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Discussion Starter · #1 ·
I have a 1994 fsuperduty 7.3 idi and it has a bad exhaust valve. I know because exhaust chuff. I bought a 94 idit for parts the guy had everything apart. I was wondering if anyone could give me some pointers on rebuilding the heads. The heads have bad roller rockers at least that is what the guy i bought the parts truck from said.
 

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Welcome to the forum!
Rocker arms are held on by either a bolt or a nut on a stud. Either way they are easy to replace. I would let a machine shop do the valve job part and then get a new set of rockers.

Installing the heads can get tricky due to their weight. Use a hoist to set them down on the block to minimize the chance of damage to the head gasket.

There are probably some tricks I'm missing at the moment, it's early and I haven't had my caffeine transfusion yet.
 

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YOU can't rebuild heads unless you have a truck/auto/or machine shop with the proper equipment. Valve/seat grind machine, valve guide reamers, layout blue, straightedge, and that's the short list. And then you have to know how to use it all. Google "valve grind machine" then click on images.
 

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roller rockers are not cheap for these engines, mine cost me 900 without pushrods.
theres only one company on the market that makes these, and they have only made 3 sets.

first things first. you MUST have the heads magnifluxed and pressure tested.
the EGT's these engines see is no joke and will crack cast iron with a turned up IP.
so first and foremost get them tested before you do anything.

2nd is checking the height of the head. ill let you do your own homework on specs.

next, inspect all rocker arm bosses, and make sure they are all good.

deck the head to ensure a true surface for the head gasket to seal properly.

inspect the pre cups. these cups crack, which isnt a big deal, until it gets large enough to extend past the fire ring on the head gasket.
if they are cracked really bad, you will need to purchase new ones.

valve guides and seats are on my list every time i do a set of heads.
my machinist hates me, because i want them ALL replaced!

spec calls for a 1 angle valve grind, i believe its a 22.5* grind.
i had the shop do a 3 angle valve grind on my last set, hopefully i dont have an issue.

new springs is a good thing to purchase. if youre going with an aftermarket cam, youre going to need the Comp Cams 910 springs, and may even need to shim them

after its together make sure you inspect the valve recess in the head THOROUGHLY.

again ill let you research your own specs, and any machine shop that works on diesels knows the min required recess.
this is a big factor to keep your valves from hitting the piston.
 

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spec calls for a 1 angle valve grind, i believe its a 22.5* grind.
No it doesn't. They're a 3 angled seat like everything else from a Briggs and Stratton push mower on up to a 855 Cummins. 15° angle on the top of the seat, 60° on the bottom, the seat to valve contact angle is 30° for an intake, 37.5° for the exhaust. How would you suggest properly narrowing the seat to valve contact with only 1 seat angle when it's too wide (out of allowable spec)? You narrow the angle with either the 60° or 15° stone. Also with one angle, after checking the contact with bearing blue, how would you move the contact area inward if it's too far out at the lip of the valve (out of allowable spec)?
And long before you'll see any cracked cast iron due to continuously high EGT's, you'll be tearing the engine down for scored piston skirts and cylinder walls, that's the first failure that occurs with high EGT. My source----I miss-spent the better part of my life doing valve jobs and replacing scored cylinder liners and pistons in Detroits, Cummins, Cats, etc.
 

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Machine shop 101:A poor illustration, but the top 2 lines shown on the seat would be ground at 15+/- degrees, the seating surface is ground the same angle as the valve so only that area contacts the valve, between the bottom 2 lines would be 60 degrees. If the seating surface (shown with Prussian Blue layout dye is too narrow then there is not enough heat dissipation (burnt valve sooner or later), too wide and carbon can be trapped between the valve and seat.
 

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thanks for the correction.
i absolutely love to be proved wrong, when someone fires tech talk back :D
and not some mumbo jumbo!

i guess because of the 30 and 37.5* angle i saw on the spec sheets i figured it was only a 1 angle.
now i know, and knowing is half the battle!

ive only been into these IDI's for a short time, but im learning lots.
the 7.3 i ran i tore down due to water in the oil. thought it was a waisted head gasket, turned out to be cracks in the driversside bank.

every combustion chamber had cracks in them inbetween the I&E valves.
the truck regularly saw 12-1300*


but, do you agree with everything else i said?
 

