Revisiting small horizontal engine

[cfellows]

About a year and a half ago I finished this little engine with it's unique, gearless cam.  As you can tell from the video, it seemed to be a smashing success, starting easily and running at a nice slow idle...

<a href="https://www.youtube.com/watch?v=IvCVVX39SLc" target="_blank">http://www.youtube.com/watch?v=IvCVVX39SLc</a>

The bore was 5/8" and the stroke was 1.25".  Unfortunately, I began almost immediately having problems keeping the engine running for more than 20 - 30 seconds.  I tried everything, but had no luck improving things.  I finally decided it might be getting a vapor lock since the intake and exhaust valves share the same intake port and it got very hot very quickly. 

So, I separated the intake and exhaust assemblies, making new ports and installing the intake port on the opposite side of the cylinder head from the exhaust port.  Still no joy and the engine was starting and running worse than ever.  And, about this time, the nifty little gearless cam suddenly started locking up, presumably due to accelerated wear.

So, I replaced the gearless cam with a standard spur geared cam assembly.  Now the engine wouldn't start at all.  It was getting fuel and spark, but it would only pop once or twice and stop.  I reasoned that maybe the extra head-space from the added intake port might have dropped the compression ratio too much, so I added a small plug to the top of the piston.  This, indeed raised the compression ratio, but still no luck.

So... back to the drawing board.  I've decided that I need to re-engineer the head so I have a more controllable compression ratio, and I need to have a cam actuated intake valve to better control the fuel intake and timing.   To that end, I've decided to convert it over to a side-shaft cam.  It will be driven by 80 / 10 degree helical gears and the entire head assembly will be a scaled down version of the larger side-shaft engine I built several years ago.

Here's a couple of pictures of the new head, 1 1/2" diameter and 5/8" overall thickness. 





I decided to make the head from aluminum for better heat transfer and cooling.   I also milled a rectangular slot on the back instead of a circular port to keep the head-space to a minimum.  Next I'll start on the valve cages.

Chuck

The intake valve cage will be on the bottom of the head and the exhaust will be on top.

[gbritnell]

Hi Chuck,
I like you have built my fair share of I.C. engines and when something like what you describe occurs it leaves me scratching my head. Valves sealing, yes, compression, yes, heat, no, ignition, good.
What on earth could it possibly be? You tinker, adjust and experiment to the tune of many hours and nothing seems to help.
On your initial build I can understand the gearless mechanism wearing out but the other factors wouldn't have changed.
It's a shame that the uniqueness of the original engine couldn't have been salvaged.
gbritnell

[b.lindsey]

Time sure flies Chuck....doesn't seem like it has been that long at all. So frustrating when these things happen. Like George, I can understand some wear on the cam mechanism, but the rest is a real "poser" as Gomer used to say. I will be following your upgrades and hoping you can turn it into a runner again!!

Bill

[cfellows]

Hi Chuck,
I like you have built my fair share of I.C. engines and when something like what you describe occurs it leaves me scratching my head. Valves sealing, yes, compression, yes, heat, no, ignition, good.
What on earth could it possibly be? You tinker, adjust and experiment to the tune of many hours and nothing seems to help.
On your initial build I can understand the gearless mechanism wearing out but the other factors wouldn't have changed.
It's a shame that the uniqueness of the original engine couldn't have been salvaged.
gbritnell

Hey, George, thanks for the comments.  You've given me pause to think about this for a bit.  You're right, it's a darn shame to lose the uniqueness of this engine and I may have been a bit quick to abandon the original configuration.  I'm going to take a couple of days to ponder how I might make less drastic changes and get this engine running again in it's original form.

Chuck

[cfellows]

Upon closer examination, I discovered why the cam was locking up.  Here you can see the red arrow pointing to the location where the tapered, pointed section has broken off and the pointy tip of the crescent shaped follower is digging in to the blunted end.



