Worth rebuilding?

[tim57chevy 12]

Hello.  I am new here so if this topic was already covered I missed it in my searches.  So here it is.  I have a C120 with the 12 hp Kohler engine in it.  My issue is the other day as i was driving it tot he shed the engine started to make a LOUD banging noise.  I shut it down right away.  So is it economically feasible to rebuild the old Kohler?  I have some mechanical ability but do not have a machine shop I know I can trust.  If it matters I live in the thumb of Michigan.  Thanks for any help.

[peter lena 8,625]

@tim57chevy first off, give us an idea of what this engine is like , hours ?  is there oil in it ? is oil black  and low on the stick ? balance gears are known to grenade . engine rebuilders reference on this site . glad you shut it down quickly , probably get a reference to a machine shop  hopefully close to you , pete

[tim57chevy 12]

I do not know hours on the engine as I bought the tractor used.  The oil is up to full or just below full.  black but not too bad.  I topped it up with new oil before first starting the tractor the first time.  Tractor was running fine then Bang!  Is a rebuild very expensive?  I have already replaced the tractor with a 520HC.  Just would like to keep it as a back up if not too expensive.

[pacer 3,169]

If you are 'mechanically' able, take the engine out and do a basic check on the 'guts' -- pull pan and head and you should be able to get a good idea of what happened. The Kohler is a pretty basic engine and is pretty easy to get off and on the bench to ck it out. As @peter lena mentioned the "Grenade gears" are notorious for coming apart and if it was them there is a slight chance that they can be removed and the rest of the engine be OK. If not, next is to ck the rod/piston - if they are still together take them out and an 'eyeball' ck will tell you if there is a lot of damage...If so... well, machine shops that will work on small engines are becoming very scarce!! As said, you done good by shutting it down quickly, if you are way up in the front of the lawn and the noise starts and you think 'Ok I'll just get down to the shop/garage' the MUCH more damage can happen.

[Achto 27,571]

22 minutes ago, tim57chevy said:

Just would like to keep it as a back up if not too expensive.

 

An aftermarket rebuild kit for a Kohler K301 can be had for under $150. Last engine that I did, the machining was around $150 ( .010 under on the crank, .020 over on the cylinder)

 

Disassemble the engine and measure the cylinder bore and the crank diameter before ordering parts.

 

Edited July 5, 2022 by Achto

[ri702bill 8,319]

AND if you go that route, the machine shop needs the oversized piston before they bore the block. All machined parts have production tolerances - to get the proper piston skirt clearance, they may only need to bore the block .017 or .018 to prevent piston "slap".

[Achto 27,571]

Most excellent advise.

[roadapples 6,983]

[kpinnc 12,024]

Pull the head. Sounds like mine when a brass screw fell out of the throttle shaft and made it's way on top of the piston. 

 

Good luck. Hopefully it's something simple! 

[sparkie333 265]

9 hours ago, tim57chevy said:

I have already replaced the tractor with a 520HC

 

Welcome---If you do your on engine repair you( should mark everything )as to the side it goes back together---An old timer told me this--He put my 341 back together and didn't put the rod in the correct place for the rod oil slinger to miss the shallow side of the oil pan--He may have put the oil pan on backwards--as it had a deep end for my rod slinger engine was destroyed-----He had got too old to do the job.-- And I will still say you should mark everything to get it back the way it came out --so you have a new mower. ----- So, take your time and get the engine built back -----Good Luck

[Horse Newbie 7,069]

2 hours ago, kpinnc said:

Pull the head. Sounds like mine when a brass screw fell out of the throttle shaft and made it's way on top of the piston. 

 

Good luck. Hopefully it's something simple! 

You could check the throttle plate shaft and see if the screw is missing…

[953 nut 55,224]

22 hours ago, tim57chevy said:

Is a rebuild very expensive?

The cost involved in an engine rebuild will probably be the same as buying a "GOOD" used replacement engine that may develop problems in a year or two.

I think of a rebuild as an investment rather than an expense. 

[Snoopy11 5,714]

Could always throw a Carroll Stream motor on it if worst comes to worst... and it would save time... effort... and money... and get a little power boost to boot!

 

https://www.carrollstream.com/13HP-Gas-Engine-With-Electric-Start-B-p/188esb.htm

 

 

 

Don

[moe1965 738]

I just rebuilt a 301. Total for bore job was 80 bucks  crank and valves were good.  Total job cost 300 I put all new bearings etc in.   Lots of good videos or there on rebuilds.  Glad I did it runs great.  

[Snoopy11 5,714]

1 minute ago, moe1965 said:

Total for bore job was 80 bucks

HOLY CRAP... THAT is pretty cheap...

 

I sure wish there was somewhere around here that bored them for that cheap...

