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Discussion Starter · #1 ·
Background:

Following a loud bang the other night where the engine suddenly stopped in its tracks, I replaced a cheap fried coil with another Bosch and installed a new voltage regulator for good measure.

I then reinstalled the spark plug after testing for spark and chewed up the threads in the head. I removed the head, tapped out the threads and installed a sleeve with a kit from Autozone, but couldn't get the thing quite square and the spark plug ended up being a couple of mm further away from the valves. I thought, 'whatever, I can just adjust with the carb'. I reinstalled the head, skipping the installation of a new head gasket.

I started up the tractor yesterday and the the engine races away as soon as the throttle is pushed up and couldn't be controlled well with the throttle back down again... it would continue to race. I had to turn the key to off to stop it. I eventually adjusted the carb to the point where it would idle at a lower speed (somewhat roughtly), but as soon as the throttle is pushed up it howls at high speed. I could adjust the high speed idle to let it not howl, but it was a little rough there too.

I noticed during all of this that fuel was leaking somewhere from the head, towards the curved end away from the valves. The carb was also getting loose on one side via one of the bolts that retains it to the block. I secured that.

Eventually after stopping the tractor one last time I couldn't start it up (no spark), so I pulled the plug and it was caked in a white / grey substance, not the usual dark carbon buildup (or dark wet engine oil) I had seen in the past. I wonder whether some oil was sneaking up into the head and getting burned off. Strange. When I removed the plug it stripped the new threads I made for the new sleeve. The head is now toast IMO.

This morning I inspected in more detail:
- I noticed that the breather was spewing oil into the air filter area through the tube and oil was leaking past the gasket between the breather cover and the block. I removed the cover and lots of nice fresh engine oil came out; the gaskets were soaked. I haven't removed all of the breather yet as I needed to remove the carb, but will try that later.
- The governor arm is still nicely attached to the shaft and seems to actuate back and forth between the correct positions. I cannot tell however whether the governor itself (newly installed after my recent rebuild http://adventureswithadeere.blogspot.com/2016/08/rebuilding-kohler-k321-governor-gear.html) is still on its shaft.

Theories:
1. Oil leak through breather / fuel leak from head gasket:
- Poor head gasket seal may have caused oil pressure build up and caused it to leak out of the breather. Tonight I will remove the head and inspect. I think the gasket leak may have been a combination of the old gasket being used (there are noticeable raised edges around where the edges of the head mate with the gasket) and/or the head getting warped or maybe even cracked (although it is aluminum so I would expect it would have physically split!) when I tapped out a new hole.

I purchased a head and new gasket on ebay; I will check for flatness when it gets in on Thursday night.

2. Surging:
a) Governor:
- Initially I thought the governor arm was loose on its shaft. That wasn't the case.
- I have a hunch that the governor may be sitting in the oil pan. I did try wiggling the governor back and forth and side to side but I don't feel a lot of play; if the governor wasn't present at all I would suspect that the arm would rotate a long way forwards. Tonight I will remove the arm and try just rotating the shaft. If the governor itself isn't there I would suspect that that shaft will rotate up to around 90 degrees when the paddle flips from one side of the block towards the shaft that the governor sits on (see pic here without governor installed: http://4.bp.blogspot.com/-iIl7582CQ...x0ULfu6AIrUTgCK4B/s1600/20160802_21-05-54.jpg).
- Maybe the teeth on the governor cog stripped?
- Maybe one or more of the weights on the governor came off, but this is a brand new governor from Kohler.
- Unfortunately with my tractor the oil pan cannot be removed without taking the block out of the frame. I would need a CCTV snake to see what's up in there!

b) Something other than the governor contributing to a runaway engine:
- Maybe the float is stuck in the carb bowl and it is just dumping fuel in?
- I don't think a runaway engine speed issue could be caused by a leaking head gasket? Could it?
- Could the points have been damaged when my last coil went bang?
- Could the spark plug electrode location being located further from the valves cause the governor want to surge to get more gas in the system? Maybe a long shot, but perhaps more likely it would just result in a rough running engine.


