Onan p220 intake gaskets, bolts being stubborn!!

[AHS 1,443]

Hello there, it’s an 89 520 (straight axle). It needs intake gaskets, with the choke half on, it runs fine. Without it, the motor is surging until it stalls. I started tearing it down; breaking the motor lift bolts on both sides. Tighten before loosen!! (It’s the name of the game!). Once I got down to the exhaust bolts, 2 felt really tight. AND then I stopped…what should I do? Start the motor, until it warms up? This would heat the bolt as much as the threads. I am unsure of what to do! Any questions/comments are appreciated?

[Ed Kennell 38,324]

9 minutes ago, AHS said:

It needs intake gaskets

Did you determine this by spraying the area while running?      Some swear by Kroil Penetrant.   

[lynnmor 7,317]

You should have been soaking all fasteners with penetrating oil for at least a week before attempting to turn them.  If the engine has been in the weather for an extended period of time, all bets are off.  Your idea of warming the engine might help.  It you do get a bolt to move, stop and soak some more.  If you do twist off a bolt, some holes are deep enough to allow drilling out the broken piece, then bottom tap and use a longer bolt.  Use nothing but genuine Onan intake gaskets, the green eBay junk might dissolve in a year.

[peter lena 8,649]

@Ed Kennell  @AHS , @lynnmor h ave found kroil , to be an amazing penetrant , very easy to start a pre removal creep , would do that days out , also any operational related usage , will attract that lube creep , the tractor vibrations  will draw in the lube . simple easy to get a related set screw / bolt , vertically , removed to assist creep action . often refer to , ( make the rust run out ) , disimular , metals / mountings , demand  kroil . just my own oily thought , pete   

[AHS 1,443]

21 hours ago, lynnmor said:

You should have been soaking all fasteners with penetrating oil for at least a week before attempting to turn them.  If the engine has been in the weather for an extended period of time, all bets are off.  Your idea of warming the engine might help.  It you do get a bolt to move, stop and soak some more.  If you do twist off a bolt, some holes are deep enough to allow drilling out the broken piece, then bottom tap and use a longer bolt.  Use nothing but genuine Onan intake gaskets, the green eBay junk might dissolve in a year.

It’s got 1100 hrs on it… not by me!! I don’t know how many owners before me. The 520H was left outside uncovered. Snow on top of it. The worst of the worst. I tightened one of the intake bolts 1 1/2 turns. All tight now, but still leaking thru the intake manifold or intake gaskets. I guess i will leave it be or buy a can of kroil!!

[lynnmor 7,317]

1 hour ago, AHS said:

It’s got 1100 hrs on it… not by me!! I don’t know how many owners before me. The 520H was left outside uncovered. Snow on top of it. The worst of the worst. I tightened one of the intake bolts 1 1/2 turns. All tight now, but still leaking thru the intake manifold or intake gaskets. I guess i will leave it be or buy a can of kroil!!

And then decide to never buy or accept a free Onan again that was left in the weather.

[Bill D 1,927]

Soak the bolts with Kroil then warm up the engine.  With it hot the aluminum will expand more than the steel bolts making them more likely to come loose without breaking.  Replace the hardware with Grade 8 bolts and use silver never seize on them when installing.

[AHS 1,443]

Ok, I cleaned the carb yesterday (11/31). I cleaned it thru the top. I cleaned a bunch of ethanol junk from the carb and sprayed carb cleaner thru all the ports in the carb. (I use non ethanol gas). I cleaned the carb spotless! AND.. same thing! Half choke when running it! I ‘bandaged’ the intake bolts by tightening them, and im 95% sure there is no leak around the intake bolts. I sprayed something flammable when running on the intake bolts and it didn’t change. What now?  Im thinking replace. The 1/4” hose from the intake to the gauge?

[cleat 6,091]

When you pulled the top of the carb off, did you unscrew and remove the brass jet tube that screws into the main carb body beside where the tube that projects from the top goes into the carb body ?

