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Neighbor gave me a 10 year old Craftsman Yard Vac that was "used once then I never used it again".
We have tons of large, old oak trees in this neighborhood that drop leaves the size of dinner plates, so a mulching yard vac is a very handy machine to have. Which is why I already have one! But mine is from 1994 and this one is close to 20 years newer.

He also stored it outside so after giving it a good external cleaning, I checked the oil level, put some gas in and started it up. After some initial sputtering (in the video) it started running great.The sputtering does not surprise me, theres no primer on this engine!

So I warmed it up for a minute, then killed it and changed the old oil with some super fresh stuff. I started it up again and it seemed to be running perfect. I brought it up to my driveway and did a bunch of passes and was really impressed with the performance. This machine sucks up leaves much better than my older one. If I can fix this one, I'll definitely use it every fall.

Here is where things went wrong. I sucked up leaves for 5 or 10 minutes. Towards the end, it felt like it was misfiring. It would run perfectly for a few seconds, then cut out for half a second, then come back. But the gaps between sputters were getting shorter, and the length of the sputters was getting longer, until the thing died. My first thought was, well the carb is probably dirty, if I keep running it with seafoam, eventually everything will clean out and be A-OK.

After doing some other unrelated things, I went back to this machine and tried to start it up. Nothing. At all. Not even a hint of firing. But more than that, the motor was spinning much faster, much more freely. It's like there was no compression at all. You pull the cord and the engine spins and spin. Now there is at least some compression, because when I pull the plug, plenty of air comes out. But I have no frame of reference so I have no idea if the air coming out is the normal, proper amount, or way less than should be coming out.

I am by no means an engine pro. But based on what I know about engines, my first thought is that it kinda feels like one of the valves got stuck open? So theres no compression and thus no firing. And that could potentially explain how much more freely the engine spins? Beyond that, I am at a loss.

I have a short video linked below.
Part 1 is me pulling the cord early on. I was trying to start it and I forgot this machine require the bag in place to start. But compression felt normal
Part 2 is when I finally started it for the first time. It sputtered a lot but never died. And once it kicked in normally, it ran great. Perfectly I'd say. And it kept running perfectly the whole 10 or 15 minutes I was using it, until the very end. The timeline is that part 2 happened, then i changed the oil, then I started it back up and used it.
Part 3 is after it died and I couldn't get it running again. I pulled the cord and the engine spins and spins way too easily. Once in a while you'll hear and feel one or to pumps of compression but then its quickly back to nothing again.


So what do you think? The odd behavior feels like it probably points directly to what the problem is, but I don't have enough small engine experience to know what that actually is!

IT is common for this type of gear to have a kill switch on the bag attachment
Being stored outside also common to haave mice living under the blower cover
IF the latter then the engine can over heat and cause a valve to stick or even bend
So remove the blower housing and check for nests, clean the fins while you are there.
Check the kill wire for chewed through insulation
Remove the rocker cover on the front and check the valve lash, easier to do with the blower cover off
While you are there record the engine details off the rocker cover , or just above the muffler and post them so we know which engine you have .

My first thought was the bag kill switch. But the engine is clearly spinning significantly free-er after it died so I don't think it's a kill switch issue. It is doing more than twice as many spins per start cord pull after the fact.

Overheating sounds very plausible. There was junk all over the engine and there was a little bit of smoke coming from the top afterwards. I thought it was just a little bit of smoldering maple tree helicopter seeds but maybe not.

So if I did overheat the engine and assuming I'm lucky and the valve is just sticking and not ruined, how do you fix that and free it up? I mean obviously I need to clean under all the covers which I'll try to do next chance I get. But after that? Do I have to take the core motor apart and work them free or might they unstick on their own after cooling off? The oil is fresh full synthetic so hopefully everything is well lubricated.

