Briggs& Stratton engine will not turn over

[JimP2014]

We call that the compression release bump or the ACR bump.
The camshaft has an automatic compression release built on to it very close to the intake lifter lobe.
At low RPMs it kicks a small little finger out which protrudes out past the base circle of the camshaft in the spot where it's fastened.
This little finger causes the lifter to bump out right after the intake valve closes as the engine turns.
Has the engine gets up above a couple of hundred RPMs , centripetal force overrides the pressure of the little spring that holds this finger out normally and then it no longer protrudes past the camshaft love at any position so the valve smoothly opens and closes without any bump.

This is why on many of these engines if you take the air filter out and start them you will hear a little muffled popping sound coming out of the intake when they're cranking and when they first start to spin up to speed running on their own. You will also hear this when you turn off the key if the air filter is off especially and as the engine coasts down before it stops spinning.

This is simply that little finger being pushed back out by the spring because the RPMs are slow enough and it's allowing some of the air to puff back out of the intake valve which blows out of the air filter.

Looking for this compression release bump is the way you can tell if the ACR is busted but it doesn't tell you anything about the valve timing from the cam.
A camshaft could have been installed incorrectly if you don't know the history of the engine without the dots lining up or more commonly, one or both of the lobes could have slipped and are no longer in their proper position in relation to the camshaft shaft and gear.

Typically if you have one of these problems you will either hear an abnormally funny noise coming from the middle or the rocker cover of the engine and you will also typically have some sort of popping or backfiring either out the exhaust or the intake that just doesn't sound right either.

That's because the piston is still going up and down like it's supposed to and maybe one of the valves is operating properly but the other one is either closing way too early or way too late and depending on how this works out, you're either going to get some combustion blowing out the exhaust or the intake or some sort of kickback.

These engines really aren't that complicated so there's got to be something that we're all missing and overlooking because we're not there to check it out in person.

This is why I'm hung up on a consistent and systematic troubleshooting approach every time.
It gets me to the root of the problem the quickest way possible.

If you have spark and the Piston is going up and down and you have compression that will blow your finger out of the spark plug hole and it doesn't suck your finger back in the hole...and you give it an external fuel source like some carb cleaner spray into the intake....THEN it should do something that sounds like combustion, backfire, popping, trying to run, etc.
Once you know that the flywheel key is not shared and you have all of the above things, about the only thing it can be is the timing messed up on the valve train from the camshaft somehow not opening the valves at the correct time.

I really can't think of anything else that could do it.

You might try spending the engine over by hand with the valve cover off until the valve starts to open or even starts to close and then put some extra pressure with your thumb and a rag as hard as you can pushing down on the pushrod side of the rocker arm.

I didn't actually test it but I'm pretty certain the one with the Chinese camshaft that was slipping would have made a clicky ratcheting sound and the rocker arm would have been able to be pushed and pushed the push rod down had I have tried this.
I know once I had the camshaft out in my hand, I could easily rotate at least one of the lobes around the shaft even though it was knurled and supposed to stay pressed on in one spot.

Okay Toby I did read this. I haven't gone over your first post. You did mention about the camshaft so basically the removal of the camshaft.

So in the past 6 weeks I have seen fire coming out of the intake. I have seen smoke coming out of the intake but not testing everyday. It's random, seemingly and sporadic. I have heard loud banging coming from the engine. I've heard explosions coming from the engine I've seen hunting and surging. I have seen 800° f on the exhaust pipe. Sometimes I've seen 500° Fahrenheit on the exhaust pipe. It's like the symptoms don't always carry over to the next day. The last time it was running 2 days ago it sounded like the engine was cheap. There was hunting and surging going on. It did start up instantly and with in maybe a minute the exhaust pipe got up to 800° f.


