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"Fat Boy" Fuel Tank Mystery ('86 VFR)


BluRoad

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During the disassembly process for my latest project I discovered something I can't really explain. The fuel tank I refinished for this project came from another bike. When I went to fit it onto Project 18 it was...too wide.

The rear portion of the tank slips between the subframe rails and this tank simply wouldn't. After taking measurements from four other bikes, I determined that this particular tank and it's subframe were actually wider than the others.

Picture

The larger tank (on the right in this photo) measures a whopping 1 1/4 inches wider at the rear and 5/8 inch wider at the mid point.

The subframes measure the same at the front (frame) mounting point but 5/8 inch wider at a point near the tank's rear mount.

I've never encountered this before, but then I've never had an occasion to measure tanks, assuming they're all the same. Did Honda get a batch of "Fat Boy" tanks from a supplier and just build a wider subframe to accommodate them? Are these tanks for a different market?  There's nothing special or different about the bike this came off that I can determine; it's a 1986 750F, RC24, production number 651.
 
Anyone have some insight into this mystery?
 
Joe
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Thats' pretty F-ing weird.  I've never ran into this before.  I ran a 750 tank on my 700 with no issues, so I don't think its a 750 vs 700 thing..  And I've swapped subframes between bikes many times.  The fact that the subframe is different is what really baffles me.

 

Was it a red/whi/blu tank to start with?  That would narrow down the possible years.

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IMG_0995.thumb.JPG.512993def61ca2efd7801853be05870a.JPGSee above: RC24, 1986 VFR750F, R/W/B, production #651. Here's a photo of the bike the day it was delivered to me.

 

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Sorry, I read it wrong. 

 

Very nice bikes.

The 750 had the lowers swapped out at some point?

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Yup, different fairings.

 

I thought of the pre-production angle. I can't believe Father Honda would allow that to happen. And the bike is #651. I've had earlier and later bikes, but, as I noted, I'd never had the need to actually measure the tank/subframe.

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Lets rethink the subframe as tank can be from a different bike they now where on, so a pre production it can be, or a X6 stuff? 

 

I know one that actually has a pre production VF1000F, and quite many things don't fit from a real production one, specifically engine parts. Its frame number is 00002 I recall

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Hot to trot race stuff that accidentally made it into your hands maybe? Possible that Honda made some slightly larger frames and tanks for more capacity or better aero or airbox breathing?

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No, but that would be interesting. Larger capacity for endurance racing? I can't imagine it would be much more, maybe a quart (liter)?

JOE

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A friend of mine bought a parts bike, it was an 87 VFR700.  It had a bunch different parts on from someone just trying to cobble something together.  One thing that we didn't notice at first was...   it had a Hurricane 600 tank.  I was amazed how very close the shapes were.  Once we realized it, the little differences started becoming more apparent.  And of course lack of the VFR style petcock was a big one.

 

Obviously not the issue here.  Did the seat integrate with the rear of the tank and the subframe properly? 

 

Edit:  Duh.  You wouldn't know yet.  Sorry.

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Pressurize the tank to increase capacity? 

 

Are the bottom of the tank seams bowed out at the back or is it just the camera angle?

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The fact that this scenario has not come up before (or no one has reported it) is so strange.  I'm sure there were plenty of people in other markets that got the 88 and 89 models swapping parts from all years too.  My vote is pre-production parts that made it out into the wild somehow. 

 

If you get a chance, please show a picture of the sub frame area where the width is different.  I would love to take a look at a couple of mine for comparison.

 

Weird.

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Here ya go....

I took a few minutes to do some accurate measurements. Referring to the photos, I took measurements of the subframe at the front mount, 6" back, 10" back and 14" back (indicated by the yellow tape).

Front= wide frame 11", normal frame 11 1/4"

6"= wide 9 3/4", normal 9 7/8"

10"= wide 7 7/8", normal 8"

14"= wide 6 1/8, normal 5 7/8"

 

Some of the difference is most likely due to manufacturing variances, but the first three "normal" measurements are actually wider. The telling difference is at 14", near the rear tank mount.

 

Speaking of the tank, I measured the tank at the widest exterior point (at the "Ho" in the "HONDA" decal): wide tank= 16", normal= 15 3/8"...

...and at the rear flange's widest point: wide tank= 9 1/8, normal= 8 3/16.

 

As a control, I measured a second "normal" tank; when compared to the first normal tank it's the same at the widest point and 1/4" narrower at the rear flange. So maybe they're all a bit different, but that doesn't take away the fact that the Fat Boy tank won't fit on my other subframes. Hmmmm...

 

Joe

IMG_3248.jpg

IMG_3250.jpg

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On 5/30/2017 at 8:23 AM, BluRoad said:

IMG_0995.thumb.JPG.512993def61ca2efd7801853be05870a.JPGSee above: RC24, 1986 VFR750F, R/W/B, production #651. Here's a photo of the bike the day it was delivered to me.

 

 

Maybe the same person who did the tank and subframe applied the graphics to the side cover and rear cowl.

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I have my -86 tank just light lifted on the bike, so could quit easy messure mine, quit easlly, have to make floor space....to many Project going on at one time...

There is some small difference on the early 86 vs late as far as I know. The early onec had small heat covers on the mufflers/silensers of metal vires, as my -86 has them, but my former -87 had them not, and also the fastners for the farings from the frame at the rear are different. So as I recall my tank has a loose fit at the rear sideways, and I think its not the orginal one there now, so a messurment would be interessting to do and compare to yours. I be back as its done.......

 

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