Stuck a Valve?

OK Ill admit it I stuck some valves. I ran out of chipped fuel and ran a batch of pellets in one of our big machines. All was fine at first but when the machine transitioned over to the pellets things changed real quick. Ive ran pellets before without issue but I think the machine needed to fully adjust first to produce clean gas.

Well anyways it was a dusy, with bent push rods and the whole works. I dont know if any one else has posted a thread on what to do in this case, so I thought I would post what I did and how I did it.

First thing you want to do is pull all spark plugs and inspect them. This should tell what cylinders are affected.

If you have raw tared gas getting into your engine those spark plugs are probably fouled and need cleaning or replacement.

Next is remove the valve covers and check all rocker arms for looseness. If you find one is loose then a push rod is most likely bent or this valve is stuck and will not return to a seated position.

Next is to remove all intake rocker arms and remove any bent push rods.

Then with a brass punch and a hammer I gently tapped each of the intake valves to free them up. If they are stuck in the seated position I know of no other way unless you have a means of some sort press to push them or you have a guerilla. I have neither so a brass punch and hammer it is. By doing this you will know right away if the valve is tared up or not. If the valve is free of tar it will recoil right away and if it is tared it will stay in the position it has been moved too. Once freed from the seated position it may then be practical to push down on the valve or continue lightly tapping it down. On a larger engine and depending on the severity of the condition the valve spring should be able to push back to a seated position. However, it may move back up slowly, this was the case for me. So I continued to tap the valves affected and letting them return to the seated position. I also sprayed some penetrating oil at the valve stems; I don’t know if this helped or not but it was worth a try. I then continued this process until the valves moved as free as possible.

NOTE: If your engine is an interference engine be careful not to hit the valves into the top of a piston.

Next is it is a good idea to check the exhaust valves on the affected cylinders. Depending on circumstances if the engine was running and a cylinder was fouled, raw gases then could flow through the exhaust valve as well.

Now that all the valves have been freed I replaced the bent push rods and reinstalled the rocker arms.

Now for the fun part. Do not roll the engine over with the starter yet. I turned the engine over by hand feeling every movement to make sure I was not over forcing things. Once I had turned the engine over enough times and felt things were free enough I moved on to the next step.

Before reinstalling the spark plugs, I turned the engine over with the starter while dosing it with gasoline and a heavy fuel additive. This is to help break down the tar on the valves before engine starting.

For this step I media blasted and cleaned all the plugs and reinstalled them. These first machines are not dual fuel so in order to run them on petrol I have to use a spray bottle. What I did was use the same additive with petrol in a bottle. I started the engine and ran at idle, with slight tappet noise, I continued to run with the solution at this speed until the noise went away. I then gradually increased throttle listening for noise and ran at those speeds until the engine ran without any noise. After 15 min of running I let the engine completely cool down.

After the engine has completely cooled down I once again turned the engine over by hand. Residual tar can still heat up and continue its path to the valves and then cure there during cool down. So once I was sure the engine was free I repeated the engine run with the additive.

All is fine now and the engine runs great. I hope this helps anyone that may ever run into this.

The engine in this example was a zero tolerance engine, meaning that the rocker arms are non adjustable. So you may need to readjust the rocker arms if the noise does not go completely away on engines with adjustable valves.

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Good post Matt. Thanks for sharing that. I have found that if you can apply some heat (carefully) sometimes it lets the tar loosen up enough so that you can run it on gasoline… haven’t had to do that for a long time, but I do keep it in the back of my mind, just in case.


Good post Matt and Arvid.

One of the first signs that tar may have gotten to the motor is a stuck throttle . This shows up on vehicles ( car or truck ) as soon as you touch the accelerator before cranking . If the throttle is stuck don’t crank it.

With most stationary equipment and tractors the speed control doesn’t connect directly to the throttle but to the governor which controls the throttle . In short on some equipment the speed control my work freely but the throttle could be stuck.

If the throttle ( throttle plates in the fuel stream ) works freely there will be no tar.

