Heavier flywheels for the Kerzel hit and miss engine

[Brian Rupnow]

I'm pretty sure the noise is in those roller bearings. As I said, they were noisy right from day one. I'm having a new thought here. This is a low rpm engine. There is no real side-load on the bearings, other than the thrust of the connecting rod. I have had similar applications in real life full size engineering projects, where I used type 901 blue nylon. It has a very low coefficient of friction,  it's not affected by oil, and it's tougher than whalebone.  The shaft is loose in the bearings. I can grab a flywheel and move it up and down. Not much, but probably enough to produce the rattle. Tomorrow I am going to call some of the plastics people here in Ontario and ask about this.

[///]

Very timely thread, thanks Brian.
I'm working on a Kerzel now and had been wondering about flywheel size.
I have some 80mm (3.15") cast iron rod for the flywheels, was the largest diameter I could find and was hoping that would be enough but now having doubts.

Here is another video with a good hit/miss ratio. (Starts at 1:20)
Not quite as good a ratio as Ronald's video that you posted (reply #2) but still pretty good I reckon.

Interesting to note that both seem to have 3.5" dia flywheels.
I guess the key is to just keep friction as low as possible.

<a href="https://www.youtube.com/watch?v=0mgjPH3B5KE" target="_blank">http://www.youtube.com/watch?v=0mgjPH3B5KE</a>

[Brian Rupnow]

Well, in for a penny, in for a pound!! Once I seen that I could grab either flywheel and move it around a bit in the needle roller bearings, it was pretty apparent where the noise was coming from. I pulled the crankshaft this morning. Back when I decided to run needle bearings, I had to make up spacer bushings, as the roller bearings were 3/8" i.d. x 0.5625" o.d., while the hole in the Kerzel frame was 0.625" diameter. I see that I also made the spacer bushings in a "top hat" configuration, so that the flange would act as a spacer facing towards the center of the engine. I have talked to some of the nylon specialties people this morning, and found that there is a specially formulated nylon "Nylatron GS" with molybdenum as part of it's make-up, which is recommended for use in bearings for motors. My local metal supplier has an off-cut of this material, and I am going to make up two new bushings from it and get rid of the needle roller bearings. One of the benefits of these nylon bushings is their noise deadening capacity. It is not a lot of work to make two new nylon bushings, just a huge pain in the butt having to redo the valve timing and ignition timing.

[Brian Rupnow]

For what it's worth--I just pulled everything off one end of the crankshaft and miked the area which fits into the bearing. It mikes at .002" undersize. I thought, Hmmmm, that shouldn't have given all the wobble I was seeing. Then I tried the 0.375" shank end of a milling cutter (which is not undersize at all) into the roller bearing and it STILL wiggled around quite a bit.

[Brian Rupnow]

The other end of the crankshaft measured about .003 to 0.006" undersize at the bearing journal. That is definitely too much too much. This is a built up crankshaft, and I distinctly remember the crank going through a few indignities back when I first built the engine. I am going to put new ends on both ends of the crankshaft while I have everything apart.

[Brian Rupnow]

The old crankshaft was silver soldered and pinned together, and although it was straight it had suffered a few abuses along the way, not the least of which was being a bit undersize at the area in contact with the bearings, and being fairly chewed up by set-screws at the outer ends. I cut one end off with my bandsaw and chucked the other up in my lathe. After center drilling I drilled thru both webs with a 1/4" drill, then with a 5/16 drill, then with a 11/32" drill. Now there was only a very thin wall of material holding the center portion to the end in the lathe chuck. I then ran thru with a 0.3735" reamer, which separated the center portion completely from the end in the chuck. Note that the reamer is 0.0015 inches less than 3/8". The new crankshaft  pressed into place is a piece of drill rod. Why is that, you may ask?--Because, drill rod comes at a full 0.375". Cold rolled rod comes in at 0.005" undersize, generally about 0.3745". I wanted as much "press" as I could get, so I used drill rod. I don't want to disturb the con rod journal by heating anything up to silver solder the new crankshaft into place, so it is pressed, Loctited, and will be cross-drilled and pinned. Then after 24 hours for the Loctite to fully set, I will cut out the piece remaining between the crankshaft web plates.

[Brian Rupnow]

And oh yeah--I put a spacer between the outer edges of the throw sideplates opposite of the rod journal before I pressed the new crankshaft into place, so as not to collapse anything.