This tube has several holes down the sides and one in the very end.

If this gets clogged up it causes lots of issues.

 

#5 in the attached diagram.

Onan parts manual.pdf

 

[Ed Kennell 38,324]

1 hour ago, AHS said:

 What now?

Clean the carb again, and again.         When I got my badly surging freebie '88 520H , I cleaned the carb three times before the surging stopped.  

[lynnmor 7,317]

1 hour ago, AHS said:

The 1/4” hose from the intake to the gauge?

 

 

Plug the hose if there is a doubt.

 

There is a welsh plug just above the idle mixture screw that can be carefully removed to clean the junk out behind it.  You will need an aluminum 3/8" plug to replace it.  Be careful to not drill any deeper than absolutely necessary to get a pick in for removal.  If you have the newest style carburetor it will have a hidden idle mixture screw and an accelerator pump.  Replace the pump and there is a way to expose the screw so that it can be removed for blasting carb cleaner thru the hole.  Of course you already removed the idle mixture screw for blasting if you have the older style carb.

[kpinnc 12,172]

My 520-H also had that same surge thing as well. Cleaning the carb was needed just like yours, but changed nothing. My intake manifold was leaking at the seam and required sealing. As soon as I did that, it ran like a champ with zero choke. 
 

Just run a small bead of silicone sealant all the way around the seam with your finger. It worked very well on mine. 
 

 

[AHS 1,443]

I cleaned my carb for the 2nd time! No, I didn’t clean the jet. But, I didn’t have a screwdriver to fit it…. But, i made one! @cleat So, i took out the jet; and I saw the hole in the side and the hole thru it. I sprayed carb cleaner thru it and took a piece of thin copper wire and pushed it thru the jet multiple times. I didn’t have a Welch plug.. so that’ll be the problem now! (Im hoping not!). Im still not done yet, Ive got replace the 1/4” rubber hose and put a thin bead of silicone on the intake down there.

[Ed Kennell 38,324]

1 hour ago, AHS said:

I cleaned my carb for the 2nd time!

Don't give up.    It took 3 for mine.

[AHS 1,443]

Ok! Enough is enough… I am doing this! Taking off the intake- sealing that up. Taking off the exhaust- I already broke one bolt! Taking off the carb and cleaning it. This is. An 88-89 with the straight axle. Please, if you could give me the serial #s off the motor? Mine are all wiped off! The Onan dealer wants serial/model #s so he can order the gaskets. I am going to get new bolts for the exhaust/intake? Also, I have an intake from an Onan 16, would that be the same as the 20HP? I want to be SURE that there are no intake leaks, no intake runner leak and the carb is 100% checked! Anything else I should do on a 1500 hr Onan 20hp? Your thoughts are welcome! Oh, the exhaust bolt I sorta broke (one more 1/8 of a turn and it will be broke!) is the bolt to the left of the exhaust. 

[AHS 1,443]

I sprayed kroil on the exhaust bolts and let it warm up twice. What’s wrong with a 1/2” breaker bar trying to loosen up exhaust bolts!?!? I was being careful! No wonder i broke it!

[lynnmor 7,317]

You should have been spraying penetrating oil on all of the fasteners at least twice a day for the past 25 days for a total of 50 times.

 

The exhaust should be glass beaded and painted with Rustoleum high temperature spray paint.

 

You can test the intake for leaks, once it is off, by sealing off the carb mounting surface and filling it with gas or diesel fuel.  I believe that most are not a problem.

 

You buy the gaskets from onanparts.com and forget the local guy that has no clue, nearly all Onans of this size use the same gaskets.

 

The 16HP intake might fit but will have no vacuum fitting if you need one.

 

A 1500 hour engine needs the valves adjusted for the second time, I'm sure it missed the first.

 

Be sure to bottom tap all of the intake and exhaust mounting holes and use bolts that are as long as possible without bottoming out, you may need to cut custom lengths.