The Ford Barn

[email protected] · 08-29-2017, 07:27 AM

I have a 48 Mercury. The passenger side head has 59A cast into it and the driver's side head has 9T then below at the center at the bottom 99T Ford USA.) Is this a truck head? Car runs fine. Is there a difference in the heads that would effect compression? Should I install a 59A head on the driver's side or just not worry about it?
Thanks!
Bill in Conn.

scooder · 08-29-2017, 07:57 AM

99T is a 239 truck head, the combustion chamber is a good chunk bigger on these, so lower compression ratio.
Best bet is to plop a 59A head on there.
Martin.

rotorwrench · 08-29-2017, 08:46 AM

Later post war cars generally have the 59AB type heads whether Ford or Mercury since they were the same engine. Prewar engines have different valve angles and can make contact in the combustion chamber if not relieved with the special tools that were available to rectify that situation back in the day. Prewar heads for 239 engines include the 99T and 29A types. These heads have value to restorers that want the original part number heads on their projects if still in good condition.

40 Deluxe · 08-29-2017, 09:12 AM

As I understand it, 1945 through '48 engines were designated 59A while the heads were designated 59AB because they fit either side of the engine. Prewar heads (with the different valve angles) were different from side to side. One side was designated A and the other side B (forget which is which).

42merc · 08-29-2017, 01:51 PM

The sky is not falling.
As you have said it runs fine. Granted , there is a difference in valve angles between early & late , but early heads on later blocks was done often without cutting the heads.
I've done it several times with no ill effects.

rotorwrench · 08-29-2017, 03:02 PM

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They started post war with the 59A-6050-A in 1945 and for a while in 1946 before making a running change to the 59A-6050-B heads (commonly refered to as 59AB). You can put the late ones on the early motors but putting the early ones on late motors is hit or miss depending on the size of the combustion chamber. It's a good idea to check before encountering the funky noises that can happen or even a bent valve or three. Many folks just used a carbide burr or vitrified grinding stone to relieve the pockets a bit. It doesn't take much. A person just has to know where.

scooder · 08-30-2017, 07:47 AM

It's not the valve angle that's an issue here, as the man said, it's running fine. So we'll say the head clears the valves.
The big difference in chamber volume, in my opinion is an issue. So fitting a matching 59A head will increase the compression ratio on that side, more torque, more responsive and less gas, are benefits of higher compression ratio. And equal compression on both sides, makes for a better smoother engine.
That's enough reason to sort this out.
Martin.

[email protected] · 08-30-2017, 11:43 AM

Thanks for all the good input. Next month at Hershey I will look for a 59A head. Sure appreciate all the help I get at the Ford Barn!

Bill in Conn.

08-29-2017, 07:27 AM	#1
[email protected] Senior Member Join Date: Nov 2015 Location: Sharon, Conn. Posts: 114	48 mercury heads I have a 48 Mercury. The passenger side head has 59A cast into it and the driver's side head has 9T then below at the center at the bottom 99T Ford USA.) Is this a truck head? Car runs fine. Is there a difference in the heads that would effect compression? Should I install a 59A head on the driver's side or just not worry about it? Thanks! Bill in Conn.

08-29-2017, 07:57 AM	#2
scooder Senior Member Join Date: Jul 2010 Posts: 2,593	Re: 48 mercury heads 99T is a 239 truck head, the combustion chamber is a good chunk bigger on these, so lower compression ratio. Best bet is to plop a 59A head on there. Martin.

08-29-2017, 08:46 AM	#3
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,426	Re: 48 mercury heads Later post war cars generally have the 59AB type heads whether Ford or Mercury since they were the same engine. Prewar engines have different valve angles and can make contact in the combustion chamber if not relieved with the special tools that were available to rectify that situation back in the day. Prewar heads for 239 engines include the 99T and 29A types. These heads have value to restorers that want the original part number heads on their projects if still in good condition.

08-29-2017, 09:12 AM	#4
40 Deluxe Senior Member Join Date: May 2010 Location: now Kuna, Idaho Posts: 3,779	Re: 48 mercury heads As I understand it, 1945 through '48 engines were designated 59A while the heads were designated 59AB because they fit either side of the engine. Prewar heads (with the different valve angles) were different from side to side. One side was designated A and the other side B (forget which is which).

08-29-2017, 01:51 PM	#5
42merc Senior Member Join Date: Feb 2011 Location: Buchanan, MI Posts: 676	Re: 48 mercury heads The sky is not falling. As you have said it runs fine. Granted , there is a difference in valve angles between early & late , but early heads on later blocks was done often without cutting the heads. I've done it several times with no ill effects.

08-29-2017, 03:02 PM	#6
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,426	Re: 48 mercury heads Sponsored Links (Register now to hide all advertisements) They started post war with the 59A-6050-A in 1945 and for a while in 1946 before making a running change to the 59A-6050-B heads (commonly refered to as 59AB). You can put the late ones on the early motors but putting the early ones on late motors is hit or miss depending on the size of the combustion chamber. It's a good idea to check before encountering the funky noises that can happen or even a bent valve or three. Many folks just used a carbide burr or vitrified grinding stone to relieve the pockets a bit. It doesn't take much. A person just has to know where.

08-30-2017, 07:47 AM	#7
scooder Senior Member Join Date: Jul 2010 Posts: 2,593	Re: 48 mercury heads It's not the valve angle that's an issue here, as the man said, it's running fine. So we'll say the head clears the valves. The big difference in chamber volume, in my opinion is an issue. So fitting a matching 59A head will increase the compression ratio on that side, more torque, more responsive and less gas, are benefits of higher compression ratio. And equal compression on both sides, makes for a better smoother engine. That's enough reason to sort this out. Martin.

08-30-2017, 11:43 AM	#8
[email protected] Senior Member Join Date: Nov 2015 Location: Sharon, Conn. Posts: 114	Re: 48 mercury heads Thanks for all the good input. Next month at Hershey I will look for a 59A head. Sure appreciate all the help I get at the Ford Barn! Bill in Conn.