Trying to remove bolts from Catalytic converter..

The front of the cat has a flexable connections with bolts and springs. No problem here. The back end of the cat has three threaded studs/bolts coming
out of the flange. I'm hoping to reuse the cat but I cannot get these three bolts out of the cat.. I had to cut the rusted nuts off to disassemble and I need to be able to bolt this end of the cat onto the new pipe I'm replacing. Looks like I'm going to have to grind the flange flush on both sides and drill the holes out to accept three new bolts????
I've never seen perminant bolts like this?? I've seen a fixed nut on one flange but not the bolt.????
When I look up new Catalytic converters it looks like there are holes there not threaded studs???
Could these bolts be badlt rusted in place? I wacked it pretty hard and have just about cut one of the "heads" off (they look like a "t" head not a nut shape) and the shaft of the bolt wont budge... Like its part of the flange..
Is this unusual????
Thanks
Steve
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What year Honda? How many miles on it?
Just want to double check: Have you tried soaking the threads as best you can in PB Blaster for a few times a day, then overnight, or similar, then tried breaking them free?
PB Blaster is remarkable stuff. It freed some nasty exhaust bolts/nuts on which I was working a couple of years ago, though it still took some serious leverage.
I think the exhaust bolts are second only to certain suspension bolts in seizing over time. The suspension bolts are prone to break before they free. People seem to have much more luck with exhaust bolts.

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Its a 98 Civic with 75,000 miles

I've never used PB Blaster, I sprayed with wd40.. Because I'm working under the car with the car on ramps and jack stands I dont have enough room to get good leverage so I ususlly have to cut off these stuborn nuts/bolts.
I expected to be able to then remove what was left of the bolts and replace them with new ones. These seem to be one with the flange???
Steve

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WD-40 is not a penetrating oil. PB Blaster is, and it might make a huge difference. It's available at Autozone, Wal-Mart, and the like. Under $5 a can.
I use a long piece of pipe on the handle of my wrenches for leverage. Working beneath the car, one can still often squeeze out that extra 1/8 inch to break free a bolt or nut. Using a hammer on the end of a breaker bar might work, too. Hitting the nut or bolt, vibrating it, can shake free some rust as well.

I haven't dug into the drawings of this car's exhaust yet, so I can't comment. I own a 91 Civic. On a car like yours that is so much younger, I'd feel the PB Blaster is worth a gamble.
Of note: Many exhaust bolts are fine threaded, to reduce the chances of their vibrating free. With rust, heat, and road salt, the fine thread is part of the problem here.
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Check out http://www.hondaautomotiveparts.com for an exploded parts diagram to see whether the original part has studs or bolts.
As for various penetrating oils, they're all just organic liquids, based on their MSDSs, and so would not react chemically with rust. Kerosene was used for this purpose on the old days, and for all anyone really knows, works as well.
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Steve wrote:

The best way to have dealt with those nuts would have been to heat them up with a torch until they were red hot and then remove them with an impact socket (which is less sensitive to heat than chrome sockets). If you don't have access to an oxy-acetylene torch then sometimes a MAPP gas torch will work. I believe that the studs are likely welded to the cat. At least they're shown as part of the cat in the service manual for my '88 Civic.
Eric
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If they are nuts, I have a trick that often helps me. If they are bolts it won't help.
Clamp a pair of vise-grips as hard as you can on a pair of the flats of a nut, then spray penetrant on the end of the stud. (As Elle says, WD-40 really isn't the best choice.) Let it sit for a minute or two and move the vise grips to another pair of flats if they are accessible and repeat. Do that to all the sides of all the nuts you can reach.
Clamping the vise-grips on one axis forces the threads to bottom out and opens up teeny gaps at right angles for the penetrant to get in, and also upsets the bond they have been making over the years. I don't know how much it reduces breakaway torque but it has freed pretty much every nut I've used the technique on.
Mike
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snip

To clarify: WD-40 is absolutely the wrong choice. PB Blaster is the only choice.
Michael's technique with the vise-grips looks real good, though.
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On Tue, 07 Feb 2006 15:33:49 GMT, "Elle"

I went through this today, they are studs that are fluted and pressed in. I cut the nut side off with a torch, then heated the flange and knocked them out with an air hammer. Chip
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