I could probably fix it if I had a small enough file or rotary tool to regrind a tapered point on that section.  Or I could remake the part using a tougher material.  My options are probably limited to cast iron or steel.  Steel would be less likely to break, but i Don't know if having a steel follower running against a steel cam disk would cause galling or not.  Since cast iron would probably have less friction and wear better, I'm inclined to try that if I can't figure out a way to repair the brass cam disk.

Chuck

[zeeprogrammer]

First step is finding cause. It's a big step. Congrats. 

[Zephyrin]

This engine is really awesome to see running, unique too, it would be great to fix it.
A small rotary tool or dental burr should do it, but a slight change in timing is expected.
You may add a blob of silverbraze to give some meat to the burr and restore cam profile;  silver brazed parts are generally toughter than surrounding brass.

[sorveltaja]

Could it be possible to use silver steel for cam, once hardened?

It would be great to see that engine running again with its unique mechanism.

[cfellows]

Well, here's a surprise, but first the video.

<a href="https://www.youtube.com/watch?v=QcjQElsMGZ4" target="_blank">http://www.youtube.com/watch?v=QcjQElsMGZ4</a>

As you can see the engine is running again.  But, some background.   Last night it occurred to me that the original cam might also work in reverse in which case the broken part wouldn't interfere with the follower.  Partial reassembly and testing confirmed that it would work in reverse, so after remaking a few small parts, I reassembled the engine and reset the ignition timing to reverse the engine direction.  After some fiddling, I got the engine to pop a few times and actually tried to run, but just wouldn't keep running more than few seconds.  So, I shut everything down and came in the house to fix some lunch and try to figure out what to try next.

After eating, I returned to the garage, pretty much convinced that I needed to re-combine the intake and exhaust ports as originally built in order to reduce the total amount of dead space in the head and increase the compression ratio.  But, first, I gave it another try, turning on the ignition and spinning it up with the drill.  To my surprise, it started right up so I grabbed my phone and started video taping.  It was still running when I finally shut off the ignition.

I'm still not sure why I was having trouble and I suspect the problem will return, but I'll deal with it when it happens.  Thanks to George B for prodding me into being a little more patient and thanks to everyone else for their comments and suggestions.

Chuck

[zeeprogrammer]

 

Congrats Chuck. Has to feel pretty good no?

[cfellows]

Congrats Chuck. Has to feel pretty good no?

Yeah, but also kind like waiting for the other shoe to drop.  I don't have a lot of confidence that it will keep working...

[b.lindsey]

Chuck, do you think the ding in the cam had anything to do with the running issues, or is it still just a big question mark? If that was the culprit, then it could happen again in reverse mode, but then you would at least know and could perhaps make a new cam out of a hardenable material. Good to see it running again though!!

Bill

[Roger B]

Glad you were successful    Could your problems be due to something like a sticky/sticking inlet valve (iirc it has an automatic inlet valve  )

[cfellows]

Chuck, do you think the ding in the cam had anything to do with the running issues, or is it still just a big question mark? If that was the culprit, then it could happen again in reverse mode, but then you would at least know and could perhaps make a new cam out of a hardenable material. Good to see it running again though!!

Bill

Bill, the poor running started long before the cam broke.  After the cam broke, the engine wouldn't turn over at all past the broken part.  If I do have to remake the came, I will probably try cast iron.  I want provide as much inherent lubrication as I can.  The follower is pretty small and delicate and will wear out fast if there is too much friction.

[cfellows]

Glad you were successful    Could your problems be due to something like a sticky/sticking inlet valve (iirc it has an automatic inlet valve  )

Roger, I do feel like the problem was/is a fuel issue.  Could be the intake valve which, as you mention, is automatic or vacuum operated as I call it.  It's hard to tell because the fuel mixer and throttle are extremely touchy and require a perfect balance.  I think a smaller carb would work better.  I have left the plug installed on top of the piston which improves the compression ratio.  That's probably also helping.  I've started it several times in the past 24 hours and and let it run for 5 or 10 minutes.  So far it's being pretty reliable.  Fingers crossed!

Chuck