Pull start repair.

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B Mann
Posts: 37
Joined: Tue Sep 17, 2019 8:07 pm
Location: Northern Indiana (Michiana)

Pull start repair.

Post by B Mann » Fri Dec 27, 2019 3:00 pm

I have a pull start for a small engine that is worn. The rope pulley ID or the shaft OD it rides on is worn quite a bit. (Probably both) The pulley is steel about 5" diameter with about a 3/4" hole. Replacement is very expensive since it is obsolete. I am a fixer guy anyway. I tried a metal shim and it worked for a while. I am the new guy to machining and might as well try a project.

I am thinking bore out the pulley on a lathe to get it true. Then weld up the shaft and use the mill on a rotary table to make it round with a larger diameter to match the pulley. The shaft is part of the cover so it is not removable. I can post pictures if that will help. Am I on the right track???

Harold_V
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Re: Pull start repair.

Post by Harold_V » Fri Dec 27, 2019 4:03 pm

Hard to say if you're on the right track, as there may be multiple methods of making the required repair. One of them would simply be to machine true both surfaces, then make a bushing so the parts mate properly. That may or may not work, as I have no idea how they are assembled. A picture certainly wouldn't hurt, assuming you can provide one without a lot of effort.

Key to how this repair would be best accomplished would be how the parts are assembled. If the bushing I mentioned can be free to float, and is not required to restrain the assembly, that would be the best scenario with the information you've already provided. It is also possible that you can make the bushing a press fit in one of the components, which would then simulate what I assume would be the original type of construction.

Welding on any project is always a concern, as the action generally yields at least some distortion of the components. I'm not suggesting that it isn't a good avenue to pursue, but consider the fact that it almost always occurs, and how it will affect your attempt at restoration.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

B Mann
Posts: 37
Joined: Tue Sep 17, 2019 8:07 pm
Location: Northern Indiana (Michiana)

Re: Pull start repair.

Post by B Mann » Fri Dec 27, 2019 7:43 pm

Harold_V wrote:
Fri Dec 27, 2019 4:03 pm
Hard to say if you're on the right track, as there may be multiple methods of making the required repair. One of them would simply be to machine true both surfaces, then make a bushing so the parts mate properly. That may or may not work, as I have no idea how they are assembled. A picture certainly wouldn't hurt, assuming you can provide one without a lot of effort.
I took it apart to get another look and the parts are severely worn. To true them up I would have to turn the shaft under .670 and open the diameter up over .840. The pulley is quite work and pretty thin. Let me see if I can post some pictures. Welding if I can do it properly would help reinforce the pulley.

The parts are hard to get and quite expensive. I am rather looking for the experience in the doing a repair.

B Mann
Posts: 37
Joined: Tue Sep 17, 2019 8:07 pm
Location: Northern Indiana (Michiana)

Re: Pull start repair.

Post by B Mann » Fri Dec 27, 2019 8:09 pm

Here are a few pictures... It looks like there might be a piece of a bushing on the shaft.
Both sides of pulley

Image
Image

B Mann
Posts: 37
Joined: Tue Sep 17, 2019 8:07 pm
Location: Northern Indiana (Michiana)

Re: Pull start repair.

Post by B Mann » Fri Dec 27, 2019 8:10 pm

Here is the shaft and the pulley on the shaft.

Image

Image

B Mann
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Location: Northern Indiana (Michiana)

Re: Pull start repair.

Post by B Mann » Fri Dec 27, 2019 8:12 pm

The shaft is .755 at its widest point and .670 at its narrowest.

The pulley is .785 in center and .840 on the edges. Quite worn.

B Mann
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Joined: Tue Sep 17, 2019 8:07 pm
Location: Northern Indiana (Michiana)

Re: Pull start repair.

Post by B Mann » Fri Dec 27, 2019 8:17 pm

There is no easy way to remove and reinstall the shaft in the housing. That would sure make it easier.

spro
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Re: Pull start repair.

Post by spro » Fri Dec 27, 2019 9:08 pm

I'm seeing that this pulley has a centrifugal clutch. Man. I thought you were going to weld on the crankshaft. Whew. Maybe that bushing alone is the cause. You can reassemble a hacksaw blade inside the pulley to cut the bushing . It will press out easier but everybody knows that. May be that you read the earlier reply and make a new bushing.

Harold_V
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Joined: Fri Dec 20, 2002 11:02 pm
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Re: Pull start repair.

