Throttle governed engine

[Brian Rupnow]

The engine did run with the Traxxas carb on it, but it didn't run consistently. I discovered it had a plugged gas line right where the line enters the gas tank. Even after I had cleaned out the blockage it wouldn't run consistently. Finally, I tore the engine down completely. I was really trying to avoid that, but ya do what you have to do. I decided that first order of the day was to replace the viton O-rings. I don't think they were the problem, but since I have everything apart that is what I will start with. The two old rings are on the left of the picture, the two brand new ones on the right. In case you were wondering---I hate this worse than snakes!!! I like to build an engine, tune it, run it, make a video of it, then move on to something else. This going back and conducting a post mortem on an engine which no longer runs the way I want gives me a big pain in the head. 

[Admiral_dk]

Well I can only agree that it's never any fun when your engines aren't running as they should 

I hope that you solve this soon, as we all hope to see it run the Edger .... 

Best wishes

Per

[Craig DeShong]

I feel your pain Brian.  I have a friend who has several dozen model engines that he and his Dad have built over his life span. He takes them to shows over the summer and he says it's a full time job keeping them all running properly.
 

[Brian Rupnow]

Engine has been reassembled with new rings. This complete disassembly has given me a chance to clean everything up and to get rust and crud off the fins of the cylinders. I found that the set screw holding one wrist pin in place had fallen out, but fortunately the pin hadn't drifted sideways and scored the cylinder wall. I don't use aluminum outer cylinder with a cast iron liner. I make the entire cylinder from one piece of cast iron. That way it is much less work, better heat dissipation, and all I sacrifice is a bit of pretty. Tomorrow as I reassemble things I will check valve and ignition timing. The engine is so clean and new looking now that it is rather startling.

[Brian Rupnow]

I may have found the culprit. The old rings were worn, but not to the point where the engine was losing compression, so they were probably doing their job just fine. However, as I proceed with the re-assembly, I have found that the adjuster for the intake valve on the right hand cylinder bank was way, way out of adjustment. It had backed off to the point where just the very tip of the cam was "grazing" the lifter. I had labelled the push-rods as I disassembled the engine, so they haven't been mixed up. I will reset all of the valve adjusters now.

[Brian Rupnow]

An update---I have hit the wall on this engine, for the moment. I have replaced gaskets, set and reset valve and ignition timing, replaced rings, replaced carburetors, and tested every individual part. Every member of the choir sings perfectly, but I can not get them to sing in harmony. This doesn't happen to me very often. I can't even get it to run with all of the self throttling apparatus disconnected. I haven't been able to identify anything specifically wrong with the engine, other than the fact that one valve adjuster was out by a fair bit, but even with that valve clearance readjusted, it refuses to run. When I turn the engine over by hand with the cylinder heads removed, it will put a good suction on my thumb which doesn't fade away, and gives a distinct "pop" when my thumb is removed. The gas lines are clear, and fuel will run from the hose when I remove it from the carburetor. The vent hole in the gas cap is clear. I have adequate spark at both plugs. engine spins freely with heads removed--no hard spots. Only thing left to do is remove the ignition points, starter hub, and brass gear cover so I can have a good look at the timing gears. Thank you for your patience.---Brian

[Brian Rupnow]

This is one of those one of those "unexplained mysteries" that you read about in the National Enquirer. I've got the poor old girl stripped right down to her undies now, having just removed the starter hub, ignition points, and brass gear cover. One of the things that I just discovered which doesn't affect the engine (I don't think)---I pulled up the detail drawings of both gears to see what I used to hold them to the crankshaft and camshaft---and found nothing!!!--I never added the set screws to the detail drawings back when I originally built this engine.  This is a bit strange, since I've sold half a dozen plan sets for this engine, and I have never had a call nor email asking about it. Next step will be to ensure the valve timing (valve beginning to open X number of degrees before tdc or bdc depending on which valve we're talking about). My software can let me set things exactly where they should be, degree wise, and then give me a linear distance from the top of the piston to the top of the cylinder. It doesn't appear that either gear has slipped from it's appropriate position relative to the shaft it sets on, but I will check it anyways. This is about as close to the "beginning" that you can get when doing engine forensics.

[crueby]

Insert Twilight Zone music here...    "The Engine That Shouldn't Have Run... Ever... "

[Brian Rupnow]

I have everything torn down to the bare essentials. I'm checking valve timing as we speak. Ignition cam is off the engine right now. Will reset everything as I build the engine back up.

