gear retention camshaft & crankshaft

[petertha]

Im working on my single cylinder 4-stroke design. Its kind of a starter / proving project that hopefully will grow into a 5-cyl radial ..one day. But first things first.

The layout shows 15-tooth DP40 drive gear engaging a (2:1) 30-tooth cam gear. The challenge (moreso on the radial) has been packaging this cluster into a compact, constrained volume. If I select a larger DP (for bigger stronger teeth) or add more teeth, the gear cluster grows & I run out of room. I could go one size down to a DP 48, the drive gear starts to get pretty teeny. Anyway, this is what I have so far. Interested in your comments on practicality or potential problems.

For the drive gear, I figured I would pre-install it on the rear crankshaft segment outside the engine. It doesnt really matter what clock position the gear is its in from what I can tell, but it would be a lot easier to do with the crankshaft outside the engine. To retain it, it I assumed a cross hole through the hub & into the CS. I have seem RC model pinion gears that have a set screw that ingages a flat or countersink on the CS. Maybe thats better?

The cam gear requires a different treatment. he camshaft needs to be clocked into position once the crankshaft is in, so is dependant on however the drive gear is positioned. I show 2 pre-drilled pilot holes through the cam gear. Im envisioning, locktite on the camshaft, clock camshaft in position, loktite sets, carefully remove 'fixed' assembly, drill through pilot (guide) holes into the camshaft body, install permanent pins with locktite. (In the case of radial, this would have to be repeated for each cylinder).

What do you think?

 

[petertha]

Here are typical RC heli pinion gears. They use a set screw on one side to retain gear on to similar (5mm = 0.197" dia) motor shaft. Shaft has adjacent flat ground on the OD. This particular heli motor gear is very likely transferring more load than I expect my engine camshaft example would be.

 

[xpylonracer]

Pinning seems to be a workable solution and should be trouble free.
For your radial 5 cylinder you may want to use flat plate cams for valve operation, certainly would be less work and a lighter engine than using 5 sets of what you propose.
Rgds, Emgee

 

[stevehuckss396]

I press fit the crank gear and use 2 set screws 90 degrees apart on my cams.

 

[petertha]

For your radial 5 cylinder you may want to use flat plate cams for valve operation, certainly would be less work and a lighter engine than using 5 sets of what you propose.

Thanks. I would agree, but then it wouldnt be a Kinner

 

[petertha]

I press fit the crank gear and use 2 set screws 90 degrees apart on my cams.

Thanks. What would be an appropriate ID/OD interference amount on parts like this be so they would stay put? Do you use locktite in conjunction with press fitting? Or heat the gear before pressing?

Re the cam gear set screw idea, I thought about that option too. But there just isn't room for an extending hub chunk like on the main gear. Well... at least the way Ive drawn it thus far.

Here is another view I should have included. The gear cluster resides inside a cam box, closed off except for a back cover plate. The tougher issue is the relatively long setscrew hole through a toothvalley? but somehow reaching it with a hex wrench. Thats why I have keyway-like pins going in laterally in same axis as cam shaft so I can get at it from behind. (green arrows on post #1 pic) Hope this makes sense.

 

[gbritnell]

I really don't understand the complexity of the cam gear train for the Kinner engine when an internal gear with the cam lobes on the outside is so much simpler. Added to that is the frictional losses of running all those gear sets. When I built my radial I used a similar setup to the Morton 5 cylinder radial.
Normally I press the cam gear onto the camshaft and key or set screw the gear on the crank. By using a fine pitch (48 or even finer if you make your own cutters) you can time the engine by moving a tooth and still be close to the desired timing points. By using a coarser pitch you have to have the timing quite close so one of the two gears needs to be moveable.
Attached is the PDF drawing for the cam gearing for my engine.
gbritnell

View attachment ENGINE RADIAL SHT 4e.pdf

 

[petertha]

I really don't understand the complexity of the cam gear train for the Kinner engine when an internal gear with the cam lobes on the outside is so much simpler.
gbritnell

I happen to share your view. From what I know of radials, Kinner's kind of stand by themselves in this regard. Quaint by quirky.

One potential reason for individual camshaft layout in home shop model engines might be mitigating sourcing/cutting internal planetery tooth ring gears at specific size. But like you say, OTOH multi camshafts introduces other challenges & disadvantages. Obviously modelers have overcome planetary gears as you have clearly demonstrated.

I'm not 100% I will build a Kinner radial. I started out drawing it at 1/5 scale, loosely off the Merritt Zimmerman 1/4 scale SIC design. Partly as a cad learning excercise & partly wishful thinking. He did his gear clusters slightly different than FS engine with an intermediate idler gear vs. banks of single cam gears running on a longer drive gear, but similar principle.

Building any radial right now would be a personal train wreck in the making. I want to get a simpler, single cylinder under my belt & that will be challenging enough. So I figured, design & make a Single with many common & adaptable features. If that works out & I pass the test, it opens the door for more complex engines thereafter. (You might be getting a call yet!). Thanks for your help. Pic of my single work in progress.

 

[petertha]

Attached is the PDF drawing for the cam gearing for my engine. gbritnell

Thanks for providing PDF. I typed in the PN for the internal gear you used. $50 sure aint bad. And I see lots of progressively larger size increments. Hmm.. 'the Kinner plan' may have just changed course

 

[Charles Lamont]

Where does the outboard camshaft bearing go?

 

[gbritnell]

When I redesigned the Morton and built my engine I added the internal ring gear cam. The Morton didn't use one. It has a much simpler system but to make mine more prototypical I went the other way. My gear train is a tight fit but it does work ok. My whole engine was kind of an experiment in design and build. There are things I would have done differently but it does run well as is so completely redesigning it is for another day. If you ever get to the point of designing your own don't hesitate to ask.
gbritnell

 

[dave-in-england]

Why not just put a pin the gear shaft and make a slot in the side of the gears like this >>

Then you can pack gears right up close together, don't need a boss which takes up space, don't need fixing screws, don't need locktite, and you can take it apart easily if needed.

Just a tight sliding fit is good enough, maybe in some cases a small screw and washer tapped in the end of the shaft to retain the gear.

dave

 

[petertha]

Where does the outboard camshaft bearing go?

The rear bearings & cam box backplate is just hiden for clarity, otherwise it would mask the features I'm talking about. There is a bearing on the aft end of both cam shaft & crankshaft. Those bearings sit in a matching recess in the cam box plate. Thats another finicky alignment bit I havent quite figured out fully quite yet, but hopefully answers your question.

 

[petertha]

Why not just put a pin the gear shaft and make a slot in the side of the gears.... Then you can pack gears right up close together, don't need a boss which takes up space, don't need fixing screws, don't need locktite, and you can take it apart easily if needed.

Thanks for the pics Dave. Ive seen that retention idea & I like it. For sure it would work on the main drive gear, but not sure about cam gears. I'll elaborate on how I think the timing procedure would go. Maybe there is a way or I'm missing your point:

- drive gear is locked on crankshaft in some arbitrary position... by pin, by setscrew, whatever, its now fixed. By arbitrary I mean the teeth are not phased/aligned to crankshaft TDC

- dry assemble crankshaft, camshaft with connecting rod & piston etc. prepare for clocking in

- rotate crankshaft to TDC datum, lock that position

- now rotate the camshaft independently so its cam is phased to open relative to BTDC position. The cam gear is engaged with the drive gear, but allowing crankshaft to rotate independantly.

- now with cam shaft clocked in relative to TDC, lock the cam gear position in exactly there (hence the pilot pins from the rear)

- (on a radial, then procede to next cylinder in firing order & repeat same procedure). Each camshaft can only work for that cylinder.

I think your cross pin idea would work but only if it was somehow pre-aligned & indexed to a given reference gear tooth or something relating to the crankshaft. If I went that route it would probably make sense to integrate the cam gear blank on the camshaft as a solid & cut the teeth. But the gear/cam lobe phasing of that machining operation makes my head spin.

 

[petertha]

When I redesigned the Morton and built my engine I added the internal ring gear cam. The Morton didn't use one.gbritnell

Very interesting. I'm not that familiar with the Morton, so never realized this before. Is this picture indicative of the original cam gear assembly? Would you say it was Kinner like in principle based on the FS pics I attached?
http://www.craftsmanshipmuseum.com/images/PK20b.jpg

My whole engine was kind of an experiment in design and build. There are things I would have done differently but it does run well as is so completely redesigning it is for another day. If you ever get to the point of designing your own don't hesitate to ask.
gbritnell

I followed your radial build closely, its one of my big inspirations. I might just take you up on that. I had this notion in my mind that ring gears were brutally hard & expensive to find in approriate size/PD's & making one seemed like extra torture. Maybe I checked into a euro model from SIC plans in the past & turned me off without further checking or diligence, really cant say. But the SP catalog & your PN reference opened my eyes, so I'm feeling good about all this now.

But I think I have to first pay my dues on a single & keep my machining errors & blunders confined to multiples of ONE for now!