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Papermaker

Kohler KT and Magnum rod failure

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Papermaker

Hi Guys—

I have a clean, relatively new 7117 which runs well. I have all of the accessories that I need (mower deck, snowblower and lawn vacuum) and I would like to keep the tractor for a long time. It has, what I think, is a very good KT 17 series II engine. The engine doesn’t smoke and doesn’t make any unusual noises. In addition, I’ve added an oil pressure gauge and filter. Overall, I’m impressed by the cleanliness of the oil and the oil pressure cold and hot.

Ok, here is the issue: what is the life expectancy of the KT engines in general and specifically the connecting rods? A rod failure would leave me with several challenges this winter and into the future. In a defensive move, I’ve started to look for either a replacement or back-up engine or a Simplicity tractor with a CH engine that is compatible with my accessories. Over the past few weeks I’ve looked at several KT series II 17/19 and Magnum 18/20 engines with broken rods. Does anyone on the forum know the failure modes of these rods?

I’ve come up with several to start the conversation.

#61550; Engine design issue.

#61550; Rod fatigue at the end of its life cycle.

#61550; Poor maintenance.

#61550; Low oil.

#61550; High rpms.

#61550; Owner abuse.

#61550; A combination of some or all of the above.

Thanks,

--John

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ShaunE

Series II was an upgrade with some type of different oiling system which was a GREAT improvement. Mowing along ditches & hillsides starved oil from the "higher side" of the crankcase causing rod failure in the first series engines.

I have owned mine for about 15 years (Allis 917H.)

The tractor is a 1986. I suspect the series II in mine is not original.

I mow 1.5 acres every week most of the time in the summer.

I installed new rings,gaskets, fuel pump & coil when I purchased the tractor. Cross-hatch was beautiful in the cylinders.

I also added the oil filter adaptor & filter with a filter-mag magnet (yes it works.)

Starter was rebuilt two years ago & I replaced cable to the next size heavier (it's a long wire.)

I use NON ETHANOL Premium Unleaded fuel.

I change the oil, oil filter, both air filter elements & fuel filter annually. I use Mobil 1 synthetic 10W-30. 56oz with the large Kohler filter.

If you ask others what oil to use, you will get 47,000 different responses & it will turn into a political arena just like every other internet forum does when the "oil" question is asked.

You asked the longevity? I can't answer that except it should last you a very long time if properly taken care of.

I believe cleanliness is the biggest factor. I blow mine off with an electric leaf blower after every use. Especially the air filter. Every three to four years I remove engine from tractor & all sheet metal & flywheel to clean the stator & cooling fins. You will be amazed at how filthy this gets. I use a pressure washer.

By keeping it clean, you can spot leaks right away & assure it's getting cooled effectively.

Mine does not use any oil & does not smoke.

And lastly...Avoid Ethanol blended fuel if you have the option. That stuff is the}:).

Many on this site are way more knowledgeable than I & hopefully they will give you their insight as well.

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Papermaker

Guys--

I maintain my tractor to a very high level. What I'm looking for is an analysis of a typical rod failure. For example, if high rpm or low oil contributes to rod failure, an owner could used reduced rpm and proper oil level to avoid failure. If the rod isn't designed properly or if there is a rod fatigue life (or other issues) no amount of maintenance is going to prevent a failure.

A couple of notes; both M20s I looked at suffered rod failure on the left cylinder, the M18 failed on the right. All three not only destroyed the rod beam but also the big-end bearing broke apart smearing rod material (aluminum alloy?) into the crank journal. The question is, did the big-end fail causing the rod beam to self destruct or did the beam break causing the big-end to follow?

--John

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Chris727

Low oil is always going to contribute to either a direct failure or a future failure. I haven't heard of anyone throwing a rod on one of these engines without doing something to cause it. Do not reduce your RPMS under load. Running an air cooled engine at low RPMs under load CAN result in overheating which can cause a major failure. Run the engine near wide open throttle when mowing or follow the guidelines in the owners manual. Lots of failures on these engines are also attributed to operation on slopes. Its my understanding that even on the series II the oil pumps are still located off to one side of the sump and running on a slope could still cause problems. Also make sure any oil leaks are fixed quickly so dirt and chaff does not stick to the fins and prevent cooling.

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MikeES

I have several KT/Mag engines all with broken a rod on the left cylinder. All were rod bearing failure which lead to rod failure. I acquired these engines already broke. I am running a KT19 with a repaired rod and welded case.

Failure is from what I believe is oil level and oil quality and/or cooling from plugged fins . Because they do not hold that much oil they can be vulnerable with being just a little bit low on oil.

The engine specs list a 35 degree angle both left and right and 30 degrees both front and back. So side hill running is probably an issue with low oil level.

So keep the oil changed and full (check it often) and keep the fins clean, and the engine should last a long time.

My experience is that these engines wear to a point that they create a lot of blow by and pressurize the crankcase. I have found that they just need a need set of rings and little else.

I like these engines, simple, smooth and powerful, and they are more durable than the newer V-twins. But not as bullet proof as the CI singles.

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Papermaker

Chris727--

Thanks for your comments.

MikeES--

How do you know that the the rod bearings failed first? Also, did the crankcase weld repair wrap any of the bearing or gasket surfaces? If it did, did you have to resurface any of the precision surfaces? I was considering purchasing a blown engine but the three engines I've seen cracked very close to the cylinder mounting surface.

If the cause of rod failure in a well maintained engine is not well understood, have any of the forum members experienced a rod failure while using and maintain their engines properly (engine rpm and maintenance as recommend by Simplicity.

Thanks,

--John

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powerking_one

John,

The other known issue with the KT series engines is the nylon/plastic governor gear grenading which overrevs the engine and if not shutdown within seconds results in a broken conn rod. Along with that the rod thusly perforates the engine block. I believe the replacement governor gear from Kohler was an improved design.

Tom (PK)

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Papermaker

Tom --

Thanks for the note. I remember seeing comments about governor gears failing. Are there any warning signs that the gear is starting to fail or have you disassembled an engine with a gear near failure (I'll put it on the list of upgrades if I rebuild the engine)?

Speaking of rebuilds, have forum members used zyglo dye penatrant on the rods before reassembly and found cracks?

I can understand a rod failure if the engine over-revs!

--John

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Papermaker

MikeES --

Can you expand upon your "they are more durable than the newer V-twins" comment? I've read that some of the CH engine have hydraulic lifter failure but haven't seen anything about rod failures or other issues.

Thanks,

--John

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MikeES

Papermaker-

If the rod journal is messed up with metal smeared on it. Then the failure was the crank shaft/rod journal interface lubrication. This caused the rod journal to start sticking to the crank shaft and not rotate freely which caused the rod beam to flex and break.

A rod breaking with no damage to the crankshaft journal is usually over revving.

I have 3 engines with a hole in the block right next to the dip stick, no other block damage. Nothing critical in the that area from a tolerance stand point. My Kt19 the block was just cracked and push out slightly, no actual hole.

The V twins are more vulnerable to overheating with plugged fins. There is less fins because of the OH valves and less clearances around the narrow fin channels.

Causing warped heads best case and complete engine failures.

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Papermaker

Hey Mike, your rod failure explanation makes sense to me. Also, reduced cooling and resultant overheating issues also sounds right. It sounds like maintenance and pulling the engine sheet metal annually should keep a CH in good shape.

Thanks,

--John

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MikeES

Yes, it was ultimately cooling that killed the TH engines also. Valve cover leaks oil, which collects dirt, which diminishes cooling.

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