Flywheel becoming loose (setscrew is used)

[borna]

Hello all,

I built this engine and trying to start it for the first time. I noticed as the engine wants to start the flywheel become loose. I am holding the flywheel in placed with 4 6-32 setscrews.
The flywheel diameter is 5.5”. Any suggestion as how to fix this without too much modification to the flywheel and crankshaft?

http://cdn.homemodelenginemachinist.com/attachments/f31/59459d1357071718-my-single-cylinder-engine-002f.jpg


This is how the flywheel is connected to the crankshaft.


Thanks
Borna

 

[rhankey]

How about a keyway?

 

[aonemarine]

Lock tite??

 

[BobsModels]

Borna

I agree with the keyway. I have a 1/8 scale Galloway with .250 crank. I have a tapered key in it. I also have set screws one on top of the key and one at 90 degrees. When I broached the keyway in the flywheel I did not
go all the way through and left a taper. I then hand filed a key to thickness and top taper. Put that in and it holds. How well you ask, on
the governor side I had been taking the flywheel off and on making adjustments. I never tightened the set screws since I was taking it off and on. Well once I got it going I forgot to tighten the set screws. It ran at three differnent shows for about 50 hours before I noticed that one of the set screws was about to fall out.

The goal is to eliminate any motion that can continue to move with each firing cycle. If all is tight and you can move the flywheel with your
hand it is going to come loose.

Good Luck

Bob

 

[MachineTom]

If I see the photo covrrectly, the setscrews are 180° opposed, not a good idea. What happens with that manner of placement if you end up with the flywheel suspended by the 4 rather small screws, as when you tighten them the force directly lifts the flywheel from the shaft, so all forces, and they are rather large from the power stroke to the coast portion, back to the power.

Remove one set of screws and place them about 60° from the other. Those are holes the screws bare against in the shaft not grooves, right.

 

[borna]

Thanks all,
Keyway would be nice. Not sure how to make that. Any special tool I need? I am still beginner.
How about put a hole all the way through the crankshaft and use pin and maybe screw?

Thanks
Borna

 

[dsage]

In addition to Machine Tom's comments, try two set screws in each hole. One on top of the other. Tighten the first one well. The second one on top will keep the first for losening. I would also put removable locktite on the outer setscrew(s).

Sage

 

[MuellerNick]

Buy/make a taper lock.


Nick

 

[rhankey]

Thanks all,
Keyway would be nice. Not sure how to make that. Any special tool I need? I am still beginner.
How about put a hole all the way through the crankshaft and use pin and maybe screw?

Thanks
Borna

You will need to get a suitably sized broach to cut the keyway in the flywheel. Broaching is quick and easy. You will need to come up with a means to press the braoch through the hole. I use my milling machine vise and some sockets to drive the broaches through the flywheel. For smaller keyways, it takes 1 or 2 passes. For larger keyways, start with a smaller broach to hog out some of the material, then move up to the desired sized broach, thus taking 3 or 4 passes. I found and purchased a small Asian made broaching kit which included 4 or 5 broaches and sleeves. I have had to make a couple of my own sleeves. The slot can be cut with a keyway cutter or an end cutter. You can buy pre-made keys, but I have made my own.

Unless the crank is way oversized for the task at hand, I would not run a pin through the crank. You will weaken the crank too much or the pin is liable to shear.

 

[Mainer]

A second on MachineTom. Put the setscrews 90 degrees apart (or 60 -- doesn't much matter) so the shaft is pressed against the side of the bore in the flywheel, not suspended on the setscrews.

 

[thayer]

I was reading "The Shop Wisdom of Philip Duclos" last night and he shows how to make your own keyway broach, saving a bit of money for something else in the shop.

 

[kvom]

Green loctite (6xx series) is very good, and it will NOT slip. To remove the flywheel afterwards requires heating with a torch to > 500F.

