Start-up issue on my 520-H

[Handy Don 12,248]

42 minutes ago, Jeff-C175 said:

 

I believe that the priming bulbs have not one, but two check valves in them, one at the inlet and one at the outlet.

As do diaphragm fuel pumps! The key, of course, being how well they seal! 

[twodogs 55]

On 2/10/2021 at 11:08 AM, twodogs said:

I like it.  I believe the order of my tasks will be:

1.  Check the voltage while cranking

2.  Pull the fuel line at the in-line filter to check flow into my new Pyrex

3.  If flow is slow/nonexistent, remove check valve and repeat Pyrex test

4.  If flow remains slow/nonexistent, replace fuel pump and repeat test

5.  Replace check valve with priming bulb (or move check valve to downstream of fuel pump)

6.  Remove and clean carb if necessary

7.  ?

Thanks for the insight folks!  I'll report back....

 

Happy to report back.  I checked the voltage at the coil while cranking and it was right around 4 volts.  I then pulled the fuel line downstream of my fuel pump and it seemed to be moving fuel just fine.  Since it was working, I jumped straight to installing a primer pump like Wallfish recommended.  Drum roll..............that worked like a charm!!!!  I installed it between the fuel pump and the fuel filter.  Prior to this, I would turn the key and hope it would fire up.  If not, then I would have to resort to the annoying steps of removing the air filter and pouring gas down the carb throat.  I've tested it several days now, and I can say that it starts every time like I had just turned the machine off.  I just give the pump a couple of squeezes and it starts within a few seconds.  What a wonderful solution.  Thanks for the tip, Wallfish!

Edited February 17, 2021 by twodogs
included link to primer pump

[lynnmor 7,315]

12 hours ago, twodogs said:

Happy to report back.  I checked the voltage at the coil while cranking and it was right around 4 volts. 

 

 

On which terminal?  Did you do anything in this area?

[twodogs 55]

On 2/17/2021 at 7:40 AM, lynnmor said:

 

 

On which terminal?  Did you do anything in this area?

Electrical tasks are definitely not my forte' so I just took a stab at it.  I just hooked my multimeter to the +/- terminals on the ignition coil and then took a reading while it was cranking. 

 

Edited February 19, 2021 by twodogs

[Lee1977 6,673]

I'm late to this tread. but I'll tell you what I did to my 520. Mine was a bear to start, and I broke the vacuum pump changing the gas lines. I installed an electric pump.

I now turn the switch on and let the pump hit 3 or4 times turn to start and come up with the choke and right back down and it's running. I also put a toggle switch on the pump.

I just fire it off yesterday after setting from October and it started right up.

[Chestnut 315]

@squonk 

 

@lynnmor

 

On 2/10/2021 at 8:39 AM, squonk said:

For the Halibut, Check your voltage at the ignition coil whilst cranking. 

 

I know this thread has been around a bit but I just got the chance to check the 520H at my mother in law's. Voltage to the smaller connection on the coil (yellow wire feed) dropped from 12.1 to about 8 while cranking. Seems kind of low to me. I won't get to the full diagnosis and correction until next visit, Any suggestions on first items to check? I'm guessing the starter and/or solenoid could have high resistance and be the biggest current draw. Could also be resistance at any of the ground spots, ignition switch, or any of the safety switches and relays. In the absence of anyone's insight I'll just have to work my way though the connections shown in the demystify guide. 

[squonk 41,165]

Clean all the connections. I'm thinking the starter itself is the culprit. If you have another battery you could disconnect the wires from the starter and use the 2nd battery to jump the starter right on the tractor. Turn the key on to power the ignition and spin the starter with the 2nd battery. See if it will start right up. Or you can do a voltage drop test Explained here:

 

 

[lynnmor 7,315]

Put the voltmeter across the battery and test again.  There will always be a significant voltage drop when the starter is engaged and the voltage available to the coil should be only a bit lower than the battery voltage.  You may have a weak battery, a starter with a draw too high or poor connections.  The 520 tractors had a 280 AMP battery when new because more capable batteries were not readily available like they are today.  
A battery with a reading of 12.1 volts is in serious need of a lengthy charge.

Edited February 27, 2021 by lynnmor

[pfrederi 17,741]

Voltage drop below about 9 volts while cranking usually means a weak battery

[Chestnut 315]

3 hours ago, lynnmor said:

Put the voltmeter across the battery and test again.  You may have a weak battery, a starter with a draw too high or poor connections.
A battery with a reading of 12.1 volts is in serious need of a lengthy charge.

