Lawnmower crankshaft.

[volvoguy87]

Well, I managed to bend the crankshaft on my Snapper lawnmower. The shop said it's cheaper for them to replace the engine than it is for them to replace the crankshaft. Since the engine is low-hours, I think I'll dive right in and replace the crankshaft myself.

Has anyone ever replaced the crankshaft on an overhead valve Briggs & Stratton? Any words of wisdom?

The engine is an overhead valve Briggs & Stratton Professional Series 875 with a 190cc displacement. It is on a walk-behind mower and it does have an oil filter.

If I totally screw this up, I think I'll replace the engine with a Honda version. It's just more $$. If I can save the old engine for half the cost, or less, I'll crack it open and see if I can fix it. I cannot make it any worse!

 

[revvinkevin]

 

 

Unless you have the extra time on your hands and are looking for the challenge of rebuilding the B&S engine, why bother messing with it?   Just buy a replacement engine and be done with it.   How much money will you save rebuilding that engine vs replacing it?   You could swap the engine and be mowing your lawn again in probably 30 minutes.

 

In auto shop class in high school we disassembled and reassembled 3 hp B&S engine as part of the class, the test was which group could get their engine reassembled, started and running first.   Being a just couple years ago **cough** the oiling system was prehistoric, only a "dipper" bolted to the connecting rod.   They are pretty simple, but it's still a 4 cycle engine. 

[this post was last edited: 4/14/2016-13:46]

 

[iheartmaytag]

That's bad news

First, is the crank bent, or just the pin?  Does the engine still run and vibrate, or total no start.

 

If actually the crank, it is involved as you will need to remove both the top end and bottom end of the engine, then remove the crank to replace.  The 8.75 is a good strong engine, and the B&S engines are very easy to work on.  If you have time and know how to invest--go for it.

 

I am seconding total engine replacement.  What was estimate for new engine? 

 

Came back to edit:

There are some videos on Youtube demonstrating this process.  May want to give them a watch to see if this is in your wheelhouse.

 

[this post was last edited: 4/14/2016-14:27]

 

[revvinkevin]

 

 

Looks like you can get an engine through Amazon (free shipping) for $329

 

http://www.amazon.com/Briggs-Stratton-121S02-2022-F1-Diameter-Crankshaft/dp/B005LTY9W0

 

[volvoguy87]

Repair vs. Replace.

The version I have is about $400.00 to replace with the same engine. I can fix it for about $180.00 in parts. It's the model with the oil pump and oil filter. My yard is small but mostly steep hills. The sections which are not steep hills are REALLY steep hills! I wanted something better than splash lubrication because I didn't want to burn up the engine because of the topography. I also mow some abandoned properties around me.

The engine still runs, in fact it starts on the 1st pull, it just vibrates badly (or extremely well, depending on your perspective). The mower is at a shop right now and they confirmed that the crankshaft is badly bent (their terminology).

If I replace the engine, I'd buy a Honda engine. They are more expensive and harder to work on, but they are quieter, more reliable, and burn less gas.

Dave

 

[nurdlinger]

Do you have adequate documentation?

Taking it apart is simple. Reassembly involves all kinds of specifications for clearance checking and tightening fasteners to specific torque values. If you have the docs, and have the tools to accomplish these things, it could be instructional and fun. Without those items it will be very difficult to end up with a well-functioning engine.

 

[askolover]

Love my Honda pusher!!! 9 years old and still starts on the first pull!

 

[robbinsandmyers]

Im a small engine mechanic by trade and its not that hard to do. Once the engine is off and fluids drained I remove the flywheel and the sump, then time the cam and crank using the marks on the gears to line them up. Remove the cam but make sure your valve lifters dont fall out. If they do no worries its easy to adjust the valves if they get switched when reinstalled. Unscrew the connecting rod screws and remove the cap. Turn the crank so the piston is at top dead center then swing the rod ( hoo boy!) out of the way so the crank can be pulled from the engine. Insert the new crank, make sure to use a new sump gasket and crankshaft seals then time your gears again making sure the oil pump drive doesnt have a slot to line up and bolt the sump and flywheel back on and reinstall the engine. If you email me your model, type and code numbers I can send you torque specs. You'll need a 3/8" drive newton meter/inch lbs torque wrench. John.
[email protected]

 

[gotwasher]

Hi you may be able to bend back by hammering on opposite side of bend shafts it can somtimes be bent back

 

[tolivac]

Replace the bad B&S motor with the Honda motor you really want and be done with it.Remember the L-head B&S motors that just about anyone could work on-now they are more complex.

