Thumper--a 1 3/8" bore i.c. engine

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a41capt

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I just went down to my "Nut and Bolt" store and picked up a dozen Belleville washers. For those of you who haven't heard of them, they are a spring steel flat washer, which have a curve built into them---They're not really flat. In situations like I have with the new timing handle, you want it to stay wherever you set it and not move out of adjustment from engine vibration. However, you do want it to swing freely "by hand" but then remain in place. These Belleville washers are the answer. You can stack 4 of them together and put one ordinary flat washer next to the part which has the slot cut in it. They work very well to put a constant "pre-load" on the part which must be moved by hand but not by engine vibration

My 1970 Maico motorcycle clutch used stacks of Belleville washers as clutch springs. Damn near bullet proof and a positive engagement, but a real SOB to get the stacks right without having it slip or be too tough to actually pull in the lever!
 

Brian Rupnow

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Today I started and ran "Thumper" with the new ignition timing handle in place. Did it make a difference?--No, not really. I could manually adjust the timing thru a range of about 75 degrees. With the engine running under no load conditions, I couldn't really see it affecting the way the engine ran. The engine ran good, but it ran good before I added the ignition timing handle. I have one more test to make, and then I will put this thread to bed. I want to set the engine up to run my sawmill edger, and see what difference the timing handle makes when the engine is under a load. If it does make the engine run stronger I will post a video of the engine running the edger and edging boards. If it doesn't make any difference to the power under load I will let you know.
 

awake

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Brian, what RPM was the engine running as you made the adjustment? I've wondered if that affects whether a difference is noticeable.
 

Mike1

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Brian, I'm thinking that maybe heavier flywheels may help to keep the engine going and create more torque when it comes up against the timber.
I'm no expert in the mechanics of flywheels and torque just my bit of practical thinking, and I want to see your edger whipping through those planks !!
Mike1
 

bruedney

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My personal uneducated opinion is that the issue is a combination of timing and carburetion. I have read some posts on RC forums about issues using 2 stroke carbs on 4 stroke engines.
 

johwen

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Today I started and ran "Thumper" with the new ignition timing handle in place. Did it make a difference?--No, not really. I could manually adjust the timing thru a range of about 75 degrees. With the engine running under no load conditions, I couldn't really see it affecting the way the engine ran. The engine ran good, but it ran good before I added the ignition timing handle. I have one more test to make, and then I will put this thread to bed. I want to set the engine up to run my sawmill edger, and see what difference the timing handle makes when the engine is under a load. If it does make the engine run stronger I will post a video of the engine running the edger and edging boards. If it doesn't make any difference to the power under load I will let you know.
Hi Brian, John again, If you set the engine
speed at say 2000rpm with the timing in retard and then slowly advance until the engine reaches max rpm advancing beyond this point will not increase the torque, but over advancing will reduce torque. You should also adjust the mixture prior to adjusting the timing. The speed of burning the fuel will vary engine rpm also fuel mixture and timing both need to be adjusted to find the best settings. The idea is to get maximum cylinder pressure occurring at around 5degrees after TDC. Spark plug positioning can also vary the pressure front also. Central position being most likely the best or shortest distance to the extremities in the combustion chamber. In smaller engines the increments of change will be very small also. Best wishes as it is a lovely build and a great design,very compact.
John
 

awake

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My personal uneducated opinion is that the issue is a combination of timing and carburetion. I have read some posts on RC forums about issues using 2 stroke carbs on 4 stroke engines.
That's an interesting thought. I've read that a smaller-throat carburetor results in an engine that is easier to start, but will develop less power. Perhaps there is also an interaction between the throat size and the ignition timing.
 

teeleevs

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Brian, I'm thinking that maybe heavier flywheels may help to keep the engine going and create more torque when it comes up against the timber.
I'm no expert in the mechanics of flywheels and torque just my bit of practical thinking, and I want to see your edger whipping through those planks !!
Mike1
It needs a governor to do uneven loads
 

Brian Rupnow

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I have a few things to say about this engine, and immediately after I do I am going to go out into my main garage and try it one more time running the edger with the new manual ignition timing handle to see if it does make the engine run stronger or not. Firstly, I am completely blown away by the compression this engine has with the rings purchased from Debolt. Secondly, the flywheel fans do move enough air to constantly be moving air over the cylinder fins and dissipating the heat. They're not going to blow your hat off, but they are moving the air. Also, there is no measurable load imposed on the engine by these fans. (At least not with any equipment that I have). I will not be building a governor for this engine. The engine has been a complete joy to build and run, and even if it doesn't ultimately have enough power to run the edger, the engine has went together and ran easily.
 

johwen

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And that's all she wrote. Time to move on to a different project.---Brian
Just another thought Brian why not change the gearing either a smaller pulley on the engine or a larger one on the edger and run the engine at a higher speed to compensate for a slower edger may do the trick. Don't give up! cheers John.
 

Peter Twissell

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Brian, I can understand your frustration and there is a right time to step away from a project and turn to something fresh.
I have several projects running in parallel. As soon as the one I'm working on starts to feel like work, I'll switch to another. That way, every part is made with enthusiasm.
Maybe some element of a future project will provide inspiration to come back to this one.
Even so, you have built a very nice engine which runs well - no reason to expect any more.
 

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