Compression again.

Bassman/NZ

Bassman/NZ

Well-known member
I had the heads milled to give me 50thou clearance in the squelch area on my 59A engine. I reshaped the area to match the piston domes, put it together and ran a compression test. I discovered the left bank (5-8) was 10lbs average down on the right bank(1-4), so have swapped heads to see if it made a difference. It sure did. The heads are C7RA-A, and my conclusion is the chamber must be slightly different one side to the other. Thought this may be of help to someone.
WOT test.
1- 165
2- 170
3- 165
4- 165
5- 170
6- 170
7- 160
8- 165
 
Impressive numbers for a flathead. Almost too impressive. By any chance are these some sort of metric measurements?
 
The compression numbers are nearly identical to what I have in one of my cars, with 59A heads,(which also has a cam with late closing) and not "suspicious" in the least.
 
Thank you JWL. I tested with two gauges and got same result. Engine has new rings and valve job. Squelch area is 50thou max, 45thou min. The advance on the crab has me puzzled a bit, I've got it set at absolute max I can get it. Wont run very well otherwise, gas is standard for New Zealand, which is 91, no ethanol.
The point I'm trying to make is that there's obviously a right and left head for these engines.
 
Accually my 276 in my 40 I have run for 40 yr's has 60# comp, It's got a wild reground track cam, pistons were hitting the heads, had to have them domed, I had a lot of pinging problem at first, broke a second ring land, I finally welded up the slots in the crab running 17* total, vacuum break about half way down, running cheap gas, it spins to 5000 in no time, I've put a lot of miles on that engine. Walt
 
Bassman/NZ said:
The heads are C7RA-A, and my conclusion is the chamber must be slightly different one side to the other.
Click to expand...

I don't know if that's true or not but perhaps the difference in valve angle from one bank to the other is affecting compression.
 
The difference is below the heads, assuming that both of the C7RA-A's are at the same spec as they should be...these heads exist ONLY as 6050's, meaning no left.right specialization. Any left-right differences should only be production variation or post-production milling.
From the spec charts, Ford Canada and USA dropped separate left and right heads by about 1941.
On heads with separate numbers (post 1936), were the chambers on the ones that were made in 6049-6050 really different CC's consistently, or were the differences simply different tappings for temperature sender and such? I don't have any experience with early stock heads. Bulletins list only one set of CC specs for each of those pairs.
Anyway, by WWII separate head numbers left and right had disappeared.
Displacement of chamber area in block would be different slightly.
C7RA-A heads are iron ones, corresponding in time and CC's with the USA equivalent 59A-B.
 
Bruce Lancaster said:
The difference is below the heads, assuming that both of the C7RA-A's are at the same spec as they should be...these heads exist ONLY as 6050's, meaning no left.right specialization. Any left-right differences should only be production variation or post-production milling.
From the spec charts, Ford Canada and USA dropped separate left and right heads by about 1941.
On heads with separate numbers (post 1936), were the chambers on the ones that were made in 6049-6050 really different CC's consistently, or were the differences simply different tappings for temperature sender and such? I don't have any experience with early stock heads. Bulletins list only one set of CC specs for each of those pairs.
Anyway, by WWII separate head numbers left and right had disappeared.
Displacement of chamber area in block would be different slightly.
C7RA-A heads are iron ones, corresponding in time and CC's with the USA equivalent 59A-B.
Click to expand...
Well, that's thrown the cat amongst the pigeons! Before I swapped heads, I was getting similar figures on the right bank and average 10lbs less on the left bank. Only thing I can think of is that somewhere in the past one of the heads must have had a little chamber work done, for whatever reason. All's well that ends well anyway.
 
It is likely one head was resurfaced a bit too much, resulting in the somewhat lower reading. If it runs Ok, I wouldn't worry..
 
My 280 with stock eab cam and Milled EAB heads (Foe .050 piston cle) has 160, and it only has about 5 miles on it so far.
 
I don't know when the LH-RH head differences were discontinued, especially for non-USA production. I am not even sure all the original equipment heads are listed in Service Bulls or Green Parts Book. I seem to recall seeing 59 heads that were 6049 and 6050.

To the instant point, there can be no doubt the heads described in the original post on this thread have different chamber sizes. The reason for the differences can not, at this point, be determined.
 
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