21 April 2016: Well,
after a couple of years and a couple of other projects have been done,
I've decided to get back to this one. As I said, poppet valves are the
next modification. Slide valve engines, as I have subsequently
learned, are always very low compression, developing around 40 PSI of
compression pressure so as to not cause the slide valves to leak when
the engine fires. This greatly impacts the performance of the engines,
makes them a maintenance headache and is a major reason why slide
valves were abandoned early-on.
What I have in mind is to remove
all of the slide valve components and replace the pressure plate with a
cylinder head that has caged poppet valves running off of the
eccentrics. I've come-up with what I think is a workable method of
converting the slow motion of the eccentrics to the fast motion of a
cam while retaining proper duration and lift. We'll see how it works.
I will probably have to raise the compression ratio but will hold-off
on this until I have the engine running. I think it will run best at
with about 80-100 PSI of compression.
Here's what I've removed.
boxed-up the take-off parts in case I decide to re-visit the slide
valves. I may retain the propane mixer, depending on how I feel about
gaseous fuel when I get to that point.
the scrap for the head.
Roughing-out the head.
head is to be made out of steel, 1-1/2" thick, sized to fit in place of
the slide valve pressure plate. It's good that the piece of steel
scrap I had on the shelf was about 0.050" thicker than 1-1/2" because
it took all of that to clean it up at size. Even then, on the opposite
of the "business" side of the head, it still shows some rust pits.
The head, sized.
The head, partially done.
you can see in the photo above, there are some irregularities in the
surface finish of the head blank but, I can't measure them and they
occurred because the cutter must have picked up some embedded rust
particles. In any case, they are unimportant to the sealing of the
head with the base plate of the engine. As you can see in the
right-hand photo above, I have machined a 0.010" deep circular ring
around each of the ports to the combustion chamber. I will make a
couple of gaskets out of 0.018" high-strength gasket material and will
cement them in place. Because of their small surface area, I think
they will seal fine even with only the four 1/4-20 studs for hold-down.
as you can see, the ports connect with the pockets for the valve cages.
Next-up is some more CAD work on the cages and then I will start on
them. I leave making the valves and their actuators until after I've
thought about it a bit more.
22 April 2016: The
whole day was spent working on the valve cages and I'm not done yet.
There's more to them that meets the eye. They have to be
accurately fit to the head and all the internal dimensions need to be
23 April 2016: Some
more got done today. The valve cages are done except for the
ports in their sides. That will wait until I have them mounted in
the head. At that time, I'll machine the ports all the way
through the head and the walls of the cages and drill and tap the
flange screw holes. Doing it that way insures that the ports will
The valves are also done although I haven't lapped
them. I did apply Sharpie marker to the faces and seats and gave
them a twirl in their seats. Initially, they look like they'll
seat perfectly. I await Mister Murphy........
Valve cages and valves.
so you know, I made the valves in my usual way. The heads are
gray cast iron. The stems are 0.125" drill rod. The heads
are drilled with a #31 drill (0.120"). The ends of the stems
where they go through the heads are turned just enough for a light
press fit in the heads. Then, the tops are peined over to secure
the head to the stem. The guides (integral with the cages) were
drilled #31 and reamed with a 0.125" reamer. The fit was pretty
snug so I used some very fine lapping compound to give a little
clearance. They're still a little stiff but I can always lap them
some more if they have a tendency to stick.
The valve springs
I'm going to use are out of a couple of empty hand lotion pumps.
They are fairly stiff for the size of the valves so they ought to
As you can see, the cages are made in two pieces.
The cages are a light slip fit in the head and the mounting
flanges are a 0.0015" interference press fit onto
the cage. I also used Loktite for insurance but am not really
sure that's going to be sturdy enough. If they slip, I can always
pull 'em out and tack weld them together underneath, where it doesn't
I'd try to explain how the valves will work but, if I do,
I'll probably botch it and leave you confused I suppose you'll
probably figure it out from the photos as I go along.
24 April 2016: I got the intake and exhaust ports drilled into the head.
Drilling intake port.
I said before, it was done with the appropriate valve cage installed so
the ports would line-up. I used the Dremel to clean up the ports
in the cages, feathering edges, etc., to help smooth the flow.
Then, the valve keepers were made and the valves lapped.
Valve keepers, springs and one installed in the cage.
was a real pain to get the keepers set on the valve stems due to the
location of said parts. After the proper amount of swearing, the
job was done. The cages were installed in the head and the head
installed on the engine.
Head on engine.
Note that I kept the studs that were used on the slide valve version in case I want to go back to it.
getting it all bolted down, I turned the engine expecting compression.
No such luck. Because the valves seemed to lap in so
easily, I thought I would be in luck. Not so! Both valves
leak so they have to be removed and worked-over again.
I know it looks weird but the valve mechanism will make sense once you see my cunning plan made into hardware.
28 April 2016: The last few days
have been taken up with some fiddly stuff. The cam followers need
to be a very nice slip fit in the cages and this took a lot of time to
The cam follower parts.
The cam followers in the engine.
rollers are actually ball bearings out of a defunct hard drive.
The spacers are brass 8-32 washers that have been bored out to
1/4". The O.D.'s of the spacers had to have 0.030" taken off so
the rollers contact the cams instesd of the spacers. I figure the
bearing pins are low-stress components so I made them out of leaded
steel. One end is threaded 1/4-28 and that is how they are
The next thing is the linear cams and the cam guides.
After I get these parts made, you will be able to see how it all
works. After that, all that is left is the pullrods and timing.
29 April 2016: The cams are done as well as the linkage to the eccentrics.
The cams with the pullrod yokes installed. One cam with rod and eccentric yoke attached.
think you will see that I made a slight boo-boo on the cams. Note
the "notch" just as the rise starts. When I eyeballed the
vertical location of the cutter, I did it wrong. It was too low
and I didn't see the goof until after the cut was done. They both
ended-up like that because I machined them while laid together.