Hi Matt, That is all part of the 75%. I keep spare push rods in the glove box usually. I haven’t had to use one in many years. On GM engines the rocker arm studs may lift a bit. They usually can be tapped back down or I add a washer over the rocker arm. On my 91 olds I would always crank it with the fuel pump off first. Many times I could hear a piston or two smacking the intake valves back into place. That was before I built the double rotor units. Even years after the last cleanup, the throttle would still stick. If you know you have run tar through an engine and it is still running, Boil a quart jar of water in the microwave and then suck the boiling water into the intake at a controlled rate to not water lock the engine. It will turn to steam in the intake vacuum and help steam clean the stems. If you turn the engine off, it will only take around 10 minutes for the tar to harden … Mike L

Great Post Technique MattR

One clarification: Tap down with a small nose brass punch ONLY as much as possible straight-on to the tip of the valve stem.
Newer engines have reduced diameter valve stems and these are easily bent by ham-handed hammering from the least angle. Hitting on the spring collar CAN/WILL pop loose the retainer shoes then spring disassembling whole works. Small pieces then either fly-way lost; or “screw-you”, rabbit like attracted to going down push rod holes and oil drain back passages. Then you swear, and sweat, restoring.

Matt your engines now are primarily V-type with wet coolant flow intake manifolds. Real PITA to intake R & R. and reseal all.
Single cyclinder engines, most inline engines, even some dry “easy” intake manifold V-engines you can much speed up the valve “freeing up” and “detaring” by intake manifold taking off then able to the desolve, work directly at the valve head and stem though the intake port.
Intake manifold off then you can really aggressively solvent wash or steam clean the manifold interior surfaces so you side step that whole later re-heated dripping down re-tarring of the valve stems.

“Port” fuel injection system offer a great in-between possibilty.
Pulling just the injector fuel rail and attached injectors then gives you a straight on direct hole to the gooed valve stem and valve head to be able to wand spray on tar solvent/de-carbonizer. Patent/commercial. Kerosene. Isopropyl.
The less gooey crap you force down through the cylinder bore the safer you will be.
Piston Rings. Rings. Rings.
Soft aluminum piston skirts and ring grooves embedding with abrasive grit then machined surfaces back and forth wearing away.
Gasifier tars can have an abrasive ash nuclei core that get carried in.
Overpulled systems can spew ash past cyclones and settlement chambers.
Bag filters notorious for woodgas heat burn-throughs, soot lite-offs and burning up.
Clogged/wetted pleated panelfilters on woodgas systems notorious for then being engine “vacuum” sucked unseated and even ballooned and torn/split open.

Steve Unruh

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Hi Steve, On my 91 S-10, one of the pushrods broke in 3 pieces and fell into the crank area. One was caught and smashed down there by one of the crank weights. Very little clearance. I also dropped a small bolt down a pushrod hole and lost it in the lifter valley below. I think I found that later. Though I walk through the valley … I shall fear no evil … etc etc … :o) … Better to never make tar … My experiments taught me a lot … Mike L

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Bad start to what ended up to be a pretty good day!

So as Ive mentioned before with the Flex Mini Im running the shop with I sometimes forget about it and run her out of fuel. I did just that last night before I left work and it made some tar as it was re establishing itself. Before I shut down for the day, it was making some smoke out the mixer. I knew it prolly a bad idea to shut down and did not have any gasoline to wash her with either. But I had enough for the day and just wanted go home and get super.

So I get there today with anticipation of a stuck intake and sure enough it gummed up good. So after some thinking I thought Id try something different getting this valve freed up and is why Im bringing this thread back to life.

So instead of pushing and pulling on the valve or even tearing the head off: I though what If I yank the carb off and heated it up from inside the chamber. ( very important first step, if there is a gas tank get it off and as far away as possible. ) I removed the gas tank, carburetor, valve cover and spark plug. Pretty gunked up in there it needed cleaning anyways. So after all this was removed I put the torch on a lower setting and stuck it in there. It started burning and freeing up that gunk and I could easily scrape it out with a screw driver. After this initial cleaning and warmed up I then slowly cranked it over until the valve was open and applied more heat. If you try this do not over do it, You want just enough heat to free things up while burning off the crud. I kept cleaning more and more gunk out and after it was good and warm, I slowly cranked it over with my hand holding the rocker arm against the push rod so it could not fall out. Once I had the valve moving, I then used the electric start with my hand still holding the rocker arm. Crank it over until the valve could move free enough to keep up with the rocker arm. Now if you let it cool it can freeze back up as I found. So you need to keep it moving while it cools, once it was cold enough I doused it down with some kero in a spray bottle, spraying in through the intake port. At this point I cranked it over a bit longer to blow out all the kero and put it all back together. Fire right up!!

