Replace exhaust manifold bolts???

[Terry]

I am pulling the heads on my 2.9. Someone dropped a fuel injection clip into the intakeAfter seeing all of the things I need to clean and or replace "motor mounts, oil pan gasket..." I will replace the exhaust manifold bolts with something better being that I have one side loose and broke four bolts. I am thinking about stainless cap screws with flat washers and some anti seize compound. What have you used to replace the stock bolts?

 

[Terry]

I cant believe that nobody has a fix for this issue. I finished removing the exhaust manifolds and I have small pile of broken bolts. I have been looking on the web for a fix on this issue. summit and other stores sell 300 stainless bolts and flat washers. Ford engineers were out to lunch on this issue. The only other issue I have not figured out is bolt head style. The bolts on the drivers side that have have threads for the small nuts are some of the only bolts that did not break.

 

[mitch4x4]

I have always just went and paid for new ones from the dealer. Yes they are failing now but you have to remember the 2.9 was discontinued in what? 92-93? so it is a fairly old engine to begin with. So anything is going to wear out. A new set of stock ones will probably out last the truck.

 

[alwaysFlOoReD]

I used stainless for the manifold to y-pipe. Stainless isn't as strong I'm told, but they were cheaper than stock ford bolts by 10-1. If they break I won't be any worse off. By the way, the stock mani to y-pipe bolt threads are a special interference fit, no wonder they don't like to come apart.

Richard

 

[AllanD]

typical stainless steel bolts are slightly weaker than grade 5 SAE bolts, but as stainless doesn't rust the bolts won't grow weaker.

But be aware that stainless steel bolts and nuts tend to gall together, particularly when heated and subjected to vibration, so smearing them liberally with never-seeze is more imporntant than on rust prone carbon steel.

THE thing to warn you about is that both the bolts and the threaded holes in the exhaust manifolds are a "Truncated root thread" which make inserting a conventional bolt into the hole an "interference fit" (threading together two interference fit parts make them really sticky)

Even so when I still did that work I averaged getting three out of four bolts out of the holes.


On the bolts that hold the manifolds to the heads there is another problem.
The threads are common metric 8mmX1.25 thread, these aren't a problem to replace.
What is a problem is that commonly available metric bolts are only available
in the necissary lengths in 10mm incrementsare either too long or too short

My usual way to deal with this has been to helicoil the twelve 8mm holes
to 5/16-18 UNC (english/american) threads to allow the use of common bolts
that I can buy ANYWHERE (Tractor Supply sells grade-8 bolts by the pound)


The only rub with this is that now when I want to tighten the bolts on my exhaust manifold
I need to keep track of my 1/2" socket.

 

[coopab]

exhaust manifold bolt replacement

typical stainless steel bolts are slightly weaker than grade 5 SAE bolts, but as stainless doesn't rust the bolts won't grow weaker.

But be aware that stainless steel bolts and nuts tend to gall together, particularly when heated and subjected to vibration, so smearing them liberally with never-seeze is more imporntant than on rust prone carbon steel.

THE thing to warn you about is that both the bolts and the threaded holes in the exhaust manifolds are a "Truncated root thread" which make inserting a conventional bolt into the hole an "interference fit" (threading together two interference fit parts make them really sticky)

Even so when I still did that work I averaged getting three out of four bolts out of the holes.


On the bolts that hold the manifolds to the heads there is another problem.
The threads are common metric 8mmX1.25 thread, these aren't a problem to replace.
What is a problem is that commonly available metric bolts are only available
in the necissary lengths in 10mm incrementsare either too long or too short

My usual way to deal with this has been to helicoil the twelve 8mm holes
to 5/16-18 UNC (english/american) threads to allow the use of common bolts
that I can buy ANYWHERE (Tractor Supply sells grade-8 bolts by the pound)


The only rub with this is that now when I want to tighten the bolts on my exhaust manifold
I need to keep track of my 1/2" socket.

I've got the top end of my 1999-2000 Ranger/Explorer engine on my work bench. I broke 6 of 12 exhaust manifold studs/bolts and of the other six five of the studs came out with the nut still attached. Only one nut came off leaving the stud intact.

I picked up a package of two 8mm-1.25 x 50mm 8.8 bolts at Tractor Supply.
It would appear that if I cut them of to the same (or slightly longer) length than the original studs, I could install them as studs by double nutting them to get them tight into the manifolds. I'm also considering getting bolts in correct length rather than the stud/nut combination. Perhaps a combination of two studs, four bolts. The idea of that would be to use the two studs to "hang" the manifold on the head and make it easier to install the four bolts.

It shouldn't be that hard to determine how long the bolts should be to reach into the head far enough to hold tight but NOT bottom out. I'm guessing that 40mm would be good and since I've got the heads and manifolds out on the bench I can test them before final install.

I wonder if I could find 8mm-1.25 pitch bolts in 5mm increments?

coopab


alternatively, if I remove the old studs by drilling and tapping, could I tap 5/16-18 threads in order to use more widely available SAE size studs? without requiring helicoils?