Is my flathead Briggs dead?

[JHZR2]

I bought this 3.5hp Briggs engine craftsman mower in 2005 or 2006. It runs great and strong. Starts first pull every time. Change the oil yearly, clean the filter, sharpen the blade, and it just keeps going.

It started to run a little bit rough in the last year or so. Not in terms of how it sounds or runs, but that it vibrates more than maybe it should. It has ultimately cracked the top cover in multiple places.

So today the cover kind of had its last stand and shook and broke in a second spot. Couldn’t mow. So I pulled the cover, plugged the dipstick hole with a plugged 3/8” npt air fitting, and used a rope around the crank to start it. Started perfectly with that old school style start all the same.

I mowed as usual, about 30 mins. A few weird things happened.

First, I did NOT fill the tank to full, but the cap started spewing gas. Never saw that before:



The cap owes me nothing. It does have its paper gasket inside.

Then I tried to turn it off. It dieseled. I pulled the spark plug cable, nothing (I guess that’s expected since the dead man handle was released). I ran the mower around back, struggled to find a flat screwdriver, and was about to pull the filter and clog the intake when it slowed and stopped. Here’s what happened:



Then after that, the whole thing smoked like crazy, from one point at the head I think.



Now, my makeshift 3/8NPT air fitting in the dipstick tube (it is threaded in there but I can’t tell what) did come loose and the engine sprays a nice fog of oil out the dipstick hole. But that should have been burned off long before this as it was at least 15 minutes of operation since that had happened.

So, is my lower dead? Is it worth it to buy a new/used cover given these running conditions? I’m fairly concerned something bad happened with it… not sure what.

Thanks!

 

[JavierH19]

Could fix it as it's still running but those vibrations that caused it is a big indicator not to. I think the old girl should have her last day in peace.

 

[AandPDan]

Without the shroud the engine wasn't cooled properly. It overheated.

 

[fantastic]

It's got some battle scars. Try fixing the top the best you can. It could be that the top missing is heating up the fuel. The extended runtime can be due to carb still getting fuel past the needle & seat. If the carbs never been replaced get an amazon chinee carb. If that doesn't work then try new ignition coil & or head gasket. You can figure out if this is worth it to you or not.

 

[JHZR2]

Without the shroud the engine wasn't cooled properly. It overheated.

That’s not good.

I did try to restart it. I can’t seem to do so.

I pulled the plug. Nothing to see there. Original plug btw.

How would overheat correlate to the dieseling?

And now that it won’t seem to start, despite fuel and air and I expect a good start, it means what? The start with both the rope and when I put the cover back on and use the recoil starter, feels the same as it ever was.

 

[eljefino]

These things are like 1970's lean burning cars, they diesel pretty easily.

If you want to fix it right you're going to have to restore what your shroud bolts to, which is likely the block casting.

She's junk. If you like the deck, stick another motor on there. OHV ones, even "Chondas" are so much quieter and better on gas.

For a frame of reference, I can go to my town dump any weekend and get a mower like yours, but with a good block and a bad carburetor or igniter and cobble something together that runs in ten minutes. This isn't worth your time, aside from donating parts, or evil experiments.

 

[brianl703]

Overheated engines are more prone to diesel.

Check for spark, then use a compression tester to check for compression. If both spark and compression are good, and you are actually getting a decent, bright spark with the spark plug connected (a bad spark plug CAN result in no or weak spark), then it's a fuel problem.

 

[supton]

Now you know why no one changes the oil in these things—it jinx’s them.

Although running it hot like that surely doesn’t help.

I agree with eljefino, might be able to find something at the transfer station.

 

[meep]

Without thinking too hard about it, the “engine whisperer” in me is reading the tea leaves and saying, “it’s worse than that, she’s dead Jim.” (-McCoy). You will have greater reliability buying a vertical shaft predator for $120 (99 if you catch a sale) and join the growing ranks of fake predator owners …

or just buy something else.

 

[Chris142]

Without the shroud the engine wasn't cooled properly. It overheated.

This. The magneto has a bunch of fins on it that move air and the shroud directs it over the engine. Without the shroud it's going to run real hot.

 

[chainblu]

might be able to find something at the transfer station.

The county transfer station here doesn't allow 'picking' or salvaging. Meanies! (I sometimes do when they're not looking )

 

[JHZR2]

Now you know why no one changes the oil in these things—it jinx’s them.

Although running it hot like that surely doesn’t help.

I agree with eljefino, might be able to find something at the transfer station.

