Exhaust manifold

idiocrates · Post by **idiocrates** » Mon Aug 03, 2009 11:06 am

I'm replacing the exhaust manifold on this m38a-1 F-head engine......two questions:

1. Does anything need to be done to the new manifold prior to mounting it on the engine?
2. Can the Prevailing Torque Lock Nuts be used in place of the old all-metallic locking nuts?
3. The other two holes in the block.....the one for the support bracket and the one to the back between the third and fourth cylinders....do they need to be "plugged" with a bolt even if they are not going to be used?

Thanks.

Jim

Post by **wesk** » Mon Aug 03, 2009 11:35 am

Brass nuts should not be reused. If the new brass nuts are quality made units they will handle maintaining the necessary torque on the manifold. The fancier modern heat treated steel locking nuts will also work. Trouble with them is arriving at an accurate torque value. You have to first determine driving torque value then add the basic torque value to it.

When you say new exhaust manifold are you referring to a repop or an NOS? Always confirm the trueness of the gasket surface of the manifold and the block.

idiocrates · Post by **idiocrates** » Mon Aug 03, 2009 1:53 pm

The manifold I got is a reproduction.....I'm pretty sure. It mates up very well with the engine and looks exactly like the old one. So are the nuts supposed to be brass? None of the old nuts were brass.....more like iron oxide...or at least really, really rusty. The only readily available locking nuts I can find locally are the nylon insert type and I know those won't work. I found a source for the prevailing torque kind that are all metal but they are steel and not brass.....and they will destroy themselves or the stud if ever they are removed.....so I'm a little lost here about what to use.

Jim

Post by **wesk** » Mon Aug 03, 2009 3:26 pm

The correct nuts are 7 each 3/8"-24NF-3 brass. The original shape nuts are impossible to find but every auto parts store will carry the standard 3/"-24 brass nuts.

Never assume a surface is flat and true. Always get a quality steel straight edge and check. Check both the block port surfaces for flat and even height for all three and the new manifold for flat and even hieght on all three. It is very irritating to have to pull and exhaust system apart to replace a blown individual gasket because you didn't want to spend 15 or 20 minutes with a straight edge and a flat surface to be sure all was correct.

idiocrates · Post by **idiocrates** » Mon Aug 03, 2009 3:38 pm

Thanks......maybe I was unclear when I asked the guy at napa if he had any all metal locking nuts for an exhaust manifold.....or I might have even asked specifically for steel and he just didn't want to waste his time on me......I'll try again......and this time ask for brass.

On the straight edge check.......is a framing square held up vertically and swept across the ports and the block sufficient to gauge flatness? That's all I got and what I used and if that isn't true enough I may have to get me a new tool.

Jim

Post by **wesk** » Mon Aug 03, 2009 7:56 pm

The straight edge has to be long enough to encompass the entire width of the manifold and all three port flanges on the block so you can be assured that all three flanges will contact simultaneously and evenly.

idiocrates · Post by **idiocrates** » Tue Aug 04, 2009 8:33 pm

okay.......does anyone know of a specific website or place where a guy can order the 3/8 x 24 brass nuts to fasten the exhaust manifold that does NOT invlove having to go to India?

Jim

OKCM38CDN · Post by **OKCM38CDN** » Tue Aug 04, 2009 8:53 pm

Brent Mullins carries the proper Brass nuts for the manifold... Well he used to... I got 7 from him and putthem on my M-38... this was several years ago... but if looking for the correct nuts try there first...

Post by **wesk** » Wed Aug 05, 2009 8:13 am

Most auto parts stores also carry them. The main supplier is the Dorman product line which you often see in the strores as the long rows of orange/black metal trays and drawers. Just get on your tele and call your local parts stores and I am sure at least one will have them.

idiocrates · Post by **idiocrates** » Wed Aug 05, 2009 11:57 am

Thanks, guys.......turns out NAPA had them all along.....they just didn't know they did. Once I finally convinced the guy to let me look through the isle where all the little pull drawers were I found them pretty quick. So now there's just one question left......these nuts are called exhaust safety nuts and they are not self locking......so do they go on with a lock washer or no lock washer? Thanks.

Jim