"Could the backfire have caused valve problems"

More likely partially or totally sheared the flywheel key.

Walt Conner

walt2002,
Do you know whether the flywheel retention bolt is right or left handed? Any recommendations on how to hold flywheel when loosening bolt?
Thanks

Flywheel nut is left for loosen, Right for tighten! Hence the saying you have probably seen here:"Lefty Loosey--Righty tighty!"
As for holding the flywheel, some use a leather strap wrapped around it. you can also smack the wrench with a BFH, to loosen it, Or, and air impact wrench will take it off right quick!

Found that the flywhel key was ok so next step was to remove the engine head. What I found was the exhaust valve seat had blown out and jammed the valve open. I have reseated the seat and will stake it in place. The problem I now have is what are the valve clearance settings?
Does anyone have a manual for a B&S model 31P777, type 0299-E1 and can tell me the required clearance and tolerance? This is a 18HP OHV Intek engine

Intake .004"
Exhaust .006"
+/- .001"
Piston 1/4" PAST TDC (important)

Thanks everyone for your suggestions and info. Looks like I'll be all set when I can get some gaskets on Monday. Hopefully the clearances are OK as B&S recommends grinding to increase clearance.

"Hopefully the clearances are OK as B&S recommends grinding to increase clearance."

Not on that engine. You have an OHV engine, so you adjust the valves at the rocker arms.
A Flat Head engine requires grinding the valve stem to increase clearance. A different kettle of fish entirely!!!!!

wow - ive not heard of this happen b4 - not that i dont believe you.

Im just wondering if that valve seat was not loose to begin with ...

and it being loose was just a potential situation waiting to happen ? In other words - a loose valve seat might have been flowing raw gas past it - and when you cut the ignition, the perfect condition for popping that seat existed...

Would a backfire typically pop a "well set" valve seat ?

anyone have any thoughts on this ?

"Would a backfire typically pop a "well set" valve seat ?

anyone have any thoughts on this "

Would not.

Walt Conner

I need a little help in assembling the engine. After I torqued the head bolts and moved the flywheel to TDC, I found that the exhaust lifter(upper) had all kinds of clearance and the intake(lower) had none. I thought I was very careful in noting which lift rod went where but maybe not. One rod is aluminum, bigger diameter, and shorter while the other rod is steel, smaller diameter, and longer. I now have located the steel rod in the exhaust(upper) position and the aluminum rod in the intake(lower) position. Am I OK to make the adjustments? Any thoughts?
Thanks

walt2002 and njdpo,
Re: Loose valve seat. I spoke to an engine repair center mechanic and he said loose seats are not uncommon. Usually caused by mice nesting around the cooling vanes causing air blockage, overheat, and seat loss of interference fit. I did have blockage at the bottom of the head but it did not seem to me to be enough to cause major overheat.

I to have an LT1000 with the 18HP OHV Intek 31H7770202E1 engine that wants to only backfire when I try to start it. I had shut it off after mowing for about 1 hour and then went to re-start it with no luck. Spark fine, fuel fine. I first looked to see if the valves were working. They seemed fine but the exhaust valve has about 1/4" of freeplay in it. Is this typical or does it sound like an adjustment is needed? The motor also seems to be turning with a lot less compression when trying to start. I live in South Florida where we mow all year and the engine has about 7 years, 1200 hours on it and was wondering where to start? Could it be a head gasket or rings? or should I just start at the valves?? One other question, how many hours would you typically see from this engine before major issues? Thanks!

***"the exhaust valve has about 1/4" of freeplay in it."***
Look at the valve which has the "1/4" free play. Can you measure the distance from the top of the valve spring, down to the bottom of the valve spring? Does this valve spring measure to be shorter than the other valve spring? (you must have the engine at TDC, or 1/4" past TDC of compression stroke for this). If you have the engine in the proper position, and one valve spring measures shorter than the other, the cylinder head needs to be removed for further diagnosis of why. You are sure it is the exhaust valve? If so, it is possible, even likely, that the valve seat has loosened in the head. Another possibility is that the valve stuck to the valve guide while the engine was shut off and cooling, and then got hammered by the piston when you tried to start it later, bending the valve. That usually only happens to an intake valve, hence my reason for asking if you are certain it is the exhaust valve.
***"how many hours would you typically see from this engine before major issues?"***
The correct answer is "Any time they dang well decide to hit your wallet". But realistically, they seem to have issues concerning camshaft wear around 500 hours.
Loosening of a valve seat is usually associated with an overheat event, no matter what engine it is.

