Dropped Valve Head Repair
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4G63 Dropped Valve Head Repair
The Subject head is a 1G 6 bolt head.
This head had extensive work done to it and would cost way more to replace than repair.
The head was loaded with SuperTech +1mm valves, and duel valve springs and Ti retainers.
How the head looked when I received it.
![](https://www.miataturbo.net/attachments/engine-performance-56/47594-dropped-valve-head-repair-dscf6527.jpg?dateline=1340816317)
A closer look at #4 cylinder, the one that dropped the valve.
![](https://www.miataturbo.net/attachments/engine-performance-56/47595-dropped-valve-head-repair-dscf6537.jpg?dateline=1340816317)
Yes it looks pretty beat. But it is fixable.
First thing to do is disassemble the head and get a parts list going.
At first look, I thought the 4 valves in the #4 cylinder would be the only ones needing replaced.
It turned out only 4 valves of the 16 could be used.
![](https://www.miataturbo.net/attachments/engine-performance-56/47596-dropped-valve-head-repair-dscf6556.jpg?dateline=1340816317)
The SuperTech duel springs and Ti retainers tested fine and will be used. About half of the Ti retainers had be rubbed on.
![](https://www.miataturbo.net/attachments/engine-performance-56/47597-dropped-valve-head-repair-dscf6551.jpg?dateline=1340816317)
At this time it was decided to install bronze guides, to replace the stock appearing cast iron guides.
![](https://www.miataturbo.net/attachments/engine-performance-56/47598-dropped-valve-head-repair-dscf6563.jpg?dateline=1340816317)
The bronze guides installed.
![](https://www.miataturbo.net/attachments/engine-performance-56/47599-dropped-valve-head-repair-img_0774.jpg?dateline=1340816317)
Once the head was cleaned, a couple small cracks were found in #1 cylinder.
![](https://www.miataturbo.net/attachments/engine-performance-56/47600-dropped-valve-head-repair-img_0773.jpg?dateline=1340816317)
The seats were cut out
![](https://www.miataturbo.net/attachments/engine-performance-56/47601-dropped-valve-head-repair-img_0768.jpg?dateline=1340816317)
Then the head was pressure tested, using 35psi in the water jacket.
The head did not leak.
So work progressed by removing the 4 seats in #4 cylinder.
![](https://www.miataturbo.net/attachments/engine-performance-56/47602-dropped-valve-head-repair-img_0779.jpg?dateline=1340816317)
New counter bores were cut, and oversized inserts were installed.
![](https://www.miataturbo.net/attachments/engine-performance-56/47603-dropped-valve-head-repair-photo0042.jpg?dateline=1340816317)
Some grinding, polishing and blending was done to smooth out some of the damaged area in the combustion chamber.
Next was to mark the spots to be welded.
![](https://www.miataturbo.net/attachments/engine-performance-56/47604-dropped-valve-head-repair-photo0043.jpg?dateline=1340816317)
What it looked like once back from the welder.
![](https://www.miataturbo.net/attachments/engine-performance-56/47605-dropped-valve-head-repair-photo0044.jpg?dateline=1340816317)
Also to note is the spark plug inserts were installed in cylinders #1 and #4 before welding.
From this point a bit more blending was done to smooth out the welds and a full valve job was performed.
As the seats were cut,
![](https://www.miataturbo.net/attachments/engine-performance-56/47606-dropped-valve-head-repair-dscf6567.jpg?dateline=1340816317)
Valve tip height was checked and set to the proper specs.
![](https://www.miataturbo.net/attachments/engine-performance-56/47607-dropped-valve-head-repair-dscf6573.jpg?dateline=1340816317)
Spring installed height was measured and set to 1.550 @ 85lbs
![](https://www.miataturbo.net/attachments/engine-performance-56/47608-dropped-valve-head-repair-dscf6547.jpg?dateline=1340816317)
New 3g HLAs were installed, along with the followers and cams.
![](https://www.miataturbo.net/attachments/engine-performance-56/47609-dropped-valve-head-repair-img_0823.jpg?dateline=1340816317)
Bottom of the head.
![](https://www.miataturbo.net/attachments/engine-performance-56/47610-dropped-valve-head-repair-img_0821.jpg?dateline=1340816317)
Close up of #4 cylinder after repair.
![](https://www.miataturbo.net/attachments/engine-performance-56/47611-dropped-valve-head-repair-img_0822.jpg?dateline=1340816317)
Head thickness after repair and rebuild. 5.159
Head build # BBB 744
The Subject head is a 1G 6 bolt head.
