Pan Head bronze valve seats...

[Steve Galli]

Hello All,
New member here,
What are the thoughts of leaving the original bronze seats be and just using oversized valves if needed...
Pick attachment showing inside head... heard bad stories of seat replacement going bad so I would like to recut seats and run if possible....
Love this site!
Steve

[T. Cotten]

Hello All,
New member here,
What are the thoughts of leaving the original bronze seats be and just using oversized valves if needed...
Pick attachment showing inside head... heard bad stories of seat replacement going bad so I would like to recut seats and run if possible....
Love this site!
Steve

Your instincts are good, Steve!

A lot of Panheads wouldn't be scrap if so many shops hadn't thought they knew better.

...Cotten
PS: I've a pile of cores if anybody wants them. Gotta walk in my door, though....

[Steve Galli]

Your instincts are good, Steve!

A lot of Panheads wouldn't be scrap if so many shops hadn't thought they knew better.

...Cotten
PS: I've a pile of cores if anybody wants them. Gotta walk in my door, though....

Thanks! I seen a lot of u tube videos boring out the old seats and I’m thinking oh man I don’t want that done...
so just run high test unleaded gas?
Steve

[kitabel]

The insert is larger than the original (1.75") seat OD, but the insert placement is not reliably concentric. When cutting the new seat the insert may expose the parent aluminum at one point, so the area should be thoroughly cleaned and the maximum bronze diameter determined. The smallest possible OD replacement valve should be used, which may not raise the seat enough to provide a direct path* to the chamber interior (viz., not obstructed by the sunken edge of the old seat).
For the intake, the easiest choice is a +.1875" shovelhead valve with its head diameter reduced as needed, for the exhaust there are +.125" O/S valves available. Re-contour the valve head to reduce margin thickness, with a back angle if desired, and reduce the seat width as needed.
* If the new seats still don't "see" the open chamber, relieve the aluminum around the seat down to the bronze line with a really shallow cutter, like 15-20 degrees. This will not complete restore the breathing but it helps.
Depending on the seat condition and new seat OD, the valve height may be either more or less than the factory height, which affects rocker geometry. In addition to lash caps, the blocks themselves can be shimmed or the iron bases machined to change the installed rocker height. Remember to include any change in valve lift due to a cam change: the rockers are (more or less) made for .400" lift. In addition to any compensation for the new valve height, a .500" lift needs either a .050" (50% of the change) taller valve or lowering the blocks .050", etc.
Don't be surprised if the intakes and exhausts don't spec out the same afterward.

[Steve Galli]

The insert is larger than the original (1.75") seat OD, but the insert placement is not reliably concentric. When cutting the new seat the insert may expose the parent aluminum at one point, so the area should be thoroughly cleaned and the maximum bronze diameter determined. The smallest possible OD replacement valve should be used, which may not raise the seat enough to provide a direct path* to the chamber interior (viz., not obstructed by the sunken edge of the old seat).
For the intake, the easiest choice is a +.1875" shovelhead valve with its head diameter reduced as needed, for the exhaust there are +.125" O/S valves available. Re-contour the valve head to reduce margin thickness, with a back angle if desired, and reduce the seat width as needed.
* If the new seats still don't "see" the open chamber, relieve the aluminum around the seat down to the bronze line with a really shallow cutter, like 15-20 degrees. This will not complete restore the breathing but it helps.
Depending on the seat condition and new seat OD, the valve height may be either more or less than the factory height, which affects rocker geometry. In addition to lash caps, the blocks themselves can be shimmed or the iron bases machined to change the installed rocker height. Remember to include any change in valve lift due to a cam change: the rockers are (more or less) made for .400" lift. In addition to any compensation for the new valve height, a .500" lift needs either a .050" (50% of the change) taller valve or lowering the blocks .050", etc.
Don't be surprised if the intakes and exhausts don't spec out the same afterward.

Sounds complicated... Best left to a pro... Thank you!

[kitabel]

It's not technically difficult, it just involves careful measurement. Once you examine the seats closely, the reasons for the specific work will fall into place naturally, it's almost intuitive.
The rocker arm work is best done at the same time, since servicing the rockers cannot be done without removing the pans (either the engine out of the frame, or the heads off). The key here is to measure the actual installed stem height with the new valves in place compared to the dimensions in the shop manual, all corrective work is based on this information.
There are few shops that do actual seat replacement, and it's very expensive.

