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Flat head combustion chamber

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tomj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Mar/20/2021 at 4:20pm
Originally posted by 43n 43n wrote:

WOW!  Thank you for the over-the-top effort in taking these photographs.…
To say I am in shock is an understatement ...really makes you wonder what they were thinking in this design??

Do you think this shape was typical all the way from 1941 through 65?… Hard to criticize especially if they spent many many dynamometer hours developing this


You;re welcome. Adding to the collective knowledge pile I hope.

It is easy, now, to see how primitive it is. but that's really a measure of just how fast technologies have been changing these last 50, and literally, 5, years. It's nuts now what's possible.

With the Lhead, or OHV, block clean and on a bench it is not hard to visualize the wooden model the mold was made from. I sliced up an dead OHV head to see the water jacketing. Its awful! "Flow" is a generous word! Better was possible then for sure, but cost mattered. Computational machines were Comptometers and Brunsviga's, and paper pads and slide rules. This iron tech was based on older crafts-based approaches to problem-solving.  Its an explosion in a hole, push a lever, wear out in 10 years, buy another. 

From what I can tell from reading, these old Nash inline sixes were considered pretty good tech for their time. I think though that applied to the seven-mains motors, not necessarily these little low-end things. The forged crank is high quality, but my good machinist says it is very ropey. I had rear seal issues, he pulled the rear main cap off (car on a lift), loosened the 3rd, the crank sagged enough to rotate a new seal in. With better metals, and stress and dynamical analysis, you can make twice as siff today with a fraction of the material. 

Also the bearings are too large and too wide. It heats the oil, lol! My ohv, 30 minutes held at 2800-3000 rpm high load the oil temp rises to 220F, and Ive got a huge 8" x 8" multi-pass cooler with fan and full-flow oil pump. 30 minutes at 3500 rpm and load and the oil runs 240F, with the cooler fan on.

THe big bearings probably seemed like a great idea back then. Bigger than small is good, but bigger than adequate is worse. Etc. 
1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
1968 American, 199ci, T14
AMC pages: http://www.sr-ix.com/AMC/

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tyrodtom Quote  Post ReplyReply Direct Link To This Post Posted: Mar/20/2021 at 8:06pm
What I did when I relieved the block was lay a head gasket on the block and grind away that sharp corner
on each side of the chamber in the block until it looked like the gentle contours in  head combustion chamber.  
That probably negated all the compression I had gained in the .030 cut,  but the car ran noticeably better after this mod than it did before I relieved the block.

Plus I think that sharp corner may have been a hot spot that was causing pre-ignition.


Edited by tyrodtom - Mar/20/2021 at 8:11pm
66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Mar/20/2021 at 8:51pm
Oh! I didn't realize you'd done these mods. Nice. I'm envious. I irrationally want one of these engines.

I agree on the sharp edges. The weird bulge on the inside of the valve pocket too is sharp edged. Id ground mine as much as I dared -- there's water jacket in there -- and rounded the sharp edges. 


One upside to primitive iron is it's susceptible to new techniques and plain old care.

How high do you dare rev it, for passing, etc?

How high rpm would you dare to cruise at?

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
1968 American, 199ci, T14
AMC pages: http://www.sr-ix.com/AMC/

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Mar/20/2021 at 8:54pm
I also want bragging rights on the ability tro change spark plugs with an adjustable wrench. I did that on the '59 I had right out of high school. It was an automatic too -- not exactly a speed demon, I did manage to hit nearly 80 on a long downhill. It wasn't in good shape when I got it, and tbh, I didn't improve it much in the time I owned it.


1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
1968 American, 199ci, T14
AMC pages: http://www.sr-ix.com/AMC/

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tyrodtom Quote  Post ReplyReply Direct Link To This Post Posted: Mar/20/2021 at 9:29pm
I had that 59 from 64-66.
It had a Fenton head with 2 1 bbls., and overdrive.

I never had a tach , I'd rev it till it till it just wouldn't rev no more sometimes.
In road test of new flatheads,  they reved to 5000.
I'm sure I was at least that high.

This was my first real overhaul of a engine.
About as soon as I got it running good I got sudden orders to Asia.
With only 10 days  warning before I had to be at Travis AFB to ship out,  I had to sell it to a friend in the USAF.
66 American SW, 66 American 2dr, 82 J10, 70 Hornet, Pound, Va.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 43n Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2021 at 12:20am
If you Google “Monitor Sealed” the origin of this engine architecture is introduced in the 1935 Nash 400..

What a creative design ... eliminating both intake and exhaust manifold castings ..machining ...fasteners ..gaskets and assembly time… Brilliant!

    As you mentioned with a 7 main bearing crankshaft and 234 ci
(The 234ci also available as an overhead valve Engine)
Both 3 3/8”x 4 3/8”..
..A little déjà vu for the future  conversion of the 196 engine??

For the 1941 600 engine they dropped  62ci and reverted to the four main bearing crank creating the economy champion
that we are still analyzing  today
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wittsend Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2021 at 9:40am
 When the spark plug location is considered it seems the ignited forces have to go horizontal..., then make a 90 degree a downward motion upon the piston. It makes me wonder how much energy efficiency is lost in that process.

When I look at the somewhat kidney shaped chamber I'm also left to ponder if any of the modern swirl technology was deliberate???
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ken Doyle Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2021 at 11:10am
My stock 1965 American with flathead, automatic, a Carter RBS 1-barrel, and 3.31: gearing would zoom right up to 80 MPH on flat ground, not that I would hold it there.  It was happy cruising all day long at 65 MPH.  If I drove it slower, it would get just shy of 30 MPG.   I don't know much about engine design, but I was impressed with the little engine for the 15 years I drove it daily.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2021 at 9:29pm
Originally posted by wittsend wittsend wrote:

 When the spark plug location is considered it seems the ignited forces have to go horizontal..., then make a 90 degree a downward motion upon the piston. It makes me wonder how much energy efficiency is lost in that process.

When I look at the somewhat kidney shaped chamber I'm also left to ponder if any of the modern swirl technology was deliberate???

It's a gas, so pressure would be essentially equal on all surfaces, standard gas behavior with the "acoustic" behavior of moving gases.

THe volume is a weird shape, flame propagation is probably terrible, dead, cold, hot spots, etc.

Combustion tech is crazy now. I read about a HOnda engine (I don't think its all that unique) that direct-injects into a cup on the top of the piston with precisely controlled swirl, that will routinely burn 60:1 A/F. WOT accelleration is stoichiometric! 

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
1968 American, 199ci, T14
AMC pages: http://www.sr-ix.com/AMC/

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Mar/21/2021 at 9:34pm
Originally posted by Ken Doyle Ken Doyle wrote:

My stock 1965 American with flathead, automatic, a Carter RBS 1-barrel, and 3.31: gearing would zoom right up to 80 MPH on flat ground, not that I would hold it there.  It was happy cruising all day long at 65 MPH.  If I drove it slower, it would get just shy of 30 MPG.   I don't know much about engine design, but I was impressed with the little engine for the 15 years I drove it daily.

Nice! That is also good to hear. I wonder if it's not more reliable than the OHV.

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
1968 American, 199ci, T14
AMC pages: http://www.sr-ix.com/AMC/

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