The amount of stretch in a top or tonneau cover for a given material is built
into the tailoring. A top is designed to have an exact, uniform clearance
around the side windows, and one can get an initial feel for the amount of
tightness or stretch needed overall by pulling on the front until that
clearance is the same all around the side windows. The rain gutters flow into
the window posts, and the front corner side flaps should come fairly close to
the posts.
The amount of stretch also varies according to the material. The original
Everflex or Vynide material was fairly hefty yet stretched just the right
amount. Same with Stayfast. Heritage repro everflex is thinner and stretches
more than the original. On the other hand, Robbins' in-house Colonial Grain
is very heavy and coarse and has comparatively little give.
As the tailoring on tops got more complicated with more double and triple
layers and built-in reinforcing flaps such as on an MGB top, there is little
stretch possible apart from the flat main roof section.
The bows themselves are often ignored. As the tailoring is hopefully based on
an original car (not always the case), the positioning of the bows should be
as close to original as possible. With fifty years' worth of abuse and
rebuilding , especially in the rear wheelarch area, the position of the BT 7's
bows' locating tubes or BJ 8's plinth can vary considerably. Make sure the
arcs are even. Measure up from the floors, especially on a BJ 8, to make sure
the bows are square and even side to side in relation to the windshield, and
ensure they fold down neatly without colliding with each other in the rear
well. BN 6 and 7 bows have adjuster screws built into the feet.
A tonneau cover of course needs the bow and stiffeners in place, or in the
case of the two-seaters, the top stowed properly (facing rearwards on the BN
6-7). Washers can be dropped into the locating tubes to level out a tonneau
bow.
Mark all centres on top & body, fix the back first, pull the material forward,
temporarily tack the front centre, and work out towards the sides.
Vinyl acquires serious creases from being folded up in a box often for years.
These creases need to be relaxed with a heat gun first (but don't liquefy the
vinyl !), as these pinch points add up and reduce the overall dimensions.
The finished job should be steamed with a hand steamer to relax the fabric and
take out creases, but this is not a cure-all for a bad fit.
Best regards
Peter
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Healeys@autox.team.net
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