Just blew a hole in my K321 head

[OoPEZoO 526]

Wow……was not expecting my mowing session to end like this today.  Little backstory before the carnage.  I’ve had this 314-8 for 17 years and it’s always ran like a champ, until the end of last season.  I use it for mowing with a 36” RD deck and plow with it in winter.  It has about 1100 hrs on it and as far as I know, the motor has never been opened up.  Starting the end of last season it would load up a little, felt a little weird, and got a little louder.  I suspected a blown head gasket and knew I was overdue for a good solid tune up. I had ordered everything I needed for that a few weeks ago, but hadn’t got around to it yet.  It started running worse and worse over the past week, especially when pushing it hard while mowing through our thick springtime grass.  It sounded ok idling, but the motor was really struggling once the PTO was engaged.  All of the bearings and pulleys involved with mowing had been checked and seemed to be fine. While mowing today I was literally expecting the motor to blow…..and that’s kind of what happened, but it also forced me to investigate things a little further and found the root of my trouble……a stupid missing hairpin

 

So here is what happened about 3/4 of the way into my mow.  The motor got REAL loud, REAL fast.  I babied it back to the garage, popped the hood and found this hole in the head. Also note the blown head gasket.  Now to the big picture of what was going on. The strange noises and behavior I was getting from the PTO being engaged were being caused by the PTO housing rod coming in contact with the PTO clutch housing pulley……and that was happening because a stupid hairpin had either broken or fell out of the bottom of the PTO housing rod, allowing it to slide down in its mounting bracket. I found all of that because I engaged the PTO and started to turn the motor over by hand and heard a slight metal on metal sound. Further investigation led to the warn grooves I found in the PTO rod and eventually the missing hairpin that caused the issue. So my assumption is that extra contact is what was loading the motor down so hard, coupled with the already blown head gasket, and something had to give……the head gave up.

 

The good news…..everything under the head looks fine.  Top of the piston, valves, cylinder walls, and even the spark plug look surprisingly good.  I believe I can clean everything up, put a new head on, and be back in business. 

 

[OutdoorEnvy 1,663]

Well all things considered it is saveable without too much of a hassle.  That does suck though and is crazy inconvenient.  Hopefully you can source a head without too much issue or cost.  I think the Kohler K series are either 12-16hp or 10-14hp are basically interchangeable with the block and head and external parts.  Someone who knows will chime in I bet.  Good luck with the fix though!

[WHX?? 49,577]

I don't think the PTO hoop issue had much to do with the hole in the head. 

Looks as if she was running a bit lean and overheating. Spark plug looks awful white. 

The head may have warped causing the gasket failure. 

Recheck your carb adjustments once you get it back together. 

[Ed Kennell 39,402]

19 minutes ago, WHX?? said:

I don't think the PTO hoop issue had much to do with the hole in the head. 

 

                                                                    That hoop riding on the PTO bell did not add any load to the engine.             

[pacer 3,174]

I agree with @WHX??, the one thing is unlikely to have even contributed to the other. Just one of those 'flukes' that come together at the same time.

Also, the combustion chamber does look like its been running pretty lean. When you get your replacement back on do a good close check on carb tuning and timing, etc.

 

Just as a side note, did yall see the guy on youtube - "project farm" (hes GOOD!!) use JB weld and sealed a lawn mower head back with it??? Dont think I'd wanna totally rely on it ..... but in a bind!! He also did one with one some of those 'miracle' weld anything rods --- several in the bunch were pretty pitiful, but a couple did pretty good.

[OoPEZoO 526]

Oh, I beg to differ on that.  I wish I had video of how the tractor was reacting.  The hoop was not just riding on the PTO, it was being torqued into it.  Go pull that bottom PTO hoop hairpin on one of your tractors and then apply the PTO lever while rotating the PTO bell by hand and you will see what I mean.  There is a lot of mechanical slop in that assembly.  The hoop can kind of get wedged into place and can apply a LOT of pressure to the PTO bell.  Previously, i think I was getting by because of the PTO clutch and mule drive belt slippage, but I just replaced the old worn belt this morning and readjusted the PTO clutch gap.  There was no slippage at all today and the load was noticeably harder on the motor

 

The hoop getting wedged didn't happen all the time, but sometimes it would happen and cause the motor to bog down and almost stall.  Release the PTO and the RPM would pop right back up run normally.  Then reengage the PTO and it would be fine for a few more mins before it wedged itself back into that spot again.  It only took a few seconds of fiddling after the fact to figure it out.  I agree that the lean condition in the combustion chamber needs addressed.......could be the carb, could have been from the blown head gasket.  I'll cross that bridge once I find a replacement head.  Between the lean condition and the added load, I'm not surprised something popped,  I just didn't expect to blow a hole in the head.  First time I've seen a motor do that.

[squonk 41,729]

What is that sticking out of the head by the plug?

 

Check the edge of the piston closest to the exhaust valve for erosion too.

[Jeff-C175 7,203]

23 minutes ago, squonk said:

What is that sticking out of the head by the plug?

 

Looks like cooling fin if you're looking at the top view.

[Achto 28,019]

4 hours ago, OutdoorEnvy said:

  I think the Kohler K series are either 12-16hp or 10-14hp are basically interchangeable with the block and head and external parts.

 

K series 10-14hp share the same cylinder head.

