BN7 top problem

[Michael Oritt]

At speed the rear (folding) bow on my wife's BN7 folds forward against the fixed (main) bow, causing the top to collapse. The rear bow fits nicely along the top's seam and the top itself is a very good and snug fit. Short of putting some kind of strut between the two bows, what can I do to prevent this from happening?

 

[Dave Russell]

Hi Michael,
This is pretty strange. Normally the rear bow is set at a considerable angle "back" from vertical. The tension of the top material tries to pull this bow even further back. it is restrained from collapsing backward by the two longitudnal straps connected to the front bow. See the attached pic.

It sounds like a mismatch between the top configuration & the frame. Or the straps are too short which keeps the rear bow too vertical. Try moving the rear bow forward on your BN1 & you will see what I'm talking about.
D

 

[Michael Oritt]

"Hi Michael,

This is pretty strange. Normally the rear bow is set at a considerable angle "back" from vertical. The tension of the top material tries to pull this bow even further back. it is restrained from collapsing backward by the two longitudnal straps connected to the front bow. See the attached pic.

It sounds like a mismatch between the top configuration & the frame. Or the straps are too short which keeps the rear bow too vertical. Try moving the rear bow forward on your BN1 & you will see what I'm talking about."
-------------------

Dave--

As you perhaps know, the top on the BN7 is much more simple than the "convertible" top of our cars. I know what you are saying, but judging by the perfect alignment of the rear
bow under the top's seam I do not think that it is a matter of them being "mismatched". I'm wondering if the rivet that holds the two bows together has simply worn over the years and that somehow I could induce more friction at the pivot joint which would make the rear bow less likely to move? I was considering peening over the rivet or putting some kind of dimple in the pivotting bow....

Best--Michael

 

[Dave Russell]

Michael,
While the BN1 & BN7 top frames are different, they still work on the same principle. The tension of the fabric tries to pull the bow down, the webbing straps hold it up. If you will notice, the pic I attached of a BN7 top, shows the bow being below the top seam. I suspect your top has the bow positioned at the balance point. If it were moved back slightly, maybe the fabric would try to pull the bow down against the web tension.

Compare the distance from rear shroud to top seam on another similar car.

Maybe your top was just made wrong with the seam too high in relation to the bow assembly. Maybe the webbing is just a little too short. If the top is cut & fitted properly, there should be quite a bit of down force on the bow to prevent it from moving forward. Can you easily push the bow forward?

I don't think any amount of added friction will help for long.
D

 

[Michael Oritt]

[ QUOTE ]
Michael,
the pic I attached of a BN7 top, shows the bow being below the top seam. I suspect your top has the bow positioned at the balance point. If it were moved back slightly, maybe the fabric would try to pull the bow down against the web tension.

Compare the distance from rear shroud to top seam on another similar car.

Maybe your top was just made wrong with the seam too high in relation to the bow assembly. Maybe the webbing is just a little too short. If the top is cut & fitted properly, there should be quite a bit of down force on the bow to prevent it from moving forward. Can you easily push the bow forward?

D

[/ QUOTE ]

Dave--

Yes I can push to bow forward rather easily and you're likely correct--the bow seems to fit AT the seam rather than BELOW it. I'll get out my webbing-stretcher and see if that helps.