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Naturally I am now thinking about a complete rebuild......"Little Murray's" shaft is bent.......rest of her seems fine though. I've done a rebuild before (25 years ago in a night class) and I have re-honed a cylinder......is this something I could do on my own?

Replace a bent shaft on a 3.5 horsepower push mower engine? I'm assuming I'd need new rings and bearings.

Where would I need to look up directions for this? Stuff like torque amounts?

What tools for this job?

THANKS

First of all we need engine numbers
If it is an aluminium bore engine then it is throw away the block and keep any good bits for spares .

a replacement short block (New crankshaft, pison, all internals) you swap over flywheel, coil etc. 398211
replacement engine is 10T8020016,

Numbers on flywheel cover:

9L902-0221 E1 04062952

Times has change a lot in the last 25 yrs.

The tools to do a proper cost more than a new engine especially for a one time rebuild. The Lisle 16000 ridge hone itself is around 150 usd. You would need this because a flex hone just makes any taper and/or oval worst. And this is just start as there other possible tools needed some of which are no longer available like the one to do the crankshaft bushings and the 1/4" valve guide repair (19269) tool set.

Basically the cost of the engine came down enough that Briggs decide to eliminate the tools plus they just weren't selling many of the tools as only us older shops were even doing these repairs anymore. By the time we buy the parts and do the repairs it is way more cost wise than just replacing the equipment when it come many of the walk behind equipment.

BTW that engine is a 2004 and is 17 yrs old. It had a long life and it time to retire it after major mishap as bending a crankshaft. The direct replacement is the 09P702-0116-F1 which Power Distributors is pushing a surplus 09P702-0144-F1 which around 240 usd which all that is left as Briggs is really screwed up lately. This is because of Covid and their bankruptcy.

Actually, what's the problem?
I don't think an old mower is easy to fix because there are no current parts on the market. My dad's old mower broke two years ago, and he found an audible review on fixing it. But it ended up that he still hasn't found a replacement for the broken part. Technology doesn't stand still, and new and improved gadgets and appliances appear daily. It's just not profitable for manufacturers to keep making parts for older models. In a market economy, everything has an expiration date. After a breakdown, the consumer buys a new thing because it's often not profitable to make repairs.

His problem is a bent crankshaft for one, another is that the engine is 25+ yrs old.

It more about economics. The OP can buy a replacement mower for less than the replacement engine. Rebuilding the engine requires several hundred dollars of tools. The crankshaft alone is 120 usd then there is the gaskets. On top if he needed to OS the piston, it is NLA. Besides the short block is 160 usd. Then of course places like Walmart have complete walk behind mowers starting around 200 usd.

Now I have the tools but have not even had them out their boxes since 2014 as no one is willing to sink that much in an used engine that will still have worn parts afterwards.

The way engine manufactures are doing now is they try to make up for their deals equipment OEM is to stick it to the end user. They simply don't want to have stock engines just sitting in the warehouses collecting dust.

Bert can explain this mode of economics better.

I still have an old crankshaft straightening tool, it actually re-bends the crankshaft so it cuts level and doesn't vibrate. Works pretty good. I might have to do a youtube video of it.

Putting on the old metallurgists hat, I could not consider a more dangerous thing to do than to cold straiten a crankshaft apart from cold straitening cast motorcycle wheels.
The fact that the engine companies actually made such a tool flabbergasts me .
The chances of a "repaired" crank having a catastrophic failure in the future is so high it is not funny and made even worse by the use of bar blades which are naturally unbalanced because the bending moments are at 180 degrees to each other .

However Star is on he right track, time for a replacement engine
Downside is you can no longer get the higher torque side valve engines which are better suited to mowers than OHV engines so you will have to fit an OHV one.
Upside is it will use a lot less fuel .

I seen those straighteners and even had plans for one. Then I was advised against them as they can cause micro fractures in the crankshaft. One fellow tech even had one crankshaft to later break off while the mower was in operation. Besides most of the engine I seen where on crappy poorly maintain mower bodies.

