drill rod?

[Brian Rupnow]

Checking an engine plan from Philip Duclos, it asks for a valve push rod made of CRS N. 5D x 1 3/4" finish nail. Does anybody knows what it means??

Mario

crs is cold rolled steel. 5D is the diameter of the nail. Look at the bore in the valve guides to determine what 5d actually is.

 

[Aydelott]

All of the drill rod I've bought has been fully annealed, about the only source of hardened drill rod would be a drill or reamer blanks and even then I'm not sure that it would be fully hard.

From experience if you make an engine to that sort of tolerance it will be very difficult to run. If you're a little over in the rod size and a little under on the bore they just won't fit. If the sizes are dead on and the bore is a little crooked same problem. If a rod is a little bent (as metal is supplied) it'll jam at one end or the other.

A steam engine which is loose at most spots and tight at only a few will run like a watch. Too loose everywhere and it'll run, but noisily. Too tight all over and you'll have trouble turning it over with a wrench. The real art here is knowing where it should be loose and where it should be tight.

well i was hopeing i could make it really close a lap everything in to a slip fit now im kinda freaking out i dont know what to do lol this is my first engine what kinda of gap should there be in the rods an the bore of the bottom cylinder cover?

 

[Brian Rupnow]

A good sliding fit with no binding, but not sloppy either. If there is a gland on the engine you are using, the packing in the gland will tighten down on the rod enough to prevent undue air or steam leakage when you tighten the gland nuts a bit. Don't freak!! These small engines are very foregiving.---Brian

 

[rkepler]

well i was hopeing i could make it really close a lap everything in to a slip fit now im kinda freaking out i dont know what to do lol this is my first engine what kinda of gap should there be in the rods an the bore of the bottom cylinder cover?

Lapping really only averages a couple of surfaces together unless you embed the lapping compound into one and use it to lap the other which I don't think you were talking about. It won't work when the 2 are too tight to go together or so far apart that they don't contact. There are some cases when lapping 2 surfaces works well - when you have a shaft through a split bearing - in this case you can start loose and tighten up the bearing while lapping is taking off the high points. In those case you need to use something like Timesaver's lapping compound as it preferentially removes material from the softer or harder surface in the process so that you don't wear down a crankshaft while lapping in the bearing surfaces.

I'd shoot for .001" fit on rod & pins, that's enough that oil will wick in but not so much that you hear a clank or click when it reverses. Be careful with less than that in dissimilar materials and heat - differential expansion can lock something like that right up. Same issue with similar materials in an area where you might lose lubrication and similar metals can and will gall against one another.

On a gland I'd shoot for good clearance - .002 is a start, I usually end up with .005 with an o-ring seal and try for less with packing as it can blow though. I'm one of those guys who doesn't have luck with packing, I usually go to the o-ring solution right away. But note that everything has to be in line - if the piston rod is off center the hole in the bottom for the rod would have to be off the same amount in the same direction, or you have to open up the hole in the cover to accommodate it. So start a few thou over nominal then open it out to accommodate the error stack. I always figure that if I made one I can always make another, and it's that thought that usually keeps me from throwing the errant part across the room.

So: take a little care in the parts you make. If something isn't a press or interference fit make it a little over and make the parts that go though on-size and you'll likely have something that works when you put it together. But taking too much care means that you're likely thrashing instead of working.

But don't freak out at making a mistake - if you're not making mistakes the odds are that you're not making anything. And most learning comes after making a mistake and not after doing something right.