Now I'm not an engine mechanic but it feels like a person has a broken arm on day one. They go to sleep the next day. They have a broken leg and there's no more broken arm. It's just very weird and I don't have the background to understand how all this is coming about and why it's happening, but not all of of the symptoms carry through to the next day you would think if something's broken it's broken. It's broken the next day. It's broken the third Day but maybe there's an explanation why all these symptoms keep swapping in and swapping out. I'm going to get the new or should I say repaired cylinder head. Hopefully tomorrow I'm going to put it all back together now. I'm expecting if nothing changed to start right up to hunt and surge and an exhaust pipe of 800° f within maybe a minute or less. That's what I'm expecting but if I go back to fire coming out of the intake and explosions then I don't get it. Maybe maybe because I'm unwilling to take the whole engine apart and look inside what's going on because I really don't know how to do that. It could get back to where my feeling is. If there are external components that I could could improve upon through adjustment than great. I want to keep going on that. If there's something definitely internally wrong then I'm not going to mess around with things I really don't know. So then at that point I say the engines garbage even though it's not to someone who's a serious mechanic. But for my purpose is it's garbage because I'm not going to attempt to fix it. So I've been going with a theory that it's all external stuff that just needs to be tweaked adjusted and properly set in some way.

You obviously provide a lot of information that's useful and a lot of that goes into someone who is willing to take apart the engine, the internal aspect of it and look things over. And I'm really just someone who wants to cut the lawn and you know you can't have your cake and eat it too. So I get that part. But that's where that stands and tomorrow I'll have a better idea.

Jim

 

[TobyU]

Okay Toby I did read this. I haven't gone over your first post. You did mention about the camshaft so basically the removal of the camshaft.

So in the past 6 weeks I have seen fire coming out of the intake. I have seen smoke coming out of the intake but not testing everyday. It's random, seemingly and sporadic. I have heard loud banging coming from the engine. I've heard explosions coming from the engine I've seen hunting and surging. I have seen 800° f on the exhaust pipe. Sometimes I've seen 500° Fahrenheit on the exhaust pipe. It's like the symptoms don't always carry over to the next day. The last time it was running 2 days ago it sounded like the engine was cheap. There was hunting and surging going on. It did start up instantly and with in maybe a minute the exhaust pipe got up to 800° f.


Now I'm not an engine mechanic but it feels like a person has a broken arm on day one. They go to sleep the next day. They have a broken leg and there's no more broken arm. It's just very weird and I don't have the background to understand how all this is coming about and why it's happening, but not all of of the symptoms carry through to the next day you would think if something's broken it's broken. It's broken the next day. It's broken the third Day but maybe there's an explanation why all these symptoms keep swapping in and swapping out. I'm going to get the new or should I say repaired cylinder head. Hopefully tomorrow I'm going to put it all back together now. I'm expecting if nothing changed to start right up to hunt and surge and an exhaust pipe of 800° f within maybe a minute or less. That's what I'm expecting but if I go back to fire coming out of the intake and explosions then I don't get it. Maybe maybe because I'm unwilling to take the whole engine apart and look inside what's going on because I really don't know how to do that. It could get back to where my feeling is. If there are external components that I could could improve upon through adjustment than great. I want to keep going on that. If there's something definitely internally wrong then I'm not going to mess around with things I really don't know. So then at that point I say the engines garbage even though it's not to someone who's a serious mechanic. But for my purpose is it's garbage because I'm not going to attempt to fix it. So I've been going with a theory that it's all external stuff that just needs to be tweaked adjusted and properly set in some way.

You obviously provide a lot of information that's useful and a lot of that goes into someone who is willing to take apart the engine, the internal aspect of it and look things over. And I'm really just someone who wants to cut the lawn and you know you can't have your cake and eat it too. So I get that part. But that's where that stands and tomorrow I'll have a better idea.

Jim

That is a very odd situation if it's that inconsistent.
I have never seen one of these that wants the camshaft lobe slipped, that would ever run anywhere near properly or even continue to spend enough to call it running after this happened.
It's pretty much like when one gets a bent push rod or a rocker arm stud loosened up or other valve train issues.
They will pop once or twice and then they will die. After that all they will do is crank and maybe pop.

