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Header to side pipe flange bolts
Over the past 4 years I have removed and reinstalled the side pipes several times for different reasons. I noticed each time that the bolts became very brittle due to the temperatures and most will snap when trying to unbolt them (I use Conical Top locknuts to eliminate vibrating loose). I switched to grade 8 bolts hoping they would hold up better to the high temp. but this didn't work. In fact, I put new bolts on 1 month ago and while driving on the freeway the side pipe broke loose and was hanging only by the bolt by the rear tire. Yes, this could have been disasterous, I lucked out that there wasn't any damage. I found 1 of the bolts and found that it became brittle and snapped in half.
What kind of bolt will hold up to the heat? Has anyone else had this problem? |
dvcobra, It sounds like the exhaust temps are extreme on your car. Normal exhaust heat shouldn't cause the problem you describe. I don't ever remember a bolt breaking from heat stress. You may want to have someone check the header temp with an infra red gun. We measure our exhaust temps on the dyno and they shouldn't exceed 1500 degress. We tune most engines to run around 1350 to 1400 degrees. Note that this is an internal header temp. Timing will play a big factor in exhaust temps as well as a lean running carb. Other than that I have no suggestions.
Don |
If I measure the temp of the header will this be about the same as the exhaust temp? or is there another way to measure the exhaust temp(besides a dyno)?
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I'm not sure what the relationship is between inside and outside temps. Our gun only goes to 900 degrees and it does peg it when we hold the engine under load at 3500 rpm. Idle is about 750 degrees. I'm sure someone else has more info on this. I didn't ask you about preload on the bolts. Are you sure you're not over tightening the bolts when you install them.
Don |
Dv,
My headers run around 400 deg at the collector, after exiting the body. I use grade 8 bolts with anti-seize on the threads to hold on the sidepipes. The split washers are toast whenever I do maintenance but never a problem with the bolts. |
Agree you may be pumping too much heat into exhaust from retarded timing, overly rich fuel mixture.
I use stainless fastners (nuts & bolts) on the header to "J" pipe and re-use them. No failures or loosning of fastners. Non-stainless split or star washers prevent fastners from heat stress or vibration loosning, but must be replaced when re-assembling. Most True Value hardware stores carry these. For really hard to find items, go to McMaster-Carr on-line (mcmaster.com). |
I just ran all the temp tests on my headers and colletors and saw 500+- idling. I have had mine off several times over the past month and use grade 8 and anti seize also. Once broke loose they come off with you fingers. I had a problem with bolts gaulding on a camaro also till I started using anti seize, but I never measures those headers for temp.
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Hmmm...
Variety of experiences here, so let me add mine to confuse things further: When I used stainless bolts they always galled - I had to snap them off and replace them every time. I switched to Grade 5 bolts and no more problems. Self-locking nuts also seemed to cause the same problem. Not the Nylocks :rolleyes: but the ones that are solid steel and deformed slightly to grip the bolt. So now I just use a regular nut and lock washer and they seem to work fine. The worst of the problem seemed to occur when there was an exhaust leak at the flange. The exhaust hitting the bolt(s) directly - or maybe it was the increased vibration - when the leak started seemed to lock them up quite well. Using solid copper gaskets made the leaking problem go away. Tom |
I like the idea of solid copper gaskets. What did you make them with (sheet size & thickness)? Hardware store?
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The best fasteners for exhaust that I have used are made of A-286 stainless steel. Do not use the 300-series stainless steels as these are not only not very heat resistant, they are also very weak. I really like the NAS1351N - series fasteners for this type of application, since they are designed for lap-joint applications and have a long shank and short threads (threads are not in line with the split). Pegasus may sell them or you could try McMaster-Carr, but I usually get them from the local fastener distributor (Copper State Nut and Bolt). They are not cheap and often have to be ordered.
Also, I agree you likely have higher than normal temps (timing or mixture), but if you go to A-286, they won't get brittle... |
Hey Jack21, ;)
I got mine at Speed Unlimited up your way. Our local muffler shop has'em too here in St Augustine so they should be available lots of places. They're made of fairly soft copper so they conform to the surfaces OK. What sold me on them was multiple reasons: the package said they use'em on AA FUEL cars (that would be more abuse than I'll ever give them), their coefficient of thermal expansion is closer to steel than the aluminum ones that failed, and I'd also blown out a set of the sandwich-type gaskets. So far the copper ones have given no problems after 10K+ miles of, um, testing. :LOL: Tom |
Don, from a previous thread the recommendation was to use " Permatex ULTRA Copper High Temp RTV Silicone " rather than a gasket, still correct or ?
.........thanks |
Just a quick comment:
Lean = Hot Rich = Cool Ed |
Yep, we still send out the ultra high temp RTV with the sidepipes. Works great.
Don |
CobraEd,
You are correct about lean and rich only up until the point where raw fuel makes it into the exhaust and combusts in the exhaust. At that point, the EGTs go way up and the curve is steeper than on the lean side. I've seen this many times in blown dragsters. I'd make the following statement: Lean = Hot Rich = Cool Very Rich = Hot |
I use ultra copper RTV AND gaskets on exhaust connections. With solid copper header gaskets, no leaks or loosening. With sandwich type header to J pipe, no leaks, but gasket falls apart when it's removed. Now that I know where to get copper J pipe gaskets, will use them next time they're apart.
Mentioned this on CACC forum but I don't think here yet. Just within the past week I've solo'd in Cobra. First time since Nov '03. Legs working much better. Navy fighter jocks may disagree with me on this, but driving a Cobra is about as much fun as a guy can have with his clothes on! |
Jack, I'm really glad you've made it back into the Cobra. I bet it was a hard road but well worth it.
Don |
Thanks Don.
It's still a hard road, but feeling somewhat human again. Driving Cobra, nothing wild, just cruising was a big milestone. Perhaps we'll see you at DVSF this year, just as soon as we figure out which DVSF folks are going to. |
Copper gaskets
I tried the silicon method and it didn't work for me, when I pulled the pipes apart the silicone seened powdery. Anyway, I made my own copper gaskets and machined them on a computerized router. They are working great so far (also changed to grade 5 bolts, couldn't find the A-286) If anyone is interested I fabricated a few extra gaskets.
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