 Roll cage bars going through firewalls,, how do you handle it? |
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| FourBlades |
 May 2 2011, 01:51 PM
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#1
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From Wreck to Rockin  Group: Members Posts: 2,055 Joined: 3-December 07 From: Brevard, FL Member No.: 8,414 Region Association: South East States 
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When a roll cage bar/chassis tube goes through a firewall, what do you do? Do you cut the hole close and then weld around it, use seam sealer, just live with a small gap? I am trying to decide what to do with bars connecting the cage to the front and rear suspension points. Thanks, John |
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Replies(1 - 16)
| rick 918-S |
May 2 2011, 02:07 PM
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#2
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Hey nice rack! -Celette Group: Members Posts: 20,494 Joined: 30-December 02 From: Now in Superior WI Member No.: 43 Region Association: Northstar Region 
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QUOTE(FourBlades @ May 2 2011, 02:51 PM)  When a roll cage bar/chassis tube goes through a firewall, what do you do? Do you cut the hole close and then weld around it, use seam sealer, just live with a small gap? I am trying to decide what to do with bars connecting the cage to the front and rear suspension points. Thanks, John Use a lazer pointer to locate the position for the hole. There are more ways to do it than you could think of in an hour but I would start with a small hole to be sure I was lined up where I wanted the tube to pass through. Then once you have proper center for the hole on the firewall use a hole saw. You will likely need to tack a patch over the small hole you made so you have something to drill the centering bit into. Cut the hole slightly larger than your tube. If your racing follow the rule book. If your doing this for you and want a clean looking passage use a split peice of vacuum hose to fill the gap. There will other ways explained her too I'm sure. Many ways to get this done cleanly. |
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| ChrisFoley |
May 2 2011, 03:52 PM
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#3
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I am Tangerine Racing Group: Members Posts: 7,935 Joined: 29-January 03 From: Bolton, CT Member No.: 209 Region Association: None
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Aluminum cover-plates (two halves) riveted in position.
No need for a precision through hole that way. |
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| enderw88 |
May 2 2011, 03:56 PM
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#4
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Newbie Group: Members Posts: 35 Joined: 20-April 11 From: Tucson, AZ Member No.: 12,960 Region Association: Southwest Region |
QUOTE(Racer Chris @ May 2 2011, 02:52 PM) Aluminum cover-plates (two halves) riveted in position. No need for a precision through hole that way. So it appears from both replies that you should avoid a structural joint between the cage and the sheet metal it may pass through? (IMG:style_emoticons/default/confused24.gif) This seems reasonable since the elements in the roll cage should only be in tension or compression. Joining them to the sheet metal as they pass though would apply bending loads as the chassis deflected. |
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| URY914 |
May 2 2011, 05:58 PM
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#5
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I built the lightest 914 in the history of mankind. Group: Members Posts: 121,091 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None |
I did what Chris said. Hole can by oversized and with covers on both sides no one ever knows.
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| Krieger |
May 2 2011, 06:00 PM
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#6
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Advanced Member Group: Members Posts: 4,729 Joined: 24-May 04 From: Santa Rosa CA Member No.: 2,104 Region Association: None
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I cut some thin aluminum plates and used seam sealer to glue them in/fill gaps.
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| Krieger |
May 2 2011, 06:02 PM
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#7
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Advanced Member Group: Members Posts: 4,729 Joined: 24-May 04 From: Santa Rosa CA Member No.: 2,104 Region Association: None
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To clarify what I did I cut a top half and a bottom half. I think this is what chris is saying too. I used sheet metal.
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| J P Stein |
May 2 2011, 06:18 PM
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#8
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
Here's what I did.