I never advise people to do any work they're not certain of being needed.
I never advise the average owner to start tearing it anything and take anything apart unless we are 95 to 98% certain we know what the problem is.
Too many times I see owners with their mowers start taking stuff apart and they're not even in the right vicinity of where they need to be considering a potential problem!

The exhaust temperatures you are quoting me got my attention because none of that is important and you never hear anybody talking about this as far as repairs or techs etc.

I have absolutely no idea what any of the tens of thousands of lawn mower engines I have worked on have for exhaust temperatures. Lol
I do know off the top of my head what is considered hi for EGT due to having a little bit of experience with some Rotax engines and reading about some Ultralight aircraft etc.

It's just never been a concern for mower engines so there's never a reason to measure it.
Yes, if they're lean the EGT will be higher and if they're rich it will be lower and there are also some patterns if the ignition timing is advanced or retarded but you don't need to check the temperature to do any of this.

Far more accurate, quicker and easier to diagnose a rich condition by the sound and how it's running and slightly restricting some air flow into the intake to see what it does.

I would love to investigate your engine in person because it seems to be a really unique situation.

If it continues to run it all in the next few days about the only thing I can think of that makes sense would be a popped valve seat and since you said it was blowing fire out the intake more than likely on the intake valve.
I recall you have switched heads on this so unless that only started occurring with the current head, this possibility makes less sense.

I have certainly seen engines though that will run fine for a period of time and then the valve seat will pop out and then they won't run it all or they'll pop quite a bit before they die. Then after a few revolutions etc the valve seat magically works its way back in to the head and seals up enough to run.

 

[JimP2014]

That is a very odd situation if it's that inconsistent.
I have never seen one of these that wants the camshaft lobe slipped, that would ever run anywhere near properly or even continue to spend enough to call it running after this happened.
It's pretty much like when one gets a bent push rod or a rocker arm stud loosened up or other valve train issues.
They will pop once or twice and then they will die. After that all they will do is crank and maybe pop.

I never advise people to do any work they're not certain of being needed.
I never advise the average owner to start tearing it anything and take anything apart unless we are 95 to 98% certain we know what the problem is.
Too many times I see owners with their mowers start taking stuff apart and they're not even in the right vicinity of where they need to be considering a potential problem!

The exhaust temperatures you are quoting me got my attention because none of that is important and you never hear anybody talking about this as far as repairs or techs etc.

I have absolutely no idea what any of the tens of thousands of lawn mower engines I have worked on have for exhaust temperatures. Lol
I do know off the top of my head what is considered hi for EGT due to having a little bit of experience with some Rotax engines and reading about some Ultralight aircraft etc.

It's just never been a concern for mower engines so there's never a reason to measure it.
Yes, if they're lean the EGT will be higher and if they're rich it will be lower and there are also some patterns if the ignition timing is advanced or retarded but you don't need to check the temperature to do any of this.

Far more accurate, quicker and easier to diagnose a rich condition by the sound and how it's running and slightly restricting some air flow into the intake to see what it does.

I would love to investigate your engine in person because it seems to be a really unique situation.

If it continues to run it all in the next few days about the only thing I can think of that makes sense would be a popped valve seat and since you said it was blowing fire out the intake more than likely on the intake valve.
I recall you have switched heads on this so unless that only started occurring with the current head, this possibility makes less sense.

I have certainly seen engines though that will run fine for a period of time and then the valve seat will pop out and then they won't run it all or they'll pop quite a bit before they die. Then after a few revolutions etc the valve seat magically works its way back in to the head and seals up enough to run.

Hi Toby, I did see this on Wednesday. I got the cylinder head back with essentially a brand new spark plug hole, but I haven't done anything further except without a highly specialized test. I disconnected the quarter inch fuel line from the carburetor and I do have a shut-off valve so after allowing the fuel to flow into a container I let it run for like maybe 45 seconds and the flow was perfect. So unless I did something wrong I believe I can eliminate something like sporadic fuel flow into the carburetor.

I will read everything you wrote above when I'm in front of a PC.


