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

[Brian Rupnow]

dsage-I agree with everything you have said.---But---Right now I'm dealing in "absolutes". The engine is finished, and I have had it running. Not great, not slowly, but running on it's own for protracted periods of time. The timing was set to "By guess or by God". Now I have brought the engine back into my workshop, and set the timing "scientifically". As soon as I get it to run smoothly, I will put up a video (somehow) and then if I want to mess around with timing I will design in a timing plate that lets me play with the timing while the engine is running.---Brian

 

[Brian Rupnow]

I must have done something right. I finished my fine tuning on Thumper, and was able to upload a video of it running. Youtube seems to be working okay for me now. There may be more videos of Thumper driving one of my mechanisms, but for now here is a video of Thumper by itself. thank you to all who have followed this build.---Brian

 

[CFLBob]

Congratulations, Brian! Nice looking little engine.

 

[dsage]

Very nice Brian. Congratulations. I don't hear any missing or mis-behaviour. It runs very smooth and about the right speed I'd say.
Not much more to do really.

Thanks for keeping us all tuned in.

 

[awake]

Brian, that sounds great! I look forward to more videos.

 

[awake]

Andy (awake)
Would you mind telling us what kind of carburetor and the engine you were setting the timing on?
Also, about how slow of RPM was you able to get it to Idle?

Bill, this was my "Steel Webster" on which I am slowly catching up the build log here on the forum - but I haven't gotten to the carburetor yet on the log. It is a slightly modified "Chuck Fellows" carburetor - pretty simple, but also seems to work quite reliably, at least in that an absolute newbie (me) got the engine running with it shortly after getting everything assembled. Since then I have come to the conclusion that I was at least a bit lucky - my needle and throttle settings were close enough to let it start by hand, as I had not yet made an adapter to allow starting with a drill.

In terms of RPM, the slowest I've had the Webster running is around 900 rpm, but it is much happier at 1000. Top speed that I've run it is around 3000, but I have not tried to run it very long at that speed - worried about bits flying off!

 

[a41capt]

That’s another great running engine Brian, congratulations!

John

 

[fabricator]

Brian, have you checked your messages lately? I'd like to order plans for Thumper.

 

[Brian Rupnow]

I have a number of requests for plan sets. Tomorrow I will open each drawing and save it as a pdf file so that no special software is needed to open and print the drawings. This will take a couple of hours, as there are 60 drawings and some of them are multiple sheets. I charge $25 Canadian funds, payable to Paypal. If you send money to [email protected] at Paypal, they will notify me and I will send you a zip file with all of the part and assembly drawings. Please specify that it is the drawing set for "Thumper".---Brian Rupnow

 

[fabricator]

I have a number of requests for plan sets. Tomorrow I will open each drawing and save it as a pdf file so that no special software is needed to open and print the drawings. This will take a couple of hours, as there are 60 drawings and some of them are multiple sheets. I charge $25 Canadian funds, payable to Paypal. If you send money to [email protected] at Paypal, they will notify me and I will send you a zip file with all of the part and assembly drawings. Please specify that it is the drawing set for "Thumper".---Brian Rupnow

Will do, no real rush.

 

[teeleevs]

Okay---I've conducted a poll. Art says 14 degrees. I thought it was 10 degrees. Three small engine shops I called answered 28 to 30 degrees, one guy was very certain that on single cylinder engines with no mechanical advance it was 23 degrees, and a third shop owner said he always set for 25 degrees before top dead center. Unless somebody can offer me up a better solution, i'm going to set my ignition timing up to fire 15 degrees before top dead center.

 

[teeleevs]

Okay---I've conducted a poll. Art says 14 degrees. I thought it was 10 degrees. Three small engine shops I called answered 28 to 30 degrees, one guy was very certain that on single cylinder engines with no mechanical advance it was 23 degrees, and a third shop owner said he always set for 25 degrees before top dead center. Unless somebody can offer me up a better solution, i'm going to set my ignition timing up to fire 15 degrees before top dead center.

