Hello guys and gals, I've got a situation here. My rig is a '94 22R-E Extended-cab 4x4. The truck runs perfectly but has one irritating flaw. The nuts which hold the exhaust manifold to the cylinder head will not stay tight. I had an issue with this when I first purchased the truck and ended up heli-coiling some of the holes and installing new studs. I had the manifold milled (it was warped) and used the factory "locking" nuts made for the manifold. Life was great and I drove the thing 25K miles before I noticed it was a little louder than normal when I started it cold. I checked and sure enough, a couple of the nuts had backed off. So one night at work (I'm a Toyota Technician, believe it or not) I removed the manifold and found that it was warped again. I had access to another manifold, had it milled as it was warped also, and installed it with all new nuts (with Lock-tite) and longer studs which reach farther into the head. I drove the thing for one day and re-checked the torque (I actually used a torque wrench on them) and guess what I found??? The two nuts in the center of the manifold had backed off. So I got the brilliant idea last night to double-nut them. I torqued each nut to 33 ft-lb and figured I had the problem licked. Nope, I found out tonight when I checked. What gives??? I have never had this problem with a customer's vehicle in the 10 years I've been doing this. The studs do not seem to be turning as I marked them. Do I have to J.B. Weld the studs into the head, and drill the nuts and studs so I can install a cotter pin? I'm sorry to have written a book here and I thank all who take the time to read it. If anybody can give me a suggestion (besides driving it into the pond, I've already considered that) I would be very grateful. Thanks again!

 

Locktite loosens w/ heat... at least in my experience. You could try double nutting , or lockwashers.... or Thats a first for me too, I just torqued mine down to 35 and was good to go.

 

Personally, I would go through and replace all the studs and nuts. Since you are a tech, I am sure you are cross-pattern torquing the nuts right?

Other than that, I would just keep tabs on them every oil change and torque them to spec while cold.

Weird.

 

Drill the nuts, chamfer the holes and use stainless steel safety wire to hold them down, no need to drill the studs. Sounds like you have a wierd vibration problem, the harmonics are at the right frequency to cause the nuts to come loose. It seems you've tried all the other options, if this don't work then weld them in place j/k.

I had a similar problem with my RX-7 and I finally safety wired the exaust nuts from manifold to the pipe, down and they never came loose after that. Make sure you run the wire thru the nut then twist the wire and wrap clockwise and then find a place to secure the other end, if the nuts are close together you can wrap the wire and secure to each other.

 

Are you tightening them in the right order? That will make a difference.

 

Locktight, JB weld and then weld'em, just kidding sorry i don't know what I'd do.

 

Thanks to all who have replied. I agree that Lock-tite may not have been good to use where so much heat is concerned. I did try lock washers and then double-nutting. I did also follow the recommended sequence, tightening from the inside and working toward the outer holes. I mean to tell you that it loosens up (not all of them, just the center holes) in ONE driving cycle. I check it after it cools down and there it is, a little loose. Please forgive my ignorance, Bruce (I've had a long day) but I'm having trouble visualizing what you are talking about drilling the nuts (but not the studs) and installing the safety wire. Where exactly are you talking about drilling and where do you run the wire if it doesn't go through the stud also? I'm reluctant to weld them in place as sometimes things just need to come back apart. Thanks again for all the replies and keep the ideas coming please!

 

The hex nut, drill a hole between the adjoining faces at an angle, not thru the threads. It's actually a common practice on race cars.


I found this link: http://www.whizwheels.com/Tips/safetywiring.html

this link shows going all the way through the nut, but you want to go at an angle to avoid having to drill the studs.

 

Here's a diagram I found that shows what I mean:

 

Well I don't know much about anything, but maybe it could be the expansion of metal when it warms up. I don't think you specified when you put the bolts on, but maybe temp has something to do with it.

I have no idea how it would get loose if it had lockwashers...