[Craig DeShong]

Insert Twilight Zone music here...  "

you did ask.... <a href="https://www.youtube.com/watch?v=-b5aW08ivHU" target="_blank">http://www.youtube.com/watch?v=-b5aW08ivHU</a>


I worked on a Kohler engine once.... guy said it ran but didn't have any power.  Upon opening it up I found the problem.  The cam gear and lobes were built as a single casting that was drilled through and rode on a mandrel.  The casting was broken completely through between the gear and the cam lobes.  I guess the gear managed to pull the cam lobes around enough to sustain running, but not enough when under power.  One of the strangest things I've seen in  a "running" engine.

[Brian Rupnow]

This set-up lets me know exactly when the cam lobe begins to contact the lifter. I rotate the crankshaft slowly by hand in the direction it normally turns, and as soon as the cam contacts the lifter, the needle on the dial indicator moves. At this point, I measure from the top of the cylinder down to the top of the piston. My software tells me that when the piston is 0.263" from the top of the cylinder, the rotational aspect aspect of 15 degrees before top dead center has been reached. Since I am leaving approximately .010" of valve lash, that figure will closer to 2.53" before the valve begins to move.  Checking the actual distance with my Vernier caliper I measure .280"  This is well within the range of acceptable, but since I have everything apart I will loosen of the cam gear and reset it to exact numbers. All of the cam lobes are 'fixed" to the camshaft, so any change I make now will affect al of the valves in the system.

[Brian Rupnow]

Okay--Something is a little hinky. Based on the intake valve having a lead of 15 degrees before tdc, the dimension from top of cylinder down to top of piston should be 0.253" which includes the valve lash of about 0.010". I have reset the left side of the engine to agree with this,(It wasn't very far out) and that automatically sets the right bank the same. However, the exhaust valves should have a 40 degree lead before bdc, which gives a dimension from top of cylinder down to top of piston of 0.894". I measure 0.710" which means a lead of 60 degrees which is 20 degrees too much. All of the four cam lobes are Loctited to the camshaft, which is an acceptable method of cam building. I now have to check the cams to generate real numbers instead of working with theoretical numbers and see what's going on.

[Brian Rupnow]

The theoretical cam has 120 degrees of movement in the area which lifts the tappet. This translates to 240 degrees of crankshaft movement because of the 2:1 ratio between the crankshaft and camshaft. 240-180=60 degrees of movement which gets split between valve lead and valve lag. Theoretical split is 15 degrees before tdc. and 45 degrees after tdc. Real cam as measured with dial indicator has 130 degrees of  movement affecting the tappets. This translates to 260 degrees at the crankshaft. 260-180=80 degrees to be split between lead and lag. 80 -15 degree lead=65 degrees of lag. 65 degrees of lag translates to measurement from top of cylinder down to top of piston of .706" and actual measurement on engine e is 0.710". This tells me that cams have not slipped rotationally on the camshaft.

[Brian Rupnow]

Tonight everything is back together. Ignition timing has been reset, Cylinders have again been pressure tested, and gaskets are all in place, nothing leaking that I can see. Liquid dish soap has been flowed around the cylinder heads while under pressure, and we have no bubbles to contend with, which pretty well assures no leaking head gaskets. Valve lash has again been adjusted. While I had the intake manifold off I gave it the old "Blow your guts out test" just to make sure there wasn't a big blob of gunk in one of the legs blocking the flow. Did I really see anything that would have prevented the engine from firing or running?--No, not really.  Tomorrow we will try to start this thing again.

[Brian Rupnow]

Yar Bugger Billy!!! We're up and running again. What a mad thrash it's been. I tore everything down to the bare chassis, checked the valve timing, then on reassembly I reset the ignition timing. When completely reassembled, still no joy. I had spark, I had fuel, but engine wasn't firing. As a last result I unbolted the left hand cylinder head, relapped the valves and made a new head gasket. This was very encouraging. When cranked I had fire in the left hand cylinder and smoke rings coming out the stack, but still not running. Then I pulled off the right hand cylinder head and done the same thing on that bank. There was more to this than it seems, because it involved retapping a few holes and making up some more specially shortened bolts. Finally I was rewarded with a running engine. Turn up your speakers. I do some "voice over" in the video, but the engine is noisy. Now that engine is up and running, I will do some fine tuning before I put the throttle governing governor back on. the engine. The video is crappy but I will make a properly lighted and sound controlled video after the fine tuning is completed.
<a href="https://www.youtube.com/watch?v=5xVBi8Ulnic" target="_blank">http://www.youtube.com/watch?v=5xVBi8Ulnic</a>