Anyone know anything about flathead 6 engines?

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jeryst

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I just bought a 1948 Plymouth 2 door coupe with a flathead 6 in it.

The motor smokes a little, and occasionally it has a loud knock when you hit the gas. Runs really good and has a lot of power.

I dont know anything about these engines, so I was wondering if anyone has experience or an opinion about them.

I'm not really worried about it because I got the car for a really good price, and a bad engine just means a V8 somewhere down the road - lol.
 
I have a couple of '40's Mopars ('47 plym convert and '47 Dodge D25c - the Canadian export one) both run the flathead. I did spin a bearing on # 5 in the convert many years back and that knock could be a bearing knock. They are pretty hard to kill though so unless it's very pronounced you may get away with it for some time. On the other hand when you can hear something wrong with any engine it does tend to make you nervous eh?
Why don't you post a pic of it?
Regards
Gary
 
The displacements of the Mopar L-head 6 were 216, 230 and 251 CID if I recall correctly. The design goes back before WWII. They were well built and gave good service so long as they weren't expected to do something they were never designed to do. They had a long stroke and 4-main cranks, and therefore were not high RPM pieces (but back then, there were no freeways and many county roads were still gravel so highway speeds were much lower).

As for the knock, it is most likely a rod bearing. You can probably just replace the inserts and get some more life out of it. If you are intent on a V8 swap and/or just like destroying stuff, keep running it.
 
Like Aussie and Chief said, probably a rod bearing. Contact Egge Machine or possible your local NAPA store for parts. Hopefully you can drop the pan and replace the bearings and make it happy again. If the crank is a bit rough, some emery cloth can polish the nastys off and a .001 or .002 under bearing can be installed so the oil clearances come out right. It's not a textbook fix but good for breathing a little life into a old engine. Keep us posted. toolman
 
I owned several when I was a kid, and I love the old flathead Mopars.

If it has a deep knock under load, it's probably a main bearing. A lighter knock when not loaded is one or more rods. I've replaced both without removing the engine from the car, though the rope style rear seal is sort of a pain.

Those engines are extremely tough and were used extensively in farm equipment. We had both a combine and a tractor with flathead Mopars and they were as good as any farm equipment made.

The military had thousands of them in trucks like the famous Power Wagons, and if a GI can't break something, it can't be broken. They even used them in flightline tugs. Back in the early 60's, a GI bought a surplus tug in England, modified the snot out of it, and ran it at the drag races. They did a story on it in the Stars and Stripes newspaper, and as a Mopar fan even then, I enjoyed showing my buddies the article.

They are also surprisingly fast. I've driven for miles with the speedometers locked at an indicated 105, and never had one break. The '48 Plymouth I sold a friend was crushed by a tornado, so he decided to see how long the engine would run at full throttle in neutral. He placed a heavy rock on the accelerator and we listened to it scream for over a half-hour before it blew.
 
As promised.
 

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I'm familiar with the marine version of the engine. As others have said, it's pretty durable. It's also very easy to work on. Parts are still readily available through Kanter (.com).
 
I have one in my 38 truck the only real issue I have / had were adjusting the vlaves, and the water distribution tube. Mine overheats after about a mile of running the tube is corroded and broken into pieces so I have to pull the motor. That is another thread but lioke everyone else is stating what do you want to do with the car mod it with a V8 or keep it with the flat head that will make your decission for you. if V8 run it until you are ready to make that conversion. If not then you can repair the bearing installed or rebuild the entire engine. Andy Bernbaum has just about all the parts you will need.
 
I used to beat the crap out of the one in my old pickup (see pic in avatar) it hated anything but straight 50 weight oil, it would smoke and make noise if I tried to use multi weight 10/40 20/50 whatever, fill it up with valvoline racing 50 and it was happy as a clam purring like a kitten
 
Fabrication of motor mounts transmission mounts / cross member exhaust system. all depends on what you want to do.
 
Here are some pics of the frame from my 51 Plymouth, the motor mounts and tranny mount were fabricated by a local rod shop. The tranny mount was from a chevelle and narrowed to fit the frame.
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This was to fit a 318 and automatic
 
only question I seen was what is a Mopar called with valves in the block? That would be a flathead... did notice username has to be 8 characters long...
 
Yeah registration on that site is a little "involved" I just joined that site recently and didn't have a problem, you can't see any pics if your not registered.
 
I have a 47 Desoto conv, had a flathead 6 in it, but with the fluid drive trans, it had a rough time pulling the heavy conv. So I put a 68 plymouth 318 in it, with a 904 tranny.Went in pretty easy used 65 cuda exhaust manifolds, and made my own mounts. Had to offset the engine a smidgen. Glad I did it cruises nicely with the stock rear end. Would post a pic if I can figure out how. Kind of a computer dummy.
 
My brother had a 48 Chrysler Windsor Highlander with the straight six. Great cruiser as longer as you drove it 60-65 mph. The engines were also used as industrial and agricultural. When my brother sold it, a farmer put the engine in his Massey-Harris 55 row crop tractor. It was a straight bolt in installation.
 
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