Toro Zero Turn smoking

[closecut]

Sounds like a valve stem seal problem.

Valve Seal​

Part Number: 690968 (double check this number versus the ENGINE Number on the data plate on the ENGINE).
They are easily damaged when installing,so don't use a screwdriver to work them down over the valve stem.Use the proper tools and do it right.The groove for the retainer can damage the seal if it is forced down over it without the proper tool to ease it over the groove.

 

[Ohio_Paul]

I had the exact same issue for years until I installed a fuel line shut-off valve.

 

[TobyU]

Well, first of all I think your boss is being kind of a weirdo expecting so much perfection out of old used worn out parts.
He should realize that's just not possible just like extreme lifespan isn't possible on a lot of this new equipment and you should never expect that or lead your customers to believe you can provide that.
People should also get out of the habit and stop offering engine rebuilds anyways. It's simply not worth it and not even cost-effective for the customer. Neither is a new engine typically because the cheapest you'll ever find one is 850 and most over a $1,000 and these are actually old prices. I haven't checked them recently so who knows what they've gone up to.
There was a time where you could get a 17 or 17.5 horsepower Briggs 31xxxx series on the shelf at rural King for 479 but that was about 6 years ago.
That made it almost feasible but in reality the only cost-effective way to fix one when people say it needs an engine is to put a good used running engine on one.
The only repairs that are feasible to do are blown head gaskets and occasionally a snap rod but even that you're probably almost always going to be cheaper just to get a good used engine and this is sometimes the case even if you're not paying for labor and doing it yourself just because the parts but if you can get lucky and use some erratic acid and or clean up the crankshaft and just replace the one rod even if you have to buy a new rod and the gasket for the sump, you can do it possibly cheaper than buying a good used running engine to slap on the machine.
A lot of those early twins got destroyed because they were sucking dirt in around the air filter and it wiped out the rings for some reason where hardly any of the singles ever had this problem and some people run those without an air filter at all and they still last for many years so I really can't figure that one out but oh well.
Have you actually run this machine and got it good and hot for over 30 to 45 minutes or an hour and actually mow with it??
Lots of times mowers especially push mowers, will get the muffler so full of oil that it will take at least a half an hour running to burn it all out of there.
It sounds like that's probably not your problem but always keep that in the back of your mind.
It's probably valve stem seals and I would pop the springs off by holding the valves in position with either compressed air or rope packed into the cylinder and the piston pushed up slightly and put the good umbrella style valve stem seals on each valve.
I think that's what this engine has anyways but I've been known on cars and some other things that just used a little simple o-ring too double up and put the umbrella style and everything or some other improved design or the small o-ring one plus and umbrella style.
That should fix it and I guess you could turn off the air pressure or back the flywheel down a little bit for the piston and see if the valve stem wobbles too much in the guide because that could be an issue too but probably not the case.
New seals would probably solve the problem but at worst case scenario then you would slap a new head on it or I believe this is a twin so heads.
It's still kind of a crap shoot though because what if it is the actual piston rings and cylinder walls and sealing and you waste the time and money to put two new heads on it??
You could go back to the old school basics and try to do a compression test and a leak down test and then do a wet test with maybe some 40 or 50 weight oil squirted in the cylinder and see if you can determine if it is the rings or the valves or maybe take the valve cover off and look and listen for any air coming around the valve.
It's still a good percentage of guessing and hoping though.
But your boss fails to understand or accept is there really are no exact things in this field.
There are maybe 80th percentile and above but slapping new parts on and boring out cylinders and putting larger Pistons if available or just honing and replacing the rings doesn't always give you 100% results or even 93% results.

 

[TobyU]

I had the exact same issue for years until I installed a fuel line shut-off valve.

Yes, especially if the fuel is kind of whitish with only a tint of blue when it first comes out and only for two or three seconds. That is a common sign that the carb is continuing to drip inside because the needle and seat are not shutting off properly and you'll get the smoke after it's sat for 10 minutes or longer but it clears right up.

 

[STEVES]

Well, quick, cheap and then continue on, would be to replace the valve seals. No tear down, put air into spark plug hole after backing off valve lash. piston will go to bottom, then remove intake valve spring and replace seal. Adjust all valves to specs. Like said before run and work engine to clear out muffler. If good = Done. Should always do seals when doing tear down.

 

[Gescha]

I work at a rental shop and just tore down a zero turn replaced rings and head gasket. Was burning oil badly like a quart an hour. Well now it smokes on start up for about a minute. Well I realize I had oil in the carb so I let it run half an hour. Anyway it still smokes on start up. Any ideas thank

Change the valve guide seals.

