Craftsman tractor engine compression or timing issue

I have inherited a Craftsman Lawn tractor and am trying to get it going. The engine seems to be having either timing or compression problems.

A mouse had made a home behind the petrol tank and chewed through some wires. I fixed the wires and the electrics are now good. It has a new starter and spark plug just before I started working on it. A neighbor has checked the timing and believes it to be good but doesn't have the knowledge to work out what is wrong.

The engine spins freely with the spark plug out but not with it in.

Videos below.

Spark plug in:

https://youtu.be/PiPghgo6POs

https://youtu.be/Ao1thHr-tlU

Spark plug out:

https://youtu.be/AXOg6eJ4fJM

https://youtu.be/3To7Y4Av2bo

https://youtu.be/CnJLimYkA4M

Thanks.

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@sandyberg what make and model is the engine? You do have spark when the engine cranks over?

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It is a 21HP model No: 917.28924

Funny but it was sparking, and we tried it with a different cool too, and that didn't help. But I just went out and now it is not sparking.

I adjusted the coil position and still can't seem to get it to spark.

Would that cause the resistance when it is trying to crank with the plug in though? I thought not...?

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*different 'coil' that is!

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No it would not. It could be timing issues as well as a valve settings issue. If it does not fire inside the combustion chamber with the gases present it will cause a lot if resistance to crank. Checked your valve clearance yet? The numbers you gave are your mower numbers. what is the actual engine number? B&S, Tecumseh, Kohler? Double check for spark, if you do not get any spark let us know.

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@sandyberg you've mentioned yesterday that the engine no longer had spark. Did you get that resolved?

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Ryan, I think I know what your problem is. On the larger riding mower engines, there is a compression release built into the engine. Basically it is there to hold the exhaust valve open when the engine is not running. Sometimes this device fails and the valve is left closed. The starter is not strong enough to overcome the compression caused by the closed valve. You may hear a partial turn of the engine and then it won't turn over. So...what to do? Remove the air cleaner so you have full access to the air intake to the carburetor. Put on a leather glove and put it tight over the air intake on the carburetor and keep it there while someone else cranks the engine using the starter normally. The engine should turn over easily and will probably start. BE CAREFUL IN CASE IT BACKFIRES THROUGH THE CARBURETOR. It could burn you.

What you are doing is, you are not allowing any air into the cylinder so there is none to compress! Therefore it will turn over right through the compression cycle without releasing the valve. Once you get it to turn over properly, let it take in some air and fuel. You should be able to get it to run.

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Damian - thanks for the help. I covered the inlet and the engine did indeed 'turn' much better. I think this confirms my fear that there is a problem with the compression release on the camshaft. However the engine would still not run. I have confirmed a good spark, now I think there is a possibility it is not getting fuel as well. I checked the fuel filter and it is clear but it does not seem to be filling up when the engine is turning. The spark plug is not wet after turning the engine a few times either. I have a half full tank so I think there is enough head over the fuel feed.

I would really like to confirm that the compression release is the only problem with this engine, by at least getting it to start, before I go about changing the camshaft.

Thanks for your help!

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Ryan, based on your response to me I am now quite sure at least one of your problems is the compression release. Your response indicated you may then need to dig into that problem if such is the case. However, I doubt very much if you really need to worry any more about it, because in my experience, once you get the engine running and warmed up, this compression release gadget will become unstuck and you will find the machine will crank normally thereafter. What usually happens is the the release mechanism hangs up after the engine sits without use for a long period of time. It usually occurs in the springtime after setting all winter or something like that. So just go ahead and solve that fuel problem, get it running in the manner I described, and I'm betting you're good to go.

A word about the fuel problem. To confirm it, with the air cleaner off, put a small amount of gas directly into the carburetor, then start it in the manner I described, i.e. leather gloved hand over the intake. I can guarantee you, that if you have spark in the cylinder, it will fire off for a few seconds. This will prove for you that all you have left to do is solve that fuel problem. Be very cautious when following this procedure with fresh gas in there, because an unexpected backfire could burn you if you are not protected properly.

Keep you face away and off to the side from the opening to the intake during cranking. Make sure you use a leather glove. An engine backfire is basically an explosion in the intake manifold directed back through the carburetor intake channel.

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Ryan, did you get that engine running ok?

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Damian. I did not. I have now found that the solenoid in the Carburettor was very soiled and jammed. I am going to strip down the carb and clean it. Hoping I don't need to buy a new one, especially if I still have troubles with the compression release!

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Damian, the carb was not I great shape, so I bought one off of a running engine to give it a try. Inside the engine inlet looked pretty gunked up too. I changed the oil and gave it as good a clean out as I could (there seemed to be a lot of gas in the cylinder which came out when I ran it again without the spark plug in there. After all that, and putting the 'new' carb on, it started! I still had to hold my hand over the air inlet as below:

https://youtu.be/Nu6zQWaTxqc

It's got better at starting, but still has some resistance on he compression stroke so I think there still maybe a problem with the compression release. I am going to run it a bit tomorrow and then post another video.

Thank you everyone one for your help!

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Most Helpful Answer

Ryan, if indeed a new starter and battery fully charged and engine turns over slow with plug in and turns good with plug out, a big reason for this is a valve adjustment is required. Use the 1st and 2nd link below to see the fix, the 3rd link you can determine the spec. to know what to set the valves at.Good luck.

I hope this helped you out, if so let me know by pressing the helpful button.

https://www.youtube.com/watch?v=0cWoEk5G...

https://www.youtube.com/watch?v=NjzX-PUj...

http://www4.briggsandstratton.com/miscpd...

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Thanks! I think this may be the problem, and the video is great. Unfortunately I can't get the OHV cover off as it has been stuck on there with some crazy weather seal I think! Any tips on how to get it off without damaging it?

I hope this is the answer, but can't say for sure yet.

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Ryan, use a sharp putty knife or a utility knife under one corner and work your way around cutting seal/gasket, pry on/off cover as you go may help, if flange on cover distorts a bit restraighten and use a bead of silicone to aid in resealing.,I have never had this problem. Good luck. If answer solves your issue select/check it off

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Thanks L Pfaff! Managed to get the valve cover off, will try and set the valves in the morning!

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Ok, so I adjusted the valves as per the videos (they were a little tight but nothing wildly out) but still no luck - engine doing the same as in the YouTube videos on the first post.

When I turn the engine by hand, the restriction seems to be just as it hits bottom before the compression stroke. This slight restriction seems to be there whether I have the spark plug in or not. Is there a possibility there is more serious damage to the engine? Or is this perfectly normal?

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Ryan, unusual for the valve lash to have been too tight on an engine unless some body else has been tinkering with it. Has the engine been taken apart by some else at one point before you inherited it, you may have to dig a little deeper and check the cam and compression release for damage/wear.

Check the attached video links for more info.

https://www.youtube.com/watch?v=tvCnXa37...

https://www.youtube.com/watch?v=dWHPHGZA...

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