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David Kerzel,     Pompano Beach, Florida     david@FloridaAME.org

Simple 4 cycle vertical, 1.00 bore X 1.00 Stroke

The work in progress has gotten rather long, so it is now in 2 parts Go to the first part, building the engine

More Testing

11/9/2006   Tonight I played with ignition.  I made a jack screw that can slide the hall sensor up and down to give 4 degrees before or after TDC timing.

I get about 300 more RPM when the ignition point is 1 or 2 degrees before TDC.  At 3 degrees before it is hard to start.  Even at 1 or 2 before TDC it often fires and runs a cycle backwards.  I think 1 degree before is best.

Next I changed from the auto coil I have been using to Mike Neal’s Exciter and observed absolutely no change in operation.  The big auto coil was put away.

While the engine was running smooth at 2300 RPM the computer fan I have blowing across the head fell over and it kept running.  A few weeks ago when the head hit about 200F the engine stopped.  Tonight it ran at 260F until I stopped it.

11/11/2006  I started to test the carburetor I recently made.  I had been using the OS carburetor and I will use that as the standard.
First I tried the jet in  the barrel Just like the OS.  Mine has the same barrel ID so it should work the same.  Not even close.  I could adjust it to get the full speed range but I could never get the engine to run when it was 100% open.   Mixture adjustments were a lot more sensitive.
I had a idle speed bypass port after the barrel, if it was open operation was miserable.

I had a second jet position after the barrel (closer to the valves), I figured the barrel would act as a butterfly valve like in a big carburetor.  It would work at a fixed speed, the mixture was very sensitive and the engine would stop if the barrel was moved.  So this is a concept to forget.

I searched for differences between my carburetor and the OS.  The OS idle bypass lets air into the middle of the barrel and even though they have a .06 needle, they only have a .040 jet.  I modified my carburetor, eliminating the after barrel jet, making the main jet smaller, and adding a adjustable bypass to the middle of the barrel when it is open.  The carburetor is brass and soldered together so it was easy to take the parts off, plug holes and add a new adjustment.

While I was doing all this the engine was running at 1800 RPM for hours.  It runs so smooth now.  Then it started sounding strange.  A flip and there was a hiss during the compression stroke.  After some searching I found it was the intake valve .  Still more poking found the intake valve has some wiggle in the stem which was not there before and is not in the exhaust valve (crusty one).  I pulled the valve and the stem is perfect so the oil impregnated bronze is worn.  Not only is the valve not sealing properly but I suspect air is leaking in through the bearing diluting my mixture. I wonder if all these hours of running on propane has failed to lubricate the intake valve stem.

So I am stopped while I figure out what to do about the valve guides before I test the carburetor changes.

11/21/2006  I took it all apart, you can see the elongated hole in the intake valve guide on the left

I made 2 new guides, they are .1 longer than the originals.

The new intake valve needed several cycles of lapping to seal, but the exhaust only needed one.  As I recall it also leaked in the beginning, so I am wondering if the original guide may have been pressed in slightly off axis causing a side load on the guide.  Regardless, I plan on adding a drop of oil in the intake port each day. 

While it was apart, I decided to do the first o'ring for a piston ring test.  I used the grove recommended by Parker for a reciprocating seal.  My piston is .005 under the bore size which is on target as well.  The o'ring outside diameter is .011 more than the piston for squeeze.  This first one is Buna-N.

It was a push to get it in the cylinder even with the ring compression tool.  If it is at rest it takes a large amount of force to get it to start moving but once it starts it moves freely.  The drag once moving is about half that of my piston with 3 iron rings.

You can feel the initial drag of the o'ring but once it moves the motion requires less torque, compression is good.  When I tried to start it caught immediately and accelerated faster.  I recorder the highest speed of 3400 RPM.  After a few minutes of this the head was smoking so I shut down.  I have about 30 minutes on the o'ring so far.

From the Parker o'ring site, at 2400 RPM the seal should last about12 hours but that was at room temperature.  The o'rings are only rated for use to 250F and I was getting close.  I plan to get a little more run time before I switch to the Viton which is harder and good to 400F.

12/2/2006  I have been working with O'rings

The Buna-N O'ring OD was 1.011.  Very difficult to compress and get in cylinder.  Very stiff after being stopped.  Once moving it moves very smoothly

Buna-N ran very well,  my head (finned version) temperature after about 5 minute stabilizes at 290F with a small fan running, or 340F and oil smoke with no fan.  Buna-N is only rated for 250F so I probably exceeded the rated temperature.  My runs were about 10 minutes each stopping to add a drop of oil to each valve.  With the O'ring there is no oil visible at the exhaust port while the engine runs so oil in the fuel or frequent oilings are important. The compression is ideal, I was going to make a short video but never got there. 

When the o'ring had been run about a hour the engine stopped compression was gone and oil was everywhere.  A flat had worn on the O'ring and it failed,  Not even close to the projected 12 hour life.. 

The Viton O'ring went in easy had lower initial breakaway force and about the same amount of drag.  Viton is good to 400F so it should have lasted longer.  It ran great, then failed at 8 minutes with black oily smoke.  It had a flat worn into the side.

The Viton, X cross section double seal o'ring was too difficult to get into the cylinder.  I use the lapp from finishing the piston as a ring compressor.  It has a small gap which is fine for metal rings but the O'rings bulge out. 

The O'rings seal perfectly and rung good, but the short life and absolutely no oil getting by makes it an interesting experiment but not the way to go in my opinion.

I did learn that my metal rings are probably bigger and stronger than they need to be.  Next time they will be .045 square and be sprung a little less. Back when I was making my second set of rings, Bob Verhaeghe said that the ring gap would decrees and it looked like too much gap.  The gaps did decrease . 

I still had some time so I started to paint the flywheel and found 2 of the 5 spokes are cracked. 

Copyright 2006,  Florida Association of Model Engineers and engine builder as noted above, All rights reserved.