Cleaning carbon from the valves?

[Brockport Bill 1,668]

I am replacing carb, cleaning breather etc on 520 HC Onan P220G -- So....... I removed the exhaust, the old carb and manifold as well as valve box cover and breather --- see from the photos attached that looking into the valves, there is carbon build up under them. Is there such as thing, or a benefit, to cleaning the carbon off the underneath of valves without removing all the tin, the head, and the valves entirely? Can they, or should they, be cleaned in the position they are in? Thanks - this is new adventure for me!!! Any insights or tips are appreciated?

[WHX?? 48,833]

Any idea of how many hours on it? I would suggest that as long as you got it this far pop the heads as there well may be some carbon build up in the combustion chamber as well. Then you can easily pull the valves and clean them up. Bonus check the valve seats and maybe lap them if required. 

[Brockport Bill 1,668]

627 hrs --  i am new owner -- it appeared it was used hard - and not well cared for --- I am aware that extra effort of removing head etc is optimum and would be big benefit --- that would be a huge adventure for me  -- and beyond anything i have done previously - sorta hesitant !!!!

[peter lena 8,639]

@Brockport Bill  dare i say it , do you use any fuel treatment in your fuel ? I  add ounces of   STA-BIL  to ALL MY FUELS  ,  ever heard of seafoam gas treatment ? my valves are clean and clear . before you tear it down , run a couple of tanks of treated fuel thru your engine ,  see what kind of a change that makes.  pete 

[lynnmor 7,309]

Since that carbon is on the back of the intake valves it would be a good idea to replace the intake valve seals.  That carbon will do little harm, and if you run the engine fast like recommended, the carbon may not increase.  Since you don't want to do a complete job, just do a valve adjustment and hope for the best.   You should have checked the compression first thing to get an idea of basic health the engine.

 

[Brockport Bill 1,668]

thanks for great feedback - I am new HC owner - it really has not been run by me except for few minutes --- just started misc clean up and maintenance - YES -- i use Sea Foam currently on all my engines - weed wackers, trimmers, my WH 312-8, Ariens snowblower, etc - and use Stabil for any storage of any engines that will sit any period of time -  Ariens snowblower, Generic generator, etc - However, i just got the HC Onan so have not really run it yet except to " test it "-- Got it started and immediately had major surge in mid throttle range - the compression tested at 115 in each cyl so that was good news...... but to solve surge i am replacing Carb, sealed the manifold with RTV silicone along joint --- and am replacing the exhaust and manifold and valve cover gaskets just in case any air leaks???? I just bought non ethanol gas so will be using that in all my equipment in future. Hope that gives you sense of where I am -- so that's why I wanted advice on cleaning carbon under valves - this is all new venture for me -- so wondered if there is such a  thing as spraying them or trying to scrape a little bit or some other strategy other than removing head? Thanks again all - please keep the wisdom coming.

[Brockport Bill 1,668]

to Peter - footnote to your SeaFoam suggestion - I discovered Sea Foam last fall - now a big fan - and now i actually add it to my empty gas cans BEFORE i go fill them at gas station 

[lynnmor 7,309]

I would never replace a carb with a cheap Chinese one if it can possibly be cleaned.  In order to seal the intake it would need to be split and a fuel resistant sealer used between the halves when it is bolted back together.  Your engine only needs gasoline and oil to run properly, gasoline can be preserved somewhat using Sta-BIL.  Ethanol free is a good idea if the engine will not be run for extended periods of time.

There are no good shortcuts to engine maintenance, sprays and solvents will only move dirt around, possibly doing more harm than good.

[Brockport Bill 1,668]

1 hour ago, lynnmor said:

I would never replace a carb with a cheap Chinese one if it can possibly be cleaned.  In order to seal the intake it would need to be split and a fuel resistant sealer used between the halves when it is bolted back together.  

i have option of cleaning present carb or new "cheap chinese"  -- what do you mean "In order to seal the intake it would need to be split and a fuel resistant sealer used between the halves" ? The entire old carb is now off the manifold -- and manifold is off the engine. Do you mean the top half of old carb or new carb would have to be split and sealer used? I took the top half off old carb and removed float and as expected there is much sediment inside. thanks for sharing your experience -- I'm learning !!!!!!!!!!!!!!!!!

[lynnmor 7,309]

To see what I am talking about go here and download the PDF file in the first post.

 

I do mine a bit different by drilling straight thru and using stainless screws and lock nuts.  i also use a different sealer.  Of course you don't need to split the manifold if it doesn't leak.  Look for cuts on the edges where the heat shields touch the manifold.

Edited September 25, 2021 by lynnmor

[Brockport Bill 1,668]

27 minutes ago, lynnmor said:

 Look for cuts on the edges where the heat shields touch the manifold.

here are some photos of what i had already done to manifold in case it had any air leaks - please don't laugh at my art work - i did not care about the apperance -- actually, i saw this solution on You tube from guy who says he works on Onans alot - I read the pdf you provided but did not want to go to that extent and did not want to risk damaging the manifold and the potential risk of worse problem and $$$ ...........I did find one cut previously on the seam connecting top and bottom half of manifold and hope the sealant worked for that issue -- thanks for mentioning that. I used Permatex copper RTV silicone as the You Tube guy suggested. First i used razor to remove any old gasket that was protruding the seam... and cleaned the seam.... then i worked in the sealant with some light finger pressure. I left excess believing appearance does not matter? Any thoughts if this will be of value??????????? Feel free to giggle.

