via the access holes. It is fairly easy to cut the openings with a fly cutter and then you can reach inside to apply a fillet of sealant along the aft edges of the tank from the inside, using a mirror to see what you are doing. If instead you were to take the baffles off then there is going to be a whole lot of extra work to clean off the old sealant with polygone or methylene chloride paint stripper, it's a horrible job!
 
I think you will probably need the access holes in the back anyway, in order to remove the baffle. This is because the baffle needs to be separated from the ribs by inserting a sharp paint scraper or similar to cut the sealant in the joints. That was my experience recently when taking the backs off my tanks for a complete clean and re-seal. I wouldn't have been able to get the back off without having the access holes to work through.

I also think that you should be able to re-seal your baffle seams just via the access holes. It is fairly easy to cut the openings with a fly cutter and then you can reach inside to apply a fillet of sealant along the aft edges of the tank from the inside, using a mirror to see what you are doing. If instead you were to take the baffles off then there is going to be a whole lot of extra work to clean off the old sealant with polygone or methylene chloride paint stripper, it's a horrible job!

Paul, Thanks for this. I was visualizing removing the baffle in my mind, but didn’t picture the pro seal joint from the ribs to the baffle. I’ve removed the inner inspection plate for the anti-rotation bracket years ago, it takes a lot of care and muscle.
 
Just ordered 8 tank repair kits…..

For most tank repairs are people cleaning/scuffing up the existing pro seal and adding a fillet over top or removing as much as you can first?
What are you scuffing it with?
What are you removing it with?
 
What I do

If the sealant inside isn't loose, soft or really in bad shape, I clean the sealant and surrounding metal surfaces with Scotchbrite and MEK or Acetone. I final clean with Coleman camp stove fuel (my personal preference) and then fillet seal with PPG 1422B-1/2 using acid brush and fingertip application. I also brush topcoat all flanges ,fasteners and fittings with 1422A-1/2 which is a thinner brushable topcoat sealant. VANs has been backorder on the tank panel kits, and I make my own from .050" 2024-T3 sheet (6" circles), and get the closed end pop rivets from ACS in large volume..they are inexpensive. I install the plates with 1422B 1/2 applied to both mating surfaces, and topcoat the closed panel with the 1422A1/2 . I like to make my initial cutouts with a #2 pin-router in a high speed grinder, and once you master using it, takes a bout 1 minute per hole followed by clean-up with a 2" drum sander. See pics of pin router and what the 1422-A1/2 topcoat looks like.
 

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If the sealant inside isn't loose, soft or really in bad shape, I clean the sealant and surrounding metal surfaces with Scotchbrite and MEK or Acetone. I final clean with Coleman camp stove fuel (my personal preference) and then fillet seal with PPG 1422B-1/2 using acid brush and fingertip application. I also brush topcoat all flanges ,fasteners and fittings with 1422A-1/2 which is a thinner brushable topcoat sealant. VANs has been backorder on the tank panel kits, and I make my own from .050" 2024-T3 sheet (6" circles), and get the closed end pop rivets from ACS in large volume..they are inexpensive. I install the plates with 1422B 1/2 applied to both mating surfaces, and topcoat the closed panel with the 1422A1/2 . I like to make my initial cutouts with a #2 pin-router in a high speed grinder, and once you master using it, takes a bout 1 minute per hole followed by clean-up with a 2" drum sander. See pics of pin router and what the 1422-A1/2 topcoat looks like.

Very Nice Bill!
I saw the tank repair “kit” was backordered, but clicking on the individual items showed them in stock. On the phone she told me they had the inventory, pieces weren’t put together in a “kit” yet. Once ordered they would assemble the “kit” and ship it out.
I also ordered the pro seal MC236-B2, but I like the idea of a thinner brush ale version to fill in nooks and crannies better.
 
Reason why the leak didn’t show

When a tank on my 6A was leaking I removed the tank and then couldn’t find the exact location of the leak. I pressurized it and put it under water and couldn’t find it. I accidentally flexed the skin where it overlaps on the wing spar to install the screws and started to bubble. The leak was at the wing root at the lower rear baffle.

