Yet Another Webster Begins

[CFLBob]

The rest of sheet 8. I'm just going through the sheets and knocking off parts. Most of sheet 8 looks pretty easy except for the cam. I've never done one of those.

I was just looking at the rocker arm spring. It says .010 thick spring steel and 0.281 wide. I have no idea what that is or where to get some in reasonable quantities and prices. My only experience making springs was with music wire. See I can get 50 inches from Online metals for $78. Since I need less than 3 inches, I was thinking of buying 6.

 

[awake]

Bob, when I made my somewhat modified Webster, I had planned to use a standard compression spring. I drilled the rocker arm to thread a bolt through, about half-way between the rocker arm pivot point and the area that contacts the cam. I was going to put a matching bolt in the stand below, so that together they would keep a spring aligned to act on the rocker arm. But I noticed that my rocker arm came out heavy on the valve end, due to the extra material on that end and the screw that acts as the tappet. As a result, it naturally "falls down" on that end, keeping the other end in contact with the cam. I decided to try it without a spring ... and it seems to work just fine, so I've never bothered putting in a spring.

Since you are making the Webster much closer to the original plans, it may be that the spring is really needed ... but even if it is, I would think you could use a standard spring the way I had planned to do.

 

[CFLBob]

Thanks, Andy. It never hurts to make it like the prints, so that's the way I'm going.

 

[awake]

Thanks, Andy. It never hurts to make it like the prints, so that's the way I'm going.

Indeed, and that is something I'm enjoying about your build - making other choices (on my first build!) has left me with questions on what I might have missed. I'm finding out, vicariously, through your build!

 

[CFLBob]

Well, I don't understand enough about engines to change it as I go, so there's that.

Not knowing what you're doing tends to make any little difference scarier than it should be.

 

[Longboy]

I was just looking at the rocker arm spring. It says .010 thick spring steel and 0.281 wide. I have no idea what that is or where to get some in reasonable quantities and prices.........

If you take out one of the thinner strips out of a feeler gauge set and cut/ trim Bob, you will have a proper spring for Webster! ..... Dave

 

[ZebDog]

Hi Bob
When built my Webster I drilled a 3mm hole in the bottom of the rocker arm and loctite in a small peg and used a compression spring from an old pen

 

[stevehuckss396]

You can get 100 foot in 1 foot pieces of steel .010 wire at McMaster Carr for 10 bucks.

 

[werowance]

This part took longer than it should have because of my "comedy of errors" (where the important word is errors, not comedy). I wasted a couple of pieces of steel before I smacked myself upside the head about not paying enough attention! I put a 4-40 Socket Head Cap Screw in the tapped 4-40 hole on the right just because. Although that does make it look a little wonky.

View attachment 116853

Bob, i think I had to re-make that part 3 times before I got it right. I kept moving in the wrong direction thus cutting it to thin. something about that drawing just would not "click" in my head so I kept doing it wrong. but yours look good.

 

[werowance]

also on the spring for the rocker arm, I used a broken band saw blade, use the grinder and the belt sander to make it to size. it was still a little thicker than plans but works well and holds its springiness (technical term) well. Brian R used a recoil spring from an old push mower blower housing or some small engine blower housing I should say. I had a Honda recoil spring and it was a bit narrower than plans so I opted for the broken bandsaw blade I had.

 

[Brian Rupnow]

Go to a small engine repair shop and ask them for the broken recoil/rewind spring from a lawn mower, chainsaw, or weed-eater. That works perfect for this application.

 

[CFLBob]

Thanks for all the suggestions, guys!

All of those give me ideas. I use my feeler gauges at the mill every time I set it up, so I'll probably keep that intact, but a pen spring or coil spring sound really easy. The one kind of spring I've made is a wound coil with music wire and I still have lots around. I probably a half dozen springs lying around I tried for some repair or something. And I'm about to replace the blade on my wood-cutting bandsaw, so I'll have plenty of possible blanks from that.

Werowance, I was half expecting someone to say, "that's exactly like the (some name) spring out of a Honda you can get at the auto parts store."

 

[minh-thanh]

Hi Bob !
Just curious, how many parts of this engine did you make?
And what's the rest ?

 

[CFLBob]

Hi Minh-Tanh,

The parts start on sheet 2 of the plans I downloaded here, and I've made everything from sheet 2 to sheet 7. I think this arm was part #17, the first part on sheet 8.

There are parts I'm not sure I'm going to make, like the oil cups that feed into various points. I hear both ways on that. I'm probably going to buy a Traxxas carburetor and there are a few things I'm not sure of.

 

[a41capt]

The rocker arm was one of the last parts I completed before my workshop turned into a 108 degree oven. I used Kasenit on the rear cam bearing surface and then Followed with a black oxide finish using my favorite cold gun blue made by Van’s. I heat the parts to be blued with a heat gun and submerge them, followed by an immediate oiling and they turn out uniformly black. This is about the only “cold” bluing solution I’ve used that doesn’t streak.

 

[CFLBob]

Does anyone have an Upshur cam fixture handy that can check a dimension for me?

I don't have the plans for one, but I found a video on YouTube where a guy makes shows one and how he works the cam. He doesn't say anything about how he made it or what the dimensions are, but at the end he shows the diagram he worked from. I took this screen shot from his video and I'm making the fixture from this:

My question is in the upper right drawing (and everywhere), the center of the rod that holds the cam blank looks closer to the edge than the center. The drawing says it should 3/16 offset from the center. I'm set to drill this hole on my mill but it looks closer to the center than the edge.

That makes sense because if the center is at 1/2", 3/16 less than that is 5/16 or 0.313. But the drawing makes it look like it's 3/16 from the edge and not from the center. Come to think of it, the center being 3/16 from the center would put the closest side of a 3/8 bar right on the center.

Can anyone measure theirs, or has made one and just knows what it is?


Thanks!
Bob

 

[Ghosty]

It may just be drawn like that for clarity, rather than being correct. Offset listed at 3/16", and dia of block 1" (but can be larger), 1" looks like the min size that the designer decided that has the best grip in the chuck.
Cheers
Andrew

 

[CFLBob]

I don't know.

I've made 3D models of this stuff and the numbers don't seem to work out. The bottom half of the cam (the base circle?) is supposed to have a diameter of 9/16, so a radius of 9/32 or 0.2812". If I put my model cam blank on the end of the 3/8 shaft, the smallest I can cut that is 0.312 or 5/16. That means I cut past the edge of the 1" cylinder, but I guess nothing is stopping that.

It seems that the fixture just does a better job of holding the blank than a person could hand hold it, but it's pretty much just shaping the cam by hand on the fixture.

 

[Cogsy]

I don't know.

I've made 3D models of this stuff and the numbers don't seem to work out. The bottom half of the cam (the base circle?) is supposed to have a diameter of 9/16, so a radius of 9/32 or 0.2812". If I put my model cam blank on the end of the 3/8 shaft, the smallest I can cut that is 0.312 or 5/16. That means I cut past the edge of the 1" cylinder, but I guess nothing is stopping that.

It seems that the fixture just does a better job of holding the blank than a person could hand hold it, but it's pretty much just shaping the cam by hand on the fixture.

The offset from the centreline is just going to give your flank radius isn't it? You can have the fixture as large as you want and it shouldn't make any difference to the size you can cut the base circle to, but the further offset you have the 'gentler' the flank curve. I don't see why you couldn't machine the base circle all the way down to 3/8" (except the part would obviously be machined away to nothing).

 

[a41capt]

Bob,

the dimensions you’re referencing are correct, the drawing just looks not to scale. Here’s a couple pics for you of my setup: