Valve design - which is stronger / better?

[awake]

I am working on a modified version of the Webster - hopefully I will do a write up and pictures soon. But for the moment, I am pondering a question. Due to only having low-quality 1mm drill bits on hand, I was having trouble drilling the hole through the stem as per the original Webster design:

Having trashed one of the valves, I had to remake at least one anyway, so I went ahead and remade both using a different design, one that I have seen in some of the engine plans here and elsewhere, thus avoiding drilling the itty-bitty hole:

Here's the question: is either design inherently stronger / better than the other? Note that the valve stems for the Webster are 0.094" diameter; the through hole in the first design in .040" diameter; the groove in the second design is .008" deep by .040" wide. At first I was thinking the first design takes more "meat" out of the valve stem ... but then I decided maybe not, or maybe the round hole offers some strength advantages over the rectangular groove, or ??

FWIW, I successfully completed the second design, and it all fits together nicely, so this is more a question for the future ... but meanwhile I got in a pack of 1mm carbide drills that I ordered, and was easily able to drill a beautiful .040" hole through a test piece, so if the first is really way better than the second, I could go ahead and make another valve and go with that design. That would only make about the tenth time I have re-made these teensy-tiny-stinking valves ... what's one or two or ten more?

 

[Brian Rupnow]

Either design works equally well. I have used both styles. Something to remember though--You will probably have that valve assembled and disassembled half a dozen times before your engine works right. (Don't ask me how I know this). I find that the style with a 0.040" hole and a short piece of 1 mm (0.039")rod thru it are much easier to repeatedly take apart and put back together. The secret to cross drilling a valve stem is to use a very small countersink tool to start the hole. A very small countersink tool is about .093" diameter with a 0.032 end, and it won't deflect and drill the hole off center like a 0.040" drill will.

 

[awake]

Thanks, Brian - very helpful. I hear you on having to disassemble and reassemble multiple times - I am hoping for the best, but realistically expecting that it will take multiple tries to get it right. I was actually thinking the c-clip style would be easier to assemble and disassemble, but I have yet to do anything more than a test assembly, minus the springs (which I still need to make or find).

I did (attempt to) start drilling the hole with a very small center drill. My setup was not great, and as I said the bits themselves were sub-par ... and perhaps worst of all, I was attempting to drill using the hand lever. With all of that, I trashed the valve stem without getting anything resembling a hole. But when I got in the new 1mm carbide drills, I tried drilling using the table, while allowed me to move much more slowly and precisely - and even without a center drill or countersink, I got a perfect hole.

I've been a hobby machinist for a dozen years, but this project has me doing far smaller parts than I've ever attempted before. Lots to learn!

 

[Cogsy]

If you use the pin method, make sure you retain the pin in some way. For both methods a slight recess in the top of the retainer keeps things in place. With the pin type I've been guilty of leaving the pin a little long for ease of removal until I get the engine running properly. Here's a video of me showing exactly why you shouldn't do that...



It only cost me a bent valve and a slightly out-of-whack crank but was relatively simple repair. Could have been a lot worse.

 

[petertha]

My valves use E-clip & spring retainer similar to your second picture. They seem secure. I followed the groove dimensions and they are DIN? standard clips, but actually take some force to remove laterally with needle nose pliers. I started using a steel jeweler screwdriver inside the little slot to un-spring them a bit, but you have to be careful not to mar the edge of the valve stem its levering on. The valves are 303 stainless unhardened. I started to notice a bit of burr snag when sliding them out of the valve cage whereas before they were lapped & nice & smooth.

 

[TonyM]

I use the same as petertha. The retainers are sized just a few thou bigger than the fitted clip so they cannot expand until the clip is above the retainer. I bought a box off assorted sizes on amazon. Enough to last a lifetime.

 

[tornitore45]

I use the E clip method as well, once the clip drops into the cap recess can not expand.
I rather turn the groove than deal with drilling 1 mm across a 0.094 rod.
The E clip method seems more realistic to me, I do not recall a full scale engine using pins.

 

[minh-thanh]

I use the same as petertha.
if the E-clip is a little loose, just need the pliers to make it smaller
I hate having to drill 1mm.

 

[WOB]

E Clip is good if groove is sized correctly. See "Machinery's Handbook". My spring caps do not have a recess for the clip to fit into. I saw no need. Have never seen a clip come loose on 44 different valve stems. One engine runs up to 7200 RPM, no problem.

WOB

 

[awake]

Thanks, all. I did think about an e-clip ... but I don't have any that small on hand. Did I mention that this project has me doing far tinier parts than I am used to? Honestly, I've been amazed, not only at the tiny size of these parts, but even more at the realization that some of you are working to even smaller scale.

 

[Peter Twissell]

My personal preference would be a half round section groove in the valve, a wire clip and a counterbore in the cap to keep the clip in place.
The round section groove avoids creating the stress raisers of a sharp cornered square groove.

 

[awake]

I thought about stress risers - one of the reasons I wondered about the strength of this approach vs. drilling the hole. Of course, that led me to the next question - how would I machine that teensy-tiny c-clip with a rounded inside profile??

 

[Peter Twissell]

I make my own wire clips by winding piano wire onto a mandrel.
The winding mandrel must be smaller than the groove diameter, to allow for the wire springing back after winding.
Then, I push the resulting wire coil onto a larger mandrel, larger than the groove diameter by the thickness of a Dremel cutting disc divided by Pi. A cut with the disc separates the coil onto a number of separate rings, which are then tweaked with two pairs of pliers to make them flat.

 

[awake]

Peter,

Wow - now that you have said it, it seems so simple and obvious - you even said it in the previous post ("a wire clip"), but I totally missed it. And better yet, this approach would be a heck of a lot easier than what was involved in machining out the tiny little c-clips that I made. I will definitely file this away for future use! Thank you!

 

[Longboy]

...

 

[Longboy]

I like the pin retainer method for the simplicity. Have not tried the e- clip method. 3/64 piano wire through a #55 hole caged by brass spring retainer. A #1 center drill tip leaves a nice dish to start the drill bit. Been using 9/64 diameter stems. I feel for you with the tooth pic stem diameters. I think I up sized to 1/8 in. stems on my Webster at the time!

 

[awake]

Tooth pick indeed. I've known tooth picks bigger than these itty-bitty valves!

 

[Cogsy]

The E clip method seems more realistic to me, I do not recall a full scale engine using pins.

I've worked on a couple of old single cylinder verticals that used pins in full size but certainly never seen it in a high speed or 'modern' engine.

 

[bluejets]

Second photo, first post version works fine on my little 4 cylinder 25cc engine and it runs out to over 10,000rpm.

 

[propclock]

Just my 1.414 cents worth. 1 thing I think I can contribute to the group
I make my my valve spring retainers out of aluminum and put a taper
aka center drill counter sink down a bit in the top. Then a small grove
in the valve stem . Then on assembly i use copper wire cut to the proper length wrap it around the grove in the stem then the spring
retainer is released to compress the wire into the stem. 2 major advantages. It works for many sized valve stem systems. Just pick your
wire size.
It is practically free, and Light and when when you have to remove the
valve,
They seal first time every time correct?
you just pick out the
copper wire. With an e clip boing! where did it go?? I have many resistors so I have many diameters of copper . and a new"clip is free"
I have them in about 6 engines and no failures so far ~ 5 years.
Personally I think this is a good tip. Tried & tested ++.