 

[sudsmaster]

Never rebuilt a small motor like that... have done big flat head sixes, though.

 

Putting a new crankshaft in may involve making sure there's proper clearance on the main and journal bearings. Not exactly for the faint of heart, although perhaps B&S makes them all the same at the factory?

 

I am curious though, how did the crank get bent in the first place?

 

 

[volvoguy87]

Honda Engine, etc.

I would buy the Honda engine, but it's close to $500, whereas parts to fix the rather nice B&S are only about $170.

The shaft got bent because I was mowing an abandoned property and happened upon a section of chain link fence that had become buried in the tall grass. It Wrapped the chain link tightly around the blade and shaft and stopped the engine quickly. I had to use wire cutters to free it. After that, it vibrated terribly and left a puddle of oil in the garage. It also did a number on the blade.

My mower shop tried to straighten the shaft, but it would not budge.

The mower is a $700+ Snapper Ninja. It's really a spectacular mower when the shaft is not bent and the blade is sharp. The drive system is variable-speed and it pulls itself in a straight line. It really does a noticeably better job and leaves a much better looking lawn than the cheaper mowers I've used in my life, even when they have been in top-condition.

Dave

 

[sudsmaster]

Well, there's always the Predator motor line from Harbor Freight. I know, they sell a lot of Chinese junk, but the Predators have gotten rather good reviews, as have the HF Predator powered generators.

 

They are OHV and come in a variety of displacements. But check and make sure the crank shaft diameter and length will fit your Snapper.

 

 

[askolover]

I was just about to say the same thing about Harbor Freight.  I bought one of their cheap horizontal 6.5hp motors to build an air compressor.  It always started on the first pull!

 

[sudsmaster]

I have been tempted to get one of their 8 hp horizontal shaft Predators to replace the balky 6 HP Tecumseh motor on my Patriot chipper/shredder. The Tecumseh runs OK once it's started, but starting is a real PITA. I have to monkey with the carb idle adjustment (bottom of float bowl) and pull the cord 10-20 times every time I want to wake it up after it gets cold. I'd go with the 6 HP Predator but the shaft is 5/8" diameter, and the Patriot requires a 3/4" diameter shaft, which is what the 8 hp Predator has. I *think* it will fit but I'd hate to go through all the tear down and replacement to find out otherwise.

 

But I've read the Predators start easy enough. Plus they are OHV, which means they will be more fuel efficient (and probably quieter) than the older flat head designs.

 

 

[supersuds]

Tecumsehs were always hard to start, weren't they? In my experience anyway. I'm sorry that an American company had to exit the market, but I could never understand how people put up with them if there was anything else available. I have one on a generator and have to use aerosol starting fluid on it every time.

 

[tolivac]

I used to have a Toro mower that has a Tecumseh motor-that was the easiest motor I had to start-better than the B&S motors I used.The Toro got stolen and the replacement had a B&S motor-That new Toro was HORRIBLE!!!Motor was hard to start-and the deck was cheaply made.Sold it-than bought the present B&D cordless mower I now have-best improvement-no more gas motored mowers for me-total Pain in the-@#%^I also had a JD B&S motored mower that I hit a small tree stump near the house-motor ran but blade no longer turned.Turned out the motor had an INTERNAL shear pin that broke.Remember the old days on any older mower-the shear pin was on the motor shaft and held by the blade holder.If that broke-a 10 min fix!!!Sold that JD mower,too.Anymore mower failures I will throw in the towel and just have a lawn service do the lawn!Let someone else put up with gas mower problems!If someone had an affordable rechargeable ride mower-I will buy it!My JD tractor languishes in the garage with a flat tire and clogged carberator.The tractor is nice WHEN IT WORKS-but a pain when it doesn't.

 

[norgeway]

Best motor ever...Was a Clinton,

But like everything good, they are out of business.

 

[tolivac]

Yes,now I remember them-they sure weree the best small motor ever-remember a freind of mine had a "Sensation" mower that had a Clinton engine-there was a flywheel on the motor shaft along with the blade-it made that little mower bust thru the tallest weeds adn grass without stalling!.