Help! First time buyer C-121

[Sarge 3,463]

The white smoke and knock can go together, if the valve guides are getting worn or no one has ever set the valve clearance there's a good chance it's put a lot of carbon on top of the piston. Carbon buildup, over time will cause hot spots on the piston and in the cylinder head - leading to pre-ignition knock. The buildup can get spots in it hot enough to fire off the fuel before top dead center, it's trying to force the piston back down on the compression stroke.

 

Generally, removng the head, de-carbon the piston/head chamber and set the valves will do the trick. If it's left in that condition and ran for a lot of hours it can start to damage the rod/crank, leading to a rod failure. If the rod does fail, as long as it doesn't blow out the engine block it's still easily rebuilt. The K series Kohler is a highly sought engine for it's known longevity - no reason one can't run and work heavily for 30+yrs, be rebuilt and do it all over again.  No other small engine can really make that claim other than the cast iron K.

 

It's not that expensive to rebuld that engine compared to others. Yes, genuine Kohler parts are expensive, but you get what you pay for in lifespan and quality. I have an old school authorized rebuilder nearby, $500 if no damage to the crank and all genuine parts - his rebuilds will last as long as the original or more easily. Even for a first time diy project, you only need a machine shop to do the bore work/ring fitting and maybe grind the valves - the rest you could handle with some help from this forum. Honestly, that C probably just needs a bit of love and it may have a lot more life left in it yet.

 

That little Briggs powered thing is not a garden tractor, it's just a simple lawn mower - even with light use it's never going to last as long as that C series . I personally would not buy anything with a vertical shaft engine - they do not last very long compared to the standard horizontal shaft versions. The I/C line from Briggs was pretty good, but still , compared to the Kohler K - it's not much more than a papeweight.

 

 

Sarge

[mikeeyre74 289]

That “rod knock” could be balance gears ready to let go or happily rattle for years, as mine have done, or it could be the famous “Kohler timing knock” which can be cured with a good points adjustment. These days, I’m no longer scared by a noisy K series unless the pieces are already flying off of it. I’d go give it another look with your “smart engine friend” and get a second opinion. 

[ClassicTractorProfessor 5,314]

5 hours ago, mikeeyre74 said:

 unless the pieces are already flying off of it.

That's a scary situation when pieces start flying off of it, ask me how I know  I've gotten now to where I can laugh about it some, but it wasn't funny when it happened almost two years ago

[mikeeyre74 289]

Yeah, been there and done that. But it was a Briggs! 😝

[Sarge 3,463]

I can weld that back together, at least the block, anyway. Rod, not so much...lol.

 

The "Kohler knock" is generally just timing, but you have to know the difference in sound. My K-301 knocks like crazy from it's balance gears and timing, plus age. One of my K-341's, it's the rod coming loose....has a gutteral, hollow knock that is distinctive of a steel rod becoming egg shaped. That's when they come apart, and why that engine is out of service - the 301 will keep on running for years. Just takes an educated ear, find an older gear head that has blown up his share of engines over the years with you - they will know...

 

Sarge

[Tuneup 1,433]

Then there is the other source of knock - forgetting to torque the flywheel. Kinda' suggests that I didn't check any other bolts but I checked them twice - really! I second the others above. You can keep the Ks running forever - pull the head and clean the carbon, adjust valve clearance and verify the timing....but you do need something running from the start that you can trust. Tough decision -  Good Luck!

[ericj 1,578]

I bought a 73 12 AUTO one time that had a big unnatural vent hole right were the starter would have been, starter was gone when i bought it, I thought that the rod let loose and put the hole in the block. Then one day when I was looking at the mess I realized the the base of the rod was still on the crank. Had my friend who did my motor work at the time take a look at it. He found the balance gears broke and blew the hole in the block. I actually reused the crank in another motor. So be careful of those knocking balance gears and rods. every motor I ever had rebuilt I had those balance gears removed. good luck. I agree that stay away from the vertical crankshaft mowers unless you only want to use it as a mower.

 

 

 

 

 

eric j