Clam wings/ improved top screws

[IamScotticus]

I was looking for hold down screws with more surface area and found these on McMaster. 

1/4-20 stainless.  Just a smidge larger than the OE 6mm. The hole in the support will need opening up slightly.

Head diameter is .75".

 

I'm willing to part with 3 pairs to who would like them, no charge, just not fast.

 

PM please

 

 

[Christopher smith]

I used the stainless steel carriage bolts and stainless washers with rubber washers to protect the fiberglass. Deems to work ok but will admit I have not taken them to top speed so far.

[IamScotticus]

I  trying to prevent spider cracks on the clams. 

not overtightend, of course. 

[Christopher smith]

I was concerned about cracking the gelcoat also, so considered epoxy bonding slightly curved, wide fender washers to the fiberglass on the underside to stiffen the whole assembly, but decided I did not need it. I think it could be done without actually removing the clamshells. The carriage bolts look nice since they have no slots in the head but I did need to file a little of the fiberglass to fit them since they have a square cross section just under the head that keeps them from turning.

[IamScotticus]

Don't tighten fiberglass too much, or make the fastener holes too tight.   GRP needs to float.

When drilling new holes on GRP, finish edges with slight bevels on both sides.

But spider cracks will happen all kinds of ways.  Just accept that you (like I am now) that a paint job may be in the footure.

Edited March 28, 2022 by IamScotticus

[Christopher smith]

Just a thought----I agree that the GRP can have issues but also noted that the thickness of the wings is not enough to take severe loadings concentrated in a fastener area. They are made by hand lay up with fiberglass mat or spray-up process with polyester resin. This is not as strong as GRP parts made with multiple layers of glass cloth or better yet, carbon fiber. One solution would be to build up just a bit more thickness of a 40-50 mm diameter using additional mat or glass cloth and suitable resin (polyester or clear unfilled  2 part epoxy) easily available at a boat repair supply place or even an automotive supply. So if you have the wings off and upside down, it is an easy fix to make that area much stronger and less prone to failure in use.

[MV8]

Other options are grommets with short spacers on the fastener that prevent over tightening, vibration damping mounts, sleeve/step washers, or a rubber washer under the head as well as underneath. Not as flush/pretty though.