 

[The Specialist]

Wow, this is interesting/the advice that is!! I do part agree with the guy about the process that you did on the cylinder. The actual way this ISVs to be done is that you have a boring machine, telescoping gauges and honing stones. Too much to get into here, but you would have been better off to replace the engine. The cylinder head- did you clean up the valves? Usually if the exhaust valve is not seating, a little oil goes into the cylinder head, hence, why you are getting the puff of smoke on start up. I think you are ok on the deglazing of the cylinder, because if you weren’t, it would smoke all the time, but the engine would be noisy. To do the valves, remove cylinder head, take the valves out, put one in a drill mounted in a vide. Get 120 grit emery cloth, and clean them up with the drill spinning. To do the face, come down with the emery cloth on a 45degree angle lightly with the emery cloth until cleaned up. IT is also best to dip the emery cloth in gas before you start.

 

[TobyU]

Wow, this is interesting/the advice that is!! I do part agree with the guy about the process that you did on the cylinder. The actual way this ISVs to be done is that you have a boring machine, telescoping gauges and honing stones. Too much to get into here, but you would have been better off to replace the engine. The cylinder head- did you clean up the valves? Usually if the exhaust valve is not seating, a little oil goes into the cylinder head, hence, why you are getting the puff of smoke on start up. I think you are ok on the deglazing of the cylinder, because if you weren’t, it would smoke all the time, but the engine would be noisy. To do the valves, remove cylinder head, take the valves out, put one in a drill mounted in a vide. Get 120 grit emery cloth, and clean them up with the drill spinning. To do the face, come down with the emery cloth on a 45degree angle lightly with the emery cloth until cleaned up. IT is also best to dip the emery cloth in gas before you start.

Now you know you're going to make some people's heads spin around talking about cleaning up valves and even daring to mention touching the sealing surface with something so unprecise as your finger!!!
I don't actually think I've used Emery cloth on them or sandpaper but I have used the fairly fine wire brush on the grinding wheel to clean them up I do however, recommend using some course grit lapping compound and then some fine grit lapping compound and lap them decently in the head once you do this because you're probably going to round off the sharp angles a little bit even though cleaning up the crap and making the surface smooth probably outweighs any problems you could cause by getting the angles off a little but then when you go and lap them you will be increasing the sealing ability quite a bit.
When I officially opened my shop in 2011 I looked around and thought about buying one of the old school valve grinding apparatuses but found out they're still pretty expensive and I'm a cheapskate and there's not really that big of a demand or need to do it and I don't rebuild inches anyways and most of those jobs that would require that are simply too labor intensive and time involved for me to bother doing when I can sit here all day long doing annual services and carb cleanouts and make a lot more money in less time and help a lot more people overall.
So I gave up on the idea but if I'm ever at a garage sale somewhere and see one that they're basically giving away I will pick it up.
The only time in my life I ever actually used one was in junior high school in the metals and small engine class where are we did a complete rebuild and ground the valves whether they needed it or not.
The fact is, lawn mowers are low performance little turds!
This makes them very forgiving and you just don't see that many burnt valves or valves that really need to be ground.
You find far more popped valve seats and way more slipped valve guides causing valve train issues but it's not the actual valve cut angle sealing surface at all.

 

[cheny]

Reading all this about replacing valves mine I found running premium gas stopped smoking was this done it didn't say anything about the gas

 

[TobyU]

Reading all this about replacing valves mine I found running premium gas stopped smoking was this done it didn't say anything about the gas

I'm going to file this in the category of things that can't happen and aren't possible until I actually see it for myself.
The problem is what's your definition of smoking?? What kind of smoke was it? Was it mostly white, mostly blue or mostly black and sooty?
There should be no way that putting premium fuel in your lawn mower or tractor should run just perfectly with no discernible smoke and then draining that fuel out and putting cheap 87 octane in or whatever your cheap low-grade fuel is in your area and running it for 5 or 10 minutes to make sure you're into 100% of that fuel....would in any way make it start to smoke at all.
I say this because that would be the only even somewhat scientific way to test it. No smoke batch out potential smoke batch in back to back.
I'm afraid that many of these personal experiences involve many days if not weeks and often they are accompanied by some other problem or repair that was recently done so it's not scientific or accurate to assume that one particular thing stopped or started another particular thing or symptom.
But as I always say, if you do this long enough you will eventually find something that you see with your own eyes that technically isn't possible.