It will make no practical difference because the bearing that is used
as the follower roller is 1/4" in diameter and it doesn't fall into the
Cams connected to eccentrics, ready for their guides.
allowed plenth of adjustment in the pullrods to allow a lot of latitude
in cam timing and duration. Interestingly, a quick check of the
timing without changing the slide valve settings on the eccentrics
gives something very close to workable. I'm sure there's some
kind of relationship between the slide valves and poppet valves so it's
not really surprising it's close.
Tomorrow, I will make the cam
guides and their mountings. I may even get it all together so I
can accurately tram the valves.
30 April 2016: Well,
I didn't get as much done today as I thought I would. The slider
blocks for the cams took a lot of time and I only got one done.
There was a lot of fiddling around and I had to rotate the
clevises on the cam ends of the pull rods to allow another axis for
motion to account for the motion of the eccentrics.
Cam and cam guide parts.
I fitted it up to the engine, I found that I had to reverse the guide.
You can see the difference between the photo above and the two
below. When I put it all together with the attendant fitting and filing,
I found out that the cam slope is too steep and the cam followers bind.
Exhaust valve open.
I will stick the cams back into the mill and increase the angle from 20
degrees off the vertical plane of the cam motion to 40 degrees to see
if I can get the follower to move without binding. This will
necessarily decrease lift and slow the opening of the valves but, since
I originally had the lift set to 0.250", much more than I calculated
I'd need, I will have about 0.125" lift which should be adequate.
After all, this isn't a racing engine!
1 May 2016: The
project seems to be back on track. I changed the "cam" angle from
20 degrees to 45 degrees and the valves now work smoothly. I then
proceeded to machine the parts for the intake valve cam guide and
The new cam angle (bottom). Both valves installed and working.
I didn't get real fancy with a degree tape on a flywheel but simply adjusted the openings and duration until the exhaust opens at a few degrees before BDC and closes at TDC and the intake
opens at TDC and closes at BDC. I spun the crank and it does have
compression, although it's kinda puny due to a dry cylinder.
I then proceeded to make the intake and exhaust flanges.
Intake and exhaust flanges and propane mixer.
everything goes well tomorrow, I may attempt to smoke-up the shop but I
can never tell when a simple thing becomes a rats nest of
2 May 2016: Today
was a good dary here at Hoyt-Clagwell & Company. First off, I
got the intake and exhaust flanges finished, got the exhaust pipe done
and made the carburetor adapter for between the throttle body of the
carburetor and the flange.
parts ready for assembly.
On the engine, governor hooked-up.
the exhaust and intake plumbing was done, I figured out how to connect
the governor and decided to see if it would run. Hooked up the
propane and ignition, oiled everything up and cranked. And
cranked. And cranked. Checked the ignition timing and it
was right on TDC. Cranked some more and worked up a sweat.
My only reward was a few feeble pops out of the carburetor.
that the intake valve needed a little more lapping, I took the intake
cam and guide apart, removed the cage and re-lapped the valve.
When I put it back together, I found that the cam was binding a
little so I made the appropriate adjustment. Cranked some more
with the same result. In addition, suddenly the piston blowby got
really bad. I stuck my finger down in the cylinder and found that
the oil was really dirty and thin so I wiped it out and oiled the heck
out of it. A little more cranking and the blowby suddenly
stopped. I think a ring stuck and cleaning out and adding more
oil unstuck it.
I cranked some more and got the same result, just weak pops out of the carburetor.
sat back and "thunk" on it some. The "AA-HAH" moment finally
arrived and another timing check showed that the valves were trammed
correctly and the ignition oas set to TDC but the ignition was at TDC
on the overlap stroke! That wasn't hard to fix. I just
loosened the setscrews on the eccentrics (one at a time) and, while
holding the eccentric, turned the engine exactly one turn then
re-tightened the setscrews. A slight tweak of the valve timing
and it was time to try again.
This time, my cranking was
rewarded with smoke! A little tweak of timing and mixture and it
settled down and ran fine. Had I been in a Victorian frame of
mind, I would have stood, raised my hand with forefinger extended
and shouted, EUREKA! or EXCELSIOR!but, being the staid individual I am, I just grunted a happy Humpf!
are a few tweaks I'd like to do but am not in a hurry. One thing
that would help would be to increase the compression. With the
slide valves, the engine had to have compression below 50PSI to keep
the valves from leaking. Increasing the compression would involve
either making a new piston with a longer compression distance or making
a longer connecting rod. I sort of tend toward making a longer
rod but that's not a priority right now.
Also, I should modify
the ignition timer so I can get more advance. Right now, with it
advanced to the stop, it's only firing a little before TDC. A few
more degrees of lead would help but, right now, I ain't complainin'.
the next few days, I will take it outside and let it run for a few
hours to finish seating the rings. With the slide valves, it
would only run until it got warm, then the valves would either bind-up
or leak so I never got over about 20 minutes of running before it would
quit. With the poppet valves, that shouldn't be a problem.
I may also make a YouTube video of it running so the valve action can be better understood.
5 May 2016: Yesterday,
I ran the engine for almost two hours with no issues aside from a pesky
occasional misfire. That will get sorted out in due time.
Chugging right along.
Here's the latest video of the engine running.
I can play with it for a while. Mixture adjustments will correct
the misfire for a while but
it still misfires about twice a minute. I think it could be made
worse by the governor, which is hunting a bit. At the present
time, I've got it set to the most sensitive setting on the throttle arm
so it hunts slightly to vary the load which should help seat
the piston rings. I think the throttle changes are upsetting the