351w Heads
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Senior User
Joined: May 2010
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From: ARLINGTON WA
351w Heads
Good morning I have a 1987 F-250 4x4 351w C-6 auto I'm working on . I was having trouble keeping the engine running at low idle. I took it to a shop for a few other things I could not fix. At that time the checked the compression. They found that bank 1 had 0 compression, bank 2 had 135 n all. They stated that the " intake valves sucked up into the cylinder head. Needs heads rebuilt. So to same money I decided I would do the work myself. Pulled the heads and found this.
Bank one all of the exhaust valves were lower in the head not flush withe surface. Bank 2 front cylinder had the same thing. Last 3 cylinders were flush. What in the world is going on. Have never seen this. Thx Dvid
Bank one all of the exhaust valves were lower in the head not flush withe surface. Bank 2 front cylinder had the same thing. Last 3 cylinders were flush. What in the world is going on. Have never seen this. Thx Dvid
Hotshot
Joined: May 2003
Posts: 11,141
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From: south louisiana
The exhaust valves will recess before the intakes because they run hotter and wear the hardened surface of the seats faster. This is perfectly normal. The seats are induction hardened at the factory and once that part of the head wears through, they wear that much faster and the valves sink into the heads and you loose the seal. That's where your compression has gone. Either get the heads rebuilt, or start with a fresher set that aren't worn and have them freshened up, this will be the cheaper route to go. You should have E7TE heads, these were in production for nearly 12 years and are a dime a dozen.
Cargo Master
Joined: May 2007
Posts: 2,071
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From: British Columbia
Valve seat recession
Maybe the induction hardening of the valve seats on those heads was not done correctly at the factory, or possibly the engine was run on propane or natural gas, both of these will cause valve seat recession.
I'm pretty sure that this problem only happens on exhaust valve seats.
Installing hardened valve seats will correct the problem.
I'm pretty sure that this problem only happens on exhaust valve seats.
Installing hardened valve seats will correct the problem.
Cargo Master
Joined: May 2001
Posts: 3,208
Likes: 13
Unleaded gas is the cause of this. If an engine is worked hard the hardened valves will recede into the seats. It is usually cheaper to buy remanned heads then to have yours rebuilt. I have used several sets of heads from these people. without any trouble.
https://www.shop.headsonly.com/FORD-...-50-58-OHV.htm
https://www.shop.headsonly.com/FORD-...-50-58-OHV.htm
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Senior User
Joined: May 2010
Posts: 188
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From: ARLINGTON WA
Thx for all of the replies. That is what I did I bought a set online from the Cylinder Head Shop. We installed them added a new manifold and carb. runs great. The only funny thing is the cylinders with the compression were the ones with the sunken exhaust valves. Go figure. Th
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