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but, do you agree with everything else i said?
Yessir. And if you're interested, referring to the above illustration, say the Prussian Blue showed the actual seating surface to be way out close to the lip of the valve (a No-No), then you purposely hit the seat with the 30 degree stone which of course makes the seating surface too wide. But then you take the 15 degree stone to the top of the seat and narrow the contact surface back down to spec (1/16"-3/32"). In doing that, if you follow me, what you've done is actually move the seating surface inward away from the outer edge of the valve. And just the opposite, if you use the 60 degree stone rather than the 15, you can move the contact surface outward.
Actually, generally engine overheating is the cause of cracked heads. It's not so obvious on these small pickup truck diesels, but with bigger diesels high EGT's and extremely high coolant temps are totally independent of each other. You can climb a grade and unless you downshift EGT's can go through the roof but engine coolant temp will stay normal, and vice versa you can have an overheating problem, but EGT's will stay normal.
 

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Yessir. And if you're interested, referring to the above illustration, say the Prussian Blue showed the actual seating surface to be way out close to the lip of the valve (a No-No), then you purposely hit the seat with the 30 degree stone which of course makes the seating surface too wide. But then you take the 15 degree stone to the top of the seat and narrow the contact surface back down to spec (1/16"-3/32"). In doing that, if you follow me, what you've done is actually move the seating surface inward away from the outer edge of the valve. And just the opposite, if you use the 60 degree stone rather than the 15, you can move the contact surface outward.
Actually, generally engine overheating is the cause of cracked heads. It's not so obvious on these small pickup truck diesels, but with bigger diesels high EGT's and extremely high coolant temps are totally independent of each other. You can climb a grade and unless you downshift EGT's can go through the roof but engine coolant temp will stay normal, and vice versa you can have an overheating problem, but EGT's will stay normal.

I couldn't have said any of that better myself. I might add that even when you buy new seats you still have to grind a little to properly seat them. Which is why most people will try to re-use if the seats aren't too hammered out. The natural gas engines I used to work on, always got new seats, because of combustion temperatures. usually did good to make 2,000 hours before there wasn't any adjustment left.
 

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Discussion Starter · #10 ·
Thanks everyone for all the information. Being that i'm not a machinist I'll probably buy a pair from Diesel Cast Welding. Iirc the last time I talked with them they said that they run $600 each. if anyone knows a place to get them cheaper please let me know.
 

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Your other thread got locked as it was an "introduction" forum not a discussion forum.

I would ask your local machine shops for a price to rebuild yours. I don't operate a machine shop, but the shop I use is run by a guy with about 50 yrs of experience and is co holder of 5 land speed records. $600/head seems a bit high to me.
 

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Ditto that Chuck
 

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Discussion Starter · #13 ·
Yeah I thought 600 was steep but I'm new to this stuff. I don't have a normal machine shop that I use. Could you recommend one in the area. I had a bad experience with a shop 8 years ago and ever sense have tried to do anything I needed done.
 

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Your in Fresno, I'm in Modesto. That's about 1 1/2hrs away so I don't have any idea who to recommend in your town.

If your willing to drive up here, call Joe @ Yosemite Machine.
 

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I agree with Chuckster, if I remember right, flat rate labor for a straight valve job on both V8 heads is 4 or 4.2 hours. New valve guides or whatever would be in addition.
 

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Discussion Starter · #16 ·
I got a quote for 400$ in town for rebuilding both heads if nothing is really bad. I forgot to ask about a warranty. I know I need at least one pair of roller rockers. Should I get them before hand and take in with my heads they are already taken apart by the po.
 

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The 7.3 IDI didn't come from the factory with roller rockers. A quick search on google and I was able to locate rocker arms. You won't need to take the rockers with you to the machine shop.
 

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Chuck, bet he means lifters.
 

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Maybe, but those are in the block and he keeps talking about the heads.
 

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Maybe, but those are in the block and he keeps talking about the heads.
Right, but with the heads off that means the IP, intake manifold, pushrods, and valley pan have to be off so the lifters are sitting there out in the open.
 
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