Board index Flathead Power-Technical Questions, Answers, and Suggestions Knuckles 74" flywheels in a 1939 EL

74" flywheels in a 1939 EL

Moderators: Curt!, Pa

Post Sun Oct 17, 1999 3:01 pm

Posts: 3134
Location: Central Illinois, USA
Yes, all BT wheels through '54 (no shovels)can be made to fit, with scraper alterations. They are heavier than your pre-war units though, so you will lose performance for a light solo machine, but gain some torque for a heavy ol' Lady payload. Ideally you should look for some flatty (U)wheels, as they are the same original diameter, but a healthy stroke. Note:I like my 61" lowers with 74" upper ends just fine. One is close to 70" anyway.

[This message has been edited by Cotten (edited 17 October 1999).]

Post Mon Oct 18, 1999 3:14 am

Posts: 3134
Location: Central Illinois, USA
It has been traditional to just use high (10:1) compression 74" pistons with the short stroke to come back to normal range. These are heavier and you will want to rebalance, of course. (I did open up a Pan once with a 61" crank and standard compression pistons; It ran,.. but I bet it was a dog.)

Post Mon Oct 18, 1999 8:35 pm

Posts: 9
Location: Bear Swamp,NC CSA
Be fore warned that early cases can be pretty weak on the left hand side.
EL 's tend to run smoother than a 74" ...less vibration anyway ...that has been my experience ...I'd stick with the 61" wheels and run the big top is a very usable combination don't need a lot of compression with these machines unless you want to hot rod ..and i have big port heads ona 61" jugs and wheels a '38 el ..and she's smooth Image

Post Wed Oct 20, 1999 1:30 pm

Posts: 136
Location: oxford, NC USA
It'll work.

Have a friend running an EL Pan with the big top end. He took a cut on the cylinder bases to get it right.

A nice, smooth engine that is stronger than many.


Post Thu Oct 21, 1999 1:41 am

Barrel heights for OHV twins (head gasket surface to base gasket surface):
1936-47 EL 5.405"
1941-47 FL 5.53
1948-52 EL 5.205
1948-83 FL 5.33

Post Thu Oct 21, 1999 2:54 pm

Posts: 136
Location: oxford, NC USA
Yeah. But you've also got to cut down the intake maniflod as the ports will also be closer. Couple of other odd, little things, but I don't remember. Roland told me it was an easy job.



Post Fri Oct 22, 1999 2:18 am

Posts: 3134
Location: Central Illinois, USA
Now I'm confused! You shouldn't have to cut your cylinders at all! Even if you converted to 74" cylinders you will still have decent compression; Remember the additional displacement has increased the compression also.

Post Sat Oct 23, 1999 1:39 am

Posts: 136
Location: oxford, NC USA

The larger cylinders have only increased cylinder voulmn. But due to the shorter stroke, the chamber volumn is increased also, leading to lower compression with a STOCK piston. Running the EL wheels under an FL top is the equivelent of de-stroking, and from what I've seen of this Pan, it ain't a bad idea.

Dunno what compression Roland runs, but it's some higher than stock. But he is also not running stock pistons.

How's that set of heads coming?


Post Mon Oct 25, 1999 3:11 am

Posts: 136
Location: oxford, NC USA

Sounds like you've got a plan, Sounds good.

With the comp and pistons you propose, you shouldn't have any valve clearence problems unless you cam it so tall it might not run anyway.

Be careful you don't take too big a cut. I would think that the difference in the 61 / 74 stroke should be about right, but I only know what I've been told about it. Never personaly done it. Reccomend that you do the math.



Post Mon Oct 25, 1999 5:17 am

Posts: 1028
Location: Ojo Caliente,NM,USA
To check valve to piston clearance. Assemble the topend with used head gaskets the same thickness as you are going to use and some modeling clay (steal it fron your rug rats or the neighbors)on top of the piston in the valve areas. Adjust the valves to normal clearances unless you have hydralics witch have to be adjusted all the way to the bottom of their travel (I remove the springs and make a little shim so they adjust lke a solid fot the test). Rotate in the normal direction of travel 2 or 3 rounds. Remove the heads and mike the clay. I wouldn't suggest less than .040 on a Hardley.

Post Mon Oct 25, 1999 1:41 pm

Posts: 3134
Location: Central Illinois, USA
You are doing it the hard, expensive way, but I'll defend to the death your right to cut up anything you want. (I often do.) Picking a proper piston is easier than cutting cylinders, cutting manifolds, etc., and it's not a one-way trip for your hardware. Your balancing will be a lot simpler also. Most EL's that have come through my shop in two decades have already been shot out to 3 7/16th plus, and some even had shovel tops!

Post Tue Oct 26, 1999 2:25 am

Posts: 11
Hello Larry;
I'm also in the mitts of an old knucklehead. when i popped it apart,it had 74" jugs that where cut down to 5.405". it had medium comp. shovelhead pistons. Both cylinder's where cracked and sleeved,an ugly sight, i bought an set of 61" cylinder's that where +.020" for $300., at an AMCA meet in Wauseon,OH. I bought my piston's and assoicated parts from Kick-Start motorcycle parts inc.
Good luck!


Post Wed Oct 27, 1999 1:34 am

Posts: 11
You'll have to send an check or money order for $5 to Kick-start motorcycle parts inc.
P.O. box 9347
Wyoming, Michigan 49509
Chuck that runs it doesn't want anything to do with the internet.
I suggest that you buy the book How to restore your Harley-Davidson, by Bruce Palmer
or sometimes called the bible from hell.
It does a very good job of identifying and explaning the how,what,and whys.

Post Wed Oct 27, 1999 3:03 am

Posts: 582
Location: meridian, id. usa
Chuck's a good guy and has a great cataloge.
And he usually has most everything in stock
so ya dont have to wait and if he doesnt he tells u up front.
And I agree with Geronimo about palmers book
good but straight from the hell of the restoRATion demons.

Post Wed Oct 27, 1999 11:55 am

Yes, the extra height is in the compression distance of the EL pistons. I would prefer a custom piston myself to shortening the barrels (if you insist - why not cut up a repro barrel instead? get one from KNS Cycle)
For Palmer's book, click here.

[This message has been edited by panic (edited 27 October 1999).]

[This message has been edited by panic (edited 28 October 1999).]

Post Sun Oct 31, 1999 5:26 am

Posts: 582
Location: meridian, id. usa
dont think you can elec. weld cast but ive used nickel brass to flame braze cast with good results. you might be able to get iron rod to flow right if you use the right flux and keep the flame moving around to equalize the heat,

Post Sun Oct 31, 1999 3:24 pm

Posts: 3134
Location: Central Illinois, USA
Weld repair on cast iron can take up a whole new thread! Please post a new topic question, and tell us what and where your hardware is cracked or broken.


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