The dreaded SWB crack

andysharrock · #1 24th May 2016, 12:58

bloody typical had it in gel coat for months no problem now its painted starting to crack on top of the window screen. The car has such a high gloss finish it stands out and catches your eye. Good job I have a good understanding with the paint shop, I give him lots of money and he repairs and repaints the car..be sorted for friday

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Jaguartvr · #2 24th May 2016, 13:23

I know it would be a bit of a bodge but could the stress crack be covered with a little alloy trim? Lots of cars have a trim on the rear and I'm sure I've seen them on the front too. Sods law says that as soon as you repair it, it will happen again.

I need to bring the bottom rear edges of the bonnet in slightly. I don't want to do the 7mm cut as I feel it will put too much stress into the GRP that might crack later. I think it may also create a ridge that could be seen and felt on the outside.
I'm going to try 3x 2mm cuts in different sections to try and spread the stress.

andysharrock · #3 24th May 2016, 13:30

think if I did an other build the same I would cut it and have a line in it. looks like its going to be a common fault if I drove it like Stirling moss or on track days I could understand a stress crack. But this has come about when its parked on the drive for two weeks not in use ,,,,buger

Jaguartvr · #4 24th May 2016, 13:32

Cracking due to heat? Had a few hot days, darkish paint?

Cut and a distinctive line would be a good idea.

Mister Towed · #5 24th May 2016, 16:23

Quote:

Originally Posted by Jaguartvr

I need to bring the bottom rear edges of the bonnet in slightly. I don't want to do the 7mm cut as I feel it will put too much stress into the GRP that might crack later. I think it may also create a ridge that could be seen and felt on the outside.
I'm going to try 3x 2mm cuts in different sections to try and spread the stress.

The Sammio kits had the same issue in that the bottom edges of the bonnet stuck out proud of the body -

I sorted that by using a 1mm cutting disc and turning the return into a sort of comb, before bending and clamping it to the desired curve and fibreglassing it in place -

It's been on the road for three years now and there are no stress cracks or cracks in the paint where I made that mod.

One thing to note though is that a very experienced professional Hot Rod body manufacturer told me that cellulose is more flexible than 2 pack so is less prone to cracking* on a panel that's subject to any sort of flex (which the Sammio bonnet is when it's open). I guess the SWB bonnet is fairly flexible when it's open too?

That was one of the reasons I chose to use old-fashioned cellulose on a fibreglass car.

I hope that helps.

*Just popped back in to edit this post as I can't find anything on the 'net that backs up cellulose being more flexible than 2 pack. All I can say is that my cellulose paint hasn't cracked where I carried out this mod.

Jeff H · #6 24th May 2016, 19:26

Quote:

Originally Posted by andysharrock

think if I did an other build the same I would cut it and have a line in it. looks like its going to be a common fault if I drove it like Stirling moss or on track days I could understand a stress crack. But this has come about when its parked on the drive for two weeks not in use ,,,,buger

I do wonder if sliding the pillar cover underneath the roof is the problem ? it puts pressure on that part of the roof.

Mine fits perfectly on the nearside, but the drivers side i have had to cut the little end piece off to get it to line up.

Good shout ref putting a slot in it, make it a feature of the car.

Did you get my PM by the way ?

andysharrock · #7 24th May 2016, 19:36

yep jeff did reply no problem

Jeff H · #8 24th May 2016, 19:38

Quote:

Originally Posted by andysharrock

yep jeff did reply no problem

Ahh ok,

It didn't show up in my messages for some reason.

smash · #9 25th May 2016, 08:27

Quote:

Originally Posted by andysharrock

bloody typical had it in gel coat for months no problem now its painted starting to crack on top of the window screen. The car has such a high gloss finish it stands out and catches your eye. Good job I have a good understanding with the paint shop, I give him lots of money and he repairs and repaints the car..be sorted for friday

Sorry to hear this - fully understand the feeling - hope it's all sorted so sale can continue.

andysharrock · #10 25th May 2016, 08:32

well better to happen now and get it sorted then after sale, typical two people phone yesterday to view this weekend put them off till next week car will be sorted finger crossed. The Z3 must have a lot of flex in the chases only time will tell with this one. andy

Roadster · #11 25th May 2016, 15:13

Quote:

Originally Posted by andysharrock

well better to happen now and get it sorted then after sale, typical two people phone yesterday to view this weekend put them off till next week car will be sorted finger crossed. The Z3 must have a lot of flex in the chases only time will tell with this one. andy

Have you considered the filler used on abs bumpers, it moves but doesn't crack

redratbike · #12 25th May 2016, 21:19

Maybe something like this may help??

http://www.strong-strut.com/body-brace.htm

andysharrock · #13 27th May 2016, 07:54

Quote:

Originally Posted by redratbike

Maybe something like this may help??

http://www.strong-strut.com/body-brace.htm

god that looks a good bit of kit

andysharrock · #14 27th May 2016, 08:11

I do think as at the moment there are only two cars we no of having this fault it is probably the amount of flex in the car causing the problem. stiffening the chases could work but with coil overs you will be in for a rough ride . Sheffield is full of pot holes and bloody speed bumps ever 100 yards where I live. I am not a big fan of the kit wrapping around the window screen it looks good but if you ever needed to change it you would have to trash the kit/paint work. Cutting the kit at the top of the window screen and have a 2mm gap may or may not help with the crack only time will tell but it would help getting the window screen out if a strip could be removed easily . andy

Nubodi Automotive · #15 27th May 2016, 08:22

We have a solution to this. If anyone wants to know how to solve this problem please call and we can help. We are booked with builds till next year now so don't have time to post tech articles any more. 01189833709.

smash · #16 27th May 2016, 17:38

"Weeeeeel-come Home.........Weeeeeelcome...."

He was blind as well

andysharrock · #17 27th May 2016, 18:03

all sorted the guy I use can have his faults but he always pulls it out the bag when I need him. Would have been nice not to happen in the first place but £80 for a quick fix and repaint happy again,just need to give it a wash

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froggyman · #18 28th May 2016, 09:48

Looking good now, glad it wasn't too stressful for you or the wallet.

smash · #19 30th May 2016, 10:20

£80 - that was a touch! GLWS...

Axel · #20 30th May 2016, 11:27

Sure it will not crack again? This area is under a lot of stress!
The metal A-pillar with its windscreen is very stiff and has a long lever from bottom to top where it is glued to the fibreglass roof...
I would keep an eye to this area if this is a structual problem or only a bad paintjob thing! Just my 2 cents...