mownie,
Thanks for the reply. On TDC the exhaust valve spring is at 1-1/8 in. out and the intake is at 1-3/8 in. out. So based on your post I would say you are right with the valve seat loosening. Looks like the head is coming of to further diagnose. I did notice that the head gasget and valve cover gasket had been leaking and the excess buildup could have caused overheating. Is this motor worth the money with about 1500 hours of usage? Do you think once the valves are fixed something else will go. I live in Florida where we mow 12 months a year and twice a week in the summer. I am mowing 2-1/2 acrea's at a time. I think it's time to upgrade which would you pick, a John Deere 26-HP 54" deck tractor model BG20449 with the Briggs engine or a Husqvarna 54" 24-HP Zero Turn Model 28982 with a Kholer engine? The difference is about $300 and I would like to stay under $3000.00 total. I would love to go commercial but just do not have the funds right now. I appreciate your advice.
Regards.
Jeff615

***"On TDC the exhaust valve spring is at 1-1/8 in. out and the intake is at 1-3/8 in. out."***
I need to emphasize that "TDC" and "TDC on the COMPRESSION STROKE".......are not the same thing. So, having made that statement, let me ask this: When you are measuring the length/height of the valve springs...do you have clearance, or lash, between the rocker arm and valve stem of BOTH valves/rocker arms???. If yes, then you have most likely detected a displaced valve seat. If, however, you have no detectable clearance or lash at the valve stem/rocker arm of the "shorter" valve spring....the engine is positioned at TDC on the EXHAUST STROKE, and the camshaft is holding the exhaust valve OPEN, thus the "apparent shortening" of the exhaust valve spring. So, let's just double check that before we declare a displaced valve seat for sure.
***"Is this motor worth the money with about 1500 hours of usage?"***
That is something that only you can really decide based on how much you want to spend to rehab this engine. You can base your decision on "cost of repair $" versus "cost of new mower $" if you like, and consider that as an "objective decision" based solely on money spent at this time. But, you will still have an older machine that will have other things to fail/wear out down the road, and sometimes......you can second guess yourself to death in these situations. The bottom line decision you have to make is not so much about the worth of repairing THIS engine. It is about how much time/money are you willing to spend maintaining an older machine/engine? AND, whether you are personally capable of doing the work (or the bulk of it) yourself.
As to a personal preferrence or recommendation of a particular brand of replacement mower.......I don't go there! But, there are many, many, many threads in this forum where the yays and nays of the different offerings of the market have been argued/debated/dissed etcetera. It almost boils down to "What color do you like?"

Let me clarify, I meant to say 1/4 inch passed TDC with valve lash on both valves. I have decided to replace this mower with another one since I have never been happy with the deck and the spindles will need replacing soon for the third time. I am going to move up to a commercial unit for a little better wear and dependability. I am going to rip the old engine down and show my boys how to repair valves and show them how small engines work. Thanks for all your continued help in your forum, I enjoy reading them and gaining the knowledge at the same time.

***"going to rip the old engine down and show my boys how to repair valves and show them how small engines work."***
OH! So you care so little about their future that you are going to introduce them to something that could very well end up having them becoming mechanics? Oh the shame! Well, any time you get to spend with them is good time. I'll warn you though, the smell of gasoline has caused many a young man to "lust for his own car" and the smell of perfume from a young lady pretty much paves the rest of the road to "ruin". Gasoline & perfume! Instant mesmerization for most young fellas. Good luck in moving up (Tim Tooltime Taylor would be proud) and good luck with your guys.

I want to thanks everyone who contributed to this thread. It looks to be 2 years old, but the symptoms were mine too and my problem was exactly the same! My posting is entitled: "Craftsman Mower Suddenly Doesn't Run - Checked A LOT of things!" for those who may have the same problem in the future.

-Tony