Heavier flywheels for the Kerzel hit and miss engine

[crueby]

Whatever you do, don't move the chair in the living room. That will lead to new carpet, might as well paint too, and that lamp needs an update....!

[Brian Rupnow]

Whatever you do, don't move the chair in the living room. That will lead to new carpet, might as well paint too, and that lamp needs an update....!

I hear you brother!! Actually, I'm glad to have this to do. I have ran out of ideas for new things to build, and I don't want to start a new engine right now.

[Brian Rupnow]

We are getting into the home stretch now. New sideplates and bearing caps have been made and installed, and in this picture I have just counterbored one sideplate for a #1606 ball bearing. The bore is finished, about .002" over so the bearing slips in easily. I now have to flip the engine over, center on the pilot hole that is reamed to 7/16" dia. and bore the other side. I made bolt on bearing caps so that I can take the caps off and lift out the entire crankshaft assembly, bearings and all without disturbing the sideplates. If the fit is good enough on the bored holes, I will lay a piece of 0.015" thick gasket material on top of the bearing and tighten down the caps to lock the outer race in place. I haven't decided yet whether to leave the seals in the bearings to retain grease, or pop the seals out, which gives a lot less friction but requires that the bearings be oiled from a squirt can.

[Brian Rupnow]

At the very last minute, I decided to pull the seals out of the bearings. There is no contamination around the engine to get into the bearings, and they are readily accessible for a few drops of oil from my squirt can. I went to Hercules O-ring this week and bought a lifetime supply of Viton O-rings for 3/4", 7/8" and 1" bore engines. I have been buying onesies and twosies for 5 years, but the last time I went over I got some flack about it. So--I bought a minimum size pack which contains 25 of each size.  I put a new o-ring on the engine while I had everything apart. I have almost everything back together, and should finish re-assembly sometime this afternoon. It is hard right now to make a judgement call on how much the ball bearings have loosened things up, but I should know by the end of today.

[Brian Rupnow]

Somehow, today I must be paying for past sins. I have everything back together, good spark, lots of gas , great compression, perfect valve timing---and I still can't get the engine to run. I haven't had to work this hard at getting an engine to run in years. We're having a blizzard outside today and it's been nice not to go out of the house. I worked all week at a factory on the other side of town designing new tooling for spin-forming lathes, so I was looking forward to getting the engine up and running today. I'm not exactly sure what I will try next, but I may put one of my other carburetors on it temporarily.

[Brian Rupnow]

All I had to do was complain a bit on the internet--and tweak the valve timing a very little bit--and I have a runner!!! tomorrow I will see about hooking up the Kerzel lever to get some hitting and missing happening.

[Brian Rupnow]

I am finding things out as I tune this hit and miss engine. I initially had the exhaust valve set to begin opening at about 50 degrees before the piston reached bottom dead center. This puts the bottom of the piston skirt about 0.145" away from the end of the cylinder. No joy----Much popping and firing along with the drill motor I use as a starter, but no way it was going to run without the drill motor. I tried various ignition timing, ranging from no advance to 15 degrees advance, and every possible needle valve setting but it wasn't going to run. I did a bunch of internet research on exhaust valve settings for hit and miss engines, but got a lot of conflicting information there, ranging from 50 degrees advance on the exhaust timing to no advance on the exhaust timing. I began to decrease the exhaust valve timing from my original 50 degrees in approximate 10 degree increments, and immediately began getting sustained runs with the engine. at 40 degrees advance, it would run, but had very little "power", just barely enough to keep it turning over. At 30 degrees advance, it ran better.  I got my test indicator out and positioned it so I could tell exactly at what point the exhaust valve began to open, and decreased the valve timing advance even farther. Finally, I reached the point of no valve timing advance at all, and the engine runs quite happily there. I have found that the ignition timing seems to perform best of all when it is set to fire exactly at top dead center with no ignition timing advance at all.  The engine turns very freely with the new ball bearings on the crankshaft. Somehow there has been enough changes in the dynamics of the engine that it is now running too slowly to make the governor engage the Kerzel lever and go into miss mode. I think I will have to add some more weight to the governor weights to increase the governor sensitivity and get it to hit and miss.

