freebird1

Hi all

I have a new 40cc gas engine. I have not ran it, but I think the timeing is off. I see the timeing marks and the El will fire way after has piston starts down. What is the best way to time the engine. I will be honest I am not totally, but somewhat ignorant about timeing it.


Thanks a ton

Freebird

tim220225

My Feedback: (4)

Freebird1, I time my conversions at 28 degrees BTDC with a CH ignition. Ignition doesn't fire until the magnet passes the sensor. Put a degree wheel on it and check it. Simple to do. What engine is it and what ignition is it?

Tim

wiz310

also check that your turning the engine the right direction........... sometimes you can mix it up and the spark should be before TDC, so it might be in the right spot and your just turning it the wrong way and it then looks like it will fire after TDC. just a thought.

freebird1

It is not fireing at TDC. The way it is set now it will fire on a down stroke. should it fire right at TDC. I would think it would fire ATDC. Like I said i am not brain surgeon on timing. It is a SPE and the EI is auto advanced. Thanks for the replys and help!

Rcpilot

My Feedback: (78)

Take the plug out and ground it to the cylinder.

Put a wood dowel or plastic stick down the spark plug hole untill it touches the piston.

Stand in front of the engine.

Turn the ignition ON.

Turn the prop counter-clockwise----------slowly.

Watch the wood dowel move up as the piston comes up in the cylinder.

Watch for the plug to spark.

Now, tell us when it sparked.
Was the piston all the way at the top of the stroke?
Or did it spark 28* BEFORE the top?
Or did the piston come all the way over the top and spark on the way back down?


If your plug really is popping when the piston is on the way down--then your magnet is in the wrong spot and it's tripping the ignition sensor at the wrong time.

Did you take the prop hub off? Did you put it back on in the right spot? Timing sensor can't really move that much. Almost impossible to screw that little bracket up.

Edited for clarity

tim220225

My Feedback: (4)

Nope, it should fire BTDC at 28 degrees. I time mine by starting with the cylinder in a verticle position held in a vise. Roll the engine CCW and the box should fire on the way back up. On a straight plug engine Rcpilot is dead on. However if you have an angled plug it is tougher. The 28 degrees is not all that critical. At TDC the piston will toggle back and forth a few degrees. Ideal situation would be to find the sweet spot of the toggle. Point being I have run them from 22 to over 30 degrees BTDC and there is little difference. Best way is to use a degree wheel. You can print one off from CH Ignitions' site. Mount it to a piece of lite ply and go from there. All you need to add is a pointer and a piston stop. I also have the CH handy dandy ignition tester and timing box. Isolates the need to deal with a hot plug. Again this is the most accurate way to do it. Another thought if I can remember right, take 3.14159265 which is PI and divide it by 360. Multiply that by 28 and you get .2443. That is how far your engine must be before TDC in inches to fire at 28. About a 1/4 inch BTDC. Put a mark on the hub at TDC and across from that on the case. Make another at 28 BTDC. Lay a tape on that and you should be the 1/4 inch or so. This is getting to sound hard but there are many ways to do it or check it.

freebird1

It is on the way down(way after TDC). The sencor is one that is adjustable. The fly wheel has marks to show TDC. I have already taken the plug out to make sure it was at TDC. I guess my question is should fireing be at TDC or shortly after. THANKS!!!!

NM2K

My Feedback: (14)

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The reason that it is called spark advance is because the spark fires before the piston reaches TDC. This is done because it takes a while for the mixture to combust entirely. Firing as the piston is going down is of no benefit at all. All of this assumes that you are looking at the front of the engine and the crankshaft is being turned counter clockwise. Good luck.


Ed Cregger

Rcpilot

My Feedback: (78)

With the piston at TDC your magnet on the hub should be at TDC.

Put the piston at TDC.

Put the degree wheel on the engine and set the sensor to 28* Before TDC.

Set the degree wheel so that 0 is pointing straight up. The sensor should now be pointing at either 337* or 28* -- depending on how you read the degree wheel. I use a protractor, so mine reads 28*. This would be on the RIGHT SIDE of the engine.

It should run now.

The magnet in the hub should always be exactly lined up with the piston. If the piston is at TDC--then so is the magnet. If the piston is at BDC--then so is the magnet.

If that don't help--then we need a picture from you or a video to sort this out.

TLH101

My Feedback: (90)

If it is C&H ignition, the instructions are here: http://www.ch-ignitions.com/CHinst.html

gapple12

I have one of these SPE 40cc engines and mine came with the timing way off. I found a picture of one on this site and got a good starting point. I then found this that helps a lot. You can even print out the wheel.

http://www.bcmaengines.com/BCMAEngin...n%20Manual.pdf


http://www.bcmaengines.com/finding_true_tdc.pdf

freebird1

Thanks gang. Learned alot. I though it was before TDC but did not for sure. I do have a slanted plug so I am printing off this thread and going to work. Thanks again!!!!

freebird1

Rcpilet thanks for the digrams. Even I can understand it from those. Thanks!!!

Rcpilot

My Feedback: (78)

Did you get it started yet?

gapple12

No problem, they helped me a lot. Glad I could help.

freebird1

Hi

yes I did get it running. I am at around 25* before TDC. It has not had much fuel so I am going to run it there for now. After a little running I will try and find the sweet spot>

Thanks again

Rcpilot

My Feedback: (78)

So, what was wrong with it? Why wouldn't it run before? What did you change?

freebird1

I never tried it because I the timing was not right. It was quite a bit.

Rcpilot

My Feedback: (78)

So, you had to adjust the timing?

I'm having trouble "reading" your answer.

"It was quite a bit"

Quite a bit what? Are you saying the timing was off? Or are you saying you had a brain fart and there was nothing wrong with the engine?

freebird1

No brain fart. As I stated it was set to fire ATDC. It was fireing ATDC about 50*. It has an adjustable position for the sencor. I moved the timeing to fire BTDC

freebird1

O yea Running. It start and ok and at low RPM seems fine, and at the high rpm range. The mid is a little rough. I figure time and running my help!