Cub Cadet 123: head differences, damaged bore, hydrostatic leak
 

Hello. I am a new forum member. If I have posted in the wrong place or
should have posted separate questions, please let me know.

I acquired a cub cadet model 123 with a Kohler K301AS engine s/n C020835 spec no. 4759B about a year ago and have been fixing it up (see attached photos 01 and 02).

I recently swapped engines due to the connecting rod breaking in the original
and taking a chunk out of the cylinder wall. The replacement engine K301A
s/n E0009326 spec no. 47138B has a block with studs for the head. My original K301AS had no studs. I have attached photos of the two heads (see photos 03 and 04). I decided to use the head that came with the replacement K301A engine, that is, the one meant to be used with the studs. After I installed the head (see attached photos 05 and 06), I realized that the thin sheet metal
plate and thicker plate (see attached photos 07, 08, 09, 10) no longer fit. I started to modify them to accomodate the new spark plug location but then realized that there is insufficient space vertically on the studs if I use the spacer bushings that came with the engine. I could use shorter bushings but maybe this affects rigidty/stiffness of the installed head?

(1.) Is it safe to run the engine without using these plates?
I'm not sure if their main purpose is heat transfer or protecting the head
from damage or what. I also don't know in general why Kohler changed from
using no studs to using studs and bushings.

(2.) Is there an advantage to using one head versus the other due to spark
plug location or because of the studs or some other reason? The head from the studded block has the spark plug aligned over the exhaust valve. The head from the block without studs has the spark plug located in between the two valves.

So the options I can think of are to use the head meant for the studs without
installing the plates (that's the way I have the tractor now), use this head with modified plates and shorter bushings, or use the head from the original engine and install the plates.

Additional questions not related to the head.

(3.) If the chunk missing from the cylinder bore from my first engine
(see attached photo 11) is below the max travel of the piston, can that
block be re-used, maybe after dremeling the edges?

(4.) I have a hydraulic fluid leak coming from the hydrostatic transmission.
It is a slow leak coming from some point near the top of the unit (see
attached photos 12 and 13) but I can't determine exactly where. The tractor
had been running for months without leaking. I first noticed it over the winter when I wasn't using the tractor and before the connecting rod broke. Has anyone used Lucas stop leak with success? The container says it is 100% petroleum and it looks like really thick oil. I'm not sure what else to try short of splitting the tractor. But even if I do that and find the spot it is leaking from, I'm not sure I want to tear into the hydrostatic transmission. I think it is beyond
my skill level.

Any comments are welcome. Apologies for the long post. I assure you it took
me far longer to write it than for you to read it.

I don't have any idea on your questions about the heads. Have not
seen one with the studs.
However at least one good possibility on the hydro leak would be the
cork gasket. Sits behind the charge pump on the hydro. It is actually
a pretty simple fix but you will have to split the tractor to get to it.
Splitting seems like a more ominous task then it really is. You will not
have to get inside the hydro pump. It is an easier job then most of the
engine work your doing. Good luck
Ken


Attachment 113012

Attachment 113013

First, welcome to OCC........... :Welcome2:

That engine was NOT specified for Cub Cadet. It was an aftermarket version.

That IS a Cub Cadet specified engine.

The "plates" or shrouds are for air flow and cooling of the Kohler Engine.

The engine will run hotter and NOT a good idea unless you are in Alaska.

I would keep the head that came with the engine. When looking for parts in the future, it is so much more simple by looking up a K301-47138 and knowing all the parts are original.

I have done it on a Kohler KT-17 with NO issues.

West Valley covered the Hydro issues.

Cub Cadet 123: head differences, damaged bore, hydrostatic leak
 

West Valley G / Ken,

That seems a likely place to look.

I found these images in the hydrostatic service manual. I suppose any of these seals could be the culprit. Is this the area you mean?

Also, thanks for your encouragement. I will probably split the tractor for a closer look. I'd rather not put goop in the transmission.

Cub Cadet 123: head differences, damaged bore, hydrostatic leak
 

R Bedell,

That's interesting that the engine I took out was not an original Cub Cadet engine. I had no idea. I had assumed everything was original. I got it from my neighbor but he hadn't used it in decades and didn't remember much about it. He bought it used in the early 70's. I also have no idea if the head that came with the engine K301A engine I recently bought is the original.

I'll hang on to the block in case I need it down the road since you were successful with yours.

Thanks for the tip about searching with K301-47138. I just did that to find the parts diagrams on Kohler's website. I looked at the diagrams for the shrouds and the head. I'm a little puzzled by both of them. The one for the shrouds is here: https://kohlerenginesparts.com/oempa...-10-10-tp-2097 and the one for the head is here: https://kohlerenginesparts.com/oempa...r-head-tp-2097

The diagrams seem to show two different heads and two different shroud configurations and none of the shrouds look like heavier plate version I have. Maybe the parts changed over time and the diagrams are trying to depict that.

I think I'll search around on this forum for someone who posted model 123 photos so I can see what the head/shrouds should look like.

For the short term, I might finish modifying the shrouds from the K301AS engine and install shorter bushings on the studs so the shrouds fit. It is kind of neat how the air flow from the fly wheel is used to cool the engine.

I'm new to cub cadets but their simplicity, ruggedness, and mechanical ingenuity are growing on me. I like that a 50 year old tractor/engine is still running. I assume the K301A was rebuilt once because it has .003 stamped on top of the piston but it's still a long life.

Thanks for your reply.

Oops. I was thinking about the charge pump gaskets which you
show because I have seen em leak. But the cork gasket which is the
most likely culprit is not where I described. Sorry for the bad lead.
Here is a better picture of the cork gasket. Between the hydro and the rear
end.Attachment 113018

Ken

West Valley G,

Oh, I see. That's the opposite side of the hydrostatic unit from where I was thinking.
No worries. I appreciate the clarification.

That heavy plate is there to support the muffler.

What he said, you need the tins like he has on his engine in pictures one and 2, smaller spacers.

Concerning the heads....