520-HC no compression

[cleat 9,064]

19 hours ago, cafoose said:

What's the best way to get the plastic knobs off the 520 choke and throttle levers?

 

Claw hammer, just pretend you are pulling a nail.

[sqrlgtr 3,334]

52 minutes ago, cleat said:

 

Claw hammer, just pretend you are pulling a nail.

I never had any trouble getting them off but have had to use a little glue to keep them on afterward.  Others may have a better solution to keeping them on, I hate to use super gliue on anything I think I might have remove again later on.

[cafoose 3,783]

Claw hammer works great 

[Handy Don 17,000]

2 hours ago, sqrlgtr said:

I hate to use super gliue on anything I think I might have remove again later on.

My go-to for these is a tiny dab of hot glue applied to the tip of the arm. 

[sqrlgtr 3,334]

1 minute ago, Handy Don said:

My go-to for these is a tiny dab of hot glue applied to the tip of the arm. 

This I will try if, I mean next time, I have to do another.

[kpinnc 18,763]

7 hours ago, cafoose said:

@kpinnc Is this the manifold you used?

 

No sir. The bend on that one is backwards from what I used. You want the shorter leg on the front and the hoop facing up. Otherwise it will interfere with the PTO engagement. 

 

You'll have to weld whichever end shut that is open and add an adapter closer to the middle to make it the way I did. I used a reducer from the auto parts store and flattened it to an oval on the manifold side. 

 

[ineedanother 2,633]

On 7/20/2026 at 9:35 PM, cafoose said:

What's the best way to get the plastic knobs off the 520 choke and throttle levers?

I use an adjustable wrench (crescent-type spanner) rather than a claw and tap it off with a hammer. You can also pry against the wrench rather than the knob if you choose to use a claw hammer.

Edited July 23 by ineedanother

[cafoose 3,783]

It's alive 

 

Edited July 25 by cafoose

[c-series don 12,145]

That thing sounds bad ass! Like it has some big cam drag racing engine in it!! 

[cafoose 3,783]

2 hours ago, c-series don said:

That thing sounds bad ass! Like it has some big cam drag racing engine in it!! 

Open exhaust and worn plugs. Seems to run lean but when I partially close the choke it evens out. May do a carb rebuild. Don't know if it had ethanol in a previous life.

[cafoose 3,783]

Got the relay today, wired it up and it works great just like it should  Also wired up the oil pressure switch and the lights pigtail. All that's left is the tach wire in the 9 pin. Would be cool if I could get the tach working. Any ideas? All I need is the exhaust fabricated, Tune up and oil change, install the hood, and the mule and mower deck. 

[cleat 9,064]

14 hours ago, cafoose said:

Got the relay today, wired it up and it works great just like it should  Also wired up the oil pressure switch and the lights pigtail. All that's left is the tach wire in the 9 pin. Would be cool if I could get the tach working. Any ideas? All I need is the exhaust fabricated, Tune up and oil change, install the hood, and the mule and mower deck. 

 

I have hooked a 520 tach to a Kohler K series and it worked just fine .

 

I just hooked to one of the AC wires at the regulator just like the 520 is wired and it got the correct signal.

 

Edited Wednesday at 11:19 AM by cleat

[Handy Don 17,000]

22 hours ago, cleat said:

 

I have hooked a 520 tach to a Kohler K series and it worked just fine .

 

I just hooked to one of the AC wires at the regulator just like the 520 is wired and it got the correct signal.

 

As long as the stators have the same number of coils (18 in the case of the Onan’s) it’ll work. 

[cafoose 3,783]

31 minutes ago, Handy Don said:

As long as the stators have the same number of coils (18 in the case of the Onan’s) it’ll work. 

 

From Grok AI:

[Handy Don 17,000]

Since tachs are essentially counting revolutions over time intervals, your Vanguard hookup will show 8 pulses per revolution vs the 18 of the Onan.

Unless the WH tach can be recalibrated (unlikely), it’ll read as approximately 44% of the actual speed of the Vanguard.

Speed ==> Reading
@1000 RPM ==> 444

@2000 RPM ==> 888

@3000 RPM ==> ~1,330

@ 3600 RPM ==> ~1,600

[cafoose 3,783]

9 hours ago, Handy Don said:

Unless the WH tach can be recalibrated

Or the numbers on the tach itself are changed. I would guess rpm can be verified with a hand held tach?

[Handy Don 17,000]

11 hours ago, cafoose said:

Or the numbers on the tach itself are changed. I would guess rpm can be verified with a hand held tach?

LOL! I’m visualizing pieces of masking tape with numbers on them! 

 

Personally, I test revs with a free iPhone app “Video Tachometer” to get within ±10 RPMs of my target. After I’ve got the carb mixtures tweaked, I set my “target” speed in the app and then adjust the throttle linkages/stops until the app shows I’ve hit the target. 

[cafoose 3,783]

2 hours ago, Handy Don said:

LOL! I’m visualizing pieces of masking tape with numbers on them! 

 I was thinking of possibly having a new decal made to go on the tach.

2 hours ago, Handy Don said:

Personally, I test revs with a free iPhone app “Video Tachometer” to get within ±10 RPMs of my target.

Anything out there for android?

[Handy Don 17,000]

51 minutes ago, cafoose said:

Anything out there for android?

I don’t follow the Android world at all.

FWIW, I would search the interweb for apps that use the camera and strobe the light that are compatible with your specific device. Hardware varies so much in the android world, especially for camera specs, your device may not have the needed oomph. 

There are not-to-expensive external tachs that work via induction (off the spark plug wire) and/or optical that are helpful for doing maintenance and sychronization like this one. 

Edited 3 hours ago by Handy Don