About 2 or 3 years ago I picked up a mower someone threw out, it was a 2019 MTD 21" FWD Deck, but it had a very old Quantum on it with the style of gas tank where most of the beauty cover was part of the gas tank, and it only has a small little circle piece that popped in that Identified it as a 4HP quantum, the Starter housing was definitely replaced because it was from 2012 so i don't have the original date and engine model, but the Gas tank had the date molded into it and I'm pretty sure it's from 89 as opposed to 99 or 09. I only mowed with it a couple times, then it completely lost compression, I figured either the valve seats were worn or the cylinder walls finally wore enough, it didn't run particularly great when I was using it, but it didn't really go out with a bang either, it just causally lost compression and died while mowing and wouldn't restart. Not until I took it apart recently did I see the rod exploded. The camshaft for being ancient nylon still appears to be in good shape despite the one gouge that's probably from me turning it over and it catching debris. Lots of ware, the crank journal completely scored, shmoo all in the bottom of the sump, there was shmoo in the rings when I popped the piston out too. Lots of scoring in the bore and along the piston skirt
1989? Briggs Quantum Carnage
- Thread starter blufeb95
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I don't think any push lawn mower engine is really worth the money or effort to rebuilt, especially it it's previously been heavily used and abused, there are very feel-able scratches in the bore. I stole the parts that I might be able to use in the future, like the good MTD 7/8" self propelled blade adapter, the gas tank, the starter housing. I used the coil to fix my dad's 2000 Craftsman mower where the plug wire kept falling off since the previous owner was using it without a kill switch and was pulling the plug and weakened it.
Ha ha ha, looks like a case of using what some here call reclaimed oil, you know old high acids no additive package used junk oil from a high mileage diesel or highly gasoline dilluted GDI, vehicle. Yeah I know. 
Three separate pieces, but the bolts are also pretty loose so there may be more cracks. I'm guessing the motor got the typical Briggs treatment most of it's life, straight 30 tar that was rarely of ever changed or topped up, when it was running it was smoking out of the crankcase vent
That oil slinger broke the rod... 
Fun Autopsy but unless it has some sentimental value or really up to a challenge, I do agree it's not worth it to rebuild. But wait... Is the deck good enough for another quantum that you can find for cheap?
Fun Autopsy but unless it has some sentimental value or really up to a challenge, I do agree it's not worth it to rebuild. But wait... Is the deck good enough for another quantum that you can find for cheap?
The deck now houses a Honda GCV160 I got off the guy who used to mow my neighbor's yard, he mowed commercially with an MTD mower that it came on until the self propel broke and the deck fell apart after about 6 or 7 years , It was an easy swap since it already had the appropriate blade adapter seized in placeThat oil slinger broke the rod...
Fun Autopsy but unless it has some sentimental value or really up to a challenge, I do agree it's not worth it to rebuild. But wait... Is the deck good enough for another quantum that you can find for cheap?
Good deal, I had one of those Honda's for just a short bit & outside of just some carb trouble it ran well.
I have another GCV160 that I trash picked recently that I think compression release is broken on, and/or the shaft is bent the blade adapter is definitely bent. But it has a manual choke assembly on it I need to steal and put on my good gcv160, because to know surprise the only real issue I have with it is that I'll start mowing and random after a minute or so of mowing the auto choke comes on again and I have to stand there a minute while it burps black smoke until it goes back off again
Briggs always had a problem with piston rods & their bearings. I had sooooo many of those, in various HP's, that I trash picked over the years. Every one had a minor rap in it. I ran them till they blew, like your's. I also had lots of Tecumseh trash picked mowers. Not one of them ever had a piston rap.....and look who's still in business. Tecumseh ran circles around Briggs in quality. It's a shame.
I never had such a failure with the many B&S engines I have owned. They are very forgiving, especially the older ones. Neglect is what does a small engine into destruction. Trash picked engines usually fall into that category.
The older ones were FANTASTIC. I just threw out a 1972 Briggs 3hp push mower / trash picked. I owned it for 8 yrs. Toward the end, before I put it out for trash,,, it was smoking, rapping, blow-by was insane that I had to disconnect tube from carb and just let oil fly. But had full compression !!! Was runnin on pure STP blue bottle. Neighbors hated it LOL 
. LOUD and SMOKEY. Never threw a rod. I disagree. Briggs quality has come down quite a bit since 1972. Again, never had a problem with trash picked Tecumseh. Those are all I have left ( My trash pickin days are over,,,,got too old and have a bad back. Can't be diggin them out of the trash and pickin them up ) It's sad to say this, but I have a leaf blower on wheels. Not too big. It has an 8hp Chinese engine on it. 15W40 oil. This thing ALWAYS starts on 1/2 pull,,,and has no primer bulb........ We're doomed. Never had a Briggs or a Tecumseh start on a 1/2 pull.
. LOUD and SMOKEY. Never threw a rod. I disagree. Briggs quality has come down quite a bit since 1972. Again, never had a problem with trash picked Tecumseh. Those are all I have left ( My trash pickin days are over,,,,got too old and have a bad back. Can't be diggin them out of the trash and pickin them up ) It's sad to say this, but I have a leaf blower on wheels. Not too big. It has an 8hp Chinese engine on it. 15W40 oil. This thing ALWAYS starts on 1/2 pull,,,and has no primer bulb........ We're doomed. Never had a Briggs or a Tecumseh start on a 1/2 pull.