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Regarding Avanti Hogtrogh replacement


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3.19Mar23RHSTorqueBoxviewfromrear-showsattachmentponttobottomendofRolloverBar.thumb.JPG.b87451be4e5d691db54a779e54b74910.JPG19Nov23TorqueBoxespulledintoplaceagainstBulkheadswithScrew.insideview.thumb.JPG.73daa099e7b7f23b5866a3fb9acfe866.JPGHi All. I have recently installed New 'Hogtroghs' in my '81 Avanti II.  I have some final riveting and End Caps to fit but HT's are 'in'. I thought I would report my experience on this task in case it helps anybody else.  I used the kit supplied by 'Classic enterprises'- this is the same two-piece set used in Dick Steinkamp's Blog, of which I utilised as a guideline for my own installation. I chose these because I liked the idea of NOT having to cut out and re build fibreglass sections, as are required with some other kits. I rapidly found out there are lots of impediments to progress that have no mention and were a rude awakening in many instances. My process took months because I am 70 miles away from the job and can only make the trip on sundays- henceforth there was only so much I could do at a time.

I did have the luxury of having the body completely removed from the Frame and despite this, the preparation and fit-up is no simple task- it was hard work, especially if you are lying on your back under the body.  Classic Enterprises sent my kit in stainless steel despite my specifying 'plain steel' (and charging accordingly !). In retrospect I think it may have been a better outcome after all even though we don't get snow & salt down here.  The Troughs are a well made product but myriad spotweld burrs and sharp edges in their fabrication are downright dangerous and should be buffed off before you do anything else.  Getting the old boxes off is cutting disc/ grinder work and simple enough, but hidden pop rivets require some tracing before you can drill their heads out, pull everything out and scrape off old mastic. It is impossible to fit the contoured 'C' channel into the sills/rockers until a number of rivet ends are ground off in some locations, as they interfere with a close fit up to the floor and prevents it pushing into place.  Lots of fibreglass lumps on the inside of the sills needed grinding out as well as removal of the white filler strips along the sill bottom edge.  A row of rivets needs grinding off flush along here as well. I bought an inexpensive Belt File tool and #40 grit belts for this purpose and found it worth every penny due to it's reach. Once this is done, the 'C' Channel fits up without much effort. The tab at the forward edge of the Channel should be bent to better fit the shape of the wheel arch panel- It will need quite some fancy manipulation but it's worth the effort. The Channel is meant to be fitted up against the meagre remains of the outer edge of the original Hogtrough to ensure proper location and riveted or screwed to it. This means that some rivet holes will need to be drilled in advance and a few dummy fitups are required- enough to assure complete lineup of parts when final fitting. In my installation I discarded the silicone sealant sent with the kit and on advice of my 'Body Man' employed Sika Auto Body Adhesive. Overkill?... perhaps- expensive too, but it's used to bond car panels together without rivets and welds.  There are a few places where the contour of the replacement parts do not intimately fit the floor so I interposed a strip of PVC sheet to shim the spaces before squeezing rivets there. Any gaps/voids are eliminated with bonding material between them, and stainless steel pop rivets pulled before it sets solid. The lip of the 'Hogtrough' Box needs to be fitted either above or below the corresponding lower lip of the 'C' Channel. Without making this story even longer- I found the corresponding joint contours did not match well on fitup and positioning the HT box lip UNDER the 'C' channel afforded a more intimate fit because it naturally pushed parts together. This meant that I had to drill holes in the HT lip to allow plug welding later. (Worst case, I may insert some self tapping screws along that seam, which may require the removal of a little of the fibreglass along  lower sill). In effect, if the adhesive I used there later does its job, I may not need welds or screws at all.  To be honest I believe fitting the HT box lip above the 'C' channel lip would have been better, but you will need to pull the parts together with screws. This requires clearance drilling the 'C' channel holes to allow the pull down of the HT lip without the screws fouling.  Fitting the 'Bulkhead' under the Rollover Bar base requires some accurate drilling of the 3/8" high tensile bolt studs under the floor. Do try to do this task accurately- otherwise you may end up with an oval hole to tap out which will  weaken your thread. Once these are drilled out the reinforcing plate comes off leaving you to re drill the holes 7/16" and tap them 1/2" UNC for the setscrews sent with the kit.  Once the Bulkheads can be bolted up, trial fit the HT Box because the Bulkhead needs to be adjusted laterally to ensure the HT Boxes position properly. I had to adjust the shape of the Bulkhead by hammering and grinding a little otherwise the HT Boxes would be out of alignment. This rectified and Bulkheads bolted down, I found I also had to use a self tapping screw through the HT Box wall to pull it against the Bulkhead and line up with my already drilled rivet holes. The final installation required two sets of hands and judicious prying with a screwdriver along the bottom lip, a lot of grunting, but it did go in. To ensure the best possible fit, we placed a 2" x 4" timber under the HT Boxes and pushed it into contact with a pair of jacks. Line up with pre drilled Rivets and Bulkhead screw was established, pulled, and the rest is history- but pre fitting and preparation cannot be overemphasized or taken lightly as the adhesive sets quickly.

