PT422 Engine shaking / sputtering

[Gravy]

http://robinamerica.com/media/manuals/128988858968757500.pdf

It's a very easy valve adjustment, except that on my 425 there is no way to manually turn the crankshaft short of pulling the engine. I pulled the spark plugs and repeatedly bumped the starter while using a soda straw in the plug hole to indicate TDC.

 

[toy]

It could be that one of the spark plugs has a crack in it that opens up when it gets hot and allows it to short out the spark plug to the engine instead of inside of the cylinder. Could be that you have a wire that is shorting out causing you to loose the arc at the tip of the plug. If you can get the machine to a place where it is really dark and open the hood and start the engine sometimes you can see the cross arcing. I noticed in your gas tank that it is pretty low on fuel, I try to keep mine full as much as possible, that cuts down on condensation inside the gas tank.

 

[KMA]

Hi all,

I finally got some time to work on my tractor and compression tested both cylinders. The right cylinder (looking from the back of the tractor) had a normal looking spark plug and tested at 155 psi (or about 11 kg/cm2). The service manual indicates that 12 kg/cm2 is expected. I did not warm up the engine prior to testing, which could account for the difference. The left cylinder had zero compression. Prior to testing, it's spark plug would be wet which leads me to think there is a problem with one of the valves (e.g. stuck open). I thought if the piston was seized, it would affect the other cylinder too... but I could be wrong.

This is all a bit over my head. Do you think I'd be crazy to try to pull of the cover and look around, maybe to try to fix it? Is there something I should be looking for?

Thanks again.

 

[Marks481]

Probably a stuck open intake valve. Pulling the valve cover off is very simple, the only issue is that you will need a new valve cover gasket to replace the old one. That part of the job takes 5-10 minutes.

The bad news is that if you have a stuck valve, as a minimum you will have to pull the cylinder head and replace the valve. You will probably need a new pushrod, as it most likely will be bent. You also will need a new cylinder head gasket.

You could also just have a blown cylinder head gasket.

If you don't like engine repair as a hobby, now is probably the time to start searching for the local small engine repair shop.

 

[woodlandfarms]

I do not have, nor have I worked on that engine. But that said, it is pretty rewarding to fix an engine, and with a minimum of tools you can probably accomplish either a bad head gasket or a bent valve / rod.

Patience, serious note taking, and keeping your work area clean will land you several hundred in savings.

I am sure that you can do this. but it will take time and maybe at that point it is worth more for you to just take it in.

Carl

 

[Gravy]

Pulling the valve cover is really easy - 4 small bolts and it's off. My gaskets survived just fine.

Even if you plan to have a shop do any repairs, I suggest that you pull the cover and take a look.

 

[MossRoad]

Pulling the valve cover is really easy - 4 small bolts and it's off. My gaskets survived just fine.

Even if you plan to have a shop do any repairs, I suggest that you pull the cover and take a look.

I agree. Not only will you most likely be able to see what's wrong, if you decide to take it to a shop, you will know what's wrong before you take it so they cannot tell you it is your planetary headlight pump and charge you for work not needed. :laughing:

I would suggest getting a repair manual for that model engine and reading it front to back. Then remove the cover and take a look. It never hurts to understand what is inside of your engine and how it works. In fact, I am always amazed that so many people do not know or care to know how a machine they use really works. Cars are a perfect example. So is the clock on a VCR. :laughing:

 

[KMA]

Thanks guys. I will take a look tomorrow. I read quickly through the service manual, but will look closer.

What should I be looking for? Will it be obvious? (sorry for the dopey questions)

 

[MossRoad]

You know... it would be a good idea to find an old lawn mower engine and disassemble it to see what's inside and how it works. I started working on my parent's car in high school and rebuilt the engine using books as my reference. Small engines were a breeze after that. It was an education.... and fun. I then started working on 2 stroke engines. No valves, pushrods, lifters, etc... but it still sucked a gas/air fuel mixture, just used ports instead of valves, ignited it at the correct time, which forced the piston down, which spun the crank.

You will know if something obvious is wrong.
Disconnect the battery and disconnect the spark plugs so there is no chance of accidentally starting the engine.
Pull the valve cover and just look around for a few minutes.
Remove the spark plugs and put something over the holes so nothing drops in.
With the spark plugs removed, you should be able to turn the engine over by hand.
Watch the action of the valves and see if they are all moving after two complete rotations of the engine. You need at least two rotations. Every valve should have opened and closed after two full rotations of the crank shaft.

 

[KMA]

Took off the valve cover and got them into a no lift position... it seems like the exhaust value rocker arm has quite a bit of play in it (especially compared to the intake side). I'm not familiar enough with engines to know how much play to expect. I'm going to pick up a thickness gauge to get them adjusted today.

Any hints on what things to look for?
How about getting it to TDC? Looking at the service manual, it appears I will need to remove the blower housing to get to the flywheel and cylinder markings. Sound right?

Thanks again everyone.