Craftsman Mower Suddenly Doesn't Run - Checked A LOT of things!

tony17112acst(PA)June 24, 2010

I just bought a less-than-10-year-old Craftsman riding mower from a friend: model 917.270650 with a Briggs and Stratton Model 28U707-1174-E1 (15.5 HP). On it's maiden mowing job for me, it was mowing fine till I turned it off to talk to someone. When I tries starting it back up, it doesn't start!

* It turns over fine (batter charged);

* I pulled off the air filter to eliminate lack of air;

* While trying to start, it backfires when I put the choke on, but not when the choke is off (I assume I'm getting spark);

* I pulled the spark plug and gave it a good cleaning (since it SUDDENLY stopped running, I'd think a bad plug would make it sputter and lead up to not starting);

* I disconnected the fule line into the carb and I'm getting tons of gas;

* I checked the seat switch with a multimeter and I get a completed circuit when the seat has no weight on it, and an open circuit with full weight. I always thought it would be the other way around. I even jumped the connector just to see if it would work; nope.

* Gasoline is only 2 weeks old.

* The brake is depressed, and the blades are not engaged.

I have good gas flow, air, and spark. What's left, the coil? It is acting as though the seat switch is stopping it from running, or that there is an imaginary kill switch activated. Am I missing something?

Any thoughts would REALLY be appreciated!. Thanks in advance. -tony17112acst

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Check for spark with a plug tester or get an old plug and open the gap wide. If you have a long spark, spray a squirt of carb cleaner into the carb and try to start it.

If the plug is firing and the carb cleaner doesn't make it kick over, you can probably eliminate the coil and carb.

That leaves timing. It's possible the flywheel is loose and it partially sheared the key. It will still produce spark, but probably won't kick over.

    Bookmark   June 24, 2010 at 9:01PM
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smallengineguy(z5 NH)

Make sure the fuel shutoff solenoid on the bottom of the carb is clicking on when you turn the key.

    Bookmark   June 25, 2010 at 3:59PM
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I would also check the compression you may have a valve hanging open? No compression, no start.

    Bookmark   June 26, 2010 at 8:05AM
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"I would also check the compression you may have a valve hanging open? No compression, no start"

You can place the palm of your hand on the flywheel screen and turn the engine clockwise and check this.

"Make sure the fuel shutoff solenoid on the bottom of the carb is clicking on when you turn the key."

Good idea.

IF you still don't find anything, there is likely a wiring terminal junction on the throttle box on the side of the engine, disconnect all the wires from this, make sure they aren't touching anything and see it the engine will start. IF it does, then there is a problem in the safety circuit.

You DID turn off any electric PTO switch after stopping and then trying to restart?

Walt Conner

    Bookmark   June 26, 2010 at 8:50AM
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As Walt suggests, find the throttle cable terminus on the engine and disconnect the wires from the junction post there. Separate the wires from each other and tape the ends or cover with something to prevent them from grounding.
If the engine runs after this, trouble in a safety switch or the wiring leading to a safety switch.
By the way, on YOUR seat switch.........the connector is a "shorting connector". This means that if the connector is pulled off the switch, the connector shorts itself and kills the engine. Attempting to jumper wire this connector also shorts the wiring to ground which kills the engine.

If checking the seat switch with an Ohmmeter, the connector MUST be removed from the seat switch.
The Ohmmeter results should then show continuity with the seat empty, and no continuity with the seat occupied (exactly what you stated in your opening post).

While you have stated that you have "Good gas flow" what you really mean is "You have a good supply of gas at the carburetor."
You really don't know for sure if gas is getting beyond the fuel solenoid or not.
To test whether this "no run" condition is due to lack of spark or lack of fuel, spray a one second burst of carburetor cleaner into the open throat of the carb and then try to start the engine.
If the engine responds by running for a second or 2 before dying again........your problem is lack of fuel (the carb cleaner is "fuel").
Never use ether based starting fluids in these engines! Much too explosive for the engine to withstand!

    Bookmark   June 26, 2010 at 1:56PM
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Thanks for all the info; these are EXCELLENT posts!

