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Pre-cat Problem

267 Views 8 Replies 9 Participants Last post by  ToolUser
I recently bought a 75k mile Spyder and the first owner said she knew nothing about a pre cat so I need to replace it. I’m really on a budget at the moment so I’m trying to figure out my best options. For some reason the current headers specifically have more rust than anything else on the car. I’m going between gutting the pre cats or buying the MonkeyWrench headers. Anyone have any suggestions?
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Just gut the pre caty...cheapest option!
If swapping out the header, beware the 3 amigos!
Use good quality system synthetic oil and change it around 5000-6000 mile intervals. Inspect the pre cats now. If they are intact I’d say you are good to go. I’ve read that pre cat failure results after the oil control rings seize. Frequent oil changes prevent oil rings from seizing.
Only gut the precats if you are prepared to be very careful with the process and make sure you do not breathe any of the ceramic dust that will be created. I recommend first inspecting the pre-cats through the O2 sensor holes (you have to do this anyway at the start) and if the precats look intact, you can sell them to someone who needs them to to pass inspection. I have had good luck with an Ebay Stainless header, though make sure you use OEM gaskets
I gutted one this weekend. I did it over a small box to collect all the material and it wasn’t that dusty but they didn’t want to come out easily. Next time I do one, I’ll spend more time working from the bottom to prevent damaging the bung threads. I was getting a little impatient at attacking it from the top even though I knew this was a possibility. The only tap I didn’t have was a 18mm x 1.5
I made a chaser from an old bolt but that didn’t work so got to order a tap. BTW, don’t try to force the oxygen sensor in a damaged bung or you’ll need a die for that.😁
I did this awhile back and would suggest spending the week before you start spraying every bolt with a good penetrating oil every day, maybe twice a day. And tapping with a hammer to help move it along... The "three amigos" in particular, but the head studs too. I snapped one of the three amigos but was able to back the stud out with vice grips and heat (and a lot more penetrating oil) after the manifold was off the car. On the head studs a couple of the nuts wouldn't budge but the studs backed out of the head which was just as good. I replaced all studs and nuts with all new hardware and used a new gasket when reassembling.
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