Exhaust manifold nuts

greencom · Post by **greencom** » Tue Jun 16, 2009 8:23 pm

I'm about to reinstall my exhaust/intake manifold assembly after putting on new gaskets, I noticed that only one of the exhaust mounting nuts are the special tapered kind, the rest are regular ones. How important is it to use the tapered type. I read somewhere that they help prevent the manifold from cracking from heat expansion. Anybody out there have any experience with this? Thanks in advance.

Greencom

knattrass · Post by **knattrass** » Wed Jun 17, 2009 1:35 am

The specific series of flat, thick, and tapered washers are there to allow the manifold to expand/contract - without cracking. JB at MWM has the correct ones. Keith

monkeymissile · Post by **monkeymissile** » Wed Jun 17, 2009 5:03 am

I recommend using the correct ones where indicated, they're cheap and exhaust manifolds are hard to come by

greencom · Post by **greencom** » Wed Jun 17, 2009 7:23 am

Thanks guys,
Hopefully I can pick up the proper nuts and washers at MWM. I now realize the importance of this, that's why I sought out info from my fellow members of the forum. I suppose this breakage problem is more of an issue on long manifolds like the 230 versus shorter modern ones. I appreciate your replies.

Greencom

monkeymissile · Post by **monkeymissile** » Wed Jun 17, 2009 7:41 am

greencom wrote:Thanks guys,
Hopefully I can pick up the proper nuts and washers at MWM. I now realize the importance of this, that's why I sought out info from my fellow members of the forum. I suppose this breakage problem is more of an issue on long manifolds like the 230 versus shorter modern ones. I appreciate your replies.

Greencom

mine was cracked when I got it and only a few of the proper nut/washers were used

peter e mark · Post by **peter e mark** » Thu Jun 18, 2009 5:46 am

Hello everyone, And coincidentally, I too am preparing to install a replacement exhaust manifold on my 52 M37. My truck came with a cracked manifold too. I shall certainly order these special nuts...

peter e mark · Post by **peter e mark** » Thu Jun 18, 2009 5:48 am

Do I dare ask this question, especially since KNATTRASS is watching: In what direction do I install these special nuts?...( be gentle guys )

monkeymissile · Post by **monkeymissile** » Thu Jun 18, 2009 5:58 am

peter e mark wrote:Do I dare ask this question, especially since KNATTRASS is watching: In what direction do I install these special nuts?...( be gentle guys )

just match the tapers and use lots of anti-seize. The correct torque is critical as well, too much and the nut/washer combo can't move enough during expansion/contraction

peter e mark · Post by **peter e mark** » Thu Jun 18, 2009 6:38 am

Thank You monkeymissle, and do you happen to know the torque value? Is it in the TM8 specs? If so, I shall look it up...

monkeymissile · Post by **monkeymissile** » Thu Jun 18, 2009 7:09 am

peter e mark wrote:Thank You monkeymissle, and do you happen to know the torque value? Is it in the TM8 specs? If so, I shall look it up...

15-20 foot pounds

greencom · Post by **greencom** » Thu Jun 18, 2009 7:29 am

Maybe I'm thinking too much on the subject but I can't seem to figure out how the tapered nut/cupped washer combo lets the manifold move with heat expansion. It is still a nut and washer pressing against the manifold flange as all the others. Must be some subtle engineering principle that eludes me. I would really like to know the theory behind it. I never like doing something without knowing why. I will of course use this special hardware regardless.

Greencom

monkeymissile · Post by **monkeymissile** » Thu Jun 18, 2009 7:35 am

greencom wrote:Maybe I'm thinking too much on the subject but I can't seem to figure out how the tapered nut/cupped washer combo lets the manifold move with heat expansion. It is still a nut and washer pressing against the manifold flange as all the others. Must be some subtle engineering principle that eludes me. I would really like to know the theory behind it. I never like doing something without knowing why. I will of course use this special hardware regardless.

Greencom

the tapered washers are brass or bronze and expand more/faster than the tapered steel nut which gives the cast iron manifold room to move when it gets hotter and grows in length
That's my understanding

greencom · Post by **greencom** » Thu Jun 18, 2009 8:05 am

Monkeymissile,

I didn't know the washers were brass! Thank you, it makes sense now, the washer's tapered opening gets larger loosening up the bolt/washer clearance a little letting the manifold move, thank you. Some places sell the nuts in brass however, I don't think that will work. Thanks again sir, that is why I love this forum, lots on knowledgeable people in it.

Greencom

Lifer · Post by **Lifer** » Thu Jun 18, 2009 8:35 am

A couple of other things to keep in mind:

If the intake manifold is bolted to the exhaust manifold, make sure you loosen all bolts to allow "wiggle room."

Pay very close attention to the tightening sequence on the manifold nuts! This is extremely important if you don't want to crack your new manifold. (You don't want to know how I learned this bit of information.

)

greencom · Post by **greencom** » Thu Jun 18, 2009 9:00 am

Lifer wrote:A couple of other things to keep in mind:

If the intake manifold is bolted to the exhaust manifold, make sure you loosen all bolts to allow "wiggle room."

Pay very close attention to the tightening sequence on the manifold nuts! This is extremely important if you don't want to crack your new manifold. (You don't want to know how I learned this bit of information. )

Hi Lifer,
Actually I'm just reinstalling my intake/exhaust assembly to replace the gaskets and broken cup washers I discovered earlier. The two manifolds are already bolted together but I will check that the flanges all line up. What I cannot find is a tightening sequence in my manuals, all they mention is the torque but no pattern. I will just use an alternating pattern similar to the head if I can't find an official sequence. By the way, I'm glad you didn't require surgery.

Greencom