CARB SOLENOID OK: I tested the solenoid without any carb cleaner (which I do not have here). When I turn the key but not far enough to start it, I can hear the clicking. AND I tested it for 12 volts and it's good. It's clicking loudly. Also, would all the backfiring during the attempred start prove there's gas getting in?

SEAT SWITCH OK: I did test the continuity of the seat switch with the wires disconnected, and it does test continuous with no pressure on it and non-continuous with it activated (as you pointed out ...great info btw!).

SPARK: I don't have a way to test spark, but I'm getting backfiring during the choke start attemp. Is that proof that it's getting spark? Can I pull the plug and set it on some rubber and just look at the plug for the arking spark?

SAFETY SWITCHES: I am very confident the safety switches are not the problem. I have traced all of the wires on this machine and it looks pretty simple. The only two switches are the seat and the blades. The blade switch doen't even allow the engine to turn over when engaged, so it is working. The seat switch tested OK. There are no other switches. I also disconnected the harness connector of a pair of wires going into the engine area that were not the headlights or the carb soleniod and got no start. All of the other wires are no-brainers (volt meter guage, blade engagement switch, starter).

COMPRESSION: This is about the only thing left. I know what the flywheel is but not the "key." I read that the key is related to the timing. My mower was running perfectly for 5 minutes and all I did was turn off the engine to talk for 5 minutes and it didn't start back up. If the key was sheared or broke, would it be running fine one second and then not without any traumatic event? If this needs a major jolting even, then I'm thinking my situation doesn't fit. The blades DID hit the ground on my first attempt to mow. It ran for like 10 seconds and when the blades hit the ground I immediately stopped and bought wheels for the deck. I can't believe wheels didn't come with this thing. Anyway, If a jolt shears the key, would my engine start right up and mow for 10 minutes and then just not start randomly the next time?

Also, When I turn the flywheel, how do I test compression? When I try to start the thing, I put my fingers over where the air gets sucked into the carb and it does suck my finger in pretty well.

POSSIBLE CAUSE: I found an old post on gardenweb : If the previous link does not show, do a search here at gardenweb: the title is: Craftsman LT1000 won't start/backfires.

This person had the same problem, and it turned out to be an exhaust valve seat had blown out. He was told that this happens a lot when the mower is in storage where mice nest in the fins and it overheats. This mower was in storage for a year and a half in a shed!

    Bookmark   June 26, 2010 at 7:04PM
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I had one case with an Onan engine in a Cub Cadet where the flywheel bolt came loose and sheered the key without hitting anything. It CAN happen.

Backfiring when cranking is another symptom of a sheered key.

To test for spark, lay the plug against a good ground, not on rubber. If you have to, because of distance, clip an alligator clip to the adjustable portion of the electrode and the other end to a good ground. Then watch for spark. That only proves that you are getting spark. It doesn't prove that it's "in timing".

You might end up biting the bullet and pulling the flywheel.

    Bookmark   June 26, 2010 at 9:39PM
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For several hours I learned online what a key and flywheel is and I pulled the shroud and found that they both looked nicely aligned.

The only thing left in my mind was the blown valve seat which was something I found on an ealier posting. I was brave enough to pull the cover off and BAM! There was the valve seat dislodged!! I FOUND IT!

I was so excited, I came here to post and now must go and figure out how to put it back together with those rods. Here's what I will be trying to do and please let mek now if you have a good way; I have NO experience doing this:

1.) How am I going to get the rods to saty in place when I put the cover back?

2.) How do I get the valve seat back in, just tap it in with a hammer?

3.) How do I even get the valve seat loose from the valve? that should be #1 I guess.

OK, back up to the garage and see if I can figre it out with logic.


Here is a link that might be useful:

    Bookmark   June 29, 2010 at 4:19PM
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OK, I got the valve seat tapped back into place!! Now all I have to do is put the cover back on with the rods somehow. I still have the engine on the riding mower, so I don't know if this is possible. I don't know if rods are to be attached somehow or are they magnetic?
If I do get them back on correctly, THIS THING WILL BE RUNNING!!!! Yaaaayyyyy!!

