Author Topic: Design and build side shaft hit and miss engine from bar stock  (Read 22632 times)

Offline gbritnell

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #420 on: February 15, 2019, 05:38:58 PM »
Brian,
I know that small engines can be very frustrating at times but yours is certainly a head scratcher. With all elements, compression, fuel and spark seemingly good I have one last idea.
When you're cranking the engine over with the drill and it's kind of firing stop after a short while and pull the spark plug. If the plug is somewhat wet or sooty that would mean the fuel isn't burning well enough to get a complete burn, thus producing full power per charge cycle. If this is the case my thought is the combustion chamber is so convoluted with the valve plugs protruding down that maybe, just maybe they are restricting a complete burn of the fuel.
This is my last thought, I have no more.
gbritnell
Talent unshared is talent wasted.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #421 on: February 15, 2019, 06:01:25 PM »
George--Like you, I have no clear answer for this. I have pulled the plug, and the plug although not bone dry, isn't fouled with fuel either. I have adjusted ignition timing and valve timing until there is nowhere left to adjust them to that hasn't been tried at least once. The engine bounces back quite readily against compression if you attempt to spin the flywheels by hand. The only issue that I am able to come up with is that the "burn chamber" is quite convoluted and quite large. This goes along with the apparent lack of power. When the engine is firing along with the drill, and I remove the drill, the engine keeps on firing for 10 to 15 seconds and just gradually dies away, giving all the appearances of just not enough power to keep things rolling. I'm working on a new cylinder head right now with a much smaller burn chamber.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #422 on: February 15, 2019, 08:10:43 PM »
Hang on boys, here we go again. Third times a charm, right?

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #423 on: February 16, 2019, 03:03:46 PM »
Before I go ahead and scrounge the valve cages and valves out of the previous head and put them into the new head, I thought a "comparison shot" of the burn chamber in the two heads would be interesting. The new cylinder "burn chamber" is roughly 1/3 of the size of the old "burn chamber".

Online crueby

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #424 on: February 16, 2019, 03:47:26 PM »
That is quite a big difference!
 :popcorn: :popcorn: :popcorn:

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #425 on: February 16, 2019, 11:00:26 PM »
For what I'm doing, it isn't imperative that I know the cubic inch displacement of the burn chamber in the head. I do know "smaller" from "bigger" without having to do a lot of measuring. The burn chamber in this new head is approximately 2/3 smaller than that of the previous head. And---On my engine the piston stops 0.176" short of the end of the cylinder when it is at top dead center. I have drilled and tapped the top of the piston so that if necessary I can add spacers to the end of it, up to a total of 0.170" in order to play with compression ratios. My whole family (all eleven of us) went out to a nice restaurant in Alliston this afternoon to celebrate oldest granddaughters 15th birthday and her younger brothers 8th birthday. Much cake was eaten and much fun was had. Then I came home, had my old mans nap for an hour, then finished the new cylinder head and pressed/loctited in the valve assemblies. This was a rather nasty experience, trying to get Loctite on the cages but not on the valves themselves. After everything was pressed into place I cleaned up the valve faces  with Q-tips, and put the entire head in my mill vice with enough pressure to raise the valve faces away from  the seats , and it can set up overnight. These valves were sealing very well against the seats in the previous head, and it is my fondest hope that they will seal as well in this new head. If not, I can take the springs and keepers off, grip the shank of the valve in my small hand chuck, and lap them a bit more.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #426 on: February 17, 2019, 05:52:41 PM »
This is a diagnostic tool I have been meaning to build for some time. The metal piece of sparkplug can be whatever fits your particular engine.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #427 on: February 17, 2019, 11:03:18 PM »
Some days you eat the bear, some days the bear eats you. I did finish the new head and put it on the engine. Everything fits, but no compression. So--I did make the new screw into the sparkplug hole compression tester. Put some air on it, and I had air leaks everywhere. I had attached a 1" diameter slug of aluminum to the top of the piston in the previous head incarnation, but it was too long for the newest head, so I took it off and made a new one  which was only 0.170" long---worked fine as I have 0.176" from head of piston to end of cylinder at top dead center. Will pull the head off to see what the heck is going on. Think I'll go up north tomorrow and see my mother. She is 98 years old and not doing too well right now.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #428 on: February 18, 2019, 10:22:29 PM »
Today is the first time in two months that I haven't been dying from lower back pain.--I didn't stand for hours at the lathe or mill today. What a strange coincidence!!! Instead goodwife and I made the 200Km trip up north to see my 89 year old aunt and my 98 year old mother. Aunty is just a bright and sparkling as she ever was. Mom---Well, mom isn't doing too well. She did know me and Aunty, wasn't real sure about goodwife until I reminded her. She isn't in any pain, but is a bit befuddled. She is very well cared for in the seniors home where she lives. Tomorrow I will pull the new cylinder head off the engine (Only four bolts to remove) and start chasing down air leaks. The valve and cage assemblies weren't really a hard press fit into the new cylinder, so I doubt that I have distorted anything. I may get out my jar of #600 compound and lap them both a bit. Due to the nature of this cylinder head, I can't get the valves out again, but I can access the valve stems and get my finger chuck on them to lap them into the seats a bit. There could be some Loctite on the valve faces or seats.--It was messy getting the loctited valve assemblies into the head. Nothing is stuck, that has to move. The valves sealed tighter than a ducks butt in the previous Frankenhead, so nothing should really have changed.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #429 on: February 19, 2019, 02:14:58 PM »
Just so you can see what I'm dealing with---I pulled the cylinder head off this morning, took off the valve springs and retainers, and lapped both valves, first with 350 grit, then again with 600 grit. You can see the dull ring around one of the valves which is the actual contact surface that touches the valve seat. Now, using the old "blow your guts out test",if I hold the exhaust valve closed and blow in the exhaust pipe, it is completely air-tight--no air gets past the valve. If I hold the intake valve closed and blow into the carburetor air inlet, again things are absolutely air-tight. I even called my tool shop this morning and asked them about ordering a new finger chuck for me.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #430 on: February 19, 2019, 03:23:56 PM »
Head is back on engine. Good compression. Same old, same old, fires just great with drill, dies away when drill is removed. I'm running out of things to try here. Last resort is a different carburetor.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #431 on: February 19, 2019, 05:16:26 PM »
Okay--Here we go. First run with third head design on it. This has not been an easy engine. I am having a difficult time getting "sustained runs". This video truly is the first run that lasted longer than 20 seconds. It ran for about 5 minutes before slowing down and stopping. In this video the hit and miss is not hooked up yet. I have to get the engine to run more predictably and constantly before worrying to much about hitting and missing.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #432 on: February 19, 2019, 08:15:31 PM »
After a LOT of investigating, remeasuring everything, I found that the exhaust cam had only .094" of lift, not the 0.156" that is called for. The previous video shows the engine running with the bad cam, but I simply couldn't get the repeatability and consistency I need. Once I switched to a cam with the required lift, everything settled right down and now I can run the engine until I shut it off with the switch. Jeez, what a struggle. I don't know how I made the bad cam--must have miss-measured is all I can think of. Tomorrow I will reconnect the hit and miss mechanism. This is a huge relief, finding out what was wrong. Ringo--Each engine is different, and even without a throttle each engine will find it's own "happy rpm" to run at. You can speed it up or slow it down (some) by adjusting the needle valve, but ultimately you want to find at what rpm the engine is happiest and leave the needle valve in that position when you hook up the hit and miss mechanism. Some engines will run in an acceptable rpm range without a throttle, while some will spiral completely out of control, scaring you half to death and have you grabbing for the shut off switch. I am running on a temporary gas tank right now, so I have to switch back to the proper tank and anti-backflow valve and make sure everything still operates correctly.

Online crueby

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #433 on: February 19, 2019, 08:50:22 PM »
Glad you found the issue, gotta be great to have it running well!   :ThumbsUp:

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #434 on: February 19, 2019, 10:05:03 PM »
And here we are---correct exhaust cam, third and final cylinder head, and using the original base mounted gas tank and anti-backflow valve.