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GWGAllisfan

How bad is this?

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GWGAllisfan

So I finally have inspected the K341 that broke several years ago. I was hoping to get a new rod and get the 7112 running again for my Father in law to use. But after pulling the pan, I found this:

So how bad: Is there any way to clean this crank, short of a machine shop? I've never completely re done an engine, seem to be more than I'm up for. Maybe not, though

 I haven't even looked at the piston yet, may get that later tonight.

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ShaunE

Muriatic acid will clean the aluminum off the crank.  Neutralize with baking soda.  I have done this on Nikasil plated snowmobile cylinders to remove piston remnants.  But you will probably be taking it to a machine shop to have it miked & or turned when you are finished.  You should have the bore checked as well while you are there.  You don't want to buy a new standard piston, rings & rod to put in an engine that has an oblong crank journal & an out-of-round cylinder bore.  If your going to buy the parts, take to a machine shop & have it bored & the crank turned so you aren't rebuilding this again in a year or two.  The machining shouldn't be that much.

Does anyone still use plastigage anymore?

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GWGAllisfan

Sounds like what I expected.  it likely will cost more to rebuild than its worth. I just haven't been able to find another engine locally.

I did get some pictures of the piston.  it came out easy, and no discernable Ridge at the top of the bore. Rings not stuck.

I think it just seized at the crank,  and the rod big end shattered.

 

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ShaunE

She's a little scuffed.  I'd say it's time for a bigger bullet & smaller bolt.  If you're going to do it, do it once. Or look for a used engine to put in the 7112.

Where is the K301S that was in the 7112?

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GWGAllisfan

Ok, so I will have to decide if I can find a shop to do the machine work, and possible cylinder boring. I'll see how out of round the cylinder is and see what that leads to.

I've looked for donor engines , but for some reason they are rare down here. If you see one (K series, Command, vanguard, etc) it's near 1000 or more asking price. More than I can spend, and if I was able to spend that, I might as well go ahead and buy the small engine warehouse vanguard conversion kit.

I've even looked into the MV to horizontal conversion, since I can find vertical magnums easily, but having trouble figuring exactly what parts to buy, and it adds up to again, more than is reasonable to pay.

ShaunE,  the K301S that was in it was removed nearly ten years ago. It is complete but smoked badly and was so down on power that it could barely pull the mower. I suppose I could see if it would run.

It was replaced with a K321, that blew when the throttle blade shaft came loose from the throttle arm, so the governor had no effect. It ran away and blew before I could stop it. Piston end of the rod gave on that one. I might be able to fix it, but I have to find a rod for an 0.020 under crank. The crank is fine on that one because it had a rod with bearing inserts. That K321 was replaced with this K341, which just sitting there running one day, shattered the big end of the rod. One tractor 3 engines, all different issues.

Both the 321 and the 341 have a small chunk out of the block about the size of a dime at the bottom of the cylinder. It's below the piston travel, so shouldn't matter.

It's always something.

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theniteowl

Cleaning the crank is easy with muriatic acid but you must be careful with the acid and with the fumes.
You do not want to splash any acid on yourself or inhale the fumes.  Also, the fumes will cause rust on any objects exposed so you want to do this in an open outdoor area.  The muriatic acid will disolve the aluminum without harming the crank.

Once you have it clean you need to measure it to see if it is within spec.  I would do this before giving up on the engine as it is low cost without locking you in to anything expensive.  If the crank is within spec then you can move on to check the cylinder.

When my K341 died the connecting rod broke off close to the piston and the rod dropped out and slammed the side of the engine putting a nice big crack/bend in the block.

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