So what I am expecting at the very least is reinstall the cylinder head that goes with a 19.5 horsepower engine. The spark plug is already in the spark plug hole and it's brand new and right before I destroy the spark plug hole I was able to get the engine to start almost instantly and then it went into its hunting and surging. So I'm expecting that but from what I've learned it could be anything that's going to happen, including fire out of the intake. Loud explosions banging. Who knows, but that's where this is at.
Jim

 

[JimP2014]

Hi Toby, I did see this on Wednesday. I got the cylinder head back with essentially a brand new spark plug hole, but I haven't done anything further except without a highly specialized test. I disconnected the quarter inch fuel line from the carburetor and I do have a shut-off valve so after allowing the fuel to flow into a container I let it run for like maybe 45 seconds and the flow was perfect. So unless I did something wrong I believe I can eliminate something like sporadic fuel flow into the carburetor.

I will read everything you wrote above when I'm in front of a PC.


So what I am expecting at the very least is reinstall the cylinder head that goes with a 19.5 horsepower engine. The spark plug is already in the spark plug hole and it's brand new and right before I destroy the spark plug hole I was able to get the engine to start almost instantly and then it went into its hunting and surging. So I'm expecting that but from what I've learned it could be anything that's going to happen, including fire out of the intake. Loud explosions banging. Who knows, but that's where this is at.
Jim

I'm going to add some text just to be clear. So essentially 3 days ago I was at the stage where the engine started up instantly and then it went into its hunting and surging. That is the last set of symptoms and then what happened because I destroyed the spark plug hole. Is the spark plug flew out and then I tested with another cylinder head off a different engine and that had pretty much no compression. So I had the really good cylinder head fixed with a problem with the spark plug hole and before I destroy the spark plug hole that compression was about 85 PSI. So I'm hoping if I can reinstall all that today that I'm back to at least 85 PSI and and if that's true, I'm probably back to instant startup but then hunting and surging but I've learned it could be anything which of course makes no sense.

Jim

 

[TobyU]

I'm going to add some text just to be clear. So essentially 3 days ago I was at the stage where the engine started up instantly and then it went into its hunting and surging. That is the last set of symptoms and then what happened because I destroyed the spark plug hole. Is the spark plug flew out and then I tested with another cylinder head off a different engine and that had pretty much no compression. So I had the really good cylinder head fixed with a problem with the spark plug hole and before I destroy the spark plug hole that compression was about 85 PSI. So I'm hoping if I can reinstall all that today that I'm back to at least 85 PSI and and if that's true, I'm probably back to instant startup but then hunting and surging but I've learned it could be anything which of course makes no sense.

Jim

If it goes back to running but surging and hunting for a proper speed, take you a shot cloth or a microfiber towel and fold it into fourths and lay it for it restricts the intake hole under the air filter. This should reaching up the mixture a little bit or you can also try moving your lever to add some choke.
If it gets better when you're rich in the mixture either way, you know it is running lean.
This is normally case for hunting idle.
This means your jet is partially restricted in your carburetor..
We can worry about cleaning this out after we know if the engine starts and runs but surges.

 

[JimP2014]

If it goes back to running but surging and hunting for a proper speed, take you a shot cloth or a microfiber towel and fold it into fourths and lay it for it restricts the intake hole under the air filter. This should reaching up the mixture a little bit or you can also try moving your lever to add some choke.
If it gets better when you're rich in the mixture either way, you know it is running lean.
This is normally case for hunting idle.
This means your jet is partially restricted in your carburetor..
We can worry about cleaning this out after we know if the engine starts

If it goes back to running but surging and hunting for a proper speed, take you a shot cloth or a microfiber towel and fold it into fourths and lay it for it restricts the intake hole under the air filter. This should reaching up the mixture a little bit or you can also try moving your lever to add some choke.
If it gets better when you're rich in the mixture either way, you know it is running lean.
This is normally case for hunting idle.
This means your jet is partially restricted in your carburetor..
We can worry about cleaning this out after we know if the engine starts and runs but surges.

