1941 ulh heads

[scooter57]

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

[Steve Slocombe]

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.

[scooter57]

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

[Flathead fathead]

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.

[kitabel]

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.

[kitabel]

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.

[41craig]

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

[scooter57]

thanks kitabel great info

[scooter57]

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

[41craig]

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

[scooter57]

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

thanks craig.....will look up.

[chuckthebeatertruck]

You may be confusing oe bars with am repos. The bars are not a reliable indicator of the chamber volume unless they are nos heads, and even then you will want to measure them.

As for am heads, there are many floating around.

V-twin had at least two different runs. First run was eh machining and you will hear reports from time to time about poor fitment of bolt holes. Second bunch seems nicer from what you understand.

Another set are cast in Poland and appear identical to me at last to the latest v twin repos. I have these heads on my 46 UL.

S&S still has blanks from when they own d the flathead power brand. You can customize the chamber volume, but it is a special order part.

Flathead power is supposed to be releasing new heads. I don't know if anders is actually selling them yet.

VT Cycle in Finland also makes a performance alloy head. I have not seen one in person, but first hand accounts say they are very good heads.

Don't fret the cr too much. These motors are more torquey than peaky. They kick over rather easily for their size.

[chuckthebeatertruck]

I forgot, yes, at one time the iron heads were used as patterns for making alloy heads. These heads have marginal finning and limited deck thickness at the gasket surface. This makes it far easier to distort the head and have leaks.

Alloy heads aren't better just cause they are alloy :-)

[chuckthebeatertruck]

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

Actually, those holes likely were for balancing. Many people forget the early u motors used an open female rod, which is substantially lighter than a later closed set.

When I balanced my wheels at 54 percent, a fair amount had to come out.

All that said, don't freak in the balancing. These motors are pretty happy anywhere between 50-60 percent, which is a massive spread. Just back calculate and determine if you can live with it.

Used wheels also often develop lips in the taper(S). Check them carefully and torque smoothly.

[kitabel]

Early V-Twin heads are easy to identify.
Examine the gasket surface - is it flat, smooth, with no imperfections? That's not his.
His look like the gasket surface was prepared by dragging it across a cheese grater. Like, you can break a fingernail on it.