One step at a time
Do what was asked of you report back and follow the instruction to repair the mower

OK I finally had time to work on this again. Here's how it went:
I took all the covers off and there were a lot of maple tree seeds shammed in all over the place. No mud or slop or typical nest stuff, just maple tree seeds. Its unclear if it was enough to cause cooling issues (maybe? maybe not?). It was enough that some particularly near the muffler were burnt from the time I did have it running.

After cleaning everything, I put it back together but still could not start it. NOTE that compression came back. Not after the cleaning, it was back before doing anything. But still not a hint of starting.

Then I took it apart again and took the cover off. Turning the engine by hand, the valves LOOKED perfect to my eyes. They seemed to be opening and closing properly and fully, nothing looked damaged or bent in any way. Spark plug also looked good.

Here is a link to another video:
The valves seem to be moving normally and properly and sealing up. But I the engine still won't start.

Now regarding the engine model number, I didn't find any ID information specifically for the engine. Here's what I did find:

The model number for the whole machine itself:
247.77013.0

Also I'll attach a photo of the engine cover which has the "marketing" information. And a couple pics of the motor itself for good measure.


So if the motor hadn't started up easily and ran perfectly for a few minutes, I would be thinking clogged carb or a bad kill switch. But the way it died out after running great and then had no compression for a day makes me think that going after those two would be barking up the wrong tree. But again - not an engine expert.

So barring any other better ideas, it does have a kill switch for the bag, like most chippers do. How would you bypass that? Would grounding the wire bypass it, or would cutting the wire bypass it? I wouldn't leave it bypassed but just to help eliminate it as a potential cause of the problem.

Beyond that, I'm kind of out of ideas.

I just had a thought. Magnets loose their magnatism if they get hot. I don't know how hot. But could I have overheated the engine enough that I demagnetized the magnets on the flywheels so the motor can't generate spark anymore? I could feel some force from it for sure but I don't know how much you actually need to create a spark so maybe its too weak now? Just a total shot in the dark.

When I made the second video above, with the valve movement, I was only paying attention to the opening and closing of the valves. And they do seem to be opening and closing fully.

But the more I look at that video, the more confused I become about the timing of the valve compared to the compression. I don't think I'm turning the engine backwards, I'm just turning the flywheel by hand. But it looks like the valves are opening and closing at totally the wrong times. Am I just not understanding the strokes properly or are the valves somehow all messed up, timing-wise?

Engine spins Clockwise from top view (think about pull rope). Did engine stop suddenly as hitting an object? Could be flywheel spun - check key alignment. Have you tried carb spray/pblaster in carb throat or plug hole to see if it burps and 2 sec run? If so, may be debris in bowl, bolt holes or main jet. Engine model # is on shroud plate above muffler - looks like 12xxxx-xxxx-xx.

I *am* turning it clockwise so I am spinning it the right way.
What I'm seeing in my own video is an intake down stroke followed immediately by an exhaust up stroke which makes no sense.
And then a full up stroke and down stroke with both valves closed. It's like one of the valves got knocked off it's timing by 90° or 180° or something, how could that possibly happen?

I did try spraying starter fluid in the air intake. It seemed to spit it back out the intake, which does jive with what i'm seeing in the valve timing.
No sudden stops. When it was running perfectly, it seemed like it was just starting to misfire. Just for a second, then for a couple seconds, then more and more, then it was like it had been shut off and it just spun itself out and that was it.

I have a general idea of how camshafts work in cars but I don't really know how they work in great detail and I don't know how they work at all in small engine. I would have assumed that what I *think* I'm seeing is not possible without machining a custom, incorrect camshaft of some kind. But maybe these motors use something else for timing.

Next time I work on it, I'll look again for the engine model number.

I looked in the parts manual for this machine and according to that, the engine is a B&S/Craftsman engine Model number 126T02
Also according to that manual, not only are my 4 cycles in the wronger order, but the engine is pulling in through the muffler and pushing out through the intake. Also looking at the diagrams, it is not clear how actually controls the valves on this motor. They don't seem to be being pushed directly from the can shaft I'm unsure.