Also slosh is very easy to remove by use professional strength Goofoff. The slosh wrinkles within 10 to 15 seconds after applying goofoff. The hard part is removing the proseal. I didn’t use Polygone to remove the proseal. If I did it would have saved me 15-20 hrs per tank. Each tank took me 30 hrs from removal to install. I cut holes in the rear baffle instead of removing the baffle
 
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While I’m inside the tank I’ld like to remove the 10+ year old flop tube. I’m carb’d with no other inverted systems so I’ld like to replace it with just a pickup tube.

Vans suggested going back to the stock setup, it would require removing the trap door/removing 2 Hangup brackets/plugging the fuel inlet in the leading edge/new cover plate&pickup tube and new fuel line into the fuse.

Any issues with making a longer pickup tube utilizing the existing an fitting in the leading edge, prosealing it in the inboard corner and making an anti rotation bracket? Seems like a lot less work.
 
What Bill says

If the sealant inside isn't loose, soft or really in bad shape, I clean the sealant and surrounding metal surfaces with Scotchbrite and MEK or Acetone. I final clean with Coleman camp stove fuel (my personal preference) and then fillet seal with PPG 1422B-1/2 using acid brush and fingertip application. I also brush topcoat all flanges ,fasteners and fittings with 1422A-1/2 which is a thinner brushable topcoat sealant. VANs has been backorder on the tank panel kits, and I make my own from .050" 2024-T3 sheet (6" circles), and get the closed end pop rivets from ACS in large volume..they are inexpensive. I install the plates with 1422B 1/2 applied to both mating surfaces, and topcoat the closed panel with the 1422A1/2 . I like to make my initial cutouts with a #2 pin-router in a high speed grinder, and once you master using it, takes a bout 1 minute per hole followed by clean-up with a 2" drum sander. See pics of pin router and what the 1422-A1/2 topcoat looks like.

I can attest to Bill's skill at fixing fuel tank leaks!!

After repairing a leak 4 times (!!), it kept moving to a new place, I took my tank to Bill. He had to open up every baffle and totally re-do the insides.

My friends at the airport saw the frustration that I went through with each fix and the happiness after letting a "professional" do the whole thing once and for all.

Since then, we have had an RV10 with a small but difficult to fix seepage get fixed by him and an RV8 with small seepage in the queue.

RV tank fixing is not his "day job" but I sure am happy that he helps us with leaking RV tanks.

BTW, he has a nice RV4.
 
Just ordered 8 tank repair kits…..

For most tank repairs are people cleaning/scuffing up the existing pro seal and adding a fillet over top or removing as much as you can first?
What are you scuffing it with?
What are you removing it with?

I check existing Proseal beads by poking it with my finger nail. If it is gummy or can be gouged with my finger nail, I scrape all visible Proseal from that area.
I fashion scrapers out of leftover canopy plexi, various shapes including hooks to snag sealant in tight areas.
Finally I scuff area with Scotchbrite & wipe clean before applying Proseal.
I see no issue with running an aluminum tube off the flop fitting back to the stock fuel pickup location other than be sure to have a stabilizing bracket somewhere near the back end of it. & clearly label what you did so possible future owners don’t think there is a flop tube in there.
 
While my tank is opened up I would like to replace my 10+ year old flop tube. No other inverted system on my plane so I would like to go back with a fixed pickup tube.

Vans suggested returning it to a stock pickup tube, I’ld have to remove the Hangup brackets, trap door and plug the an fitting in the leading edge and make a new fuel line into the fuse in addition to making/buying a new access plate/pickup tube and anti rotation bracket.

Thinking a new metal fuel pickup tube from the existing an fitting in the leading edge to the inboard corner. I would proseal and add some sort of anti-rotation bracket to the tube. Any issues with this?
 
Flop tube removed and basic pickup tube made, I still need to pinch the end of the tube and cut some slots but this is what I’m thinking.
Also I don’t see a need for any sort of anti-rotation bracket, with the An fitting loose It has very little movement and the fact I can proseal it and verify with the access plate off.
 