StarTech said:

I seen those straighteners and even had plans for one. Then I was advised against them as they can cause micro fractures in the crankshaft. One fellow tech even had one crankshaft to later break off while the mower was in operation. Besides most of the engine I seen where on crappy poorly maintain mower bodies.

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I actually have one. Used it once to straighten a crankshaft on my own mower. Refused to straighten any for customers due to liability. And the dealer that I bought out was the original owner and was told by him to never mention that you straightened a crankshaft for a customer. Make up some other service that was performed on the customer invoice so if anything went wrong they couldn't hold you liable.

The US banned swing back blades because of the potential for them to come off and injure people but allow crankshaft straiteners
It is indeed a very funny world we live in .

bertsmobile1 said:

The US banned swing back blades because of the potential for them to come off and injure people but allow crankshaft straiteners
It is indeed a very funny world we live in .

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evidently the anti-swing back blade lobby had more money.

Scrubcadet10 said:

evidently the anti-swing back blade lobby had more money.

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More likely the economics won out. Swing back would save a lot engines but of course that means less parts sold over time.

StarTech said:

More likely the economics won out. Swing back would save a lot engines but of course that means less parts sold over time.

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And probably around 500,000 tons of steel a year.
I send about a ton of old blades to a friends foundry a year .
He thinks I am God because he gets a ton of high quality scrap of known composition for free & that is a big win
I get him to occasionally cast motorcycle parts for me so it is a win win
The swing backs are a different alloy so go into a different drum.
Despite doing 3 times as many swing backs as bars, the swing back drum has only been filled once .

The planet is dieing because we are dong things like making too much steel much of which is not being reused or recycled

I have one of those crankshaft straightners. Got it a very long time when an old guy closed his shop. Haven't used it in probably 20 years. I really doubt if i would use it on a customer engine now. I also have the tools to install valve guides. Haven't used them in probably 20 years also. They are in the drawer with the battery hydrometer i don't use any more. I have a 18.5 Briggs all apart on the bench right now getting the cam replaced. Would a push mower engine be worth doing the same? I doubt it.

Boy I hate those Briggs money maker 793880 camshafts. I just returned from a customer that I install a new just back in Summer 2021 and its ACR is already broken again.

StarTech said:

Boy I hate those Briggs money maker 793880 camshafts. I just returned from a customer that I install a new just back in Summer 2021 and its ACR is already broken again.

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Was that one of the Aftermarket cams or OEM?

Hammermechanicman said:

I have one of those crankshaft straightners. Got it a very long time when an old guy closed his shop. Haven't used it in probably 20 years. I really doubt if i would use it on a customer engine now. I also have the tools to install valve guides. Haven't used them in probably 20 years also. They are in the drawer with the battery hydrometer i don't use any more. I have a 18.5 Briggs all apart on the bench right now getting the cam replaced. Would a push mower engine be worth doing the same? I doubt it.

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Would you consider selling that shaft straightener device? I was mowing for a guy the other day and hit a pipe! Old guy had really let his place go and it was hidden in some tall grass. I currently have that mower in the shop for them to try their shaft straightener on it but If I keep up with this business, I assume I'll have that happen every so often.

Check the Stens 751-032 Crankshaft Straightener but is sample of the prices.

Having considered the math of rebuilding older 4 - 5 HP engines, as others have said, it is less expensive just to buy a replacement. I recently replaced a head gasket and carb on a 20 year old engine, spark plug, air filter, adjust the valves, clean up and paint, and maybe had $85 in it when done*. I can't imagine adding a new rod, maybe piston, rings, gaskets and crankshaft etc.. It would be more than a new engine. These aren't collectors items unless one means the bone yard out back kinda thing.

* and that is a gamble because if the pressure washer pump on it fails it isn't worth throwing another $180 at it.