 

3 hours ago, squonk said:

Clean all the connections. I'm thinking the starter itself is the culprit. If you have another battery you could disconnect the wires from the starter and use the 2nd battery to jump the starter right on the tractor. Turn the key on to power the ignition and spin the starter with the 2nd battery. See if it will start right up. Or you can do a voltage drop test Explained here:

 

 

 

Thanks everyone for the suggestions.

Battery voltage directly across the terminals is 12.4. Not perfect, but better than 12.1 at the coil. Distinct indication of poor connections. Cleaning up the connections will be the first order of business when I get back to it. Good video provided by @squonk . I can run through the diagnostice sequence there. I also have a couple of other batteries I can install. One of them fires the other 520H almost instantly. I guess the other thing I could do without just throwing a $300 starter at it would be to swap starters with the other Onan. It'll be  a few weeks before I'm back again and I may not have time even then. Moving soon after 32 years, so cleaning up "stuff" and prepping to move is taking a lot of time.

[Chestnut 315]

Hello all, I have a morning update. I did a variation on @squonk 's suggestion of using another battery to spin the starter. The solenoid on the tractor has a protective cap over the main feed lug so instead I just fed the coil from a spare battery using test wires with alligator clips. Battery has been sitting in the basement since October but still read 12.6 on the voltmeter. Voltage at the coil was 11.9 during cranking. Still no fire, so I'm still in the testing mode (at least when I'm back there, I left after running the test this morning. 

Just as a preface to my plan, this is a relatively low hour Onan, around 630. It had the dirty carb surging issue which was fixed by the on-engine cleaning. The hard start issue didn't change with the carb cleaning. Runs like a bear once it's started. Fairly new plugs and wires (within the past 10-20 hours of operation, but the plugs are Champions. I have some NGK's on the shelf. I have a primer bulb installed. Will also do the following with a known good battery. Hopefully won't need the snowblower so that battery will be available.

When I get back my order of attack will be:

1. Check resistance and clean all the connections in the starting and ignition circuits.

2. Pull the coil and check primary and secondary resistance. I have a Chinese knockoff coil I could try at this step as well. 

3. install NGK's

4.  Check starter amperage draw. Compare to my other Onan.

5. Pull the carb and do full cleaning, adjust valves, decarbon, and so on.

6. Check ignition module? This seems an unlikely cause since it runs so well once started, but if all else fails...

 

[squonk 41,165]

How did you go from 12.6 to 11.9 at the coil with the other battery? Did you disconnect the original 12V power lead at the coil? If not the tractor starter circuit (Key section will draw some power away from that.  

 

Starter draw test. Remember if cranking voltage is low, starter amp draw will go up. You might get a high starter amp draw and condemn the starter when low voltage at the starter is the cause.

 

What kind of voltage are you getting at the coil of the tractor that starts right up.

 

1 other thought. Leaking intake manifold. I have seen several stories of these leaking on Onans between the manifold halves. That would lean out the mixture and make it hard to start.

[Chestnut 315]

2 hours ago, squonk said:

How did you go from 12.6 to 11.9 at the coil with the other battery? Did you disconnect the original 12V power lead at the coil? If not the tractor starter circuit (Key section will draw some power away from that.  

 

Starter draw test. Remember if cranking voltage is low, starter amp draw will go up. You might get a high starter amp draw and condemn the starter when low voltage at the starter is the cause.

 

What kind of voltage are you getting at the coil of the tractor that starts right up.

 

1 other thought. Leaking intake manifold. I have seen several stories of these leaking on Onans between the manifold halves. That would lean out the mixture and make it hard to start.

 

You are correct in surmising I didn't disconnect the yellow wire from the coil. I'm sure the starter circuit dragged the voltage at the coil from 12.6 down to 11.99. I figured 11.99 to the coil  

You can be sure I'll be digging through that starter pretty thoroughly before I spring for $300 for a new one. I'm optimistic it isn't the issue because it spins the engine over pretty well. Starter looks like the Denso. Somebody on the auction site is selling an aftermarket solenoid which has a lot of interchanges. I'm sure the brushes and a lot of other parts are common as well. 

Haven't checked the other tractor voltage. When I get back.

I read about the intacke manifold ant figured there was a reason it was pinned in the #1 spot in the "engines" thread. I'll vacuum check it if the carb comes off. I'm not thinking it's too lean because when it does start it's usually after it starts puffing a little black soot. The lean condition usually causes some surging and need for a little choke when it's running. Doesn't need any choke after it starts and warms up.

Thanks again for everyone's input.