Throttle governed engine

[Brian Rupnow]

Everything fits like the 3D model says it would. Not a lot of spare room, but a miss is as good s a mile. Tomorrow I will  make up the hardened rollers which bear against the end of the valve stems, and the axles that the rocker arms pivot on.

[Admiral_dk]

Nice progress Brian 

And I really hope you get completely on top off the problems with this solution 

Per

[Brian Rupnow]

The new cylinder heads are completely finished and assembled. Everything fits, but there isn't very much real estate left anywhere.  For those who were wondering, the compression springs are made from 0.020" wire, and are purchased.  The valves are lapped and held in place by circlips. The next move will be to remove the existing cylinder heads from the engine and install the new ones.

[Brian Rupnow]

 All of the moving components could probably have been made of aluminum. Aluminum weighs almost exactly 1/3 of what brass weighs. I was limited to brass for the bracket, because I don't have the equipment to weld or solder aluminum. Would the difference in the way the engine runs have been measurable?---Probably not, at the speed I am asking it for. The original heads were aluminum, the original rockers were steel, and the original knurled adjusters were brass. The new heads are aluminum, the new rockers are brass, and the new knurled adjusters are mild steel. The engine in it's original form ran very well, but there was always a problem on cold starts--oil would separate from the fuel and foul the sparkplugs, because they were right at the very bottom of the cylinder. I'm not reinventing the wheel with these new heads, All I'm doing is correcting what I determined was a design flaw. I haven't dismantled anything from the old heads, the design flaw only appeared when the cylinders were horizontal. The old heads may get re-used on a new engine with multiple vertical cylinders. 

[Jasonb]

Brian, you could have cut the new rocker supports from a single piece of aluminium quite easily, only really an issue if you were putting the engine into a plane model.

do wonder if the weight of your adjusters may reduce the ability to stay in contact with the rods as the speed goes up, are they really needed as the cap head screw can be turned by hand or if you are using smooth sides screws change to ones with the straight knurl.. Or simply make from 5/32" steel and put a fine knurl on the "head" and use a ball endmill in place of the hex hole.  Screwdriver slot on the top would also work if you have fat fingers. Ditto the bulk of the rocker arms.

4mm version of what I describe above

[tghs]

reducing the weight of the moving parts of the valve train might be worth doing,, making sure you are keeping free play in the valve adjustment is important to the running of a flat twin..having been a BMW motorcycle mechanic since the mid 80's, the 81-84 were the first engines to see problems with unleaded fuels, the selection of valve seat material caused valve deformation,, loss of free play,, first symptom loss of normal idle speed,, adjust valves idle would return.. changes in seat material and valve angle grind were the long term repair.. keeping proper free play at all times is very important..making sure the valve springs don't have to do more work than needed..

[Brian Rupnow]

People have been asking about the relative size the engine is that I am working on. Canadians don't use pennies anymore, so the only closest thing I could find for a visual comparison is a matchbook. In this picture, I have my adapter screwed into the sparkplug hole and 50 psi on the air hose. No leaks at the exhaust pipe nor the carb air intake. Having established that cylinder as being okay, I will now move over to the other cylinder and perform some magic over there.

[Brian Rupnow]

I had an interesting day today. I went to a heavier valve spring of .038" wire diameter. These are beefy little buggers. Too strong to compress with my thumbs and slide the locking collar into place. I had to figure out how to make a spring compressor. Honestly, I have never used any springs that are over 0.020" diameter on any of my engines. The "lift" on the cams for this engine is just a bit more than 1/16". The coin is a Canadian $2, called a "Twoney"--that name was derived form the 1$ coin issued a few years ago that had a loon on one side, so of course it immediately got named a Looney!!!

[Brian Rupnow]

Combustion chamber hasn't changed at all, other than the location of the valves and sparkplug. Biggest change of all was the shape of the rocker arms. They went from simple "straight' pieces of steel with rollers on the center to the new ones with the cantilevered rollers at the end. In test mode, with the adapter screwed into the sparkplug hole, the cylinders sealed up tight up to 50 psi. of air pressure No leakage of air out the exhaust pipe nor out of the carburetor throat, nor past the rings. The valves sealed great under "test" conditions, but engine had no (or very little) compression when cranked over. Nothing gets past the Viton o-rings, no leaky head gasket. Conclusion is that the valves aren't seating properly. They are lapped, and do seal under "test" conditions but not in normal "start the engine" mode. Normally, if I can get an engine to fire at all, the force from igniting fuel will force the steel valves against the brass seats hard enough to make a perfect seal. Tried to start it already, and there simply wasn't enough compression for the fuel to ignite. It's rather coincidental that Boomer has been talking about valve springs.--That is where I ended up going anyways as that's about the only thing left to try. Ignition and valve timing hasn't changed since the last time I had the engine running. I can push the valve off the seat, against the new spring pressure when gripping the head between my thumb and finger. It is noticeably harder to do that now, but my cams, lifters, and rollers on the rocker arms are all heat treated 01 steel. I did have to make a spring compressor, because it is very finicky work trying to get the spring compressed, the keeper in the right spot, and the c-clip on without something to compress the spring and let me work with both hands.  The push-rods are 1/8" diameter about halfway up their length, then are reduced to 1/16". I will probably make new pushrods tomorrow that are 1/8" diameter over the full length.

