Onan Ignition Rotors

[TC10284 113]

For Onan ignition rotors, is there a way to test that they are good short of placing them on the shaft, reinstalling the flywheel, and trying them? The magnets inside appear to still work, so what makes them go bad? Does anyone know if the magnets have a certain magnetic pole orientation (north/south)?

 

I'm asking because I think I'm facing one now that has a "bad" rotor on a P220g. I could only get it to run for a few seconds because it's a swapout engine from one that had a broken rear connecting rod, and I couldn't get the fuel pump to pump, so I installed a new pump on this replacement engine. But when I got the new pump on there and tried starting it, it's acting like it is wanting to backfire sort of - and does that thing where it fires and wants to send the flywheel backward - meaning, it fires and stops the flywheel dead in its tracks.

 

Prior to installing the new fuel pump, it would run for a few seconds and die as the fuel was used. I know it's not the fuel pump causing it. But I'm hoping it's not the ignition control module, although I do have a spare that I think works that I can test. And the shroud isn't installed currently, so it wouldn't be that much of a pain to test out a few rotors and a spare ignition control module. 

 

 

Edited May 31, 2021 by TC10284

[lynnmor 7,651]

The rotor is simply a plastic ring containing two magnets, if a screwdriver sticks in two places, it is probably good.  The older black ones has problems, but the newer gray ones are good.  You can test the timing by rotating the flywheel and note the position where the plugs fire.

 

See page 8-2

[TC10284 113]

Since it says the timing is not adjustable, if it is off, what do you do to correct? 

 

I plan to check the coil as well. 

Edited May 31, 2021 by TC10284

[TC10284 113]

Did a check of the timing according to page 8-2 and the first  chaff screw after the voltage flips from 1v to 12.5v is right in the center of the two blower housing marks. 

[lynnmor 7,651]

Sounds like the ignition is OK, that leaves fuel, air and mechanical issues.  Check the compression to see if the engine is sound.

[TC10284 113]

I took the flywheel off and found the source of my problem. The key is stripped now. I had the flywheel tight and I can turn the engine crank itself over by hand. It's not locked up. 

I have a spare key and flywheel, but now I am left wondering, what the heck?

How? 

 

Pics here:

https://pic8.co/a/e6e5e0a9-815c-4d7a-b7b1-6399604534b0

Edited June 1, 2021 by TC10284

[lynnmor 7,651]

The key is often installed backwards, so check that.  Clean up the crank and the flywheel bore with 400 grit paper, then wipe it with mineral spirits.  I then use a very small amount of rust preventing oil and wipe it with a clean paper towel to get all but a trace off.  Lastly, oil the bolt threads and torque to 55 lb. ft.

[TC10284 113]

Yeah, not sure. I've installed them before so it shouldn't be backward. I guess it was just rusty and not tightened enough.

 

Anyway, I'll do all that and try it again. 

 

Thanks

[TC10284 113]

Checked compression. 90psi on front. 89psi on rear.

 

So I did all that. Working fine so far. Found out that the fuel shut off was stopped up. So I replaced it and the grommet as well. 
It runs but has to be 100% to 90% choked. So I'm going to try swapping the carb with another that should be clean and see if that helps. 

[lynnmor 7,651]

3 hours ago, TC10284 said:

Checked compression. 90psi on front. 89psi on rear.

 

So I did all that. Working fine so far. Found out that the fuel shut off was stopped up. So I replaced it and the grommet as well. 
It runs but has to be 100% to 90% choked. So I'm going to try swapping the carb with another that should be clean and see if that helps. 

 

Since swapping the carburetor is a bit of work, try removing the top and cleaning in there first.

[TC10284 113]

20 hours ago, lynnmor said:

 

Since swapping the carburetor is a bit of work, try removing the top and cleaning in there first.

 

Swapping the tops didn't help any. So I have already removed the exhaust and intake/carb to swap with another. 

I've done it many times before, but Luckily it was easy this time since I didn't have the air filter base or any of the pto stuff on, including the exhaust base bolts. 

We'll try'er again tomorrow I hope. 

[TC10284 113]

On 6/3/2021 at 4:00 AM, lynnmor said:

 

Since swapping the carburetor is a bit of work, try removing the top and cleaning in there first.

 

Swapping the intake and carb that I manually cleaned didn't help much. Still has to be choked at 90%.

 

I ordered an aftermarket carb to try. 

 

I've checked for any leaks from both intakes. And from the workload gauge hose. No discernable places where it's sucking in unmitigated air. 

 

Could there be any other part that causes this? 

[lynnmor 7,651]

I have an IV bottle to feed carburetors when testing.  It is simply a can with a hose attached and I hang it well above the carburetor and add gas.  This will eliminate any fuel delivery issues from the equation.  You might also dump all the gas and try some from a fresh can.  I had a chainsaw from a neighbor that I couldn't keep running, yep, it had kerosene in it.

 

Other than that, I would suggest pulling the heads and checking for loose valve seats and other damage.  Your compression is on the low side and I have seen an engine with higher pressure with a completely loose valve seat.

[TC10284 113]

I'll try the new carb and some fresh gas soon. 

 

I know the gas in it is kind of old, but I mixed it with fresh. 

 

Anyway, I'll keep trying. Hopefully nothing internal. 

[TC10284 113]

I got the aftermarket carb a few days ago. I finally had a chance to install it and thus far it seems to have resolved the issue.