replacing a burnt valve - Diesel Forum

northernford · 01-27-2013, 12:24 PM

greetings from alaska and thanks in advance for any advice. been addicted to this forum since i bought a 86 F350 4 speed with the 7.3. I just came across another F350 6.9 c6 quad cab with a great body and am interested in swapping the engine and transmission into the new truck. However, the seller says "Has a burnt valve, runs but blows exhaust out the intake. Easy fix for the right mechanic or DIYer." The truck is about 100 miles from where i live so i don't want to have it towed. Are exhaust valves doable in a driveway in the winter time?

chuckster57 · 01-27-2013, 12:37 PM

You could do it under the right circumstances. Not snowing or raining would be the first thing. Freezing temps would probably deter you from grabbing a wrench, but you could wear gloves.

I would figure a trip to the machine shop in the total cost of the job, as you won't have any idea how much damage there is until you take the head off.

Then BEFORE you put it back together, you need to figure out WHY it happened, and address that issue so it doesn't happen again. If the seller has an idea, I would take it with a grain of salt.

northernford · 01-27-2013, 12:57 PM

thanks chuckster57. forgive my ignorance, when you say a trip to the machine shop would that be to have the burned valve reconditioned? If i'm not interested in keeping the 6.9 would i be better off loading the truck on a trailer and hauling it home?

chuckster57 · 01-27-2013, 01:09 PM

If all you want is the truck and not the drive train, I would drive it home. If you plan on repairing the 6.9, then I would trailer it home to avoid possible further damage.

What I meant by a trip to the machine shop is, yeah they can inspect the valve itself and the seat and guide. They will have the tools and equipment to replace/repair the seat and or guide and reface the valve if it can be saved.

LMJD · 01-28-2013, 07:48 AM

Quote:

thanks chuckster57. forgive my ignorance, when you say a trip to the machine shop would that be to have the burned valve reconditioned?

I wasted the better part of my life doing valve jobs and it's never standard procedure to grind or replace just one valve. All the valves are removed from the head, carbon removed, head checked for cracks, all valves are refaced at the proper angle. After grinding if the lip left on the valve edge is within specs it's OK to use. The seats are ground at 3 seperate angles ( e.g. 15, 45, and 60) and how the angles are done governs the contact area of the seat in regards to where it contacts the valve, which has to be correct---not too far out towards the lip. Also the contact area has to be a certain width, not too wide, not too narrow. There's way more to it than that, but thats some of the basics, point being a valve replacement isn't like changing a tire.
On Edit: If I remember right, flat rate labor for a complete valve job for two V8 heads (already removed) was right at 4.0 hours. Not including any special valve guide work.

chuckster57 · 01-28-2013, 08:08 AM

I agree, work on one valve is not the norm. Since I have a great relationship with my machine shop, I bet he would do just one.

One or sixteen valves, a proper complete valve job isn't something the average person can do at home. I have done benchtop valve jobs using nothing more than compound and a drill, but those were for customers that didn't have the funds for a trip to the shop.

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LMJD · 01-28-2013, 08:58 AM

Quote:

One or sixteen valves, a proper complete valve job isn't something the average person can do at home.

Yep, there would be that $30,000+? valve grind machine.
Northernford, if you're interested you can probably search on YouTube and see videos of a working valve/seat grind machine. Kind of hard to describe with words and no pics.

Mitchalvin · 01-28-2013, 11:04 AM

Before you condemn a intake valve you should check and make sure that the exhaust lobe or the lifter is not worn for that cylinder.

northernford · 01-28-2013, 12:29 PM

thanks for the info guys. in the end i really don't want the 6.9 but to get the truck home i would either have to drive with valves as they are or trailer it 100 miles north. i'm always cautious when someone trying to sell me something says it's an easy fix. the truck was owned by a church group and never driven so the body and interior are cherry. i have another 86 4door 4x4 that has the 7.3 in it but the truck looks like something out of mad max. i think i'll low ball an offer and try trailering