Any thoughts from anyone on my theories?

Shame, because after my rebuild it was running SO GOOD!
 

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It does sound governor related to me too Rob
 

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I am leaning toward air leak also. I had a k321 with a bad throttle plate shaft. Badly worn and it would run away like that at slightest touch of throttle. I am not suggesting your throttle plate but I would go back and torque head and more importantly make sure the carb gasket is there and things are tight.


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I have seen painted governor's do that as the paint sticks the mechanism. It is an odd but reasonable theory. Especially if the governor still stops when setting it.

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Discussion Starter · #8 ·
Thanks all for the responses...

Tonight I did the following:
1. Removed the breather assembly completely. Fortunately there's a hole through which I could see the governor! Sitting there and turning freely when the crankshaft is turned by hand. I could have foudn this out this morning had I spent more time but I had to remove the carb first.
View attachment 116553

2. Upon removing the carb the gasket was somewhat soaked in fuel, likely because I saw the nuts were loose during all this chaos. The gasket has a thick rubber part and it looks in OK shape so probably very reusable.

3. I removed the governor arm then wiggled the shaft without removing the brass bushing. It rotates freely around 45 degrees only between one side of the block and the governor. I think that's in good shape. What I cannot tell is whether the weights are still intact on the governor.

4. I removed the head. Oh boy, lots of oil / gas mix coming out the edges, but not relaly much in the way of wet gas/oil mix as it was all getting burned up. Out the side of the head past the gasket it was really evident that the gasket wasn't holding. As I suspected probably the gasket should have been replaced when I took of the head previously and maybe I had warped the head while boring out that new spark plug hole. Pics below. Ignore the metal shavings... that's aluminum from the spark plug hole. I cleaned that right up.

Interestingly I did see some damage to the underside of the head over the intake valve. Somehow it was hammering into the head. Maybe a result of this overspeeding due to way too much air getting mixed with the gas (or something). Not good. The valve looks ok.

View attachment 116561

View attachment 116569

View attachment 116577

View attachment 116585

Audio equipment Auto part Metal Technology Space

Green Water Close-up Leaf Macro photography

Auto part Metal Automotive engine part Engine

Auto part Metal Circle

I cleaned up the mess carefully.

Thursday I have the new head and gasket arriving. I will buy some blue(?) loctite for the carb bolts plus new spark plug and get this all back together. I am a little concerned about that intake valve; I will check the valve stem to tappet gap clearance again. That hammering issue is a new one that I didn't see before I took the head off on Saturday to deal with that spark plug problem.

At this point I suspect a combination of the loose carb and gasket issue were the culprits. Time will tell. Stay tuned and thanks for the help once again!
 

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Discussion Starter · #9 ·
Thinking about the valve to head contact problem: when I had the head skimmed they had to take a lot of metal off to make it level, it is possible they went beyond the limits. If the head was also warped as a result of the spark hole boring I did then it could have been just enough distance change to make it contact. At least that's my story until I check the valve to tappet gap (job for later).

Sorry about the pic problem above.

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What does the underside of the head look like, where that valve is? You could place the head back on without the gasket and turn by hand and see if you have any contact. By keeping the gasket out you have decreased the cleanse. Even with that out you should not have contact.
 

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Discussion Starter · #11 ·
What does the underside of the head look like, where that valve is? You could place the head back on without the gasket and turn by hand and see if you have any contact. By keeping the gasket out you have decreased the cleanse. Even with that out you should not have contact.
Good tip, thanks. I will try with and without the gasket on the current head, then on the replacement when that comes in.

Here's what the underside of the head looks like



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well it does look like your valve was hitting the head. Now you have to make sure that the valve stem is not bent!!!! What is weird is only one side as if either the valve was already bent or the guide is not straight???
 