[Brian Rupnow]

Before I go any farther with modifications to this engine, I have to right an old wrong. When I first built this engine 6 years ago, I had only built one engine before it, the Webster. I had a terrible time getting this engine to run at all, and finally, in a rather desperate move, decided that the cam design per Mr. Kerzel must be wrong. So---since I had great experience with the Webster, I decided to make a clone of the Webster cam to run in the Kerzel engine. As you can see from the attached picture, the grey cam (as per Mr. Kerzel) and the blue cam (as a clone of the Webster cam) are very different. Since I am head and shoulders back into this engine, I will make a new cam according to Kerzel's original plan and install it. The dwell on the blue cam, which I am currently running, is about 4 times greater than the cam designed by Kerzel. This has to be having a pretty radical effect on the engines performance, so I will make a new cam and install it before I do anything else.

[Brian Rupnow]

Tomorrow I am going to make a new cam, using the Chuck Fellows method. Chuck doesn't want to take any credit for this, saying he learned it from somebody else, but Chuck is the one with the youtube video showing how it is done. It is a really easy way to make a cam, once you get your head around it. If you Google "chuck fellows cutting cam" you can see a video of him doing it. I used that method on the cam for my oscillating i.c. engine, and it worked great. It gives a nice radius to the cam flanks.

[Brian Rupnow]

So---Here we have the old cam on the left and the new cam on the right. The new cam has since been installed on the engine. I did use the method that Chuck Fellows shows in his YouTube video, and it works so well that I am going to start a separate thread on setting up a cam in a vertical mill to use that method. It is remarkably fast, and it gives a nice flank radius on the cam, instead of just flat sides. This is the second cam I have made using that method, and a large part of today was spent writing down all the "step by step" procedures in setting it up so that I could dial in the dimensions of the cam and not just take a guess at the flank radius being cut. It took me longer to write everything down than it did to machine the cam.

[Brian Rupnow]

Okay guys--stay with me on this. It gets a bit theoretical at times---. this is the cam, as designed by Kerzel. Using some cad magic, I "machined" the cam exactly as Kerzel advises in his original plans for the hit and miss engine. I then matched a circle to the resulting profile, and discovered that Kerzel had done his job very well.--the resulting diameter of the circle is exactly twice the base diameter of 0.6". The radius described by this circle is called the "flank radius". I then did a little more cad magic and see that the angle of "cam influence" is 122 degrees. Since the cam revolves at half the speed of the crankshaft, that 122 degrees actually translates to 244 degrees of "influence" at the crankshaft. As the piston moves from bottom dead center to top dead center, the crankshaft revolves half a turn which is 180 degrees. We want the exhaust valve on a hit and miss engine to close when the piston is  right at top dead center, with no overlap, because the intake valve is operated by atmospheric pressure and will not begin to open until that exhaust valve is fully closed. So---we subtract that 180 degrees from 244 degrees. and this tells us that the exhaust valve should begin to open 64 degrees before the piston reaches bottom dead center on the power stroke. This does not take into account any "valve stem clearance", but that amount is very minimal when set to .005". This seems like an awful lot of "lead" on the exhaust valve timing.

[John Hill]

Brian, I am thinking about the exhaust valve closing at TDC. 

To my thinking as the piston comes to the top and stops exhaust gases will still be travelling down the exhaust tract and there will be a period of low pressure.  Obviously if the exhaust valve is closed this low pressure will be a slight drag on the engine whereas if the valve is open it will tend to open the inlet valve earlier than it otherwise would.

Just my thoughts although I must say that the hit and miss engine we used on some farm equipment responded somewhat   to adjusting the length of the exhaust pipe.

[BillTodd]

The valve timing can not be calculated without taking the cam follower geometry into consideration.

What is the follower like on the Kerzel?

Bill

[Roger B]

The joys of small internal combustion engines   

If I have calculated correctly the total cam lift is around 60 thou. A valve clearance of 5 thou will have a significant effect on the actual valve timing. A quick bit of CAD work should give the actual opening period at this clearance and as Bill says the follower profile will also have an effect.

[Brian Rupnow]

The cam follower is a 1/4" outer diameter bearing.