SC head casting numbers

[fixerupper]

Do any of you guys know what the difference is between a 5617 casting number and a 5618 casting number on a head for an SC? I found a used head but it's a 5618. My head is 5617. Thanks Jim

 

[L.LAMP]

The 5618 head is the low compression head. The 5617 is the high compression head. You will be much
happier with the 5617. I have replaced most of my 5618's. The valves are the same, only the
combustion area is different. It is easy to tell by looking.

 

[fixerupper]

Thank you. I suspected it is a low compression head as most of the heads I have seen are 5617's.

 

[Ken Christopherson]

I have also seen A5617A heads, and believe they are either high altitude/LP heads. Could be wrong, but I know there are 5618A (distillate), 5617A (gasoline), and A5617A.

 

[oldproudvet]

The parts book dated Dec '48 calls the 5617A head high altitude, must not be used below 6000ft. They
have the A5617A listed and they are interchangeable, so maybe a production change? The 5618A head they
label: Cylinder head regular.

The latest parts book I have for SC's is dated Dec 1960 lists just the A5617A head as: Low cost high
altitude 3 1/2" bore. The 5618A they list: Low cost fuel high altitudes on 3 3/5" bore. Low cost fuel,
except for high altitudes on 3 1/2" bore. They also list another casting number 6378A: Regular for low
cost fuel on 3 5/8" bore.

Perfectly clear right? More than a bit confusing. I'll get into my service bulletins and see if they
say anything. I know I've got a bulletin listing the application for DC heads, so there may be one for
the SC's

 

[fixerupper]

That’s interesting. Both SC’s I’m working with have 5617A heads with no A prefix. One is a 51 model and the other has a serial number that starts with the numbers 56xxxx I forget the rest of the numbers so I assume it’s a 52 model. I assume the heads are original to the tractors.