What caused this engine failure?

[JohanR]

My lawnmower has been smoking for a while and it got a lot worse lately so i took it apart just to realize that simply replacing the rings probably wouldnt help. But what i found out happening to the casting left me curious, looks like its crumbling. Was thinking that something must've been thrown around in there but i didnt find any major chunks, just small debris.

Im amazed how well it ran concidering the look on those valves and cylinder.

 

[itsid]

the first (well second) pic just likes cast imperfections to me, nothing out of the ordinary tbh.
many cases have imperfections like these somewhere.

the last looks like someone didn't changed the oild too frequently
really just an accumulation of metal shavings and old oil as far as I can tell.

the middle one though makes me baffle.. it looks like someone put acid in that crankcase!
Like IDK some sort of engine cleaner left to eat away on the metal for too long or something.
I no like!

personally, I'd say:
clean the inside good and proper with loads and loads of soapy water and a sponge
rinse , keep in a warm dry spot to fully dry add a cup of oil and slush it around manually to get into all the nooks and crannies,
if it turned opaque, pour it out & repeat.

and then proceed as normal (close crank case refill with fresh oil you know the drill)

'sid

 

[Hellion]

Engine looks pretty healthy overall. Minor carbon on the piston head and valves. I've seen worse, much worse. Cylinder looks normal. See if any of those scoring marks (vertical lines) in the cylinder catch on your fingernail. Most times they can barely be felt.

I'd add new crankcase gaskets and a new head gasket maybe, and drive on.

Slight imperfections or casting "artifacts" in the crankcase walls, nothing to be concerned about. These aren't Ferraris you know.

Sid is right though. Change that oil on a strict regimen. I do mine every summer. It's a short cutting season when you think about it.

What kind of compression are you getting?

 

[JohanR]

It came with the house i bought last year, the previous owner even said he never serviced it, just filled it up every once in a while... damage was already done. shame on a real quality mower overall.

I did not do a compression test but i could easily turn the crank by hand even with the brake applied. And it was burning quite a bit of oil.

There are a few deeper scoring marks, i dont know if a hone will be enough. How much meat can i hone away before i need a oversize piston?

Might aswell give it a try though.

 

[ML-TOYS]

My mower has been blowing smoke since last year, my brothers too.
It just fouls the plug every two mows but its like the energizer bunny.
Still going

 

[mckutzy]

If its a grass cutter... Let it be... Most sound horrible and blow some smoke...

 

[JohanR]

I'll give it a hone, new rings and a lil clean-up. Cant get worse anyway.

Thanks for your input.

 

[KartFab]

post the results when you are done. a brass brush will clean up the carbon nicely on the head. Might want to lap the valves and check valve lash after you clean the carbon off for good measure.

if you are still getting smoke, you could always put like a 10w40 weight oil in there instead as it is thicker and will have less blowby. I doubt it would do any harm to try it out. Also, if you are getting a good seal, but still are seeing oil burning, it could be the valve guides are wearing out, If you pop the springs out for a second and pull the valve out just enough to grasp the valve end, you can try to wiggle the valve around. If it wiggles, then its the guide that is causing the smoking, not necessarily worn rings.

 

[JohanR]

Did some measuring, seems the rings are long gone.

Top ring: 0,041
Second: 0,039
Oil: 0,047

Cylinder: 2,685
Piston: 2,677

From what i can find the ring gap should be around 0,003-0,010, and a maximum of 0,030. Can anyone confirm?

Came up pretty nice after a clean, some play in the exhaust valve which also needs a bit of sealant grinding but i misplaced my grinding compound. Inlet valve is tight and non leaking.

 

[Hellion]

I don't know your engine. Give us the engine serial number/type/code or note them yourself and look up the specs. Silly me, I'm assuming it's a B&S.

Show us the whole kit and kaboodle; photos of the mower and the engine identification labels, tags, etc.

Low compression, smokes like a chimney but runs fairly well, right?

Nice cleaning job.

 

[JohanR]

Sorry, its a b&s quantum.

Engine code 12F887-3510-B1
Date code 02082856

Found a parts list but no specs so far. Torque values would be awsome too

Exactly

 

[KartFab]

In my opinion the bore looks too far gone to just hone and re ring.

A decent shop around here charges $60-$80 to bore and hone if you provide them with the piston. That and having them press in New valve guides might be the best thing to do long term.... it sucks seeing a bore that scratched up

 

[Hellion]

And, if it's a kool bore (no iron cylinder liner), they cannot be bored, or is it honed in the traditional sense of the word, if I understand correctly.

?????

 

[JohanR]

I was just reading up on that and its a kool bore. What will happen if i try to hone it a little? Seen some do it on the web but most seem to not really know what theyre doing.

And then theres talk about chrome rings in some and iron cast in other, thin nicasil walls in some and on and on. These small simple engines are getting more and more complicated by the minute

Think ill just throw new rings in it and see how it goes.

---------- Post added at 10:31 PM ---------- Previous post was at 10:29 PM ----------

Ive found torque and clearances specs though

http://www4.briggsandstratton.com/miscpdfs/RNT/Engine Specifications Chart_ms3992.pdf

 

[Hellion]

Chrome rings go in the Kool Bores and there's some word that no honing for chrome rings is needed...IF this is a simple re-ring job on a normal, basically healthy cylinder(?). The chrome rings bed-in best by themselves.

Of course, often times Briggs won't mention old timey refurb practices in their tech manuals and instead just state to replace the worn parts with new.

For instance, I had my 5HP valves refaced at a local machine shop. Manual doesn't recommend it and instead proposes new valves.

The plot thickens.

 

[Kennycash12]

Of course they want you to get new parts they wouldn't make money if the engine ran for 30 years with out a hitch


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[ML-TOYS]

Is the mower woth the money putting into it ?

 

[Hellion]

If the repairs cost less than a new mower, most certainly I would guess.

And he got this thing free...or it was part of the house as a package deal, depending on how you look at it.

 

[Bbqjoe]

I want to see someone here do the lawn mower engine hovercraft like they used to have in the back of magazines.

 

[Kennycash12]

Joe post a link to one would ya


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