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Thread: 1941 ulh heads

  1. #1

    Default 1941 ulh heads

    i,m building a 41ulh 80" engine. being a ulh, i would like to go with high compression (squish-"wr" heads). doe's anyone have an opinion about the re-pop aluminum heads, that look like cast iron heads. they are marked with 4-lines. or any sugestions.
    are the high-compression heads a lot harder to kick over than the 1 or 2-bar heads.
    got a chance on some original flywheels, a dozen or more 1/2" holes drilled in one. im guessing to lighten not balance. is this a problem?
    any help is appreciated, this is my first big flatty. scooter

  2. #2
    Join Date
    Jan 2003
    Location
    England
    Posts
    1,323

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    I think 1941 was the first year for the ally heads, so at least you won't have young kids pointing at you and shaking their heads as you drive down the street. I've got 8.2 ally heads on my 35VLDD 80, and cast iron 9.3 heads on my 35VLD 74. You can feel the difference in compression when kicking them over, but the VLDD is by no means hard to start. The WRs didn't seem to go over about 7 to 1 compression ratio, and relied on some serious gas flowing work for the power and traction. You should be OK.

  3. #3

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    thanks Steve. at 62 i'm starting to consider not having a grabber, trying to kick start my scooters.

  4. #4
    Join Date
    Jun 2017
    Location
    Charles Town, West Virginia
    Posts
    38

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    I've got a 41 UL With .20 over 80" pistons and run 5:1 heads with stock intake and stock valves it seems to run fine. It is my first big twin flathead so I have nothing to compare it to. But from what I've been told and read anything over 6.7:1 diminishes perfomance. I'm also building a 45" stroker and been told by someone I have alot of faith in that 5:1 stock WLA Military heads are the best heads for my motor.

  5. #5

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    All H-D sidevalve engines have quench, it's just not very effective because of sloppy tolerances and head gasket thickness variations. Some U series as loose as .080" between negative deck clearance and thick gaskets; this (and the large distance between the spark plug and the left end of the chamber) makes them very knock sensitive. If possible, reduce this to .035".
    The choice of head or head milling has no effect on quench clearance (exception: pop-up with the crown above the gasket surface @ TDC - look at a late WR or K for the shape), it's entirely piston location + gasket thickness.

    Your balance guy won't like you, he may have to make even more holes to zero those out.
    All balance holes should be in the inside face of both flywheels. If any exist in the outer face (pretty common for post-sale), is it worth filling those in and starting over? I don't know.

  6. #6

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    The ideal static compression ratio is not fixed, even for a specific engine type. The CR is a balance between cylinder pressure (small chamber volume) and high RPM flow between the intake valve and the bore (large volume). Racers with Ford V8 flatheads discovered that drag racing where torque was important could use CR as high as 9:1, but LSR where peak HP was more important have lower ratios. Adapting a known ratio from a different engine only works by accident.
    The ideal static ratio varies with the bore to stroke ratio: strokers can use more. Indians, WR, & K can use more than W, V, U because their valves are closer to the bore.

  7. #7
    Join Date
    Nov 2010
    Posts
    181

    Default

    Quote Originally Posted by scooter57 View Post
    i,m building a 41ulh 80" engine. being a ulh, i would like to go with high compression (squish-"wr" heads). doe's anyone have an opinion about the re-pop aluminum heads, that look like cast iron heads. they are marked with 4-lines. or any sugestions.
    are the high-compression heads a lot harder to kick over than the 1 or 2-bar heads.
    got a chance on some original flywheels, a dozen or more 1/2" holes drilled in one. im guessing to lighten not balance. is this a problem?
    any help is appreciated, this is my first big flatty. scooter
    scooter57; Welcome to the forum. I've owned a '41 ULH for over 46 years. Even with the original 2 bar aluminum high compression heads, the compression ratio is only 5.7 to 1. This means that it will run on the cheapest gas from the pump. I've said for years that it is an overgrown lawn mower engine. It's a great motor that needs little attention other than regular maintenance. As kitabel advised, if you go with the drilled flywheels, you will have to have your flywheels rebalanced. Stock flywheels are balanced for stock rods and vice versa. Maybe check with Truett & Osborn for new flywheels. With lightened flywheels you have to slip the clutch when you leave the stop sign. That's because the heavy weight of the stock wheels gives you the low end torque. I ran shaved flywheels for 2 yrs. and went back to stock. Lightened flywheels do give you more top end. I got a ticket for 80 in a 55 m.p.h. zone in 1973. The first year for aluminum heads was 1940. I'm not sure about the aftermarket aluminum heads that look like iron heads, but your motor won't look correct. But if that is the look that you are going for than Do It !
    Craig

  8. #8

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    thanks kitabel great info

  9. #9

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    thanks craig.....those were the only high compression heads i've come across. seems like most of the re-pops are 1-bar

  10. #10
    Join Date
    Nov 2010
    Posts
    181

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    I believe Flathead Power makes the correct 1940-1948 style heads and I think that they sell heads with higher compression than stock. They are made in Sweden.
    Craig

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