[T. Cotten]

My K.O. Lee outfit is for sale, Folks!

And a healthy stash of hardened seats, too.

....Cotten

[Steve Galli]

My K.O. Lee outfit is for sale, Folks!

And a healthy stash of hardened seats, too.

....Cotten

Hi Cotten
What’s this for?

[Steve Galli]

It's not technically difficult, it just involves careful measurement. Once you examine the seats closely, the reasons for the specific work will fall into place naturally, it's almost intuitive.
The rocker arm work is best done at the same time, since servicing the rockers cannot be done without removing the pans (either the engine out of the frame, or the heads off). The key here is to measure the actual installed stem height with the new valves in place compared to the dimensions in the shop manual, all corrective work is based on this information.
There are few shops that do actual seat replacement, and it's very expensive.

Hopefully I won’t need seat replaced
Did you see the picture of the head I uploaded?
Thanks

[BigLakeBob]

Steve,
Nice looking combustion chamber, too bad there are some broken fins. Are you sure they are original seats? Enlarged pic but hard to see, the distance between the seats looks too close to be orig. That distance should be 3/16" or more. Not saying they aren't orig because the pic is so vague but possible. I have installed quite a few bronze seats in pan heads, so just because they are bronze doesn't mean they are orig seats. If you can use over size valves and also obtain the 'correct flow which is difficult' that is the way to go. But, correctly installed new seats is not necessary a failure waiting to happen. It all goes back to the correct material being installed for proper expansion of similar materials. Too many 'unleaded fuel hardened seat cowboys' got carried away and gave pan head seat replacement a bad name in my opinion.

[Steve Galli]

Steve,
Nice looking combustion chamber, too bad there are some broken fins. Are you sure they are original seats? Enlarged pic but hard to see, the distance between the seats looks too close to be orig. That distance should be 3/16" or more. Not saying they aren't orig because the pic is so vague but possible. I have installed quite a few bronze seats in pan heads, so just because they are bronze doesn't mean they are orig seats. If you can use over size valves and also obtain the 'correct flow which is difficult' that is the way to go. But, correctly installed new seats is not necessary a failure waiting to happen. It all goes back to the correct material being installed for proper expansion of similar materials. Too many 'unleaded fuel hardened seat cowboys' got carried away and gave pan head seat replacement a bad name in my opinion.

Thanks Bob,
I have no idea if the seats are original or not... these heads have been sitting in my basement since the seventies...
You gave me quite a scare about the cracked fins! It’s just the cut outs for the push rods... yes I just ran down the basement to check! Will let everyone know what the shop says when I take the heads in....

[BigLakeBob]

Must be the angle of the pic, the left cut out just doesn't look right, too sharp on the right side of it. Glad its all good. It looks like at some point when a valve job was done, someone used too large of a stone or cutter and took some of the aluminum away around the top outer diameter of the seat. This could be why the seats look closer than original, could just be this recessed area. Have you checked valve height yet?

[Steve Galli]

Must be the angle of the pic, the left cut out just doesn't look right, too sharp on the right side of it. Glad its all good. It looks like at some point when a valve job was done, someone used too large of a stone or cutter and took some of the aluminum away around the top outer diameter of the seat. This could be why the seats look closer than original, could just be this recessed area. Have you checked valve height yet?

Hi Bob,
No I have not... Heads are still all together... I will see if I can make some kind of measurement...

[T. Cotten]

Hi Cotten
What’s this for?

Installing seats, Steve!

I've replaced them on Pans, Shovels, Knucks, and Chiefs with this early tooling.

What you really want installed are OEM bronze replacements;

They do not require the enormous interference fit that split so many Pan heads with hardened seats.

....Cotten
PS: Lead is highly over-rated. Propane motors I serviced in the early '80s had bronze.

[Steve Galli]

Installing seats, Steve!

I've replaced them on Pans, Shovels, Knucks, and Chiefs with this early tooling.

What you really want installed are OEM bronze replacements;

They do not require the enormous interference fit that split so many Pan heads with hardened seats.

....Cotten
PS: Lead is highly over-rated. Propane motors I serviced in the early '80s had bronze.

How about that... Learning so much here!! so will they run ok with the unleaded gas?