Exhaust mainfold and downpipe connection
 

Hello,

I have a 71 chevy c20 with a 350

According to the inspection station, I have an exhaust leak. It's pretty obvious because the downpipe connecting to the exhaust manifold can be pivoted and moved around a little, since the bolts holding it on aren't tight.

This image (found on another thread) shows the connection between manifold and downpipe: http://67-72chevytrucks.com/vboard/a...1&d=1341063890

However, I'm having trouble getting the bolts off- they are essentially fused together because of the rust. So before I spend more time trying to get them to move, I'm wondering if there's a gasket in between the manifold and the downpipe, that i would need to order? I want to order it before hand so I can save some time, but I'm not sure if a gasket even goes in between there?

Thanks

-David

Re: Exhaust mainfold and downpipe connection
 

Yeah there is a gasket. I think the official name is "exhaust flange gasket" They are referred to as doughnut gasket because they look like a doughnut. Here is a pic from summit, they can be found at most local auto parts stores. You may need to use a healthy amount of PB blaster or a torch to get those studs to let go of the nuts. Seems every time I try I break at least one stud off. My last set of ram horns I took to a local mechanic to remove the studs and they did a great job for $25 with the manifolds off the vehicle of course.

Re: Exhaust mainfold and downpipe connection
 

Those old super rusted studs will probably snap off if you put any torque to them. Which you'll probably have to do anyway to get the pipe seperated from the manifold. Then you'll need to remove the manifold to remove the busted studs. Then install new studs with new nuts.

If you have to remove the manifold from the head. Try not to bust off any of the manifold bolts... because then the head usually has to come off for a machine shop to get it out.

Gary

Re: Exhaust mainfold and downpipe connection
 

Dave
I believe it has a "doughnut" style , but if your fighting the rust monster you may want to look into taking it to a local independent exhaust shop and have them replace the studs and fix it (theres a couple of good shops in Hamilton ) or if your not using it as a DD you might want to look into doing historic QQ plates so you don't have to deal with the "fun" called the NJMVC inspection stations anymore

Re: Exhaust mainfold and downpipe connection
 

i always used a torch getting the area cherry red and they clamp on to them with visegrips to get them out// about a 75% success rate and if they snaped i'd just drill and tap for new studs

Re: Exhaust mainfold and downpipe connection
 

Not sure how bad the rust is but if you can get in there, you could split the nuts with a... wait for it.... nut splitter. :lol:

Re: Exhaust mainfold and downpipe connection
 

I would highly advise against registering it as antique/ classic/ historic for the purpose of circumventing the safety standards. I have vehicles registerd as antiques but not for this purpose. An exhaust leak could be putting carbon monoxide into the cab creating a deadly situation. In the least the exhaust leak sounds really bad.
Posted via Mobile Device

Re: Exhaust mainfold and downpipe connection
 

Hi everyone, thanks for all of your suggestions. I was glad to find out that my local parts store carries the gasket; thanks for identifying it for me.

And yes, I'll need to fix the leak before registering as a historic. It backfires quite frequently and upon deceleration. Once the weather clears up I'll try it again, and hopefully the studs cooperate. I'll let you guys know how it goes. Thanks again!

-David

Re: Exhaust mainfold and downpipe connection
 

I would say this too before NJ changed the inspection to just ODBII on 96 and newer and idle test on 95 and older emissions test .
Theres no safety testing what so ever , so no brakes, bald tires , no mirrors a head sized hole in the windshield or no lights of any kind working your good to go as long as it passes emissions.

Most of us here on the list take way better care of our trucks then 95% of the people on the road , I was trying to help Dave from dealing with the numb nuts at NJ MVC (most likely I same one I use ) who tried one time to "sniffer test" my diesel and also dropped my wife's truck off the front end rack and caused $1000 of damage back when they checked the front end.

The other reason I said to Historic plate it is to keep NJ from taking even more money from Reg fees every year as the Historic plates are paid only once then no more reg fees

Re: Exhaust mainfold and downpipe connection
 

About the gaskets- I see on the website several inner diameter sizes. At Autozone, there's the 2 17/32" inner diameter and 2 1/32" inner diameter. According to the them, both should fit. But which one should I get? What effects does the inner diameter have?

-David

Re: Exhaust mainfold and downpipe connection
 

Ones more or less 2" and the other is 2 1/2" . If it was me Id just get both since they're pretty cheap and see what comes out when you pull down the pipe , Its easier to take one back later on then have to clean up your mess and go back to the parts store in the middle of the project