I'd hate to have to do this job ever again but at least I'm forewarned. If you have access to a hoist for a considerable time, by all means that will speed the job up and make things easier by far- failing that lift your body a high as possible. I don't believe a top quality, accurate job can be achieved in just a weekend by one person and suspect that every car will have it's individual variables. Budget for a far longer time and ask yourself "what if..." .



Edited by Zedman
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Wow, sure seems like you did it correctly. Doing what you did can you guesstimate the amount of hours involved for that job? Thanks for posting and explaining the work involved.

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Posted (edited)
1 hour ago, Stacey said:

Wow, sure seems like you did it correctly. Doing what you did can you guesstimate the amount of hours involved for that job? Thanks for posting and explaining the work involved.

Hi Stacey-

Firstly, I DO repeat- this is for Classic's multi piece kit and is no criticism of their version- I did not want to be cutting and repairing Fibreglass and this kit addresses that issue very nicely.  :-0)

I've got quite a lot of pictures but they'd need reduction in size before I'd post 'em.

To be honest I reckon I dithered about this job far longer than necessary but I wanted the best outcome possible- and it's not completely over, because I'd like more rivets installed and must fit the End Caps. I may still need to plug weld/ screw seams together if adhesive bonding is insufficient.  Bear in mind working on my back, being really anal and finding one's way slowed things considerably.

  • Removal of both old HT's (not much left on RH Side!) and scraping old mastic off  took about 5 hours.
  • Clearancing for the C channels (grinding fibreglass and rivets out) realistically took 7 hours.
  • Tracing and drilling old rivet heads took 1 hour.
  • Buffing down hazardous sharp edges and spotweld burrs took 1 hour.
  • C channel front tab- bending to fit took 1 hour.
  • Adjusting the fit of the Bulkheads to the Boxes for accuracy's sake took 1 hour.
  • What did take me far longer than necessary was struggling with pulling the seams together with screws- The idea is very sound but made difficult because I failed to appreciate the need to clearance drill the lower lip and was shredding the screwdriver slots in the screws (I was using Galvanised Self drilling posidrive pan head screws, but should have been hex heads IMHO for initial fitup.) This was a terrible waste of time and should have been a far better outcome. I must have wasted at least 6 hours on this alone. Stainless Steel can be tough to drill, too!
  • Marking and drilling new Pop Rivet holes took two hours.
  • Too many trial fitups of Boxes C channels and Bulkhead would have taken at least 4 hours.
  • Drilling and tapping holes for the Rollover Bars Bulkhead took 4 hours (bloody tough material, those screws !).
  • Final fit with two of us on the job, Sika adhesive all over, most pop rivets pulled and a 2"x4" jacked up took about 2 hours.
  • Total time approx 32 hours whilst headscratching- with the benefit of bitter experience.... half that time. All the online blogs are beneficial but you can't tell how deep the puddle is until you stand in it  😉
Edited by Zedman
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Thanks for the very accurate summary of what's involved with this job. I did this on my own Avanti way back in 1993 (pre-digital photo era) and your report brought back a lot of memories! I remember that the roll-bar bolts were quite challenging as the only access was through the ashtray openings in the rear armrests. Removing the old, rusted troughs was one of the dirtiest jobs I've ever done - I recall filling an entire garbage can with rust! 

Thankfully, this is a job that if done properly, only has to be done once. My hog troughs are still holding up well 31 years later. Good luck with the rest of your project. 


Adam DeRosa

Edited by AD
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