[Brian Rupnow]

The crankshaft has been cross-drilled, reamed, and had 3/32" dowel pins Loctited into the reamed cross drilled holes. I ended up with a 1 3/4" diameter piece of super duper molybdenum nylon from my metal supplier. It was a short left over from a job they had done. I have never machined nylon before, but I had read that medium high speed and very sharp tooling was the trick. I ran it at 400 rpm and used a new hss lathe tool and it was beautiful to machine.

[Brian Rupnow]

HELP!!!---I am getting ready to reassemble this engine, and I can not find anything in my notes, build thread, nor original David Kerzel drawings about the exhaust valve timing. I think it should begin to open at about 50 degrees before bottom dead center on the power stroke but I can't confirm that. Does anybody see or know where Kerzel gives that information.---Brian

[Brian Rupnow]

Everything is back together again with new crankshaft and Nylatron bushings. Flywheels have gone from being rather "loosy-goosey" to "Oh my gosh, that feels snug"!--A word for any first time builders following this thread--If when you first assemble a crankshaft assembly it spins freely in the engine, odds are about 95% that after the engine has ran for half an hour, everything will be too loose. On the other hand, if everything is too stiff, then you won't be able to get the engine to run to free itself up. This is kind of a moving target, and although experience certainly is a big asset, even after 24 engines I still have to guess at it a bit.

[Brian Rupnow]

As Robbie Burns once said "The best laid plans of mice and men, gang aft agley!!"---and mine seen to have went "agley" today. I hunted around until I confirmed that the exhaust valve on the kerzel should begin to open when the piston is 50 degrees before bottom dead center. I set the ignition timing---In fact I set it many times today. NO JOY---the engine fires like a devil, but I can't get it to keep running. I have tried all of my usual (and some rather unusual) tricks, and I do not have a runner. My wonderful new Nylatron bushings seem to have a great deal of "stiction"---resistance to free rolling of the crankshaft. I have one trick left in my arsenal of "things to try". I may just pull the sparkplug, coat everything that moves liberally with lubricating oil, mount a pulley on one end of the crankshaft and let my 1/2 horsepower electric motor drive things for a couple of hours. If that doesn't loosen up the "grabbiness" of the Nylatron bushings, then we will move on to plan "D". Plan "A" was 660 bronze bushings, which wore out very, very quickly when I first ran the engine 6 years ago. Plan "B" was to use the roller bearings, which worked, but was very noisy. Plan "C" was the Nylatron bushings which are currently installed. Plan "D" will be to pull out the Nylatron bushings and install a set of Oilite bronze bushings. I haven't changed anything on the piston nor the valves, so lack of compression is not a factor here.

[Johnmcc69]

Brian, could the bore on the bushings be too tight or collapsed when installed? I don't know anything about this material or how it "wears in", but you may need to re-size the bores for them.

 John

[John Hill]

Brian, I may be mistaken but I do seem to recall that bushes of the nylon variety grab when hot so is it possible you can spray some freeze liquid on the bearings just prior to attempting to start?

[Brian Rupnow]

Lincoln, Lincoln, I been thinkin'-----If I take this thing apart again to change to yet another set of bushings, I think maybe I will completely forgo bushings and go straight to ball bearings. This involves making a few more parts which bolt directly to the existing base to capture the ball bearing. The ball bearing is the same one as was used in the Rupnow vertical engine, only this time I won't get sealed bearings. Sealed bearings are great if there is a lot of contamination around or if they are hard to access to lubricate. However, the seals do create a small amount of "drag" and in the case of this hit and miss engine they are quite accessible for a squirt of lubricating oil, and there is really no contamination around the bearing. I have about 500 little scraps of aluminum plate kicking around, certainly enough to make the new pieces without buying material. I'm a bit disappointed in the Nylatron bushings, but if you don't try something a bit different sometimes, then you never learn anything new. After playing with the engine for two hours to try and get it started, the Nylatron bushings had loosened up quite a bit. After setting overnight and cooling off, they are all "Grabby" once again this morning.

[Brian Rupnow]

Oh, my poor old Kerzel. Heavier flywheels I said. Yeah----Which lead to different bushings. which lead to ball bearings instead of bushings---which lead to new bearing support side-plates and caps. And since we have everything apart, we might as well put a new Viton ring on the piston. And put the whole engine in the tank and get 6 years accumulated dirt and grease off it. The new side plates and caps are semi finished---I didn't want to put the mounting holes in the sideplates until I had taken the engine apart to confirm that I actually have the mounting holes in the base where the drawing says they are. I do!! As well as a plethora of other holes that were put in for various reasons back when I first built the engine. Fortunately, when the new ballbearing sideplates are mounted all of the "extra" holes will be covered up.----Sure am glad I enjoy this!!