Riding Mower with no compression

[bigalpha]

Last week, I was cutting grass and the engine idled down a little bit then about 5 minutes later I hear a 'pop' sound and the engine died.

The starter engages and spins the flywheel and the whole assy spins and spins the belts. There is spark at the plug but it doesn't even attempt to turn over.

If you check out [URL="http://www.youtube.com/watch?v=5J6SBAmsVvA#t=3m10s"]this video,[/URL] it shows exactly what mine is doing.

Here's a link with pictures of my mower.

 

[bigalpha]

Alright, I tore into it and removed the front cover that covers the piston and valves. When I turn the assy that opens and closes the valves, the piston does not move through the full stroke. It actually does not move inwards unless I push it in, then it does not move smoothly outwards.

Also, the top valve (exhaust?) has a lot of crud built up on it but the other (intake?) looks very clean and looks good. The sealing surface between the top valve and the block isnt that great and the sealing surface of the lower valve looks really good and shiny.

Something tells me this is not a quick fix.

 

[bigalpha]

After some further research, I wonder if I broke the pushrod on the piston?

 

[mcantar18c]

My first guess would been a cracked block, seen more than a few of those.
But if the piston moves outward and not inward, you definitely have a broken rod (btw it's a connecting rod, not pushrod).
Open up the crankcase, see how bad it is... it's very possible that the broken rod may have scored the cyl walls, in which case you'll need a new engine (not as bad as it sounds, grab a new B&S for a couple hundred). If the cylinder wall looks good, all you'll need is a new rod and new bearings. Go to your local repair shop, give em the engine model and all and have em order the part you need, install and be done with it.

If you need any help, PM me and I can walk ya through whatever it is. I was a small engine mechanic through highschool, worked on mower and tractor engines, and now I'm ASE certified.

 

[bigalpha]

Yeah, I'm not very schooled on engine internals at this point but after watching some videos and doing more research I'm getting the hang of it.

The crank stills turns but the piston doesn't move at all. I stopped messing with the piston, tho, just in case there is debris in the cylinder. From what I can see, there is no scoring in the cylinder at all.

It will probably take a week or two to get the engine pulled and disassembled since I'll take it to a buddy's with a garage and nice tools. Other than just rebuilding the thing, is there any cheap and easy things I can do to this engine to make it any faster/stronger/better?

 

[mcantar18c]

You're not looking at the right side. There's three basic parts to these engines, just like their bigger siblings in our jeeps... crankcase, block, and head. If I'm reading right, you have the head removed and can see the top of the piston, correct? Well, the side you need to look at is on the other side of the piston, and usually requires removing the engine from the mower. FWIW, most broken rods I've seen in these engines broke around or close to the top, where it connects to the piston.
Here...

This is a cutaway of your engine. The valves on yours are probably on the side of the block, parallel to the cylinder, but it all does the same stuff and we don't care about the valves right now so ignore them.

You can see how your piston goes up and down based on the push/pull of the connecting rod. Well, if the rod is broken, then it will push the piston up but won't be able to pull it back down. The rod is still connected to the crankshaft and therefore still moving up and down, and the broken tip is likely scratching up the cylinder walls, but on an engine like this you won't be able to see the scratched area from the top. There's usually a crankcase cover either on the side of the engine or on the bottom... these engines are as simple as it gets, just remove any bolts you see that aren't holding down the carburetor, exhaust, or the head.

Here's another pic that shows the crankshaft and all that better, but this is a diesel engine so it's got a different kind of piston, just ignore that part.

As far as modding them, I suppose you could mess with the fuel and whatnot a bit. Look around online at go kart engines and forums and whatnot, they use the same engines and probably know a bit more about performance mods and upgrades.

 

[bigalpha]

Thanks for the pictures - I know that all the broken pieces will be contained on the rod-side of the piston, but just from looking at what I can see, it looks like the piston and cylinder aren't in horrible shape. The one valve is pretty toasted, though. The top valve (intake?) has lots of crud built up on it and the valve seat looks dull. The bottom valve (exhaust?) looks pretty good and the seat is nice and shiny.