So that is the easy way that I have found so far to free up a gunked up valve and also clean the port out. If I ever do this again Ill do a video of it, to show how I did it. Much better way to do this if you ever get into this situation. :fire:


thanksfor the post Matt…


Thanks for posting tar fix clean idea plans, sorry too hear you tar’ed one up, glad you found an easy way too clean and free up. By the way did the tar make your throtle plates stick.? Now i may extend my char bed on my 4.3 s10 design plans. Due too bridgeing i think my small charbed cooked up and toasted my ammo can seal ash door. AFter going intoo heater mode.NO FIRE CAUSED JUST A SMALL TRAIL OF SMOKE WHILE DRIVEING HOME ON PETRO, WHILE ASHH DOOR LEAKED OUT SOME SMOKE.

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I think most of us running daily experience a smoky startup from time to time. I’ve actyally stopped drilling the lightup hole with the poker if I’m not in a hurry. A piece of wood often gets pushed down into the char doing that. Most of the time the torch reaches nozzle level anyway. If I run the blower only half a minute longer before I add wood I’m still making gas/fire at reverse.

Both my gasifiers made the throttles a little bit sticky when they were new and not broken in but no issues after that. However I never, ever use damp wood.

I wonder how much damage one single chunk pushed down into the char can make?


Hi joe its been dry season here now allmost a month, grass is still 75% grean though so still need rain. Well in Matt Rider case useing pellets might tar up easyer being small fuel ororü it is not keeping a researve charbeorümore char bed criticle.? mine was smokeing a little at the ammo can bottom ash /cher dump, after the seal burned up from either heater mode low on char and bridgeing, or i got ash in door when cleaning the ash out and created a leak at the ash door and caused the heat too burn the seal out and caused me too stall from no hopper draw. I gess i am at leist learning the orher 75%,operator skills.I probbly got ash in the door when cleaned the ash bin and i forgot too insulate a top the ammo can lid for heat bearier.

No its not because of the pellets: the reason is opperator error nothing to do with the machine or pellet fuel. I keep running it out of fuel and then it has to re establish itself. I dont give it time to do this because my batteries are junk and so is my charger. So I dont have time to just run under blower. If it does make some tar I just run gasoline to clean it out. But in this case I didnt have any to run to prevent this.

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Hi Matt glad too meet you at argos, i never used pellots so i dont know much about them other than what WK book says smaller fuel can make tar easyer than big fuel, though you still seem too have good gas with good size resticktor, operator error is me too, mught just need too find a hot spot that works every time too put a warning low on fuel buzzer. I need a hopper rotater stirrer for small stick size wood too keep bridgeing away with the small wood, it burns and runs well and clean, long as like you say can keep it full and moveing down too maintain a good char bed. Maybe you could use on your units is a timer too set a buzer for refill reminder when out working once you know about when it will run low.


Hi Kevin,

We’ve finally had some rain now for the past week but unfortunately too late for most grain farmers.

Right, the 75% operator is a never ending learning curve. As soon as you think you know your machine it will teach you something new :smile:


Yup Ive been at this for 6 years and I do this as a living. These machines always humble me!!! lol

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Hi Matt, similar to Kevin’s idea. How about a temperature alarm or a low hopper pellet level alarm that has a loud horn or buzzer to let you know when you need to refuel. So even in the shop you will hear a alarm when you are busy working. You already have the automation to do it.

Temp wont on this one as the hopper temps stay linear even if you burn thing to the grate it wont get hot. However, since its running pellets and the fact it dont have that nasty gas or the hot temps I can but a level sensor in there. On the Power System this is exactly what they will have in the auger feed hopper so the primary will never be below it the feed sensor.

On the shop machine, Im just going to build a larger funneled hopper and that will lay the foundation for the level sensor.

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