Hey, guys.
As part of the rebuild of the engine on my 1948 Model 16H, I'm planning to make some performance modification and am interested in improving the strength of the crankshaft.
I fully understand that there are better bikes to start as a basis for improvements, but I have chosen this model for a very particular reason. I understand I could go buy a more modern machine used for far less that what it will cost me to do what I plan to do, but that's not the point. My goal is to explore what's possible with a lowly Model 16H.
Because the crankshaft is cast iron, I'm interested in learning more about the procedure where one turns down a portion of the crankshaft's most outer diameter and shrinks a steel ring around it to make up the reduction in diameter and to help keep the crank in one piece at extended high RPMs.
For reference, my crankshaft measured approximately 7 1/2" at the outermost diameter, by approximately 1 1/4" thick. Please refer to the attached pictures.
My questions are as follow:
- What do folks use replace the material that has been removed? I can buy commonly available 7 1/2" OD steel tube of various alloys and turn the OD of my crank to match an inside diameter carefully turned on the ID of the pipe.
- Approximately how much of the cast iron material is removed from the OD? The typical wall thickness of the readily available tube is 0.375". Let's assume that it cleans up at 0.370"? Would that be sufficient, depending, of course, on the particular alloy?
- What methods are used to ensure the bands stay in place? Is it just a shrink fit? Are they staked? Plug-welded? Mechanically fastened? Duct tape? Bubble gum? Youthful optimism?
I understand I will need to rebalance the entire assembly, but I will need to do that anyway due to the piston, and possible connecting rod being replaced.
Thanks!
-Robert
Hi Robert, You may want…
- Log in to post comments
No doubt part of the reason…
No doubt part of the reason to do it is the satisfaction of doing it yourself. But steel flywheels for Norton Singles appear to be available from Mike Pemberton (as you no doubt already know).
The crank pin is already not far from the edge of the flywheels. So even if a ring is strong enough to carry the centrifugal stresses, I would worry that there might still be a local stiffness issue close to the pin hole.
- Log in to post comments
Thanks, Richard!
Hi, Richard.
I did read your appraisal and found it quite helpful. I will look into sourcing the big-end bits from another machine, or I might just buy a complete off-the-shelf steel flywheel.
Thanks again!
-Robert
- Log in to post comments
Thanks, David!
Hi, David.
Your point about the proximity of the crankpin bore to the edge of the flywheel is well taken. After further consideration and based on the input of other club members, I will likely pursue an off-the-shelf option.
Many thanks!
-Robert
- Log in to post comments
Hi Robert,
You may want to read my appraisal of the 16H/ES2 crankshaft assembly in Roadholder 376 of April 2019 listed as Achilles' Heel, which might give you a general over-view.
The method you out-line has been used in these engines, but this is a bit like a plaster cast on a broken leg as it does not address the the inherent weakness of the original design. If you did want to try this method, you need to use the most suitable material such as EN24T or it's modern equivilent. I wouldn't think the steel used in the tubing you mention will be good enough for this job. The inside of the rim needs to be machined to have the tightest interference fit possible when heated to a high temperature. You will need to keep a slave crankpin in the flywheel while this is done to avoid distorsion. When this is done you will need to turn the sides and rim face of each wheel to within .001 inch of each other.
You should not use full width rollers with-out a roller cage as when they are running loose they could skew with-out a cage to control them. A centre seperating washer could affect the lubrication of the second line of rollers and at the width described may soon break up and sieze the rollers.
Your best option would be to use steel flywheels/big-end from some other engine, perhaps a speedway J.A.P. which is 99mm stroke, but check all relevant dimensions and if you can fit the Norton mainshafts before taking that leap.