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Drip Soapy Water on Bubble Free

I pressurized the tank slightly with a balloon on the vent line and sprayed the blue stained areas on the rear baffle with soapy water. Weird, No bubbling from the rivets shop or factory side nor baffle. I’ld really like to verify the leaks….

The trick to finding small leaks is to drizzle the leak detection liquid on to the area without bubbles (get a bottle of “Snoop” for this because it works really well). When you have a lot of bubbles in the solution when it’s applied, it’s really hard to see the small “fizzers”.

Skylor
 
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The trick to finding small leaks is to drizzle the leak detection liquid (get a bottle of “Snoop” for this because it works really well. When you have a lot of bubbles in the solution when it’s applied, it’s really hard to see the small “fizzers”.

Skylor

I might try “snoop” when I button things back up, but I don’t think it was leaking. The ballon stay inflated for over 3 days in my garage until I loosened the first screw of the fuel sending unit.
Temps when I found the leak were in the single digits in my hangar, temps in my garage hover around 40. Thinking that might be how I flew a year without finding the leak in the first place.
 
Flop tube removed and basic pickup tube made, I still need to pinch the end of the tube and cut some slots but this is what I’m thinking.
Also I don’t see a need for any sort of anti-rotation bracket, with the An fitting loose It has very little movement and the fact I can proseal it and verify with the access plate off.

The current location for the open end of the pickup tube will draw in any water that may be in the tank. I was advised to mount the pickup so that there is a litre or two of unusable fuel in the tank above the drain, for a bit of protection against this.
Otherwise, I think it should work fine and it's unlikely that the B nut would require safety wiring or clamping as per the normal L shaped pickup tubes.
 
In the last picture, there is some sort of angledy-looking thing on the bottom of the access hole that is in contact with the tube. Is that right?
 
The current location for the open end of the pickup tube will draw in any water that may be in the tank. I was advised to mount the pickup so that there is a litre or two of unusable fuel in the tank above the drain, for a bit of protection against this.
Otherwise, I think it should work fine and it's unlikely that the B nut would require safety wiring or clamping as per the normal L shaped pickup tubes.

A *liter* of water is a huge amount, IMO. If I'm still sumping water after getting 1 L out, I'm going to be a helluva lot more worried about flying.

Plans call for it just about right where it is in the pics. I've never had so much as a drop of water, and I have << .1 gal unuseable fuel in each tank. Like, a few *ounces*.
 
A *liter* of water is a huge amount, IMO. If I'm still sumping water after getting 1 L out, I'm going to be a helluva lot more worried about flying.

Plans call for it just about right where it is in the pics. I've never had so much as a drop of water, and I have << .1 gal unuseable fuel in each tank. Like, a few *ounces*.

I never said there would be 1 liter of water in the tank. The point is that if the pickup is in the absolute lowest corner of the tank then any water that may be there will get sucked into the engine. The flop tube has a collar on it that lifts the openings off the bottom of the tank. The Vans pre-bent pickup tubes are also off the bottom of the tank.
FWIW I have found water when sumping tanks and don't plan to be in a situation that depends on needing the last litre for safe flight.
 
Yeah, I don't see his installation being any different than this

Capture.PNG

Capture2.PNG


but it's hard to tell precisely from the pics.
 
In the last picture, there is some sort of angledy-looking thing on the bottom of the access hole that is in contact with the tube. Is that right?

Angledy thing is what’s left of the anti Hangup bracket that spans the access hole, I just cut it and rotated it for now. It is riveted to the doubler plate but underneath the rib so the flush rivet heat is covered. I’ll address that prior to finalizing the pickup tube.
 
Everything is sealed up except waiting to grab a ring connecter for the fuel sending unit ground. I know I overdid it but I resealed EVERYTHING on the tank inside and out while it was opened up.
It wasn’t leaking but resealed the outermost bay lower rear baffle through the fuel filler neck with an acid brush taped to a paint stir stick. The lighted makeup mirror I bought from Walmart years ago still amazes me how good and useful it is, worth $100 but I know I paid less than $10.
 