Post by Harold_V » Sat Dec 28, 2019 3:04 am

I'm having more than a few doubts that you would be able to weld on the shaft and have the thread end up perpendicular. I also don't think that the amount of wear you have would be a problem to sleeve. There's not a lot of stress on that part when it's used, so breaking isn't much of a concern. I also think that, with care, you could machine the shaft in a lathe, assuming you have enough swing. That would be preferable to attempting to true it up with a rotab, although I suspect either method would yield acceptable results. The problem with a rotab is the depth of cut. You may get deflection, resulting in a tapered turn. Not the best scenario if you're trying to resurrect the piece reliably. If, by chance, that's your only option, I'd recommend a carbide end mill, which is far more rigid than HSS, and most likely would yield a better surface.

Unless I'm missing something, I think what I'd do is clean up the shaft, then apply an oversized bushing. Once pressed in place (or held in place by Loctite, although, I'm not a huge fan), then machined to a size that would fit the bushing you'd place in the newly bored pulley.

It looks like the original setup has steel running on steel. Correct? If so, you could improve on that by using a heat treatable material for the sleeve, hardened to, say, 30-34Rc (4130 or 4140 comes to mind). That's not too hard to machine, and would yield a longer running sleeve than mild steel. You could use an oilite bearing in the pulley, which would, again, be far better than running steel on steel.

I'm not suggesting this is the only way to pursue your project.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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carlquib
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Re: Pull start repair.

Post by carlquib » Sat Dec 28, 2019 2:33 pm

I've made repairs like this. I clamped the housing down on the mill and used a boring head with a left hand tool to turn the shaft down. I next made and pressed/loctited a sleeve on the shaft. I think Harold's idea of making an oillite bushing to bush the clutch assembly is a good one.
What is this assembly from? The last one I did was from a Honda 110 three wheeler.

My name is Brian and I'm a toolaholic.


B Mann
Posts: 37
Joined: Tue Sep 17, 2019 8:07 pm
Location: Northern Indiana (Michiana)

Re: Pull start repair.

Post by B Mann » Sat Dec 28, 2019 11:19 pm

spro wrote:
Fri Dec 27, 2019 9:08 pm
It will press out easier but everybody knows that. May be that you read the earlier reply and make a new bushing.
It would be nice if it would press out, but I am not that lucky. I am guessing the shaft has a flange and it is under the cover on the inside and the cover is spot welded in place. Tearing that apart may open up another whole can of worms.

B Mann
Posts: 37
Joined: Tue Sep 17, 2019 8:07 pm
Location: Northern Indiana (Michiana)

Re: Pull start repair.

Post by B Mann » Sat Dec 28, 2019 11:38 pm

Harold_V wrote:
Sat Dec 28, 2019 3:04 am
I'm having more than a few doubts that you would be able to weld on the shaft and have the thread end up perpendicular. I also don't think that the amount of wear you have would be a problem to sleeve. There's not a lot of stress on that part when it's used, so breaking isn't much of a concern. I also think that, with care, you could machine the shaft in a lathe, assuming you have enough swing. That would be preferable to attempting to true it up with a rotab, although I suspect either method would yield acceptable results. The problem with a rotab is the depth of cut. You may get deflection, resulting in a tapered turn. Not the best scenario if you're trying to resurrect the piece reliably. If, by chance, that's your only option, I'd recommend a carbide end mill, which is far more rigid than HSS, and most likely would yield a better surface.

Unless I'm missing something, I think what I'd do is clean up the shaft, then apply an oversized bushing. Once pressed in place (or held in place by Loctite, although, I'm not a huge fan), then machined to a size that would fit the bushing you'd place in the newly bored pulley.

It looks like the original setup has steel running on steel. Correct? If so, you could improve on that by using a heat treatable material for the sleeve, hardened to, say, 30-34Rc (4130 or 4140 comes to mind). That's not too hard to machine, and would yield a longer running sleeve than mild steel. You could use an oilite bearing in the pulley, which would, again, be far better than running steel on steel.

I'm not suggesting this is the only way to pursue your project.

H
It sounds like a good idea. I guess I was leaning toward a weld up and machine down because I have been welding for decades and it is what I am familiar with. The mill and lathe are new tools to me.

OK, the oversized bushing sounds good. I am thinking I would want to clean up the pulley and press the bushing in that. Hard to see in the pictures, but the center of the pulley is worn so thin it is beginning to crack.

I am familiar with oilite bearings. It sounds like a good idea. Like you said it is a metal on metal situation. I am not sure how thin you can go. if I clean up the shaft and pulley I am looking at about .170 room. By the time I put a bushing in the pulley, how thin of a oilite bearing can I use before I destroy it just trying to machine it???

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