I'll be back with an update. -Tony

    Bookmark   June 29, 2010 at 4:40PM
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P.S. The cooling fins were completely packed with dense grass ...ALL of them. So this must have overheated, same as the older posting I found on gardenweb (Craftsman LT1000 won't start/backfires). -Tony

    Bookmark   June 29, 2010 at 4:49PM
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YEAH!! I put the rods back in hoping they's sit in the right place and slapped everything back together and SHAZAAM! IT's running!!! I didn't check the valve clearance, but I did confirm that the steel and aluminum rods needed to go to the exhaust and intake respectively from a youtube video.

Thanks for all the advice folks! The internet has saved me thousands of dollars over the past 10 years or so, and I'm chalking up another $200 saved in labor on this one!


    Bookmark   June 29, 2010 at 6:36PM
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Did you punch all around the edge of the valve seat to secure it?

By using a flat punch you can punch and expand the aluminum around the seat to fit snugly against the perimeter of the seat.

    Bookmark   June 29, 2010 at 8:46PM
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I just used a happer hitting an extension to a rachet set which is flat on the end. That's how I got it to seat into place.

Are you saying that once it's seated into place, I should punch the inside of the valve seat to try to expand it? Or punch it just to seat it in place?


    Bookmark   June 30, 2010 at 8:04AM
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If you don't punch all the way around the exterior of the valve seat, it will probably push out again. My buddy had this happen a few years back and fixed it like this, and hasn't had any trouble yet.

    Bookmark   June 30, 2010 at 11:17AM
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Best results will be had if you tap the valve seat back down and then reassemble the valve to its normal state.
After the valve is assembled, the valve spring tension keeps the valve seat from possibly moving when you strike the cylinder head with the pin punch to peen and "tighten" the head's grip on the valve seat. Use a 3/32" or a 1/8" "flat end pin punch" for the peening, nothing larger than 1/8" punch.
Begin peening by selecting a position for your first peen strike, say........12 o'clock. Strike the punch just hard enough to make a mark in the head that you can see the round imprint of the punch end, you are not trying to bury the punch or make a deep hole!!
After your first strike, make your second strike at 6 o'clock position, then 9 o'clock, then 3 o'clock. The start dividing the quadrant sectors in half with your strikes.
Continue the peening in an alternating fashion until you have peened the entire perimeter surounding the valve seat.

    Bookmark   June 30, 2010 at 12:04PM
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Great posts! ...thank you guys. Also, thanks for the great image. So it sounds like I should punch the head itself. I can do that, since the valve cover is easily reachable on this thing. -Tony

    Bookmark   June 30, 2010 at 6:56PM
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Yeah, the valve cover is easily reachable........but to peen around the VALVE SEAT, the head must be off the cylinder and laying on a work bench.
I don't believe you know the difference between a VALVE GUIDE and a VALVE SEAT, or a CYLINDER HEAD from a VALVE COVER.
I re-read your "breakthrough post" again and I am confused now at just what you have been tapping back into place.
If the object you have been calling the VALVE SEAT was found in the same place where the VALVE SPRINGS are, that is not the valve seat, that would be the valve guide.
I'm glad you got it running, even if I don't know how, or did. :^)

    Bookmark   July 1, 2010 at 1:29AM
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I would Knurl the things anyway and then use a arbor press to seat them, much cleaner than peaning the head. Well that's the way I was taught to do things.

    Bookmark   July 1, 2010 at 2:38AM
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I probably should explain Knurling, Knurling may also be used as a repair method: because a rolled-in knurled surface has raised-up areas surrounding the depressed areas, these raised areas can make up for wear on the part. In the days when labor was cheap and parts expensive, this repair method was feasible on pistons of internal combustion engines, where the skirt of a worn piston was expanded back to the nominal size using a knurling process. As auto parts have become less expensive, knurling has become less prevalent than it once was, and is specifically recommended against by performance engine builders. Still a good way to seat Valve seats and guides in a alloy head.

