Author Topic: Flathead Heads  (Read 295 times)

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Offline JamLazyAss

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Flathead Heads
« on: June 05, 2021, 10:44:37 AM »
Anyone know if these heads are for 45 or 74 ?

I'm not a proctologist, but I know an asshole when I see one...

Online PC_Hater

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Re: Flathead Heads
« Reply #1 on: June 06, 2021, 01:47:15 AM »
In that bottom pic you can see the circle from the bore.
Measure it.
2.75" they are 45.
3 and 5/16" 74 flathead.
3 and 7/16" 80 flathead.

Those heads look old and the bore mark and valve cut-outs look big to me.
I vote 74" flathead but I have never seen 74" parts, only 45s. Not many big flatheads in the UK.
1942 WLA45 chop, 1999 FLTR(not I), 2000 1200S

Offline JamLazyAss

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Re: Flathead Heads
« Reply #2 on: June 07, 2021, 06:21:26 PM »
If that black circle is the bore, then a quick measurement put it at roughly 3 1/2 inches.
I'm not a proctologist, but I know an asshole when I see one...

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Re: Flathead Heads
« Reply #3 on: June 08, 2021, 12:46:15 AM »
They are 74" heads. The 9 bolt heads were first used in 1935.

I've been having a look at my bike and in my library...
45 heads have 8 head bolts, those have 9.
The advertised bore was 3 and 7/16" but the actual bore was 3.424".
« Last Edit: June 08, 2021, 01:06:23 AM by PC_Hater »
1942 WLA45 chop, 1999 FLTR(not I), 2000 1200S

Offline JamLazyAss

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Re: Flathead Heads
« Reply #4 on: June 08, 2021, 09:15:58 AM »
Sweet.
I'm thinking there's not too many of these around.

JC:
Why 74 and not 80?
I'm not a proctologist, but I know an asshole when I see one...

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Re: Flathead Heads
« Reply #5 on: June 08, 2021, 03:20:37 PM »
Your measurement of the circle the marks the bore.
About 3.5 inches is nicely close to actual 3.424". And you are right, they just might be off an 80". I will have to  recheck my sources, one of the books might have a typo!
1942 WLA45 chop, 1999 FLTR(not I), 2000 1200S

Online PC_Hater

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Re: Flathead Heads
« Reply #6 on: June 08, 2021, 04:54:15 PM »
OK.
Harley changed the bore and stroke on the 74s from the 1930 3 and 7/16" bore and 4" stroke to 3 and 5/16" bore and 4 and 9/32" stroke in 1937.
The 80s up to 1937 had the same 3 and 7/16" bore but with a longer 4.25" stroke.
In 1937 the 80s got the same even longer stroke but kept the 3 and 7/16" bore.

1930 to 1937 are VL and VLH models, 1937-on are the UL and ULH.

You will need somebody that knows their stuff to work exactly which model 74 or 80 flathead those heads fit!
1942 WLA45 chop, 1999 FLTR(not I), 2000 1200S