How to replace a seat in an Aluminum Head
 

How to replace a seat in an Aluminum Head


The head being worked on is a 2002 Ford Focus 2.0l SOHC
This style of head, the “split port” Intake
I have seen this as a common problem.


https://www.miataturbo.net/attachmen...ine=1333028854


The first step is to mount and level the head into the head shop.
(I am using a TnS 2000 Head Shop)
https://www.miataturbo.net/attachmen...ine=1333028854

The next step is setting 90* carbide cutter to a smaller diameter than the original seat counter bore. Appox. .006-.012 smaller
https://www.miataturbo.net/attachmen...ine=1333028854
Here you can see where the intake seat fell out of #3 Clyinder and “pebblized” and beat up in the quench areas of the combustion chamber.
A quick touch up with a die grinder to smooth and remove the burs. All the damage was inside the fire ring, So head gasket sealing will not be an issue.
https://www.miataturbo.net/attachmen...ine=1333028854

Now we cut out the remaining intake seats, I am a firm believer, if one has fallen out, the chance is too great for one of the other three to fall out. The cost is also reasonable.
https://www.miataturbo.net/attachmen...ine=1333028854

Now once the seat has be shelled out, take a small flat blade screwdriver and pry and/or chip the shell of the remaining seat out.
https://www.miataturbo.net/attachmen...ine=1333028854
This is will be about what is left.
https://www.miataturbo.net/attachmen...ine=1333028854
These are the new seats, they are larger OD and smaller ID and have a greater depth then the OE seats.
https://www.miataturbo.net/attachmen...ine=1333028854

To fit the new seats in the head, I have to cut new counter bores. This will insure a round counter bore and the proper press fit. Between .005-.007
https://www.miataturbo.net/attachmen...ine=1333028854

Here the seat depth is set, I like to have a minimum depth of .220, and these seats will go in to appox. .260-.270.
The hard stop will make sure I will not exceed the maximum depth of .300
https://www.miataturbo.net/attachmen...ine=1333028854

Most aluminum heads like to tear and not cut with a smooth finish. I few squirts of oil will help the cutting, along with a faster cutter speed.
https://www.miataturbo.net/attachmen...ine=1333028854

How the new counter bore looks after machining
https://www.miataturbo.net/attachmen...ine=1333028854

Next is to knock in the seat inserts. Use the proper sized driver and a large hammer.
After all the seats are knocked in, the head must be re-leveled before any more machine work can be done.
https://www.miataturbo.net/attachmen...ine=1333028854

Next is to set seat placement on the valve.
Where the point touches, is where the top of the valve to seat contact area will be on the valve face.
https://www.miataturbo.net/attachmen...ine=1333028854

Now with that locked down, put the guide pilot in the setting fixture and then slide the cutter over it. Now the bit holder gets moved in or out as needed to achieve where contact will be made.
https://www.miataturbo.net/attachmen...ine=1333028854

A test cut is made on the new seat, and contact area is checked by dying the valve face and spinning the valve on the seat. Placement was great here, center of the valve face.
https://www.miataturbo.net/attachmen...ine=1333028854

Now seat placement has been set, I have to set the seat depth so proper valve tip height is achieved.
https://www.miataturbo.net/attachmen...ine=1333028854

now all that is set, the rest of the valve job will be completed, cut the exhaust seats. Valves will be loaded into the casting, new seals installed, spring pressures checked, springs, retainers, and valve locks installed, a vacuum check for seal of seat and valve. Now it will be ready to be bolted back on.

Macro mode!!!!!!!!!!!!!!!!!!

aka The Flower!!

Nice write-up, but I thought I was drunk looking at all those blurry pictures.

I love these threads. Keep them up, they are so interesting. Thank you so much for taking the time to post these for everyone!