Brian, I tried to send a short video of my model Fairbanks Morse powered railway trolley (but was unsuccessful ) which I could easily start at 15 degrees by flicking it over with my fingers but I had to advance it much more than that to get it to run properly so then I needed to fit a rope start. How can I email such videos? It works hard and I ride it around the model railway track.

 

[Brian Rupnow]

Post the video on Youtube. Then copy the url at the top of the screen while the video is playing and send it to me.----Brian

 

[johwen]

Quick question--What degree of ignition advance do you guys use on single cylinder four cycle engines? I have always set my ignitions up for 10 degrees advance. I am into fine tuning on this engine, and I'm curious. I tried to google it and got 4 billion answers and non of them really answered what I was trying to ask.

Hi Brian Here's how I do it... Set the engine speed at around 1500rpm with the timing set at TDC. Then advance the ignition timing to obtain the maximum rpm and that should be your best setting.
If you have a taco to read the rpm it is even more accurate to just stop advancing when it reaches max at that throttle setting and advance. You don't gain anything by having it too far advanced.
You want the maximum burn pressure to occur in the cylinder at say 5 degrees after TDC and at speed you need to advance the timing for the fuel burn to reach that phase. When you set the engine speed to 1500rpm adjust the mixture of the fuel to maximum rpm first then the timing. As compression and mixture will change the burn rate and consequently the ideal timing.
Hope this helps as I'm a retire Auto engineer and spent many years engine tuning.
Johwen JohnSamphier

P.S. I just noticed you have your points at a fixed setting This makes it difficult! Have you though of mounting your points on a movable plate so you can advance and retard with the engine running. With you excellent engineering talet would not be very difficult and remove the guess work?

 

[payner]

Brian . Engine looks and sounds great , can't wait to see a video of it driving a load .
Bill

 

[Brian Rupnow]

Johwen--I may add an adjustable plate between the points and the engine casing. I have done that before and it worked well to set the timing while the engine is running.---Brian

 

[Peter Twissell]

Congratulations on a very pretty and sweet running engine Brian.

 

[Brian Rupnow]

I was asked yesterday what rpm the engine was running at in the video. I checked it this morning with the engine driving the clutch. It seems very comfortable at 975 to 1000 rpm. If I turn the idle screw to let it run slower, it stumbles and stalls.

 

[teeleevs]

There is no magic wand on where to set the timing. Advance is totally dependent on the engine you're setting it on and the conditions it is running in. That's why it's one of those things that even the simplest engines that have a variable load have to manage. i.e. vacuum advance - centrifugal advance in order to get peak performance.
If you're going to just sit it on the bench and run it at a certain rpm then set it anywhere reasonable that it's happy. It won't care.
Your process is perfect to get it set exactly for what ever you've decided to set it at.
But I assumed all along that you were going to un-leash this beast on "the saw"

Do yourself a favour and enlist some of your wonderful design talents and make it at least manually adjustable. Or if you want to get fancy have the advance increase with throttle position (to a ratio). (a simple linkage)
In most cases a simple lever adjustment is just a matter of turning the plate the points are mounted on.
Once you have it adjustable you can set it depending on the running conditions (half the consensus reached here). You can retard it slightly for starting and in general the engine will run smoother and have more power if you advance it with rpm. If you're going to load it i.e. "the saw" then it will be necessary to be able to adjust it for best performance (ability to carry the load). You'll find a marked improvement in it abilities.

Looks really good.

Of course - all this coming from a guy who can't even get the Atkinson to pop

I learned to drive at 14 in a 1925 Buick, had to work on the manual spark advance all the time, every hill you had to set it back a little, then down the other side you set it up more, woubetide if you forget to retarded it before you put that crank handle in!

 

[teeleevs]

I was asked yesterday what rpm the engine was running at in the video. I checked it this morning with the engine driving the clutch. It seems very comfortable at 975 to 1000 rpm. If I turn the idle screw to let it run slower, it stumbles and stalls.

Looking good Brian