An easy "key" is to drill or machine a round hole into the boundary at the end of the axle shaft and then press in a piece of round stock to fit.

 

[MachineTom]

This is a broach I made as I didn't have the size I needed. It is a piece of O-1 rod ground to the width needed, then flame hardened and quenched, no temper drawn. This is mounted in the BP with a collet and pushed through with the quill, DOC was .005 of so. I cut it after the photo as you need to keep it as close as possible to the collet to avoid deflection. This is .250 rod 3mm wide keyway. Keep the side straight to guid the cut, put about 3-5° relief on the back, and rake on the front.

 

[Philipintexas]

Sorry, I must have bounced the enter key.

 

[Philipintexas]

I built an IC engine with a 10" flywheel on a 1/2" shaft and could not keep it in place with a key so I used this method. Drill and tap a hole on the circumference of the shaft exactly on the joint, so the hole is half in the shaft and half in the flywheel. Then counter-bore a tight hole for the head of an Allen Bolt. It has never loosened. Obviously, if you remove the bolt you must replace everything in the exact relationship to be able to re-insert the bolt.

 

[chucketn]

I built an IC engine with a 10" flywheel on a 1/2" shaft and could not keep it in place with a key so I used this method. Drill and tap a hole on the circumference of the shaft exactly on the joint, so the hole is half in the shaft and half in the flywheel. Then counter-bore a tight hole for the head of an Allen Bolt. It has never loosened. Obviously, if you remove the bolt you must replace everything in the exact relationship to be able to re-insert the bolt.

Phillip, isn't that called a 'Dutchman'?

Chuck

 

[Gedeon Spilett]

you stopped things just in time !
For such a flywheel and engine setscrews are a nono, otherwise take care when the flywheel will go into orbit …
A keyway without lateral play plus a bolt (already present I guess) is the solution. cut the keyway on the shaft with an end mill, and in the flywheel (if you don’t have a broach and a press) cut the slot on your lathe transformed in a shaper with a dedicated tool you can grind.
spendid engine, you are almost there

 

[MuellerNick]

To tell the truth, a plain keyway really isn't the best way for alternating loads.
A flywheel stores and releases energy every revolution. As they always do have some play, they will not survive for too long.
If you use a wedge shaped key, things get quite different. The wedge increases the frictional force between shaft and hub. So it is this area that transmits the torque.

If you are using setscrews, it makes no sense to have them in two directions, as they do not increase friction between hub and shaft. More important is to have a flat on the shaft for the setscrew(s) to sit on. Only this way, they can contribute in transmitting torque and they do not tend to dig in that fast.

A cheap way is to drill through the hub and the shaft and drive a rolled pin (C-pin) through. Not very elegant.

If you want/need to transmit torque securely, use a taper lock; a cone with a nut; or a flange with some bolts that press the flywheel against that flange.


Nick

 

[borna]

Hello all,
Thanks so much for all the comments. So I learned my lessons.
Even though this engine is 1” bore x 1.5” stroke with 5.5” flywheel, I think still produce a good amount of torque. So as I mentioned before, the flywheel was hold in placed with 4 6-32 set screws and as the engine was trying to start, the flywheel was becoming loose. After reading all the comments I came out with a simple solution, but since I am new to engine building, I like to know if this will work and I won't be surprised again by this thing become loose again.




As you can see in the picture, I used two piece clamp-on shaft collar and then drilled 2 holes on the collar and all the way through the hub of the flywheel. Used 6-32 tap so now the collar is attached to the flywheel hub with two 6-32 screws.


It seems to be holding very well. Do you guys think the two 6-32 screws are strong enough and will not break?

 

[Gedeon Spilett]

Hi
Borna : I think the screws between collar and hub would be easily sheared while running your engine...
Muellernick : I thought that a key would be a good solution without any great modification, namely reboring flywheel. yours explanations are clear and convincing, must not be stingy with the flywheel mounting.
Cheers