Broken Exhaust manifold bolts.

[TLarsen]

While tearing down the '91 Cummins from the donor truck I found 4 broken exhaust manifold bolts. To make matters worse, the previous owner tried to drill the two upper bolts and made things, well, much worse.



I believe that I can remove the 2 lower bolts, but does any one have suggestions for the upper two?



Right now I think I'll have to pull the head and put it in a mill to fix it. (fill the holes, then redrill and tap)



Also, the manifold appeared to be "short", like it had shrunk. With the other 8 manifold bolts in place, the 5th and 6th manifold ports didn't line up, like the manifold was 1/8"-1/4" too short. Is this normal? Could this be what broke the bolts for the previous owner?

 

[bmoeller]

Unfortunantely, a shrinking manifold is normal. I did catch mine before the bolts broke. Have heard of the ears being broken off also. All but 2 of my bolts were bent. An ATS or HTT 12v second gen. manifold will fit your '91 engine.

 

[PToombs]

I've seen small block chevy manifolds shrink too. As for the bolts, if you can drill a hole thru the orignal bolt, use your oxy-acetylene torch and blow the broken piece out. The steel heats/cuts faster than the cast. Then take a tap and clean the hole.

I've done this many times, you can do it without drilling, but it's much easier when you can blow thru an open hole.

 

[Philip]

Pete look a little closer. See how far the P/O drilled the two uppers holes off center.



Time to drill a larger hole and make a plug. Then drill it to correct centers.

 

[PToombs]

Yeah, Philip, I saw that. I never thought about the tap not starting because of the hole. Blow it out and put a nut on the backside!

There! How do ya like me now? :-laf

 

[Simplysmn]

how about taking a mig welder and building a haystack on broken bolt then put a nut over that and weld nut to haystack then after letting it cool some it should back right out I had to do that on front axle pass. side spring bolts when they broke off it will save haveing to drill ?

 

[TLarsen]

Blow it out and put a nut on the backside!

That seems like an obvious solution, but I didn't think of that. Thanks. Oo.

 

[TLarsen]

An ATS or HTT 12v second gen. manifold will fit your '91 engine.

Either of those would be nice, but the budget is already stretched. Will any stock 1st or 2nd gen manifold fit?

 

[Joseph Donnelly]

Get cheap bolts, grade 1 or 2, red loctite into the upper holes. Cut off, and redrill and tap where they should be. For the lowers, soak in penetrating oil for a few days, drill and use an easy out. The stock bolts are M10 x 1. 5 thread.

 

[DPetrey]

when you remove them weather you try to weld it or not use lots of heat and let it cool and lots of Kroil the heat it again and spray Kroil on it and let it cool do this a few time's will amke your job easier

 

[MMiller]

Man, what was that guy aiming at???? I know its very difficult to drill out a bolt in the center, and yes I've been off a few times, but come on... ... I stop long before its in that shape!!



Good luck on getting them out. Some left hand drill bits on the bottom ones, and center punch them first. Joe had a good plan with putting bolts in the already drilled holes and re drill correctly.



Michael

 

[dpuckett]

A 12valve manifold is a 12valve manifold from a fit to the head standpoint. You may have to move some of your heater hose supports, but that is quite minor in the grand scheme of things.



I'm with MMiller- how in the WORLD do you get that far off without first comsuming a large quantity of fermented grain or fruit before starting?



Daniel

 

[DPetrey]

I bet he tried to drill them with the manifold still in plac that is y it is so off

 

[DPetrey]

better change those valve cover gaskets too

 

[TLarsen]

A 12valve manifold is a 12valve manifold from a fit to the head standpoint. You may have to move some of your heater hose supports, but that is quite minor in the grand scheme of things.

Thanks!

I bet he tried to drill them with the manifold still in plac that is y it is so off

I think he pulled the manifold off, but it was drilled while still in the truck. The top bolt on #6 is drilled at a pretty large angle, it's at least 20 degrees from perpendicular.

better change those valve cover gaskets too

I plan on replacing a lot of gaskets.

 

[JohnsonG]

To remove the bottom broke off bolts, find some big nuts (sqaure nuts have worked the best for me) the size of the bolt, rig some way to hold the nuts over the broken bolts, then arc weld them to the bolt. Now you have to drill the rod into the bolt then work it up the inside of the nut so as to get a good latch on the bolt... the arc wont stick to the cast, but will stick to the bolt, run the bead all the way up to the top of the nut and get the nut red hot, let them cool completely, the cast iron cools different than the steel. then apply a liberal amount of liquid wrench or the like and carfully turn the nut back and forth, it will usually move just a little one way or the other, work it back and forth keep it lubed and it will eventually come out. if the nut comes off the bolt, do it again.





as Joseph Donnelly above indicates, you can plug and re drill the holes. . I worked in an old shop for a while, and the old guy had some cast iron screws that we used to fix miss drilled holes like your top ones in heads... it worked well. .

 

[TLarsen]

The bolts were seized in the head really good.



I drilled the bottom two bolts out most of the way, and tried a square easy-out, they wouldn't budge at all. So I drilled them out the rest of the way using a "Q" drill bit and tapped them with a M10-1. 5 tap.



For the upper two bolts, and plugged the drilled holes with the unthreaded portion of a 3/8" bolt and tack welded them to the head. Then I center drilled the original bolts. The #5 cylinder bolt went pretty smooth, except I had to tack near the center of the bolt to fill a big gap, the weld was, of course, very tough to drill through. The #6 cylinder bolt didn't go as clean. As I opened to hole up, it started to walk to the left and ended about . 030-. 050" off center, I tapped it anyways.

 

[TLarsen]

I test fit the manifold to recheck the fit. I loosely threaded in the manifold bolts and with the manifold pushed back, this is how far off the #5 and #6 bolts are. I'm going to try and slot the mounting holes about an 1/8" and see how bad it looks. If I don't like it I'll find a replacment.

 

[KOG]

You really need a replacement. The port/manifold misalignment will really mess up flow and power when it's that far off.

 

[PToombs]

Yeah, KOG's right! That is way off! You should find a good used, new or aftermarket manifold. I personally wouldn't run that, not after all that drilling and tapping.