This head had extensive work done to it and would cost way more to replace than repair.
The head was loaded with SuperTech +1mm valves, and duel valve springs and Ti retainers.
How the head looked when I received it.
![](https://www.miataturbo.net/attachments/engine-performance-56/47594-dropped-valve-head-repair-dscf6527.jpg?dateline=1340816317)
A closer look at #4 cylinder, the one that dropped the valve.
![](https://www.miataturbo.net/attachments/engine-performance-56/47595-dropped-valve-head-repair-dscf6537.jpg?dateline=1340816317)
Yes it looks pretty beat. But it is fixable.
First thing to do is disassemble the head and get a parts list going.
At first look, I thought the 4 valves in the #4 cylinder would be the only ones needing replaced.
It turned out only 4 valves of the 16 could be used.
![](https://www.miataturbo.net/attachments/engine-performance-56/47596-dropped-valve-head-repair-dscf6556.jpg?dateline=1340816317)
The SuperTech duel springs and Ti retainers tested fine and will be used. About half of the Ti retainers had be rubbed on.
![](https://www.miataturbo.net/attachments/engine-performance-56/47597-dropped-valve-head-repair-dscf6551.jpg?dateline=1340816317)
At this time it was decided to install bronze guides, to replace the stock appearing cast iron guides.
![](https://www.miataturbo.net/attachments/engine-performance-56/47598-dropped-valve-head-repair-dscf6563.jpg?dateline=1340816317)
The bronze guides installed.
![](https://www.miataturbo.net/attachments/engine-performance-56/47599-dropped-valve-head-repair-img_0774.jpg?dateline=1340816317)
Once the head was cleaned, a couple small cracks were found in #1 cylinder.
![](https://www.miataturbo.net/attachments/engine-performance-56/47600-dropped-valve-head-repair-img_0773.jpg?dateline=1340816317)
The seats were cut out
![](https://www.miataturbo.net/attachments/engine-performance-56/47601-dropped-valve-head-repair-img_0768.jpg?dateline=1340816317)
Then the head was pressure tested, using 35psi in the water jacket.
The head did not leak.
So work progressed by removing the 4 seats in #4 cylinder.
![](https://www.miataturbo.net/attachments/engine-performance-56/47602-dropped-valve-head-repair-img_0779.jpg?dateline=1340816317)
New counter bores were cut, and oversized inserts were installed.
![](https://www.miataturbo.net/attachments/engine-performance-56/47603-dropped-valve-head-repair-photo0042.jpg?dateline=1340816317)
Some grinding, polishing and blending was done to smooth out some of the damaged area in the combustion chamber.
Next was to mark the spots to be welded.
![](https://www.miataturbo.net/attachments/engine-performance-56/47604-dropped-valve-head-repair-photo0043.jpg?dateline=1340816317)
What it looked like once back from the welder.
![](https://www.miataturbo.net/attachments/engine-performance-56/47605-dropped-valve-head-repair-photo0044.jpg?dateline=1340816317)
Also to note is the spark plug inserts were installed in cylinders #1 and #4 before welding.
From this point a bit more blending was done to smooth out the welds and a full valve job was performed.
As the seats were cut,
![](https://www.miataturbo.net/attachments/engine-performance-56/47606-dropped-valve-head-repair-dscf6567.jpg?dateline=1340816317)
Valve tip height was checked and set to the proper specs.
![](https://www.miataturbo.net/attachments/engine-performance-56/47607-dropped-valve-head-repair-dscf6573.jpg?dateline=1340816317)
Spring installed height was measured and set to 1.550 @ 85lbs
![](https://www.miataturbo.net/attachments/engine-performance-56/47608-dropped-valve-head-repair-dscf6547.jpg?dateline=1340816317)
New 3g HLAs were installed, along with the followers and cams.
![](https://www.miataturbo.net/attachments/engine-performance-56/47609-dropped-valve-head-repair-img_0823.jpg?dateline=1340816317)
Bottom of the head.
![](https://www.miataturbo.net/attachments/engine-performance-56/47610-dropped-valve-head-repair-img_0821.jpg?dateline=1340816317)
Close up of #4 cylinder after repair.
![](https://www.miataturbo.net/attachments/engine-performance-56/47611-dropped-valve-head-repair-img_0822.jpg?dateline=1340816317)
Head thickness after repair and rebuild. 5.159
Head build # BBB 744
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