[lynnmor 7,309]

I would call your orange blossom special better than nothing, it is not a great fix.  You should have tested for leaks first, the orange goo can now temporarily hide a fault.  When you think about it, only a tiny amount serves a purpose and the remainder is Halloween decorations.

[Brockport Bill 1,668]

ya gotta love halloween

[Brockport Bill 1,668]

how do you test for leaks?

[Brockport Bill 1,668]

related question --- i am installing new gaskets to reattach the manifold and exhaust -  as well as new gasket for the breather valve box -- Do i just install the gasket - or do I need to use any sealant? If yes - what kind?

[lynnmor 7,309]

1 hour ago, Brockport Bill said:

how do you test for leaks?

At the beginning of the PDF I linked to, you will see the intake clamped upside down on gasket material.  Pour some gas in it and see if any leaks out the seam.

 

Use only genuine Onan gaskets, especially the intake gaskets, because the cheap Chinese ones fail quickly.  I spray a light coat of this stuff on the valve cover gaskets.

Be sure the threads in the block are clean, I run a tap in each one.  I'm sure that you downloaded the Onan Service Manual, follow the torque specifications carefully and put a drop of oil in the threads, DO NOT over tighten any of the bolts, they strip easily.

 

When you reassemble, look at where the heat shields may touch the intake and grind about an eighth of an inch off of the shield.

[Bill D 1,926]

10 minutes ago, lynnmor said:

At the beginning of the PDF I linked to, you will see the intake clamped upside down on gasket material.  Pour some gas in it and see if any leaks out the seam.

 

Use only genuine Onan gaskets, especially the intake gaskets, because the cheap Chinese ones fail quickly.  I spray a light coat of this stuff on the valve cover gaskets.

Be sure the threads in the block are clean, I run a tap in each one.  I'm sure that you downloaded the Onan Service Manual, follow the torque specifications carefully and put a drop of oil in the threads, DO NOT over tighten any of the bolts, they strip easily.

 

When you reassemble, look at where the heat shields may touch the intake and grind about an eighth of an inch off of the shield.

I would recommend grey never seize on the bolts and new grade 8 bolts for the exhaust flanges.

[Brockport Bill 1,668]

great suggestions --- thanks for the coaching -- I purchased from Onan the genuine gaskets so all set to use them -- I will buy the gasket spray tomorrow - I will do the gasoline leak test tomorrow as well. I will be certain to clear out the threads -- I usually put a drop of oil or anti sieze on bolts I reinstall - thanks for reminder. I was aware of the "cut" on the manifold seam from an exhaust or tin touching..... and was planning before refitting it to find the location to trim it back. That's bizarre that the design was flawed to create that contact. Had not thought of new grade 8 bolts.

[Brockport Bill 1,668]

yes, I have the manual and the torque specs

[Brockport Bill 1,668]

On 9/25/2021 at 9:35 PM, lynnmor said:

At the beginning of the PDF I linked to, you will see the intake clamped upside down on gasket material.  Pour some gas in it and see if any leaks out the seam.

 

Use only genuine Onan gaskets, especially the intake gaskets, because the cheap Chinese ones fail quickly.  I spray a light coat of this stuff on the valve cover gaskets.

Be sure the threads in the block are clean, I run a tap in each one.  I'm sure that you downloaded the Onan Service Manual, follow the torque specifications carefully and put a drop of oil in the threads, DO NOT over tighten any of the bolts, they strip easily.

 

When you reassemble, look at where the heat shields may touch the intake and grind about an eighth of an inch off of the shield.

will the gasoline test damage the original seam sealing material in the manifold? an added challenge is if using gasoline for leak test is to find way to seal the hose fitting - - as well as seal the carb attachment surface thats now at bottom of manifold ???????

[Handy Don 12,237]

On 9/26/2021 at 1:14 AM, Brockport Bill said:

That's bizarre that the design was flawed to create that contact

It's an issue of tolerances. On some engines, the shields don't touch; on others they do. As per @lynnmor I just trim anyway!

 

13 minutes ago, Brockport Bill said:

will the gasoline test damage the original seam sealing material in the manifold?

No, it is gasoline resistant. It is metal differential expansion/contraction and age that can introduce the failure.

 

15 minutes ago, Brockport Bill said:

find way to seal the hose fitting

Not sure what hose fitting you are referring too. The test is on the manifold separated from engine and carb so that there are (or should be ) only three openings--the two inlet ports upward and open plus the carb throat port downward and sealed with a cover gasket.

[lynnmor 7,309]

1 hour ago, Handy Don said:

Not sure what hose fitting you are referring too. The test is on the manifold separated from engine and carb so that there are (or should be ) only three openings--the two inlet ports upward and open plus the carb throat port downward and sealed with a cover gasket.

 

I believe he has a hose barb fitting for the vacuum/horsepower gauge.  He can simply plug the hole or attach a hose and bend it upward higher than the manifold.

[Brockport Bill 1,668]

thanks - I was concerned the original "rubber like" seal between the manifold seams would be subject to gasoline damage if using gas for the liquid test? Just out of curiosity, why wouldn't water work for the leak test? I would have planned to blow out any remaining water moisture with my leaf blower or compressed air to be sure it was dried. To Don - yes, Lynnmor is correct -- there is a hose that goes from the manifold to the dash vacuum guage that has to be sealed to do the leak test.

[Brockport Bill 1,668]

that hose fitting is in the photo in my original message at beginning of the thread

[Brockport Bill 1,668]

heres photo of the vacuum hose fitting