Around here, everywhere, trash is picked up curbside. I can’t recall finding a mower in even the heavy trash in the longest while.

Without thinking too hard about it, the “engine whisperer” in me is reading the tea leaves and saying, “it’s worse than that, she’s dead Jim.” (-McCoy). You will have greater reliability buying a vertical shaft predator for $120 (99 if you catch a sale) and join the growing ranks of fake predator owners …

or just buy something else.

Are the bolt patterns and whatnot all the same? Is this a drop-in?? That could be interesting though I’d prefer a US made Briggs. Not sure that’s a thing anymore though.

I value lightest weight as I push mow on some 45 degree slopes and don’t really want something heavier or self propelled.

So if there’s a light drop in (or a reasonably good engine from another mower) I’m game. I guess. Though taking this one apart to fix it might be fun.

This. The magneto has a bunch of fins on it that move air and the shroud directs it over the engine. Without the shroud it's going to run real hot.

I didn’t realize it made that much of a difference! Ugh.

 

[Gyro Gearloose]

The gas is spraying out of the cap because the tank mounting bolts are loose and the tank is vibrating violently. Possibly, it may not be restarting because the tank is sagging and the intake pipe isn't sealed. There is a O ring inside the carb side of the joint that seals everything.

If the vibration is severe enough to tear the bolt holes out of the fly wheel shroud how are you managing to mow with it.

 

[jeepman3071]

Without the shroud it will definitely overheat, also it sounds like it is running a bit fast. 3600 RPM is really the max for these small engines.

 

[spasm3]

Over heating due to no shroud. I agree with @jeepman3071 . Sounds way fast. With the vibrations i see, and that its breaking things on the mower, i'd have to suspect a bent crankshaft.

 

[mk378]

It looks like the governor is not hooked up, it's running wide open which will shake everything to death.

Turning up the speed seems like a good idea at the time but it makes them guzzle gas and eventually throw the rod.

You can add washers so the bolts catch on the broken holes in the shroud cover. As others said, that part is essential for proper cooling.

 

[Rand]

45% hills? you need a 2 stroke.

 

[JHZR2]

The gas is spraying out of the cap because the tank mounting bolts are loose and the tank is vibrating violently. Possibly, it may not be restarting because the tank is sagging and the intake pipe isn't sealed. There is a O ring inside the carb side of the joint that seals everything.

If the vibration is severe enough to tear the bolt holes out of the fly wheel shroud how are you managing to mow with it.

I just mowed with it today. I do t think it’s as bad as the video makes it look. Obviously something is vibrating though…

45% hills? you need a 2 stroke.

yes not very large/long, this is suburbia, but it’s about 45…

It looks like the governor is not hooked up, it's running wide open which will shake everything to death.

Turning up the speed seems like a good idea at the time but it makes them guzzle gas and eventually throw the rod.

You can add washers so the bolts catch on the broken holes in the shroud cover. As others said, that part is essential for proper cooling.

How would I check that? I think it has a spring loaded thing on the carb, right?

Over heating due to no shroud. I agree with @jeepman3071 . Sounds way fast. With the vibrations i see, and that its breaking things on the mower, i'd have to suspect a bent crankshaft.

I would say you’re on to something. A number of years ago it wasn’t running as I thought it should, I checked everything over, and believe it ran faster after. But I didn’t change anything that I’m aware of. What shoukd I check?

 

[Lubener]

I just mowed with it today. I do t think it’s as bad as the video makes it look. Obviously something is vibrating though…



yes not very large/long, this is suburbia, but it’s about 45…


How would I check that? I think it has a spring loaded thing on the carb, right?



I would say you’re on to something. A number of years ago it wasn’t running as I thought it should, I checked everything over, and believe it ran faster after. But I didn’t change anything that I’m aware of. What shoukd I check?

A bent crank shaft is the most likely cause for a vibration.

 

[supton]

would say you’re on to something. A number of years ago it wasn’t running as I thought it should, I checked everything over, and believe it ran faster after. But I didn’t change anything that I’m aware of. What shoukd I check?

Springs on/around the govener, the plastic flap that gets air coming off the flywheel. Not sure if partstree.com or any other small engine parts place would have the schematic for how the springs should be installed; maybe you can get a service manual from Briggs for free? download that is. You might just have a spring not put back properly, wrong hole or similar.

Not having the shroud on might cause it to speed up, not sure, as the flap is inside of the shroud, and as such, the air is ducted past it—so just having the shroud off, I could see that having an impact too.