[RED-Z06 2,330]

3 hours ago, OoPEZoO said:

Oh, I beg to differ on that.  I wish I had video of how the tractor was reacting.  The hoop was not just riding on the PTO, it was being torqued into it.  Go pull that bottom PTO hoop hairpin on one of your tractors and then apply the PTO lever while rotating the PTO bell by hand and you will see what I mean.  There is a lot of mechanical slop in that assembly.  The hoop can kind of get wedged into place and can apply a LOT of pressure to the PTO bell.  Previously, i think I was getting by because of the PTO clutch and mule drive belt slippage, but I just replaced the old worn belt this morning and readjusted the PTO clutch gap.  There was no slippage at all today and the load was noticeably harder on the motor

 

The hoop getting wedged didn't happen all the time, but sometimes it would happen and cause the motor to bog down and almost stall.  Release the PTO and the RPM would pop right back up run normally.  Then reengage the PTO and it would be fine for a few more mins before it wedged itself back into that spot again.  It only took a few seconds of fiddling after the fact to figure it out.  I agree that the lean condition in the combustion chamber needs addressed.......could be the carb, could have been from the blown head gasket.  I'll cross that bridge once I find a replacement head.  Between the lean condition and the added load, I'm not surprised something popped,  I just didn't expect to blow a hole in the head.  First time I've seen a motor do that.

You could cut the hoop in half with the pto disc and it would only draw a fraction of a horsepower, you should be able to run up near 100% load for a bit of time before anything becomes a problem, with that small deck and 14hp you were probably barely on the governor.

 

The loss of compression from the head gasket was causing it to lose power, efficiency, and run lean.

Edited April 29, 2022 by RED-Z06

[roadapples 6,983]

1 hour ago, Achto said:

 

K series 10-14hp share the same cylinder head.

16hp has 10 head bolts...

[oldlineman 1,487]

Just a suggestion, if you put a flat washer under that cotter pin it will help on not wearing out the cotter pin, just a thought  Bob

[OoPEZoO 526]

Have a used head on the way from A-Z.....hopefully its in decent shape.  Should have it in a day or two as they are only an hour up the road.  If not, I'm seeing NOS and new 3rd party replacements for $150.  Probably should go that route anyway, but the used one will get the tractor put back together quicker.  The thought of push mowing my back yard does't sound appealing.

 

Thanks for the insight everyone.

[Snoopy11 5,717]

19 hours ago, pacer said:

JB weld

That is what I was thinking. I also know of a pair of nuts who actually physically mig welded the head, and it held up fine.

 

Don

[Bill D 2,037]

Use new head bolts for reassembly.  I've used the Grade 8 bolts from TSC.  Pull the flywheel cover off and clean the cooling fins.  Find the S on the flywheel and mark it.  Set the timing with a timing light.  Run it slightly rich in the future.  Just my two cents.  Bill

[RED-Z06 2,330]

Ive seen these heads milled, ported, releaved, then had exotic fuels thrown at them turning 6000+ rpms and never seen one pull a Curt Cobain...i wonder if it was a victim of core shift when cast, and it was just paper thin?

[richmondred01 2,270]

Do yourself a favor and resurface that used head and confirm that’s it’s in spec using a feeler gauge. 
If you don’t feel confident in doing it take it to your machine shop and have a pro ascertain that the head it true. 
If not, you will be revisiting this issue. 
just my two cents….

[OoPEZoO 526]

Noted….I’m good with that.  Already have a corian slab cutoff and sand paper ready for some wet sanding.  If I can’t get it perfect, it won’t even go on the tractor. I’ll just suck it up and order a NOS if that’s the case.  First time working on a Kohler single, but not my first engine rodeo.  Many years of car, truck, Jeep, and motorcycle repair stories under my belt. 
 

pulled the carb and guards off yesterday, cleaned everything up, along with a very minor valve adjustment.  I always felt I did a good job keeping it clean, but damn there was a lot of crud packed into the fins and crevasses around the backside of that intake port. Glad I took the time to clean that out. Definitely going to be a regular maintenance item from now on. Going to install new points, condenser, plug, and filter while it’s torn down as well.  

[OoPEZoO 526]

Got my replacement head yesterday.  It looked “ok” for a used part. I should have just ponied up for a NOS one.  That being said, I spent an hour wet sanding the mating surface and worked out all the imperfections.  Bolted it up, turned the key, and she fired right back up. It’s running, but not as well as I’d like.  It’s seemed to be hunting a bit, but I was also just driving around the yard and periodically letting it sit and idle. That may change for better or worse when there is a load applied to he PTO. While it was torn apart, I went ahead and replaced the points, condenser, plug, air filter, and drive belt. I swear I own a timing light, but we moved 2 years ago (2 weeks before the Covid fiasco) and hell if I can find it. Statically, everything is lining up correctly, but I would feel better checking things out while running.  Hopefully I can tune things in and try to cut grass with it again by the weekend. 

[953 nut 56,335]

           Now that the replacement head has been run in for a while do another torque sequence.

[Fordiesel69 263]

dont waste the time using a timing light.  The procedure is very hard and unless done right you may be worse off.  Set to .020 if using ethanol fuels or .018 if using ethanol free.  From there listen for a combustion knock.  If so close the gap a little .002 at a time.  

 

Also you may need to play with both adjustment screws on the carb to get it dialed in.  

[OoPEZoO 526]

Good to know....thanks.  Its running fairly well right now.  I wrote down the settings on the carb adjustment screws.  The low idle screw was still set per the manual, but the high idle screw was an extra 1/2 turn out.  I set both to the factory settings and went through the carb tuning procedure outlined in the K321 manual, then opened up the high idle a 1/4 turn to get it a little rich....it put me within 1/4 turn of where it was initially set.  Then I rode it around the yard for a few mins and pulled into the garage.  I pulled the spark plug wire to shut it down so I could get a look at how it was burning.

 

Looks a little rich to me, but I'm used to doing this on motorcycles and not Kohler Ks.  Anyone with more experience feel like chiming in?

Edited May 5, 2022 by OoPEZoO