Motorcycle engine: Flathead Vs Shovelhead?

Danny (AKA "The Count, on the tv show “Counting Cars”) told his motorcycle restore guy to swap the flathead for a shovelhead. What does that mean? & Why would he want to do that?

Flathead is from late 20’s and 21hp

Shovelhead is from mid 60’s and 60hp

Ok, but I’m not seeing anything “flat” on the 1929 F-Head photo; nor am I seeing anything that looks like a shovel on the 1983 Shovelhead photo.

Do these two images copied from Harley engine pages help?

[Edited my original post to show a pic of a flathead cylinder head instead of a cylinder]



I see, the difference makes sense now, thanks.

Flat is inside the head. No dome, no valves in head but it doesn’t have to be totally flat to be a flat head. Valves are in the block. With that setup the head would be flatter or the compression pressure would be really low.

The others I don’t know about.

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F heads (also used in some cars) have one OHV, for intake, one valve in block for exhaust.

Air cooled flatheads have cooling fins, therefore do not look like water cooled flatheads.

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Old school lawn mower engines are flatheads.

I think the terms flathead, panhead, shovelhead, etc come from the appearance of the heads from the top. See how the shovelhead kinda looks like the steel part of a straight blade shovel lying face down on top of the motor? Knucklehead kinda sorta looks like the knuckles of your balled fist from the side. Panhead, yeah that ones obvious. Looks like a transmission fluid pan lying on top of the engine. Flathead, well, it’s sorta flat on top and bottom. Mostly, I guess it’s more fun saying “I got a knucklehead Harley” than saying “My Harley Davidson is equipped with a 1947 1200 cc engine”.

The F h`ad is not a flat head. It is an engine with one overhead valve on the intake side and the exhaust valve in the block. It was a good engineering solution when available gasoline would not allow compressions over 4.5 to one. If you could not make power with compression, you could use much larger valves because they did not have to share the cylinder diameter.

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Thanks oldtimer for that clarification on the “F-head” engine. Your post got me curious and I did some reading up on it.
Here’s one informative link I found:

F Head Engine - General Discussion - Antique Automobile Club of America - Discussion Forums

In regard to the HD flatheads I will just add that in the engine time line shown above that 74 inch flathead was not the only one built. The 74 inch used in the VL model is shown.
There was a 45 inch motor used on the DLs which became RLs in 1932 and WLs (civilian) and WLAs (military) later on. The 3 wheeled ones were G models.

In 1937 the 74 flathead was redone on the U and UL models. Same displacement but completely different engine. From 37 through 41 it was also offered as an 80 inch on the UH and ULH models. The H and L designations meant higher compression ratios.
The 74 inch continued until 1948 but the 45 inch was used up through 1973 and the 2 wheeled 45 inch models were discontinued in the 50s although I do not remember the year. 52 I think.

In addition to the flathead (both valves in block on one side) and F head (one in block, one in head), there was the T head:

I like the symmetry of the T-head.

Harley also used the flathead on the first Sportsters, the K and KH from '52 to '56, and on the flat track KR from '53 to '69.

Some years ago a few guys were putting Sportster top ends (a mini-shovel if you will) on 45 flat head lower ends. My understanding is that the extra 150 CCs and the compression bump from the flathead 5.5 to 1 up to 9 to 1 was a bit tough on lower ends.

Back in the 70s a friend of mine bought a 45 Harley flathead in the works. A chopper. It was finished in metal flake paint and was done except for installing the trans and finishing the engine up. It was beautiful.

So the day it was done off he went to tool around town and profile a bit. These 2 wheel bikes had 3 speed transmissions. Unknown to him the trans provided was a Harley 3 wheel Servi Car trans which looks identical; BUT it has reverse in it.

So he comes to a stop at the stop sign and a lady in a car pulls up behind him. He reaches down and moves the gear shift farther back than he intended. He assumed he was in the neutral between 1 and 2 but was actually in neutral between 1 and Reverse.

He lets the clutch out while revving it and the bike darts backwards; smashing into the woman’s car and putting her in a panic. That is when he learned the trans had an extra gear…just not a forward one.