Tiny Inline 4 Cylinder IC

[GailInNM]

Kermit,
Your physics texts are correct, The problem is that breakdown voltage for a spark to occur in gas has nothing to do with the resistance between the electrodes.

With a voltage between two electrodes, the volume around the negative electrode (cathode) will become ionized and the free electrons will be accelerated generally toward the positive electrode by the electric field. But along the way they strike other gas molecules and if the energy is sufficient they in turn have an electron stripped. Some of these electrons will head toward the anode, but some become diffused. The higher the pressure the more the diffusion because of the increased number of molecules that are between the anode and the cathode. Only when a complete conductive ionized path is constructed does a spark occur.

This is a simplified description, but is just to show that the mechanics of a spark are very different from the resistance between two electrodes.

Gail in NM

 

[mu38&Bg#]

Refer to "Internal Combustion Engine Fundamentals" John B. Heywood, pg 427. There are probably online references, but this is one of my most used engine references.

 

[Lakc]

This is a simplified description, but is just to show that the mechanics of a spark are very different from the resistance between two electrodes.

Gail in NM

That also explains that if you research early avaition engines they wound up pressurizing the ignition wires to prevent misfire at altitude. It took a long time for me to make sense of that, but as Gail points out, the mechanics of spark follow their own rules.

 

[kcmillin]

Well, with all the great information, I have managed to make the spark plugs more reliable by increasing the gap.

There is another bug which I cant get figured out. Ever since installing the cooling system the engine can take quite awhile to start. It requires the assistance of the dremel until it gets warmed up. Then it will run all day long. The whole time I am trying to start it I am playing with the timing and needle setting, so there are many variables. I am going to try eliminating the cooling system somewhat by removing the belt for startup. Any other ideas on cold starting?

The engine runs more freely when it is cold, then when it is warm. Which seems strange, because when it revs, it revs smooth and can rev very high. I am still seeing the 8400+ RPM spikes, and can hold the engine at a 7800 for 15 seconds. (I know, I know, why would I do this? Because I built it, thats WHY! :big

Kel

 

[mu38&Bg#]

If you are burning gasoline, it needs a substantial enrichment to start and run cold. A choke might make this easier.

 

[stevehuckss396]

If you are burning gasoline, it needs a substantial enrichment to start and run cold. A choke might make this easier.

I never adjust the timing after it is set. I unscrew the fuel screw an extra 1/4 turn and choke with my finger just for a second. Usually works with little trouble. As it warms up, screw back in slowly.

 

[kcmillin]

Well, I may have found a problem. I was adjusting the valves, and noticed that one of them was not adjusting, it just kept getting deeper and deeper in the valve seat. Upon removal of the head I noticed that valve's seat was completely gone, and the valve was getting close to going past the intake runner. This undoubtedly was causing problems. So I will be installing a couple new valves.

I also noticed again that 3 out of 4 cylinders were sloppy on the crank journals. I just fixed this! (I thought) perhaps it don't really like to rev. One of the bronze bushing was completely gone, and the rest were quite worn down. There is a layer of bronze powder in the bottom of the oil pan. Darn these crank journals are a PIA. I will now be doing some design work to help solve the problem. I plan on making the bushing larger, and reducing the bolts from 2-56 to 0-80. This will give me more room for bushings. The entire time the engine is running I like to keep it oiled, if it stops smoking, I add more. Since the main seals were an afterthought, they don't work so well, and leakage is an issue.

Kel

 

[gbritnell]

Hi Kel,
I'm confused by your explanation. You said that the valve was going deeper and deeper into the valve seat so why would you be making a new valve? It seems like the seat would need to be repaired.
On my 4 cylinder engine I use split bronze bearings for the crank with a splash oil system and I've never had to replace them. Now the big end of the rods is another story. I have had to refit them several times because of wear. Not bad but they were still a little loose.
George

 

[Lakc]

I also noticed again that 3 out of 4 cylinders were sloppy on the crank journals. I just fixed this! (I thought) perhaps it don't really like to rev. One of the bronze bushing was completely gone, and the rest were quite worn down. There is a layer of bronze powder in the bottom of the oil pan.

What did you use for the final finish on the crank journals? I usually take that last 1.5 thou off with progressive grits of emery cloth 180-320-400 grit, and make sure the crankshaft is rotating the same direction as it would in final assembly, so the "hairs" of the crank lay down in the correct direction.

 

[kcmillin]

George, the valve itself has been hammered smaller. The valve got quite thin during machining, and was delicate to begin with. The other valves are a bit thicker on the big end and subsequently stronger. The valve seat on the worn out valve is in good shape still, I will need to make a light pass with the valve seat cutter, and then burnish the new to its seat with a jewelers rouge concoction.

