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  #1  
Old 02-10-2019, 11:12 AM
steve murray's Avatar
steve murray steve murray is offline
 
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Location: Flat Rock, North Carolina
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Default Need Ideas on Cowl Fiberglass Repair Approach?

Had the cowl looking pretty good, then realized my prop spacing simulator was off by about 1/2".....^%$%^&(&..... the cowl is too long and would hit the spinner.

OK, decided to remove all the firewall hinges and then remove 1/2 inch off firewall side of the cowling. Normal routine of many times cowling on\off as I try to sneak up on a good fit the 2nd time around....

Now as I try to reinsert the cowl split line hinges I understand the outside circumference of the firewall is larger than the cowl. and the cowl will no longer fit. Picture below is with the horizontal pins inserted as far as they will go. Both sides of the cowling are about the same gap.



Looking for ideas on the best way to repair this issue.

1) Should I remove top or bottom split line horizontal hinges and scarf a new piece in place and reinstall the hinge? If I take this approach, do I need to remove both hinges or just top or bottom?

2) Am I better advised to split the cowl with major surgery just above the honeycomb area and perform two sided splice and leave the old hinges in place?

I have read some the the "Sticky" posts in fiberglass repair section, a bit nervous about having a small scarf joint next to the hinge that starts a 0" and goes to about 1/2"?? Can I (newbie fiberglass skills pull this off?)_
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  #2  
Old 02-10-2019, 12:18 PM
Kyle Boatright Kyle Boatright is offline
 
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Location: Atlanta, GA
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Me?

I'd remove the hinges and scarf in new material. You should only have to do the scarf repair on the top or the bottom - not both.

Clamp your cowl in place without the hinges, and measure the gap. Make a set of marks on <say> your bottom cowl to let you know how much material to add along each side. Leave those reference marks so you can trim after your scarf repair.

Now, get your grinder, make a 1:10 or thereabouts scarf, back the area with something flat, and do your layup. Mark your trim line using the reference marks you made, trim it, and you're back in business.
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Old 02-10-2019, 12:48 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Kyle Boatright View Post
Me?

I'd remove the hinges and scarf in new material. You should only have to do the scarf repair on the top or the bottom - not both.

Clamp your cowl in place without the hinges, and measure the gap. Make a set of marks on <say> your bottom cowl to let you know how much material to add along each side. Leave those reference marks so you can trim after your scarf repair.

Now, get your grinder, make a 1:10 or thereabouts scarf, back the area with something flat, and do your layup. Mark your trim line using the reference marks you made, trim it, and you're back in business.
+1

I would do this on the top cowl. If you do this on the bottom, your new rivets will end up close to the transition line of the scarf joint where it will not have much fabric reinforcement.

Larry
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Old 02-10-2019, 01:16 PM
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Kyle & Larry, thanks for the quick posts, rainy day here in Western North Carolina, probably good day for fiberglass work.

Larry, Good idea on performing scarf on top cowl vs bottom for rivet edge distance, obvious once you pointed it out but I have tunnel vision at this point and it would have been 50\50 chance of me starting on choosing top or bottom - Thanks.

Kyle, need a bit of clarification, 1) would you remove both the top & bottom hinge or if I scarf only on the top side, is it feasible to reuse the bottom hinge?2) Can you elaborate on the trim line reference marks, I am not following this part of the concept.
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Old 02-10-2019, 02:13 PM
lr172 lr172 is offline
 
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Quote:
Originally Posted by steve murray View Post
Kyle & Larry, thanks for the quick posts, rainy day here in Western North Carolina, probably good day for fiberglass work.

Larry, Good idea on performing scarf on top cowl vs bottom for rivet edge distance, obvious once you pointed it out but I have tunnel vision at this point and it would have been 50\50 chance of me starting on choosing top or bottom - Thanks.

Kyle, need a bit of clarification, 1) would you remove both the top & bottom hinge or if I scarf only on the top side, is it feasible to reuse the bottom hinge?2) Can you elaborate on the trim line reference marks, I am not following this part of the concept.
No need to remove the hinge from the bottom. Perform your work on the top with its hinge removed. Get the new line/edge on the top piece to give a good fit. Then mount the upper hinge, as you did initially.

Do a search, as DanH has a very good post with details on how to make a good scarf for this type of repair.
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  #6  
Old 02-10-2019, 02:17 PM
lr172 lr172 is offline
 
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Originally Posted by steve murray View Post
2) Can you elaborate on the trim line reference marks, I am not following this part of the concept.
Take measurement of the gap. When you clamp some metal onto the outer edge of the cowl to form your outside edge, you can make some marks based upon your measurement and use this for trimming. You don't really need to do this though. You can just be sure to make your repair long enough to close the gap with some extra and then progressively trim to fit, just as you did for your initial cowl fit up.

Larry
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  #7  
Old 02-10-2019, 03:30 PM
Kyle Boatright Kyle Boatright is offline
 
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Quote:
Originally Posted by steve murray View Post

Kyle, need a bit of clarification, 1) would you remove both the top & bottom hinge or if I scarf only on the top side, is it feasible to reuse the bottom hinge?2) Can you elaborate on the trim line reference marks, I am not following this part of the concept.
1) I'd try and do it only removing one set of hinges. Might be easier to remove the ones on top.

2) The trim line... Let's say you decide that at the front of the cowl, you don't need to add any material, but at the back, you need to add 1/2". So, maybe you make a mark on the top cowl, 2" from the split line at the front and a mark 1.5" from the split line at the back. Draw a line to connect the two and that's your reference line.

Now, if you scarf in new material (and don't destroy the reference line) you can use that line and draw a new line 2" below it which will give you a pretty good starting point for where to trim the scarfed material. Obviously, you don't want to have to do this over, so make that first trim a bit long and shape to fit.

This is a very doable repair. But a pain.
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