The mower itself I got for free so it's not in the best of shape. Should I pull the whole motor and clean and refresh it while I'm in the process of rebuilding, or should I just leave it on the mower? Seems pretty easy to remove from the mower.

 

[mcantar18c]

Thanks for the pictures - I know that all the broken pieces will be contained on the rod-side of the piston, but just from looking at what I can see, it looks like the piston and cylinder aren't in horrible shape. The one valve is pretty toasted, though. The top valve (intake?) has lots of crud built up on it and the valve seat looks dull. The bottom valve (exhaust?) looks pretty good and the seat is nice and shiny.

The mower itself I got for free so it's not in the best of shape. Should I pull the whole motor and clean and refresh it while I'm in the process of rebuilding, or should I just leave it on the mower? Seems pretty easy to remove from the mower.

The broken pieces will be on the rod side, yes, but my point was that the piston doesn't travel down far enough to see the area that could be scratched by the rod so you need to look at it from the backside.

The inside isn't really clean per say, but clean doesn't exist in those 2 strokes lol, I haven't seen one that isn't all carbon covered inside. What I find strange is how clean your intake valve is, not how dirty the exhaust valve is (no matter the engine, big or small, the exhaust valve sees higher temps than the intake valve and because of that is bigger).
How do the valve stems look?

As for the rebuild, you're getting ahead of yourself. You first need to determine if you're engine is rebuildable... they don't make oversize pistons for bored out blocks for these things, so if your cyl walls are trashed you're in need of a replacement block. If the walls are fine, just get a new rod and bearings and you'll be good to go.

And yeah, they're pretty damn easy to remove from the mower... if there's more than 4-6 bolts holding the thing down, I'll be shocked.

 

[Shorty]

What I find strange is how clean your intake valve is, not how dirty the exhaust valve is (no matter the engine, big or small, the exhaust valve sees higher temps than the intake valve and because of that is bigger).
How do the valve stems look?

am I looking at the same head? It appears that the bottom valve (smaller one) is the exhaust valve-- and rather clean. Isn't that an exhaust pipe exiting the head next to it?

X2 on the valve stems-- it almost looks like the intake (top) valve is being held open a bit.

 

[southernrebel20]

I am a small engine mechanic and have been for the past 8yrs, your motor has a broken the connecting rod. What you need to do at this point is 1. remove the motor from the mower
2. remove the sump (oil pan)
3. at this point you will be able to see the broken connecting rod
4. next, you will need to remove the piston and check the bore
5. look at the piston, are any rings stuck? Is the bore still smooth? Does the bore still have any of its crosshatch on it? (post pics of bore)
6. if bore is ok, and none of the piston rings show signs of overheating, you will next want to remove the crankshaft.
7. undoubtedly the bearing surface on the crankshaft (where the connecting rod rides) will be rough do to the aluminum from the connecting rod adhering to it during overheating.
8. you can soak the crankshaft in muriatic acid, this will remove the aluminum (just don't breath the vapors) and leave you with a surface that can be polished.
9. next install new connecting rod and close the motor back up.

If you give me the model - type - code of your motor I can get you part numbers and assembly drawings if you wish.
Good Luck,
-Cole

 

[southernrebel20]

Oh, and the valves will be ok, these little motors all have crud on the valves, just gently clean it up if you wish (making sure to not get debris between the valve and the valve seat). And, over-size pistons and rings are made for these motors, you can usually go .020 overbore and be ok. But you will most likely not have to worry about this.

 

[bigalpha]

Yeah, I believe the top valve is the intake valve ... plus, that's where the plug lines up with. That valve is really cruddy. The exhaust valve is nice and clean with nothing too much built up on it.

I was thinking that depending on the price of a connecting rod and piston, boring it out wouldn't be too bad of an option as opposed to buying another engine. Plus, who can pass up a little more oompf.

