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CFLBob

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Just an input: yesterday, I put some fuel in the tank cranked it for a while. It still doesn't run, but it's getting closer. For the first time, I noticed some popping sounds and could smell exhaust! (I thought it was funny when I got the thought out of nowhere, "hey! That smells like exhaust!")

I tried adjusting the carburetor a little, the lever that adjusts the amount of air, and there's a narrow zone in which that happens. I didn't think of trying the low speed idle adjustment.

Still not running but the closest I've been so far.
 

minh-thanh

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I noticed some popping sounds and could smell exhaust!
It's a signal of compression and burning of fuel
If that's my engine, I'm sure it will run
Just adjust fuel, ignition timing or camshaft or or intake valve springs
 

Brian Rupnow

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Bob--What can I do to help? I've been where you are before, and it is terribly frustrating. Some things you can check---Take the sparkplug out and push a long piece of wire down the sparkplug hole. Set the sparkplug out on the engine block and turn the engine by hand with the ignition on. The spark should happen when the piston is about 1/8" before top dead center. (That's what the wire is for, to let you know where the piston is.). If you have run the engine in with an electric motor to loosen it up, then with the sparkplug in place give it a spin by hand. It should bounce back when it comes up on the compression stroke. If it doesn't bounce back, then either your valves aren't sealing or your rings aren't sealing. Take the sparkplug out, squirt some thirty weight oil into the sparkplug hole, then put the sparkplug back in. Spin it again by hand. If it bounces back now, then you know your rings aren't sealing. If it still doesn't bounce back, then your valves aren't sealing. Unhook the gas line from the carburetor and blow on it. You should hear it bubbling in the gas tank. (Make sure that the tank has fuel in it.) Use the factory pre-sets on the carburetor if you are running an after-market carb. About 80% of small engines that won't run can be traced directly to the valves not sealing. As I said before, sacrifice a spark-plug by breaking the porcelain out of it and solder a tube of approximately 0.175" outside diameter into the sparkplug. Screw the modified spark-plug back into place and put an airline on it--give it about 20 to 30 psi (block the crankshaft so it can't turn unexpectedly). When the piston is at top dead center on the compression stroke, there shouldn't be any air coming out the carburetor nor out of the exhaust. Make sure when you are trying to start it that the engine is turning at least about 300 rpm.---Brian
 

CFLBob

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Bob--What can I do to help? I've been where you are before, and it is terribly frustrating. Some things you can check---Take the sparkplug out and push a long piece of wire down the sparkplug hole. Set the sparkplug out on the engine block and turn the engine by hand with the ignition on. The spark should happen when the piston is about 1/8" before top dead center. (That's what the wire is for, to let you know where the piston is.). If you have run the engine in with an electric motor to loosen it up, then with the sparkplug in place give it a spin by hand. It should bounce back when it comes up on the compression stroke. If it doesn't bounce back, then either your valves aren't sealing or your rings aren't sealing. Take the sparkplug out, squirt some thirty weight oil into the sparkplug hole, then put the sparkplug back in. Spin it again by hand. If it bounces back now, then you know your rings aren't sealing. If it still doesn't bounce back, then your valves aren't sealing. Unhook the gas line from the carburetor and blow on it. You should hear it bubbling in the gas tank. (Make sure that the tank has fuel in it.) Use the factory pre-sets on the carburetor if you are running an after-market carb. About 80% of small engines that won't run can be traced directly to the valves not sealing. As I said before, sacrifice a spark-plug by breaking the porcelain out of it and solder a tube of approximately 0.175" outside diameter into the sparkplug. Screw the modified spark-plug back into place and put an airline on it--give it about 20 to 30 psi (block the crankshaft so it can't turn unexpectedly). When the piston is at top dead center on the compression stroke, there shouldn't be any air coming out the carburetor nor out of the exhaust. Make sure when you are trying to start it that the engine is turning at least about 300 rpm.---Brian
My absence for the last week was due to another project imposing itself. I had been saying for quite a while that when I laid out my shop I made some mistakes and wanted to fix them. You know that made up stuff about walking 10,000 steps in a day? I'd do that in a day in the shop going back and forth between the mill or whatever I was working on to get a drill bit or some tool. I told myself I needed to add some bigger shelves and move things to be more centrally located.

Over the holidays and early January, my wife and I talked and planned and then I spent the last week, cleaning and rearranging. Do you remember these puzzles they had 50 years ago where you're supposed to put the numbers in order? You'd have to move a lot of things to get to the one you really wanted to move.
NumberPuzzle.jpg

That's like rearranging the shop. I guess a more modern version would be Tetris with real things.