Toby, thanks for this reply. A few weeks ago I bought a brand new carburetor for it and what had happened was when I began using the brand new carburetor nothing changed. So for whatever reason the carburetor that was running the best was the older one so that is still inside the engine. Now tomorrow I should have everything put back together. The only thing really left that's somewhat challenging is setting the valve clearance, but everything else is in place I could very easily. Begin with that brand new carburetor that I have there is. I believe nothing wrong with it. There certainly won't be a problem with it, Jets or anything else inside it. However, how well is it built and all that compared to the one that's been in the engine for 3 years that I don't know? This morning I went out and I was hoping there was a problem with the fuel line in some way but there absolutely is not. So when the fuel is allowed to flow I got a bucket and the hose that would connect into the carburetor was now pouring gas into this bucket. There was no obstruction. I ran it like this for like 45 seconds because I wanted to keep the gas I have for now anyways because that gas is like brand new. The whole tank has been thoroughly cleaned. There's nothing inside the tank and there was brand new gas in it say about a week ago. When I put the cylinder head back the one that had the spark plug blown out of it. That whole install as far as I'm concerned went very well. I bought all new gaskets for the cylinder head and all the stuff around it. It comes with this gasket kit designed for the cylinder head. The only thing I can't do right now is put the muffler back because it goes inside a cage which would need me to remove the cylinder head which I just put on. So I'm just going to leave that but I can get an exhaust pipe onto the exhaust manifold for the cylinder head part ignition coil that air gap is like 101,000 of an inch. Spark plug is brand new. The only thing is if I use the brand new carburetor I might swap the solenoid which is currently in place because the tip of that plunger thing is cut off and I want it that way for now to rule out any weird thing going on with the electronic fuel solenoid. I want constant gas flowing and just keep track of that meaning for me.

Jim

 

[TobyU]

Toby, thanks for this reply. A few weeks ago I bought a brand new carburetor for it and what had happened was when I began using the brand new carburetor nothing changed. So for whatever reason the carburetor that was running the best was the older one so that is still inside the engine. Now tomorrow I should have everything put back together. The only thing really left that's somewhat challenging is setting the valve clearance, but everything else is in place I could very easily. Begin with that brand new carburetor that I have there is. I believe nothing wrong with it. There certainly won't be a problem with it, Jets or anything else inside it. However, how well is it built and all that compared to the one that's been in the engine for 3 years that I don't know? This morning I went out and I was hoping there was a problem with the fuel line in some way but there absolutely is not. So when the fuel is allowed to flow I got a bucket and the hose that would connect into the carburetor was now pouring gas into this bucket. There was no obstruction. I ran it like this for like 45 seconds because I wanted to keep the gas I have for now anyways because that gas is like brand new. The whole tank has been thoroughly cleaned. There's nothing inside the tank and there was brand new gas in it say about a week ago. When I put the cylinder head back the one that had the spark plug blown out of it. That whole install as far as I'm concerned went very well. I bought all new gaskets for the cylinder head and all the stuff around it. It comes with this gasket kit designed for the cylinder head. The only thing I can't do right now is put the muffler back because it goes inside a cage which would need me to remove the cylinder head which I just put on. So I'm just going to leave that but I can get an exhaust pipe onto the exhaust manifold for the cylinder head part ignition coil that air gap is like 101,000 of an inch. Spark plug is brand new. The only thing is if I use the brand new carburetor I might swap the solenoid which is currently in place because the tip of that plunger thing is cut off and I want it that way for now to rule out any weird thing going on with the electronic fuel solenoid. I want constant gas flowing and just keep track of that meaning for me.

