Going to build my first engine!

[clevinski]

Hi, All...

So... I was a bit unhappy with the loose fit of the crankshaft on my Lucy air motor to the bronze bushing. For some reason, it rapidly became too loose, even with only 15-30 minutes of total run time. So I thought, before I moved on to a new motor, that I would resolve this by replacing the bushing with a needle bearing; this one: (SCE47 1/4"x 7/16"x 7/16" inch BA47ZOH Miniature Needle Bearings BA47Z ).

I drilled and reamed a 7/16" hole to mount the bearing and pressed it into place. The press fit went well; it required some force on the arbor press, but not what I would consider an excessive amount. I then cut a piece of 1/4" diameter drill rod (which measured 0.2510 inches in diameter) to act as a crankshaft. To my surprise, the drill rod was a loose fit (by a few thousands, I would estimate) in the bearing. I can machine a stepped crankshaft to get the right diameters, but I don't understand why the oversized drill rod is loose. Can anyone shed some light on this?

 

[Cogsy]

I worked for SKF for quite a few years and I can only guess that the bearing you bought is a 'cheapy' maybe? The tolerances on bearings are very tight and I wouldn't expect an oversize shaft to fit at all. I have some chinese ball races I bought a heap of (skate board size) and their bore sizes do wander around a bit.

Your needle roller is designed to run on either an inner race (which you can buy separately but you'll need a bigger bearing) or a hardened shaft. Your shaft may not last long if it's not hardened.

 

[clevinski]

I worked for SKF for quite a few years and I can only guess that the bearing you bought is a 'cheapy' maybe? The tolerances on bearings are very tight and I wouldn't expect an oversize shaft to fit at all. I have some chinese ball races I bought a heap of (skate board size) and their bore sizes do wander around a bit.

Your needle roller is designed to run on either an inner race (which you can buy separately but you'll need a bigger bearing) or a hardened shaft. Your shaft may not last long if it's not hardened.

Hi, Al,

Thank you for the reply and the information. I bought the bearing from a storefront on eBay, and I assume they are a cheaper brand, so that is probably the issue. I am just surprised at the dimension; if I had to guess, I would say the shaft needs to be .255" or so, which is WAY oversized.

Regarding the shaft, I realized after ordering the bearing that the shaft would need to be hardened. Since my little wobbler doesn't DO anything, it will see very little use, and I can always replace the shaft, if necessary.

 

[bouch]

Excellent looking and running first engine. For your next one I would suggest one of Elmer's engines. There are lots to choose from and many are good for beginners. I have built six of them so far with more to come. Plans can be found at http://www.john-tom.com/html/ElmersEngines.html.

There are a lot of great engines there.

His #33 is quite popular. That would be a good choice if you want to tackle something more challenging than a simple oscillator.

If you want another oscillating engine, then I would suggest either "Fancy" (#15) or "Wobbler" (#25). I've built Wobbler, nice little project.

Engines to avoid for a 2nd project, IMHO, are "Geared Steam Engine" (#5) and "Kimble Engine" (#20). Those require VERY careful tolerances...

 

[clevinski]

There are a lot of great engines there.

His #33 is quite popular. That would be a good choice if you want to tackle something more challenging than a simple oscillator.

If you want another oscillating engine, then I would suggest either "Fancy" (#15) or "Wobbler" (#25). I've built Wobbler, nice little project.

Engines to avoid for a 2nd project, IMHO, are "Geared Steam Engine" (#5) and "Kimble Engine" (#20). Those require VERY careful tolerances...

Bouch,

Thanks for the advice... I am definitely not ready for VERY careful tolerances!

 

[gus]

that would be a fine choice for a first engine.
no need to worry about side loads or packing. you can always ad a washer or spacer if you like.
My lucy has probably ran a few hundred hours at this point had it over ten years,
Tin

Hi Tin,

We all grew up with '' Lucy'' .Was among very first few engines.

 

[gus]

Bouch,

Thanks for the advice... I am definitely not ready for VERY careful tolerances!

Hi Clevinski,

No worry. As you go along,you get to improve you machining skills.
Getting to print dimension will eventually happen.If a part is undersized,machine another piece.

Every engine project will demand new skills or higher skills.

High Speed Cutting tools are best to get to spot on O.D. or I.D. Properly sharpened and honed HSS Cutters can remove minute thick metal.I seldom use carbide cutters.

Mark out,centre punching and spot on drilling are skills that need constant practice. Practice makes perfection.

 

[clevinski]

Practice makes perfection.

.......... Thm:

 

[bouch]

Bouch,

Thanks for the advice... I am definitely not ready for VERY careful tolerances!

Don't worry. Nobody is when they first start out! The more stuff you make, the better you get. I don't want to think about how many pieces I've made at least twice!

Heck, when I build my "wobbler" a few months ago, I build the main body 3 times before I got one what wasn't ruined...