Attached thumbnail(s)  
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| stewteral |
May 2 2011, 06:31 PM
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#9
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Old Member Group: Members Posts: 384 Joined: 4-December 07 From: Camarillo, CA Member No.: 8,424 Region Association: Southern California |
QUOTE(FourBlades @ May 2 2011, 12:51 PM) When a roll cage bar/chassis tube goes through a firewall, what do you do? Do you cut the hole close and then weld around it, use seam sealer, just live with a small gap? I am trying to decide what to do with bars connecting the cage to the front and rear suspension points. Thanks, John Hi John, Given that the 914 moncoque is a "Flexy Flier" on a good day, when it came to sealing the holes through the firewalls, I took a different approach: 1) Chassis stiffness comes from a complete rollcage that reaches fore & aft to brace the load point at the top of the suspension at each corner. 2) Rather than trying to weld to the Flexy Flier, which I'm betting would creak, groan and make continually annoying noises. I got some THICK wetsuit foam sheeting, wrapped around the tubes, glued it all together creating a membrane barrier and pop-riveted the outer edges to the PURE 914 sheet metal. 3) The dirt & dust stays out and once I get on track with the V8 roaring, I don't hear ANY unusual chassis noises at ALL! Obviously, this is a brilliant plan!! (IMG:style_emoticons/default/smile.gif) Terry |
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| Krank |
May 2 2011, 08:02 PM
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#10
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Member Group: Members Posts: 140 Joined: 11-October 09 From: Winnipeg, MB Member No.: 10,922 Region Association: Canada |
Although I have never installed on, nor been apart of an installation, I would think the priority would be to seal the hole. After all, it is a "FIREWALL" aint it? Smoke, fire, fumes all have to be isolated from the passenger compartment by law and by good sense.
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| Mike Bellis |
May 2 2011, 08:13 PM
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#11
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Resident Electrician Group: Members Posts: 8,345 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None
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My holes are tight. 1/8" bigger than my tube. I used black silicone to seal the gap. Looks good and I don't need an extra cover plate.
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| J P Stein |
May 2 2011, 10:03 PM
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#12
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Irrelevant old fart Group: Members Posts: 8,797 Joined: 30-December 02 From: Vancouver, WA Member No.: 45 Region Association: None |
QUOTE(kg6dxn @ May 2 2011, 07:13 PM) My holes are tight. 1/8" bigger than my tube. I used black silicone to seal the gap. Looks good and I don't need an extra cover plate. Interesting.....let's see a pic. |
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| Mike Bellis |
May 2 2011, 10:23 PM
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#13
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Resident Electrician Group: Members Posts: 8,345 Joined: 22-June 09 From: Midlothian TX Member No.: 10,496 Region Association: None
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QUOTE(J P Stein @ May 2 2011, 09:03 PM) QUOTE(kg6dxn @ May 2 2011, 07:13 PM) My holes are tight. 1/8" bigger than my tube. I used black silicone to seal the gap. Looks good and I don't need an extra cover plate. Interesting.....let's see a pic. Too dark tonight for a new pic but here's the best one I could find. You can see in the background the tube going through the firewall. It's welded to the hoop and the rear shock tower through the factory hole. The firewall was cut with a hole saw...   |
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| FourBlades |
May 3 2011, 06:46 AM
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#14
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From Wreck to Rockin Group: Members Posts: 2,055 Joined: 3-December 07 From: Brevard, FL Member No.: 8,414 Region Association: South East States
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Thanks for all the great replies. I am looking at what the original builders of my IMSA car did and it looks very rough. They cut way oversize holes and then riveted aluminum or very thin sheet metal around it. I am trying to decide if I should leave it "original" or make it a little neater and more functional. They did not seem overly concerned about holes between the passenger and engine or front trunk area. I'll post some pictures tonight. John |
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| FourBlades |
May 3 2011, 06:48 AM
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#15
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From Wreck to Rockin Group: Members Posts: 2,055 Joined: 3-December 07 From: Brevard, FL Member No.: 8,414 Region Association: South East States
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QUOTE(J P Stein @ May 2 2011, 05:18 PM) Here's what I did. I like how you did this JP. John |
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| stugray |
May 3 2011, 09:33 AM
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#16
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Advanced Member Group: Members Posts: 3,825 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None |
Just an observation:
1 - For the fronts, the heater hose holes are perfectly lined up to put a support from my front suspension shock tower plate to the base of my rollbar. I am considering putting a support in there, but there is some confusion about whether I am allowed to do this or not in vintage racing (I'll wait a season or two). 2 - 914s have THREE firewalls: One between engine & driver, one between gas tank & driver, and one between front trunk & gas tank. Since I removed my gas tank and replaced it with a fuel cell in the front trunk, WHICH wall is my firewall now? Stu |
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| URY914 |
May 3 2011, 10:14 AM
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#17
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I built the lightest 914 in the history of mankind. Group: Members Posts: 121,091 Joined: 3-February 03 From: Jacksonville, FL Member No.: 222 Region Association: None |
Bulkheads. They are called bulkheads. A fire wall is between the driver/passenger and the engine.
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