[Brian Rupnow]

I haven't installed the head with new springs yet. I'm ready to go, but I want to mount a 0.060" spacer under the rocker arm bracket but wife isn't up yet. This has become my morning routine. Wake up, get dressed, make a coffee, then head down to my computer and look at the forums to see what everybody else has done.---Quietly. My bandsaw is out in my main garage right under her bedroom. I am going to saw the spacer out of 1/16" plate, and the bandsaw makes a Hell of a racket. I'm putting the spacer under the bracket to raise it up 1/16" because as you can see in the picture, clearance between the adjusting bolt in the end of the rocker which adjusts the valve lash is uncomfortably close to the head of the bolts which hold the intake and exhaust flanges in place.
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[Brian Rupnow]

There is no joy in Mudville---I have no good news to report. The engine is reassembled with my new cylinder heads (the uber strong valve springs are only on one of the cylinders). With my adapter screwed into the sparkplug holes, the cylinders both hold 60 psi air pressure, with no air escaping past the valves.  I have tried to start the engine and it isn't happening. I even went so far as to set it up on my bench and drive it for half an hour to see if that would seat the valves a bit better but it didn't seem to do anything.  I am going to go out today and buy a socket and pigtail for a 12 volt bulb and wire it up through the points so I can get a really good concept of the ignition timing. I will also do one more check of the valve timing. This time I will check valve timing on both cylinders. The cams are made as four individual components and Loctited to the camshaft. I doubt very much that they have spun on the camshaft, but I will check it. I know a thousand things to check for on engines that won't run, and I've used up 998 of them. If this engine doesn't run after a final ignition and valve timing session, it's going up on the shelf. I have an idea for a new and different engine in my head that I would like to spend some cad time on, and I'm ready to move on.---Brian

[Craig DeShong]

Brian.  You’ve been working hard on this and I really feel your pain.  You need an “engine buddy” to step back and ask the right questions, like, “is it plugged in?”.  I have a good friend I can turn too when this happens to me and I can give him a visit and he usually comes across with something I hadn’t though of.  I’d be lost without him. 

I wish you well.  Start thinking “outside the box” and maybe the problem will surface.  Good luck my friend.

[Brian Rupnow]

Okay--An update. this afternoon I checked and reset the ignition timing. I even wired in a 12 volt light thru the ignition points so I could see exactly when the points opened the circuit. Stuck  a hex wrench down the sparkplug hole and turned the engine over by hand, one hand hanging onto the hex wrench which was in contact with the top of the piston and the other hand slowly turning the vaned flywheel. I didn't really like the ignition timing it was set at, so I changed the timing a bit until I was happy with it. Then I slowly turned the engine over by hand , still hanging onto the hex wrench, and got a good reading of when the intake and exhaust valves began to open. That was right, so I then moved over to the other cylinder and repeated the act. Valve timing was good on that cylinder too. So---the cams haven't slipped on the camshaft. Tried to start the engine, and it didn't start, however the right hand cylinder was puffing smoke and getting warm. The left hand cylinder was too (that's the side with the heavy valve springs) but not as much as the right cylinder. I put new fuel in the tank, although I don't really think that Naptha goes bad with age. Tomorrow I'm going to set the engine up on the bench and drive it with the electric motor, until it flies or dies. I'm not going to work on this anymore. Now, an observation::--This is fairly important. The crankshaft has bronze bushings on it, not ball bearings. There is some runout on the crankshaft, but not much. The thing is, and you'll have to believe me on this---If there is any runout AT ALL on a crankshaft, it's going to squirm as it rotates in the bushings which support it. Consequently, the bushings will be worn away on a taper on both sides of the bushing centerline. Then it is only supporting the revolving crankshaft on a thin "line of contact" in the center of the bushing, which quickly wears away. The result of this is sloppy fit between the crankshaft and bushings. This won't prevent an engine from starting, but it will clunk and clank while running, and if your ignition cam is supported on the crankshaft, the points gap will not be stable. HOWEVER---And I wouldn't have believed it if I hadn't seen it---A single race ball bearing will tolerate a small amount of squirm without damage to the bearing or the  shaft. I have found this out by my own personal experience, and will never again build an engine with bushings supporting the crankshaft. Again, on a 4 cycle engine this will not keep the engine from running.  It will screw up a 2 cycle engine because a squirming crankshaft will quickly wear out the crankshaft seals and the crankcase will no longer be "air tight". That's it folks. I'm done with this. If the engine does decide to run tomorrow, I will shout "hurray" and post a video of it, and tell you all how clever I am. If it doesn't, it will go up on the shelf and stay there.---Brian

[Jasonb]

Brian as you are not getting leaks with your adaptor in the spark plug hole but lack compression when trying to start have you checked the plugs are sealing? maybe a new copper washer as they deteriorate if you keep taking the plug in and out. Bit of soapy water around the plug as you turn the engine over may show. any leaks.

Those strong springs will just add to the load the engine needs to overcome to be able to run on it's own, The one I got going the other week has 0.4mm wire on the inlet and I will probably change that to 0.3mm when it goes back together after painting as it feels a bit too strong.

As for bearings maybe try to build a non squirming crankshaft.

[Roger B]

Some tricks I have learned:

Hold a flame over the exhaust whilst cranking the engine. If the flame can't ignite anything nor can the spark plug.

Rest the sparkplugs next to their holes whilst hand cranking the engine and see if they really spark when you think they should.

Try different sparkplugs if you can, although I can't see both of yours failing (I think that you may have tried this already)