The good news is I think I'm done or close enough to done rearranging. I was very encouraged by the ignition pops I was getting a week ago. It happened over a narrow range of the lever on the carburetor. I was going to experiment with the idle speed adjustment and see if anything made the pops more consistent over a wider range of movement of that lever.

Brian, I was thinking about the strength of the intake valve spring and calculated that normal air pressure of 14.7 PSI would cause about 10 ounces of force if there was a vacuum on the cylinder side of the intake valve. I measured how much force it takes on the valve to open it and that was about 5 ounces. That tells me if the piston pulls even half the air pressure the spring would open. I don't know if that's good or bad. Would it be better if it took half that force to open that valve? More? Less?

I don't have access to the compressor right now due to rearranging the shop. Not sure how long it will take to be able to run your tests.

Bob if you are close to Sarasota bring Webster be glad to help get her running Bill Burnett
Thanks, Bill, but I'm in Melbourne, over near the Kennedy Space Center. I think that puts us about 200 miles apart.
 

CFLBob

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Thanks, Ray. The same program says you're only 120 miles from me, so two hours instead of three.

I'll file this away.
 

werowance

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Bob, ill say you will not have nominal compression or vacume until it actually runs for a bit and the rings bed in. i know this doesnt help with the how do you get it started but just to point out that the spring preasure cant be calculated like that until after everything is perfect. i also see that you are saying even at half preasure it should be opening. my only reason to point this out is so you dont assume bad things or bad machining or something based on math because the math cant compensate for break in under fire. just need barely enough to get it to fire and then it will get much better. - and i know i said i would shut up a few posts back lol. so take it with a grain of salt and ill shut up again lol. best of luck.
 

coulsea

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Bob, ill say you will not have nominal compression or vacume until it actually runs for a bit and the rings bed in. i know this doesnt help with the how do you get it started but just to point out that the spring preasure cant be calculated like that until after everything is perfect. i also see that you are saying even at half preasure it should be opening. my only reason to point this out is so you dont assume bad things or bad machining or something based on math because the math cant compensate for break in under fire. just need barely enough to get it to fire and then it will get much better. - and i know i said i would shut up a few posts back lol. so take it with a grain of salt and ill shut up again lol. best of luck.
I Agree the best way to seat valves and get rid of tight spots is under fire. it sounds like you were nearly there, put the throttle in the middle of the range that works and adjust the mixture while it is banging away. 10 to 15 second burst on the drill and you will get there. the mixture will need fiddling with as it runs in and even on different days, richer to start and lean off as it warms.
There are lots of annoying things that may happen like the timing slipping or trying to start it with a flat battery or no fuel, makes it all the more rewarding when it does run for the first time.
 

CFLBob

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Bob, ill say you will not have nominal compression or vacume until it actually runs for a bit and the rings bed in. i know this doesnt help with the how do you get it started but just to point out that the spring preasure cant be calculated like that until after everything is perfect. i also see that you are saying even at half preasure it should be opening. my only reason to point this out is so you dont assume bad things or bad machining or something based on math because the math cant compensate for break in under fire. just need barely enough to get it to fire and then it will get much better. - and i know i said i would shut up a few posts back lol. so take it with a grain of salt and ill shut up again lol. best of luck.
Don't shut up. Until I post my video of it running, I'm trying to soak in all the advise I can get. I don't have any answers on what's wrong, but I've been suspecting the fit between the piston and cylinder for a long time.

I didn't even get to spend time in the shop yesterday - more house stuff. After 5 days of rearranging things, now I can't find stuff that I put away.
 

CFLBob

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Take the sparkplug out and push a long piece of wire down the sparkplug hole. Set the sparkplug out on the engine block and turn the engine by hand with the ignition on. The spark should happen when the piston is about 1/8" before top dead center.
The spark appeared to be a bit over 1/8". I measured about 5/32 or maybe a bit less; 0.155 is a good number. The marks are a bit tricky to get high accuracy on. Anyway, I marked a .125 mark on the other end of the wire and moved the cam a little a bit until the spark happened closer to there. All I can say is it's closer.

No difference. I get pops and a faint smell of both exhaust and fuel. The cylinder gets warm to the touch, the end without fins feels warmer than the fins and cylinder head, but I know it's trying. It won't keep running. I can feel suction if I put my finger over the intake on the carburetor. It's not super strong, but easily felt. If I mess with the idle mixture, the position of the throttle may make move, but the end result is the same.

