That courage had 68 hours on it. The problem had nothing to do with Nylon parts. If I had to blame something it would be dull drill bits,wore out tapes leaving a 50% thread contact on all the hole they drilled, not sure if thread locker would have held them.Workmanship not Nylon. I have been seeing Nylon for some years on tear downs but never the reason for the tear down. I am attaching a picture of a 6.5 Briggs Nylon Camshaft , it was a bent crankshaft from mowing fence post again Nylon had nothing to do with it. I am sure Kohler will be carefull after the Kohler Triad walk of shame.
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Nothing to do with bad machining or bad bolts.
It is a vibration affect that loosens the bolts allowing the crank case to flex then crack.
Each & every part that is moving inside the engine sets up a vibration at some particular speed these vibrations can become resonant and increase in magnitude by several factors.
It is these vibrations that undo the bolts and crack the crankcase.
The cure was not bigger , stronger , longer bolts or using thread locker.
The solution was changing the principle cause of the vibrations, the crankshaft.
When the engine was designed it used the forged Kohler crank.
For reasons of cost reductions ( most likely) this was changed to a cast crank.
Nothing wrong with that 1/3 of the cars use cast cranks on engines putting out 10 + times the Hp of the mower engine.
The CI crank is balanced by the counter weight and the primary balance is good, the engine is smooth in operation.
However there are secondary & tertiary vibration frequencies and the changes in these was not taken account for in the swap to the cast crank.
Bad tooling or assembly problems are easy to fix because the warranty control section would quickly recognise a cluster of serial numbers that had the problem then issue a dealer bullitin for rectification.
However a random vibrational failure is a different animal, very hard to diagnose.
I have about 20 or so customers with Kohler powered Huskys that have sequencial engine serial numbers, yet only 1 in that batch cracked.
Nearly all of the Kohler cracks are pre 2008 engines and there is almost nothing to connect them in useage conditions or operating hours.
The only connection is the front 4 bolts start to come loose so I just check them every service.
If they stay tight the case does not crack and it takes about 4 minutes to check them or an additional 30 seconds if you do scheduled service & remove the blower housing every year to clean the cooling fins.