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Discussion Starter · #13 ·
well it does look like your valve was hitting the head. Now you have to make sure that the valve stem is not bent!!!! What is weird is only one side as if either the valve was already bent or the guide is not straight???
Right, the damage to the head is in roughly the right / lower right corner. This seems to correspond with the opposite side of the head where fuel / oil (that came up through the valves) was leaking out of the head. If the head was warped or torqued up too tight in one corner I would expect the opposing corner would be higher and that would be where the leak was.


I think I need to buy a new torque wrench as it is a cheaper Powerbuilt model and after all this drama (and after I think it was the culprit of over-torquing the spark plug on Saturday) I just don’t trust the thing. It does seem to click fine but not sure about its precision.


There wasn’t a lot of metal left on the ridge of that head after it was machined to get flat; the machinist did tell me he had to remove a lot as it was really far out. It could be that just a bit of warp or torque too tight in one corner could have caused enough of a difference in height that the valve banged into it.


The ‘new’ head I get in Thursday will hopefully be better.


Thanks for the tip on the valve, I will remove the valve spring and check the valve stem to ensure it isn’t bent If I insert the valve into the guide without the spring installed and rotate it around the valve seat it should be clear whether the valve head is square against the stem and whether the stem is warped by looking at it against the tappet as it rotates.


I will also check the valve to tappet clearance while I am in there.
 

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If I remember right the valves sit tilted in towards the piston. So that might explain why it wasn't hitting flat against the head. But yes I agree that the valve should be inspected. Since you say the machinist had to take quite a bit off the head I'm sure that didn't help.

I learned the hard way too about using a torque wrench for the spark plug. My main problem though was I used JD's spec at 27 ft lbs instead of the 18-22 ft lbs (if I remember right) from Kohler. So from now on I just use a ratchet and tighten it to whenever it feels tight.

Also, just curious what kinda washers if any do you have under the carb mounting bolts????

I've had tooth washers under mine and never had them come loose. I've never seen an engine like this run away due to an air leak but I guess some say it's happened.
 

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For washers I use grade 8 flat washers. The bolts don't usually come loose from turning but more often from heating and stretching. Roger
 

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Discussion Starter · #16 ·
If I remember right the valves sit tilted in towards the piston. So that might explain why it wasn't hitting flat against the head. But yes I agree that the valve should be inspected. Since you say the machinist had to take quite a bit off the head I'm sure that didn't help.

I learned the hard way too about using a torque wrench for the spark plug. My main problem though was I used JD's spec at 27 ft lbs instead of the 18-22 ft lbs (if I remember right) from Kohler. So from now on I just use a ratchet and tighten it to whenever it feels tight.

Also, just curious what kinda washers if any do you have under the carb mounting bolts????

I've had tooth washers under mine and never had them come loose. I've never seen an engine like this run away due to an air leak but I guess some say it's happened.
Hmm, will check the washers, good tip on the tooth washers.

Hopefully the valve is good. I can order a replacement easy from isavetractors.com if it isn't.

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Discussion Starter · #17 ·
I have flat washers, will get some toothed ones to sink into the carb to block gasket

I checked the valve by removing the valve keepers. Checked for flatness against caliper arm and also by inserting back into block and pushing down on the valve head while turning to ensure it was snug against the seat. Looks good, not bent by the look of it.

There is some burned on oil on the underside of the valve head that I may try to remove to get it smooth again.

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Discussion Starter · #18 ·
Got the new head and gasket today:

Auto part Compact car

Interesting write up of heads: http://gardentractorpullingtips.com/cylhead.htm noting that they shouldn't be milled or you could end up with valves hitting the head or head gasket leaks. Well there you go.

Hopefully my cam lobe on the exhaust side isn't toast :S

I will install maybe tomorrow night / Friday night. I still have to get the valve spring back and gapped correctly first (must remind self to put engine in correct position)

This head has been bead blasted according to the ebay seller. Does it matter if the inside of the head isn't polished? Should I polish?
 

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Discussion Starter · #20 ·
New cylinder head, gasket installed using a new torque wrench. Fired right up and no racing!

I still have some oil leaking out of the breather, but that's a different topic. I think this particular case is closed for the racing engine - put it down to a leaky cylinder head.
 
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