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GT12G (UT 34001A) Engine Problems

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#1 Irontooth OFFLINE  

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Posted May 28, 2016 - 08:10 AM

This is more of a general troubleshooting question, but here goes:

1983 12 HP , Gear Transmission, UT 34001A, new aftermarket carburator this spring. New points and condensor in 2015.

I was mowing my lawn this week, and when turning around, caught the mower deck on some dirt, which popped the left front side of the deck off its support bar, misaligning the deck. It was still cutting level, so did not notice it at first, because of my hearing protectors and the heavy nature of the grass. I thought it was just working hard. After about 10 more minutes of cutting, I stopped to give both the mower and myself a break, at which time I noticed the deck misalignment problem. I shut the mower off and then the engine, which was running normally at the time. I remounted the deck, took a break, and then tried to start it up again. No start.

This unit has had a tendency to quit after about an hour of mowing, even with trying to keep the blower screen scrupulously clean, and cleaning the fins of the engine that are reachable by removing the top of the shroud about once a month. Cooling off and making sure the blower screen is clean usually makes it good to go for another hour. This time, I was running without the sides but had only been going for about 20 minutes, including the time with the deck misaligned.

I pushed it into my carport to cool off more, verified the oil level was OK,and gave it a couple of hours break. When I cranked it over later, it still would not start, but at one point gave a really loud BANG! I had the sides off and the hood up, and my impression was that it was at the front/right side of the engine, not backfiring throught the carb.

I recharged the battery, and let it set (partly so I could go out and purchase a spark tester).

Since the bang, I get no apparent ignition at all. My new inline spark tester shows that it is sparking. It turns over but doesn't start. It was usually starting after turning over two or three times, so I may not be a really good judge of the sounds, especially since I usually use hearing protection. However, I have also convinced myself that it sounds different when cranking with the choke on as opposed to off. With the choke on, it makes a bit more of a 'chuff' sound compared to the choke off. However, no smoke at all. Starting fluid has no effect.

There is fuel to the carburator (pulled the inlet fuel line to verify).

Turning the drive shaft as one would do to manually check the point gap seems easier to me than it used to. I can hear what I would attribute to a valve opening or closing when I turn it over by hand.

So - Any advice on how to spend my energies? My own thought is that I have blown a gasket, giving no compression.
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#2 Eric OFFLINE  

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Posted May 28, 2016 - 09:18 AM

Just because you have spark does not mean it is good enough to fire, Is the spark bright blue or hard to see in daylight? I am not familiar with your tractor but a bad condenser would cause eratic symptoms like you have described. condensers have been known to fail if they are installed incorectly and oil or moisture can find its way in the casing. Another thought would be the plug wire may be failing causing intermitent ignition. About your choke question, all carbs sound different when choked because you are esentially closing the air intake which in turn gives the carb a throaty sound due to it now acting like a sealed speaker instead of a megaphone if that helps explain it. You should download the manual and use the troubleshooting guide for that specific engine. Good luck.
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#3 boyscout862 OFFLINE  

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Posted May 28, 2016 - 09:26 AM

I agree with above. I add two things to check when you are going through the troubleshooting guide: Check the gas cap vent and Check the flywheel key. Good Luck, Rick

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#4 New.Canadian.DB.Owner OFFLINE  

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Posted May 28, 2016 - 10:30 AM

... suck, squeeze, bang, blow, in the right order and at the right time.  You have spark, but do you have compression?  Maybe you have a stuck valve.

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#5 Dayton_King OFFLINE  

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Posted May 28, 2016 - 02:51 PM

Or sheared flywheel key

#6 skyrydr2 OFFLINE  



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Posted May 29, 2016 - 06:50 AM

Kohler K series will run with out a flywheel, as it runs the points off the cam.. Check your condensor and replace it, also you can remove the cylinder head and check the gasket, it probably popped when it backfired.
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#7 Irontooth OFFLINE  

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Posted May 30, 2016 - 08:58 AM

Pulled the cylinder head this morning (worked all weekend). It was a 'no suck, no squeeze' issue. Big chunk blown out of the head gasket toward the front of the engine. I ordered a new head gasket. There are a lot of deposits on the valves, cylinder, and around the valve seats. What are the recommended practices for cleaning up the mess?

This engine seems to have a case of 'previous owner-itis'. The head bolts were not tightened to any degree. I could almost have loosened them without putting the handle on my socket! The nut on the stud that attaches to what I presume is a lifting tab on the top of the engine was not even hand tight. The blowout was between the stud and the adjacent bolt on the head.

Pics attached...Photo.jpg

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Edited by Irontooth, May 30, 2016 - 09:01 AM.

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#8 KennyP OFFLINE  



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Posted May 30, 2016 - 09:51 AM

Nasty! Time for a good cleaning! I scrap off what I can, then use a fine wire brush in the drill. Once the deposits are off the head, looks like it needs trued. I use a piece of heavy glass and start with 200 grit wet/dry sandpaper on it. A little water and an oscillation motion with the head. Once it gets close, I may switch to 400 grit.

#9 Irontooth OFFLINE  

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Posted June 06, 2016 - 08:37 PM

I ordered a Primeline replacement head gasket from Amazon, but for whatever reason, there was a delay in shipping. I cleaned the head, cylinder and valves as well as I could, given the mess of deposits. I found the most effective tools were a laboratory spatula (stainless with rounded end) and a wire brush on my Dremel. I wore out two brushes! The brushes themselves were steel that seemed to be a bit harder than the metal on the cylinder head, so a really light hand was indicated. I then used the Dremel to buff polish the cylinder head. There were encrustations at the top lip of the cylinder bore as well, so those got removed.

Replacing the head, I followed the torque guidelines and order of tightening of the bolts in the Kohler manual. As long as I had the shielding off, I did a thorough cleaning of the cylinder cooling fins.

Before putting the GT back in service, I put in a new spark plug and adjusted the timing. I don't have a timing light (barn fire about 6 years ago took most of my tools), so I did a static timing. I disconnected the coil-to-points wire at the coil and used an ohm meter to get a good read on the opening of the breaker points. Seems to have worked like a charm. BTW - the Kohler manual shows the condensor wired to the coil on the same stud as the breaker wire, while the Ford service manual seems to show the condensor on the other stud (at least in the schematic). I went with the Kohler schematic, as that was the way it was wired when I got it, and it makes more sense to me that way.

Between weather and work, today was the first day since the head gasket blew that was available for me to mow the lawn. The GT ran like a champ! With two weeks growth, I had a lot of do-over work where the tires rolled, I clogged the deck a few times, and had to mow parts of the lawn in creeper gear, but got it all done. I did take a few breaks (for me as much as for the GT), but it didn't overheat that I noticed, and it had been quitting after about an hour mowing prior to the blow.

Now I need a baler to run off the GT...

- Don
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