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Mounted the tank a week or so ago, remounting went better than expected and I only had to use a punch twice to line up holes on the zbrackets.

Basically flushed and drained the tank twice with a small inline filter while recalibrating the sending unit for in flight and ground. Must’ve done a decent job cleaning the tank as I didn’t find anything in the filter.

Tested the fuel flow at a little more than 22 GPH and unusable fuel about 7 ounces.

Left the inspection cover off and a mostly full tank to check for leaks when I return. Hoping to fly soon.
 

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Good thread here.

Drained the fuel and pulled the tank.

For those not aware, take a good look at the grounding arrangement in the photo. Static electricity has ignited more than one airplane while draining tanks, as the fuel picks up a charge while flowing in a non-conductive hose, or while falling through the air. Eventually it will build enough potential to arc. Prevention requires only a few wires tying the airplane to the fuel in the plastic jug and to a good local earth ground, so everything remains at the same potential. Particularly note the metal rod in the fuel. Smart man, that Andy.

Id bet a dollar your baffle is leaking at the lower edge. The baffle is the leak point on 95% of all leaks...I've fixed a bunch. When the baffle is installed, its a goop and close event with no way to perform a proper fillet like the other areas. Yours looks like a classic case.

More than a decade ago, while researching the blister problem, I sent a Vans tank drawing to the senior tech rep at a sealant manufacturer. His immediate comment was "That's a hard tank to seal!", and the subsequent explanation precisely matched what Bill wrote above. Cut access ports in a few tanks so you can see the sealant along the rear wall, and you'll quickly recognize how right they are. Installing the rear baffle wall just pushes up a pile of sealant along the inside of the seam...some luck involved, certainly no pretty fillet.
 

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Good thread here.



For those not aware, take a good look at the grounding arrangement in the photo. Static electricity has ignited more than one airplane while draining tanks, as the fuel picks up a charge while flowing in a non-conductive hose, or while falling through the air. Eventually it will build enough potential to arc. Prevention requires only a few wires tying the airplane to the fuel in the plastic jug and to a good local earth ground, so everything remains at the same potential. Particularly note the metal rod in the fuel. Smart man, that Andy.



More than a decade ago, while researching the blister problem, I sent a Vans tank drawing to the senior tech rep at a sealant manufacturer. His immediate comment was "That's a hard tank to seal!", and the subsequent explanation precisely matched what Bill wrote above. Cut access ports in a few tanks so you can see the sealant along the rear wall, and you'll quickly recognize how right they are. Installing the rear baffle wall just pushes up a pile of sealant along the inside of the seam...some luck involved, certainly no pretty fillet.

Well thx Dan but I’m just a watch and learn guy, I do believe I picked up the grounding method in one of your comments on VAF years ago.
 
I'm working on my fuel tanks now. Seems like that rear baffle seal to skin is a hope and prayer that it works and lasts. Even watching the Van's tank video, seeing the bead of sealant along the baffle edge makes me uneasy. For those in the know, what are your thoughts of punching holes in the baffle prior to installing it to insure a good filet of sealant against the baffle. Seems that patching up the holes afterward is easy especially if planned out in advance.
 
I'm working on my fuel tanks now. Seems like that rear baffle seal to skin is a hope and prayer that it works and lasts. Even watching the Van's tank video, seeing the bead of sealant along the baffle edge makes me uneasy. For those in the know, what are your thoughts of punching holes in the baffle prior to installing it to insure a good filet of sealant against the baffle. Seems that patching up the holes afterward is easy especially if planned out in advance.

I would most certainly consider doing that! My tanks needed complete re-sealing and this involved cutting access holes in the back and removing the rear baffle. When I re-installed the baffle it was easy to inspect the bead of sealant with a mirror and it was apparent that it was just pushed out of the seam and sitting proud. I was able to work through the access holes and make a proper fillet as well as visually inspect everything before closing up the access ports. The access plates are very easy to fit and they will make a positive seal. So I think it is definitely worth putting in the access ports as part of the initial build. It is a small investment that will more than pay for itself. I think that Van's should make it a standard part of the design!
 
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