 

Don

[lynnmor 7,305]

Since the engine in question had a sudden noise, this is not a rebuilding situation, it is a failure needing repair.  Until the engine is opened up there is no way to estimate cost or if the engine needs to be replaced.  I didn't look it up, but is this an engine that contains the balance gears that grenades?

[Achto 27,571]

43 minutes ago, Snoopy11 said:

I sure wish there was somewhere around here that bored them for that cheap

 

About the going rate around here. 80 to punch the hole 70 to turn the crank.

[tunahead72 2,412]

16 hours ago, kpinnc said:

... Sounds like mine when a brass screw fell out of the throttle shaft and made it's way on top of the piston ...

 

13 hours ago, Horse Newbie said:

You could check the throttle plate shaft and see if the screw is missing…

 

As a non-expert just trying to keep my Wheel Horses running forever, I think this is where I would start.  It's very simple to pull the air filter off and take a look at the carb for missing screws.  You'll be looking directly at the choke shaft/plate, and you might also be able to poke something small at the throttle plate to see if it's obviously loose.

 

I might also try to very gently rotate the engine by hand, clockwise facing the flywheel screen, listening and feeling for anything unusual, and stopping immediately if it doesn't sound or feel right.

 

And then probably pull the head -- it's an easy place to look for anything obviously wrong with the piston, valves, combustion chamber...

 

1 hour ago, lynnmor said:

Since the engine in question had a sudden noise, this is not a rebuilding situation, it is a failure needing repair.  Until the engine is opened up there is no way to estimate cost or if the engine needs to be replaced...

 

Agreed.

 

[kpinnc 12,024]

11 minutes ago, tunahead72 said:

Since the engine in question had a sudden noise, this is not a rebuilding situation, it is a failure needing repair.  Until the engine is opened up there is no way to estimate cost or if the engine needs to be replaced...

 

I also agree. My point is that pulling the head (also true for the oil pan) is an easy peek without dismantling the engine entirely. You may find something with minimal intrusion, or you may not. It's just an easy way to see inside that requires only a gasket if you don't find anything. 

 

My example was obviously one of many possibilities- I rebuilt a carb many years ago, and almost used stainless screws on the plates. I'm so glad I didn't, because I'm sure that a SS screw would have destroyed both the head and piston. The brass one just flattened out and didn't damage anything other than a perfectly good pair of shorts.  It was my first rebuild, so of course my "listening" was over-sensitized for a while beforehand. I'm happy to say that engine still runs like a champ now 20+ years later.

Edited July 6, 2022 by kpinnc

[clueless 2,991]

You said the engine started to make a loud bang that's not much to go by for you or us to assume it needs a rebuild. You need to dig a little deeper and let us know what you find. 

[squonk 41,104]

I'm going to be in the minority on this one. Engine started banging. Not good . There is no local machine shop you can trust. No mention on what you use the tractor for. Is it your primary mower that needs to be fixed right away? Do you have a decent shop,tools and the ability to do your own work? 

 

After checking the obvious stuff like the carb screws, spark plug still in the head, noise roughness turning over by hand ect, I would find another 12-14 HP Kohler from another horse. They are pretty plentiful and a couple of hours to change out. Get your machine back up and running. Then at your leisure you can look deeper into what happened. A bang is usually more than a cheapo ring and gasket kit. You need to find a machine shop. You may be shipping a block and crank a ways away. It will take time. You may find out you need a crank that aren't all that plentiful anymore. Get the tractor running if you really need it then go from there. Same thing with transmissions..Get it back moving. Worse thing is you end up with a rebuilt spare that odds are you will need in a year or so.

[mrc 812]

all advice above is good.  i especially agree with 953nut and squonk.  i look at my wh tractors as lifetime investments that get some serious work done. they are rugged, simple, relatively easy to maintain and affordable.   one of the members here  (richmondred)  specializes in rebuilding these old kohlers.  you might want to contact him.

whatever you do, take your time and do it properly.  you will be glad you did!

regards

mike in mass.

[tim57chevy 12]

Thanks guys.  I believe I will be tearing into the K301 Kohler at lease as far as to be sure the block is still OK.  I may not get to if for a month or so due to other issues at home.  

[tim57chevy 12]

Well I took the head off the K301 and the piston is no longer attached to the crank.  Busted connecting rod I suspect.  Guess I need to go further in to see how bad the damage is.  I Hope shutting it down right away saved it.

 

P.S.  I purchased another Wheel Horse to do my mowing and snow blowing now so rebuild is just to make it workable for my sister to inherit.  

Edited July 8, 2022 by tim57chevy

[Tuneup 1,433]

So, now you're really curious, right? Did the crank survive unscathed? The cam? Did the bore get chipped at the base? Oh, that bang! You'll know in about 45 minutes of wrenching. All will be revealed. These engines are so tough - you might just be perfectly fine and $100 in parts will have you back in action.