Look at camshaft 46 in IPL. 2 teardrop lobes push rods for valves. The cam gear mates with crank gear. Cam gear could have jumped time. Also, 43 Oil slinger/gov can blow up. Can't tell from IPL but cams can have a boomerang compression release - spring loaded and clears away at run RPMs. It can blow up.

I never would have guessed that these engines had PLASTIC camshafts. So it again sounds fairly plausible that I overheated it and I guess just severely deformed the plastic camshaft. I'll have to take everything apart to get a closer look. The movement seems so smooth, that my guess is that the gears didn't skip, just the shaft itself got very deformed. Not sure when I'm going to get to this and it's a bummer this free machine is going to cost me $100 or so but it is a nice machine.

~10 years ago, when I had these internal parts failures - it was $140 in parts.

Not that I would ever do this for a yard vacuum engine, but does anyone make an aftermarket aluminum camshaft for these engines?

There are many USED plastic camshafts for this engine on ebay for like $10 shipped. Given that you only put like 5 hours per year on these machine, I'm thinking about it. But we'll see once I confirm the problem first. I need to figure out how to even get to the camshaft before i can confirm it and then start buying parts

If it worked and you did muck the internals, then the valves are opening and closing properly as it worked before.
I doubt you have a compression issue, but if you have or can borrow a compression meter, now is the time to use it.
next. SPARK: Does your spark meter spark or not?
next GAS - is it old or dirty or fouled. drain, clean and try again with fresh clean stuff.
You can leave a spark tester in-line with degraded performance to monitor if you get it started. This may help if this is a electric issue of maybe hot coils. doubt it.

jviews12 said:

If it worked and you did muck the internals, then the valves are opening and closing properly as it worked before.
I doubt you have a compression issue, but if you have or can borrow a compression meter, now is the time to use it.
next. SPARK: Does your spark meter spark or not?
next GAS - is it old or dirty or fouled. drain, clean and try again with fresh clean stuff.
You can leave a spark tester in-line with degraded performance to monitor if you get it started. This may help if this is a electric issue of maybe hot coils. doubt it.

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Did you look at the video of the valve movement? That can't possibly be the correct. I don't see how an engine could ever run with the valves opening and closing in that order.

l008com said:

Did you look at the video of the valve movement? That can't possibly be the correct. I don't see how an engine could ever run with the valves opening and closing in that order.

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It is highly doubtful that you overheated the engine with 10 minutes of operation. The cooling fins and top of engine need to be really caked up with oil, grass, dirt and debris for an engine to overheat usually.

That is an L-head engine, so it is at least 20 plus years old. Valves do look fine from video I watched. Spray some carburetor cleaner in throat of carb and see if it starts. If it does you know you have spark and compression, and have a fuel delivery issue.

Tiger Small Engine said:

Valves do look fine from video I watched.

Click to expand...

Are you sure? Did you look at the timing? I don't see how an engine could possibly run with that valve timing. It's doing an intake stroke then immediately an exhaust stroke, THEN with no possible air and fuel, it's doing a combustion and then a compression stroke. How can that possibly be normal? Or am i totally misunderstanding what I'm seeing?

A melted plastic camshaft is the only way I can imagine the engine went from running well to what's in that valve video in just a few minutes.

Ok I'm finally getting back to this. I'm not sure how I found the parts list above because I can't get any results from jacks except parts lists for the body. I can't find a parts list/breakdown for the motor. I'm going to assume the camshaft is melted and needs to be replaced.

I do know my motor is a B&S 675 series, but I assume that's not specific enough to order parts off of?

I'm also watching a camshaft replacement video right now and it looks like a big project. BUT this is a larger motor with a metal shaft so I'm hoping my smaller engine is going to be a little easier to disassemble.

You need engine model#. Will be on valve cover or engine block near spark plug. Eg:

At one time these camshafts were having problem of slipping the lobes as the plastic gave way.