    Bookmark   July 1, 2010 at 2:51AM
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HUGE BREAKTHROUGH!! blown valve seat which was something I found on an ealier posting" Should of found it in 20 mins. about the third thing to check, also it would of make a funny cranking sound when you attempted to start it. Let's see? getting gas? check,getting spark? check, compression? No. I don't know what the big secret is or the big breakthrough. Also taking the time to read the owners manual covers cooling fin pre-ventive maintenance. Thats a problem buyig used mowers, you don't know what was done to them, so it would be wise to review the owners manual and do all the pre-ventive maintenance checks, Why cause mostly none of them was done requardless how old the equipment is. This is a good example for others just jump on and mow need to think what there NOT doing?

    Bookmark   July 1, 2010 at 5:59AM
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RC, you may be technically correct in saying a competent professional mechanic should have found this in 20 minutes, but I don't know if the same time line should apply to a novice.
I too was a bit off base with my post last night when I mistakenly thought tony was getting his parts names mixed up. I just now found the link he posted to a photo of the ejected valve seat. Boy is my face red!!!!!!
Tony, you have done pretty well on this project even if I got myself off course a bit.

    Bookmark   July 1, 2010 at 9:31AM
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I was a mechanic in the knurling days, mostly on pistons, but if a valve seat was knurled, you'd almost have to expand the head and cool the seat before dropping it in place, otherwise you'd score the head when pressing it in. Beyond most homeowners. Other than that, who has a knurling machine today? I've never seen one.
This man's best bet is to use the punch method.

    Bookmark   July 1, 2010 at 11:12AM
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I agree with baymee on this.

    Bookmark   July 1, 2010 at 11:56AM
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Thanks again Guys,

Yes, this is the first time ever(!) I have taken an engine apart ...or partially apart. A beginner isn't going to figure this out within 30-60 minutes. I'm on the web for hours learning just one thing, like what a key is. Then another hour for how pushrods work and which is for exhaust or intake (steel vs. aluminum). Every little thing about an engine, I had to learn for the first time.

The HUGE BREAKTHROUGH wasn't one for all mankind, it was my breakthrough on the discovery of what the problem was. A computer geek with degrees in philosophy and mathematics actually diagnosing a non-running engine for the first time felt like a huge breakthrough after all the things named that could be the cause. :-)

Mo: I didn't get the names right on a few things when I look back, but I am never offended when someone knowledgeable corrects me. I have my strengths and others have theirs; I am all ears when I need correcting. I have been on the other end too in the 1980's when workers started using PC's, they'd call their computers "hard drives" or "CPU's." When describing a problem in words, it IS very important to use the correct names for everything, so I do not take any offense. One sentance story: I had a lady whos PC had an expansion card cover missing on the back of her PC and she thought she was losing files through it. :-O ...RC would have a HAY DAY with her, LOL.


    Bookmark   July 1, 2010 at 4:35PM
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Congratulations Tony. I completed my first mechanical job 46 years ago and I still don't know it all. (And I still use it) But, I started out just like you.

And I have come to realize how much time can pass on the computer without even realizing it. It's not like I have loads of time on my hands either, but I enjoy helping others learn. And so do the other guys on this forum.

    Bookmark   July 1, 2010 at 5:21PM
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Tony, ya done good! And if you have any more problems you just lets us know and we'll be glad to help out. You are a diligent student.

    Bookmark   July 2, 2010 at 12:37AM
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FWIW, I had a similar problem where the engine would run just fine and then suddenly quit. Finally found the solution yesterday. When I replaced the starter a while back, I sandwiched two wires between the starter and the block. Over time, when the motor would heat up, the wires would short out as they were being compressed. I think these were the wires to the solenoid on the carb.

    Bookmark   July 4, 2010 at 11:36AM
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Hell Boys I remember when they Knurled Valve Stems , that goes back a few Decades :) .

    Bookmark   July 4, 2010 at 3:02PM
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Boy,did the mention of knurling of piston bring back old in the 50s,anytime you did a ring job on a motor,you got the pistons knurled. I also used the center punch method to tighten up a bearing on a slightly worn spindle.

    Bookmark   July 5, 2010 at 7:07PM
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