Jim

New doesn't mean right... Especially with eBay and even more so amazon carbs.
I NEVER recommend replacing carbs as opposed to cleaning it the old ones or fixing them because sometimes the new ones don't run correctly and you are almost always installing a worse quality carb than you are taking off.
People are obsessed with "throwing a new carb on".
I do hundreds of carbs a season and haven't replaced over 3 in the last 10 years. Lol

 

[JimP2014]

New doesn't mean right... Especially with eBay and even more so amazon carbs.
I NEVER recommend replacing carbs as opposed to cleaning it the old ones or fixing them because sometimes the new ones don't run correctly and you are almost always installing a worse quality carb than you are taking off.
People are obsessed with "throwing a new carb on".
I do hundreds of carbs a season and haven't replaced over 3 in the last 10 years. Lol

Toby, when I got this engine the entire machine should I say it was destroyed? So 3 years ago I purchased a brand new carburetor on Amazon. That carburetor has been awesome for the last 3 years. But I will admit the problem is I can't figure out which one it is that I ordered back then. Also, I have seen so many videos and so many topics including carburetors for Briggs& Stratton engines. I've seen people that hate the Nikki carburetor and say they should all switch to the wall. Bro carburetor. So if I end up cleaning the carburetor that is currently on the machine right now I just want you to know I will be cleaning an Amazon so to speak carburetor the only problem is like I said I can't figure out which one it is and I agree with you if you don't get something safe from a certain vendor like walbro you end up getting an Amazon sponsored carburetor. It could be maybe from 10 different places to make carburetors for the Briggs& Stratton engine. They're all compatible but they're all from say a different machine shop. However that all goes which I don't know. The only thing I know is maybe 10 days ago. Because of all the strange things that were going on with the engine, I decided to purchase another carburetor on Amazon. I installed that carburetor and it run just as poorly or just as good as the other one. And you know my conclusion was that it was the same issue but I think you're saying maybe cleaning the one that's been on there for 3 years which I did get on Amazon. Which maybe is just. Let's call it potluck where I got the right one out of say 10 different vendors. Maybe cleaning that would be the solution. I don't have time to perform this test but a good test would be get a perfectly running engine and buy 10 carburetors on Amazon. All from different vendors. Install them and see which ones run and which ones. Don't sort of like consumer reports I guess but I don't have time to do any of that nor do I want to. I recently watched a video on a a flywheel which was a knockoff of a Briggs& Stratton flywheel and this flywheel which is not manufactured by Briggs& Stratton. The guy concluded it was better. If I could figure out exactly which carburetor Abbot 3 years ago or if there's some unusual markings on the ones currently installed on the Briggs& Stratton engine then I know that one works and maybe just go back to the original vendor where I got that from.

Jim
Send for my phone. Please excuse any typos above

 

[JimP2014]

Let me cut to the chase with this as to what I'm really saying. Maybe the one that's been in place for 3 years is just all messed up and the one I bought on Amazon say 10 days ago. It's just garbage and I thought they were essentially the same test but maybe they're not the same test. And I think that's maybe kind of like what you're saying. Clean the one you got.
Jim

 

[JimP2014]

Toby, thanks for the input and now that I'm totally more awake, you know I agree with what you're saying. Something goes wrong with the engine. Consider that one variable and then you still have that one variable. But now you introduce another variable some other carburetor. Now you got two variables. You had one but then you now have two and I'm very familiar with that. I will clean the carburetor but you don't really know the history of this. So 6 weeks ago everything was running great until the engine just stopped and it could have been lack of oil. And during that same event the exhaust pipe got so hot that the muffler separated from it in a couple days prior to that. What prompted me to do anything repair wise was there was a lot of smoke and it was either coming out of of the head gasket area or the valve cover gasket area. And I also did drain the oil maybe 2 months ago or maybe it was right around the same time as when all these issues all came about you don't know that because you read what I write. In any case, I'm going out in a couple hours and see if this thing runs but the only takeaway I can give you the more I think about all this there was no carburetor issue. It was really running very well. Say a couple months ago there was nothing going on except smoking and then from there I could have potentially made the whole thing worse because I didn't exactly know how to fix the smoking issue but the carburetor was not what caused every the engine is shut down while cutting. It was instant and the carburetor was perfect. But who knows, there's not. I'm not arguing with you about this. It's just a good idea to clean it and keep it the way it was. I just want you to know it probably wasn't the event that caused everything to go wrong, maybe 6 weeks ago.

Jim