Jeff, I used sandpaper up to 600 grit. I also inspected each journal with a magnifying glass. They are quite smooth, but may be out-of-round. I used emery cloth and sandpaper to get the journals back to round, then using a blade micrometer as a gauge slowly worked them to a true round. But because I did not do this on the lathe, it may not be perfect. My last resort is to make yet another crankshaft. I am surly getting my practice in.

The bushings I originally used were .005", brass shim stock. These probably wore down immediately. My second bushing were made from a bronze bar. They were .010 thick, these were better, and the crank was much less worn after inspection, but alas they did not last. So, my third option is to make .020" bushing from bronze. I am currently half way through fitting them. They physically appear to be much larger and perhaps better at handling the impact. Well see.

One major flaw of my bushing design may be that they are one piece, split in one spot with a very thin dremel cut off wheel. This leaves a gap in the bushing. Now that my bushings are getting larger I may be able to use a split bushing design which is more traditional. Using two pieces of bronze soldered together then machined.

Plan D, or E, or whatever. Will be to make square holes in the connecting rod ends, then machining square bushings. This will guarantee the bushing will not spin in the connecting rod.

Kel

 

[Lakc]

Ok Kel, years ago as I was discussing making model crankshafts, with a crankshaft engineer of all people, he stressed the final direction of emery cloth was extremely important, thought I would pass that along.

Your valve problem is likely heat, and the head had too thin a cross section as you mentioned. Valve heat is dissipated through the stem and seat, so it helps to have a little extra meat in those places.

 

[kcmillin]

Thanks Jeff, I do appreciate any input, and your advise is sound.

Here is a video I took before I tore it down. By the time I decided to take a video its performance had been increasingly getting worse. I found two hammered valves, both intake and both of them were on one side of the engine and share an intake runner. Not sure if this has anything to do with the problem, just thought I would mention it. Also the rod issue, which was pushing 3/32" on the worst one. Good thing I notched the pistons to clear the spark plugs.

It is running on three cylinders for the majority of the video, towards the end of the video it cleans out and runs a little better, still not 100% though. Hopefully my new enhancements make a better engine.

<object style="height: 390px; width: 640px"><param name="movie" value="http://www.youtube.com/v/V-bM0m1-ynI?version=3"><param name="allowFullScreen" value="true"><param name="allowScriptAccess" value="always"><embed src="http://www.youtube.com/v/V-bM0m1-ynI?version=3" type="application/x-shockwave-flash" allowfullscreen="true" allowScriptAccess="always" width="640" height="390"></object>

Kel

 

[Rustkolector]

Kel,
I think your rod bearing problems are due to the combination of high rotational speeds and splash lubrication. I don't think splash systems work well in engines over 4000-5000 RPM, especially tiny ones. Can you describle you splash system i.e. oil volume, oil type used, rod dipper type and size, etc?

Jeff

 

[kcmillin]

Jeff, I have to admit that the lubrication system is incredibly crude. I rely on the rod cap bolts to skim the oil, but I think there may be something els going on.

When I run the engine with the pushrod cover off, oil is literally getting sprayed out the breather holes, which are located between each cylinder. Granted the camshaft is right there, but it does spray. This is leading me to think that the crankshaft, and connecting rods are creating turbulent air splashing the oil around. Although I could be wrong. The engine smokes when there is sufficient oil in the crankcase, and I also add WD-40 to the gas. I am using regular 10-30 oil in the crankcase.

There is an acceptable amount of blow by from the o-rings, and the cylinder bore and piston are in very great shape. I also am replacing the drill rod wrist pins. They were also worn down. It seems that the aluminum in this engine is winning all the fights. Even the lead-steel tappets are wearing down. The all brass gears are wearing down a little bit, but are still acceptable. The idler gear is showing the most signs of wear, and the bevel gears are doing the best. They do get plenty of oil, since that is where the oil that leaks comes from. I have yet to see clean oil coming out of the engine.

I should say I am having a blast finding problems. I have always enjoyed inspecting wear in my engines, and this little guy is is giving me plenty. Even better, this gives me the knowledge and experience to build a better engine, which I can then proceed to destroy :big:

I am in the rebuild process right now and hope to have her running by tonight, or tomorrow.

Kel

 

[t.l.a.r. eng]

Perhaps a pressurized oiling system could be added?

I believe while you are seeing the oil being churned into a mist, the centrifical forces are trying to throw the oil out of the rod bearings.

Looking at it backwards maybe, but imagine trying to lubricate something under pressure that is flailing about over 5-6k with just a mist?