That intake valve may be stuck open just a tad, but I don't remember if I had rotated the crank to make sure both of the valves were closed when I snapped the picture. It'll be cleaned up anyways. I've seen on a couple of videos of rebuilds where the rebuilder will grind a few thousandths off the end of the valve to make sure that it doesn't contact the lifter and keep it a smidgen open.

I found the parts I needed through B&S directly, but I wasn't sure if there was someplace else I could get them without the mark up.

Are there a lot of other seals and o-rings that can and should be replaced while the engine is apart?

I am reading these from a picture I took so they might not be right. I'll have to check in the morning to verify.
model: 289707
Type: 015-01
Code: 94092320

 

[RedHeep]

Given the age of your mower and the work/cost involved in repairing an old engine, I'd be looking for a used one.

Even when you replace the rod, clean everything up and get it running, you're still putting old parts back together in an old engine. You can probably spend the money you were going to spend on parts and upgrade to a newer rider.

http://clarksville.craigslist.org/search/?areaID=465&subAreaID=&query=riding+mower&catAbb=sss

 

[kastein]

I'd agree with RedHeep, unless you want the experience of rebuilding the motor and the parts are cheap, find a better mower. I've seen all kinds of still working mowers available on the CL free section up here.

 

[bigalpha]

There are no free riding mowers listed up around here. I don't exactly have the $ to buy another riding mower either, which is why I am thinking of just rebuilding what I have, if it's possible.

 

[bigalpha]

Alright, so I pulled the engine and got it about 85% disassembled. Took a while to find all the bolts for everything since the engine was caked in dirt and grime.

I broke the nut that holds the flywheel on. Do I need to pound off the flywheel before I try to separate the head and block? What's the best way to separate those two pieces?

 

[RedHeep]

Alright, so I pulled the engine and got it about 85% disassembled. Took a while to find all the bolts for everything since the engine was caked in dirt and grime.

I broke the nut that holds the flywheel on. Do I need to pound off the flywheel before I try to separate the head and block? What's the best way to separate those two pieces?

Hard to say without ever taking one apart. Have you found a service manual online?

 

[xjtrailrider]

Alright, so I pulled the engine and got it about 85% disassembled. Took a while to find all the bolts for everything since the engine was caked in dirt and grime.

I broke the nut that holds the flywheel on. Do I need to pound off the flywheel before I try to separate the head and block? What's the best way to separate those two pieces?

You broke the nut or the end of the crank? Anyway, you need a flywheel puller. Some motors you can tap on the flywheel with a deadblow and it will pop off

 

[WB9YZU]

You broke the nut off? WTF? If there were threads in that nut, you F'd up the crankshaft.

I don't know how many mowers I worked on as a kid, but I never used a "Flywheel Puller" to remove a flywheel. You put the nut back on so it covers the threads... OH, that's right, he Bwoke that

Alpha, that's not a VW engine, it's a B&S. The Cylinder does not come off the Crankcase. The back of the case comes off. That would be the side opposite the flywheel. Clean the accessory side of the crankshaft so it is spotless so you can get it past the bearing. Remove the 8 or so bolts, tap the cover with a small mallot to loosen the case cover, and slide it off.

The Head was the part you removed so we could see those perty pictures

Keep going, at the very least it will provide us with some good laughs, and you with a better appreciation of things mechanical.

 

[bigalpha]

Sorry - when I said I broke the nut, I meant that I unscrewed it. It took a 5' fence pole on a 1/2" drive socket and two people.

Also, I assumed that the piece I already took off that covered the piston and two valves was the valve cover. I'm not very familiar with terminology in regards to this engine; I figured the two parts left stuck together were the head and the block.

I already removed the 8 bolts holding the two pieces together, but the damn thing won't separate. I've pounded on it and tried to wedge a screw driver in between the two halves but it just won't break loose. Guess I'll hit it harder.

I've already removed everything else - carb and such.