I kind of hate studs. I can never feel confident that they are actually appropriately torqued into place. I can't count how many times I've taken some sort of mechanism apart to find the studs coming out with the nuts (phrasing). Backing up two nuts on a stud to set it (phrasing) is really annoying. Anyway, does anyone know if anything bad could come from replacing them with bolts? Toyota put them there for a reason, but I don't know what that reason is.

 

I find at least one or two studs to be handy in most situations. It allows for a nice point to align or hang what ever you’re reinstalling. The exhaust manifold, fan/fan clutch, tires, etc, are much easier to align when you can hang it on studs as you install it. It also makes it so you don’t have to catch the parts or risk dropping them as you remove them. Bolts however are easier in many spaces where clearance is an issue. It is annoying when a nut is seized and the stud comes out, but is that really any different than replacing it with a bolt. Usually loctite on the stud and anti seize on the nut solves future problems. In the end it’s mostly preference when replacing things, but I definitely appreciate studs in some situations.

 

Good points. I'm doing a rebuild and was thinking of chucking them all out the window, but maybe I'll save 2 on the exhaust side.

 

Parts like the exhaust manifold are generally most loaded in shear, so the stress on the fastener is right along the gasket. A properly installed stud has all the threads in the block, so the stud under shear load is full-diameter (no threads). Compare that with a bolt; you're not going to get all the threads of any bolt into the block (the bolt would stop turning there before torqueing against the manifold). So the shear load would be on a threaded part of the bolt.

A bolt-and-nut connection can be designed so that the unthreaded part of the bolt covers the shear line, with the threads starting somewhere inside the nut-side of the two pieces. There is enough threaded part to torque the nut.

What about head bolts? a) the main load on head bolts is tension, so it has be designed strong enough to carry the load through the threaded part, b) some folks like to swap out head bolts for studs, for the same reasons as described, and c) head bolts usually have counter-bored female parts, so the unthreaded part of the bolt extends past the gasket line into the block.

Bottom line: a bolt is more likely to break than a stud in an exhaust manifold. How likely? YMMV

 

Really good, that's what I was wondering about. Strangely, I had always thought that the pressure the exhaust side is under was not as great- looking at the FSM warp-gap is more permissive than other surfaces, and then there's the fact that exhaust is exiting the system, releasing pressure. Of course, these aren't the only factors affecting shearing forces. I was hoping no one would come up with a good answer and I could naively use a handful of bolts. No such luck.

 

I'm quoting this post to say this is exactly correct, and extremely well worded! Good work!

 

One other benefit of studs is you can cut off a corroded nut without damaging the stud. This means you don't disturb the interface into the softer aluminum head and risk damaging those threads. Less cycles on those threads is a win in my book!

A variant of the traditional stud is a Rosan stud. These get threaded in, and then there's a lock-collar that secures them in place. Nasty to remove, but they definitely won't back out. Huge PITA if one ever twists off, though.
https://www.ptp-inc.com/Ring-Key-Lock-Studs.html

 

Originally Posted by scope103 View Post
Parts like the exhaust manifold are generally most loaded in shear, so the stress on the fastener is right along the gasket. A properly installed stud has all the threads in the block, so the stud under shear load is full-diameter (no threads).

I think not.... https://www.disher.com/2016/06/01/bo...ded-fasteners/

 

One place I would definitely recommend keeping studs is the exhaust manifold. The studs allow you to thread into the soft aluminum without any tension on the threads, then tension the studs (by torqueing the nuts) without turning the studs. Using bolts means that the tensioning will take place at the same time as the rotation and with soft female threads you're more likely to pull the threads out in this scenario.

 

Pulling the threads on the exhaust manifold is a problem these trucks are well known to have. Even happened to me when I did the head on MY 87 4Runner. A couple thread-zerts, though, and awaaaaay it went.
Known for the threads of the spark plugs, too, so do NOT over tighten them. Also, many recommend NOT using antiseize on the plugs, as it will change the torque readings.

Pat☺