Great job on the engine, sounds great ;D

 

[Lakc]

Looking at it backwards maybe, but imagine trying to lubricate something under pressure that is flailing about over 5-6k with just a mist?

The nice thing about mist lubrication, is that its awful hard to avoid inside the crankcase. A diagonal hole from the piston side of the con rod big end can use that mist to lube the crankpin. Most commercial 4 stroke model aircraft engines lube the crankpin at ungodly rpm's with the blowby from the rings alone. Most American V8 engines lube one of the hardest loaded parts, the camshaft, with the mist from the crankshaft.

 

[Rustkolector]

Kel,
As I have found on much slower speed engines, a wide dipper can totally suspend the oil contents of the crankcase. I would consider a 3/32" wide dipper excessively wide for even medium speed. Too much oil in suspension creats friction that actually adds heat to the oil. With your high speeds, splash is difficult and needs some control. On some older motorcycles and older multi cylinder model engines, a baffle was used under the crankshaft which provided controlled flow of oil into a trough where the oil was picked up by each con rod dipper. It prevented the dippers from pulling all the oil into suspension. The best example I could find is this photo from the Edgar Westbury designed "Seal" engine team build:

http://www.craftsmanshipmuseum.com/images/SealCooneyPan.jpg

The hole in the bottom of the trough apparently limits the amount of oil available for the rods, allowing splashed oil to constantly drain back to the sump. The Seal doesn't appear to use dippers on the rods. This system provides lower rod lubrication as well as an internal oil mist for fhe rest of the engine parts, but not a flood of oil. Ideally on slower engines, the rod dippers are small narrow scoops (sometimes hollow tubes) that direct a portion of the oil directly into the rod cap. The rest is splashed radially about the engine. The dippers can be solid but there should be a hole or two in the rod to allow splashed oil to directly enter the rod journal. It is a reasonably good system for medium speed engines, but I don't know the upper RPM limit of splash systems. You migh want to talk with someone that was on the Seal team build project.

Jeff

 

[kcmillin]

Thanks for the tip on the baffle Jeff. I will be thinking about that.

Well, I got her back together last night and tried to start it. I tried and tried but to no avail. I noticed that the "acceptable" amount of blow by had turned into an excessive amount. So teardown of the bottom end was in order. It the time I tried to get her running it did here and there, and it would rev high. Upon inspection of the con rods they are in excellent shape. No slop. So with new o-rings in the pistons if was back together. Nothing, still would not run reliably, but the compression was there. I had suspected my spark plug wires for probl;ems from the get go. I just had freyed ends inside the boots. I decided to make a new set with soldered ends like Steve. Once I had these installed it was time to start it again. This time, BAM!!!! it started right up and ran beautifully, except for one major thing. It had a bad knock. OH NO!! I thought, my con rods again!! Argggg. So I decided to tear it down once again, I think this makes about ten times already. The rods were in good shape still, so it must be something els. I looked closer at the oil pan and noticed that the connecting rods were hitting the inside of the pan. Hmmmmm, why is this? It did not do it before. But I realized that I had shimmed the rod caps to pre-tension the new, larger bushings. So a quick swipe with the dremel and it was assembly time again. I am happy to report that it started first try and ran nice with no knocks.

Now, off to a problem with the cooling system. I am getting leakage out of the radiator cap. If I seal it with teflon, than it just builds presser and leaks elswhere. I am contemplating an overflow tank. What do I have to know to get the coolant to siphon back up into the radiator? Like on the real deal.

Kel

 

[gbritnell]

Hi Kel,
Here's how the closed cooling system works. The water heats and builds pressure to the point that the radiator cap allows the excess pressure, and water, to overflow into the overflow tank. As the radiator is totally full of coolant the line is constantly full, kind of like bleeding brakes. Now when the heat is removed (engine no longer running) the radiator cools and upon doing so creates a vacuum in the system. The same principal was used in the early 'steam engines' to pump out the mines. Steam was applied to the piston which would make it move then cold water was introduced to the cylinder which would create the vacuum and move the piston back to the other end of the cylinder, and so forth and so on.
Now the only problem for model engines it creating the pressure cap with the vacuum check valve small enough to make it work.
What I do on my engines is to screw the cap into the radiator tightly then drill a hole from the side through the flange and into the center of the cap. I then solder an overflow line into the hole and pipe it away from the cap and down the side of the radiator. When the engine gets to the point that it's hot enough to push the coolant out of the overflow I shut it down and let it cool. The water boils at 212 degrees so I figure that's hot enough to run the engine.
George

 

[gbritnell]

Hi Kel,
I should have attached these in my last post but didn't think of it till after I hit the post key.
George