Take the sparkplug out, squirt some thirty weight oil into the sparkplug hole, then put the sparkplug back in. Spin it again by hand. If it bounces back now, then you know your rings aren't sealing.
Next thing to do. I did it, but forgot the 30W oil.
 

minh-thanh

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I usually set the ignition at 15 degrees before TDC, then, I start the engine, if the engine seems to want to run, I will adjust the cam lobe a few degrees (in reverse and the same direction of rotation) If the change looks better I will adjust a few more degrees
With intake valve springs: if it is too pressed or the valve body and the valve direction is not smooth, it will affect the intake of fuel as well as difficult to adjust the needle.
with my engine: the intake valve spring only works to keep the valve in the closed position, and try to make the force of the spring as light as possible
Check the valve body and valve guide are still moving smoothly after starts engine?
 
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CFLBob

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@Brian Rupnow - would you look at this video?

This is the first test you mention. I snap it into compression and the piston bounces back. 13 whole seconds, a few demos.


No SAE 30 oil in there, just the piston, everything as it is while I'm trying to start the engine. Is that enough?
 
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stevehuckss396

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seems a little tight. I would work on it until the crankshaft turns a little more free. Maybe the crank bushings are too tight. Maybe the ring is too tight in the cylinder. Hard to say but from the video it appears to want to freeze up. Does it turn better when the sparkplug is removed?
 

Brian Rupnow

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That looks okay to me. It's bound to be a bit stiff, since it's brand new. Take the sparkplug out, put a 6" pulley on it, oil everything up good, and then drive it for half an hour with an electric motor to take any stiffness out of it.---Brian
 

CFLBob

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I think I've run it with my battery powered drill (600 RPM?) for 45 minutes. Maybe an hour.

I did some experiments while I was out there. Raised my fuel tank a half inch and it started blowing oil and fuel onto everything. I put down the starter and lowered the tank to the point that all the fuel ran back into the tank. Then put the tank back on the holder and I could see the fuel getting sucked into the carburetor leading to the popping starting back up. The carb. kept twisting in the intake slice so I put on some LocTite 680. It will sit overnight before I try anything else.

Steve - there have been times I was concerned it was too loose.
 

werowance

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Bob, if thats compression kick back as per the video then ill have to say you have more than me.
i cant say for sure but your symptoms seem simliar to mine at first. which i had a ton of problems

mainly i timed the spark cam with the crank going in the wrong direction. that said i almost timed my valve timing in the wrong direction. i would rotate the base arround and then lose my orientation and on top of that i had it in my head that the engine could run either direction (wrong) so at any rate that was my big deal. in other words when i did gear valve timing i was looking on one side then on spark timing i was looking at the other side but when i spun the engine arroung each time i rotated the flywheel in the wrong direction. dont ask me why but when i spun it arroung i figured i needed to spin the wheel the oposite direction.

all that said. if the engine will spin much free'er without the plug assuming the plug was inplace in your test video shows then you have good enough compression. if that test video was without the plug then yeah its got some drag but should start and run badly at first with that much drag (assuming video was with plug) hard to tell watching on my cell wthout glasses on.
 

minh-thanh

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As stevehuckss396 and werowance said : seems a bit tight

I feel your engine seems a bit tight
but the important issue is that your engine have pretty good compression .
Again, with that good compression, I'm sure the engine will run
Let's make it smooth
 

CFLBob

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Bob, if thats compression kick back as per the video then ill have to say you have more than me.
i cant say for sure but your symptoms seem simliar to mine at first. which i had a ton of problems

mainly i timed the spark cam with the crank going in the wrong direction. that said i almost timed my valve timing in the wrong direction. i would rotate the base arround and then lose my orientation and on top of that i had it in my head that the engine could run either direction (wrong) so at any rate that was my big deal. in other words when i did gear valve timing i was looking on one side then on spark timing i was looking at the other side but when i spun the engine arroung each time i rotated the flywheel in the wrong direction. dont ask me why but when i spun it arroung i figured i needed to spin the wheel the oposite direction.

all that said. if the engine will spin much free'er without the plug assuming the plug was inplace in your test video shows then you have good enough compression. if that test video was without the plug then yeah its got some drag but should start and run badly at first with that much drag (assuming video was with plug) hard to tell watching on my cell wthout glasses on.
Just so everyone is on the same page, and new people come along to read, the spark plug is in the engine in that video.

I think I've got the timing right, but now I'll check it again.
 

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Hi Bob, just and odd point. It looked to me that you need to remove the sharp corners on the flywheel to stop it shaving the skin off your thumb and finger?
Maybe an arrangement to use you power drill for a starter is better anyway. But it looks like good compression to me. If you can make an adapter to fit in the plug hole and measure pressure, it should be a runner anywhere between 4 bar and 9 bar, but mixture varies with cmpression. Too rich wets the plug and won't start, too lean won't fire and run.
Enjoy!
K2
 

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