I'm ready to settle the Z120-Z129 cylinder head debate

Jason S.

Well-known Member
I scored a Z129 cylinder head which should be here tomorrow. I am going to cc both heads and calculate what the compression would be when they are interchanged. I still say the reason the manual says they cannot be interchanged is because of the smaller combustion chamber on the Z129 head. When the Z129 head is installed on a Z120 it would raise the compression too high because the Z120 used flat top pistons. We shall soon see if that is right.
 
my dad work for a Ferguson dealer back in the day and we had a TE 20 and he put a z129 head on it the z129 head had bigger valves and used caps on the stems and if I remember you have to use a z120 head gasket because of bore size
 
(quoted from post at 19:00:24 12/31/14) my dad work for a Ferguson dealer back in the day and we had a TE 20 and he put a z129 head on it the z129 head had bigger valves and used caps on the stems and if I remember you have to use a z120 head gasket because of bore size

The Z129 head also had rotocaps on the exhaust as well. I am aware of the valve differences between the two,but I'm wanting to show that the main difference they shouldn't be swapped is because of the compression, but I could be wrong. It is the same head gasket for the Z120 and Z129.
 
(quoted from post at 03:09:37 12/31/14) I scored a Z129 cylinder head which should be here tomorrow. I am going to cc both heads and calculate what the compression would be when they are interchanged. I still say the reason the manual says they cannot be interchanged is because of the smaller combustion chamber on the Z129 head. When the Z129 head is installed on a Z120 it would raise the compression too high because the Z120 used flat top pistons. We shall soon see if that is right.

Well here they are side by side. The Z120 is on the left and the Z129 is on the right. As you can see all the holes are the same, so the difference is the bigger intake valve and smaller combustion chamber on the Z129 head. I am going to try to CC them in the next few days but I did measure the chambers and there is a considerable amount of difference. A Z120 head will work on a Z129 but it will lower the compression and the Z129 head when installed on a Z120 will raise the compression a considerable amount. I will try to get the exact numbers soon.

99623E58-9B88-49FA-9DA0-EF4DB3936635-3594-0000030BF9356ABD_zps8485b16e.jpg
 
(quoted from post at 03:09:37 12/31/14) I scored a Z129 cylinder head which should be here tomorrow. I am going to cc both heads and calculate what the compression would be when they are interchanged. I still say the reason the manual says they cannot be interchanged is because of the smaller combustion chamber on the Z129 head. When the Z129 head is installed on a Z120 it would raise the compression too high because the Z120 used flat top pistons. We shall soon see if that is right.
I realize this is an 8 year old thread, but this topic is of great interest to me.
I need a head for my TO20. These are scarce but I do see a few Z129 heads around.
What is the downside of raised compression?
 

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