It's not a rod knock, but what is it?

[mikeeyre74 289]

This is a bit of a long story, but I'll try to keep it condensed.  I'm at my wits end for an answer. 

 

 I have a 1977 wheel horse C120,  that originally had a 301 Kohler engine.  The original owner beat that to death before I got it, and destroyed the piston.  I took a Kohler 321 out of another tractor (Alis Chalmers), swapped the oil pan, then slid it into place into my 120.  All went according to plan.  When I removed the oil pan from the original 321, I was able to look around inside and saw that the piston was tight, the connecting rod was tight, and the bearings appeared to be OK. After getting it back together, I drove it around a bit  and heard what I originally thought was a rod knock.  I thought this was impossible, since I had literally just had it in my hand a few hours before and it was fine.  But it sure sounded like a rod knock, and when I changed the oil on it after about 45 minutes of run time, it definitely had metal particles all contaminated in it. Also, the brand-new oil was now black. 

 

 That was a couple of days ago. Last night, a friend of mine came over and we pulled the motor back out and got it up onto the bench.  We Removed the oil pan and saw that the connecting rod was as tight as the day it was installed. The piston was also fine, and  The valves are pristine.  

 

 After looking around for a couple of minutes, we finally noticed the problem.  It was the balance shaft gears.  We noticed one of the teeth was missing right off the bat.  That probably accounts for the metal particles in the oil.  Having read some of the Brian Miller stuff, we revisited that a bit and decided to do away with the balance shaft gears, clean everything up and then reinstall the engine and see if that has cured the noise. 

 

 After all was said and done, we had the engine running, and it definitely sounds different… Quieter with less background noise…( I attribute this to not having noisy, partially broken balance shift gears spinning around)  But the "rod knock" noise is still clearly there.  The problem is, I know for a fact that it isn't a rod knock. I've had the connecting rod in my hand twice in the past week and it is fine.  So it's just not a rod knock. 

 

The question is; what the heck is it?   What sounds like a rod knock, but isn't a rod knock?   It comes up under load, when you're going up a hill it starts tapping louder, but going downhill it goes away.  it even does it when just accelerating the tractors engine from a stand still, but then it smooths out.   I suspect it has something to do with how the governor works, but I'm not really an expert in how that functions… Is there something inside there that could be flailing about when it gets under load that's causing that noise? Like when the governor starts to call for more power it does whatever it does and that causes the knocking sound? 

[MalMac 1,328]

Glad you got those balance gears out. There nothing but trouble in a K series.

It still could be rod knock. A out of tolerance crank journal can cause rod knock even though you can't fill it. Sometimes piston slap can cause internal noise. Do you have a mechanic stethoscope or hollow metal tube to put against the motor to try and determine what location noise might be coming from. Not always but a cracked flywheel can make noise when different stresses are put on the motor. The noise can sound like it's something internal. If it sounds like a rod knock good chance it is. If it is, it won't getter better. I would tear it back down and get some measurements on that crank journal and pull that rod and visually inspect it. Aftermarket rods are cheap enough. Try that. Believe me if it's s rod it will demand attention one way or another.

[953 nut 51,735]

Pick up some "Plastigauge" at an auto parts store and check the rod/crank clearance at several points on the journal. Only costs a couple of bucks but it will let you know what you really have.

[woodchuckfarmer 333]

Recheck the timing , it might spark knock.

[rmaynard 14,906]

If you removed the rod cap, be sure to put it back on with the oil hole facing the cam shaft, otherwise you will not get proper lubrication and you will definitely lose that rod.

[953 nut 51,735]

             Just an off the wall thought, is the pan on the  the same depth as the pan that was on the engine? Could the splash dipper on the rod cap be contacting the pan?  

[C-101plowerpower 1,605]

2 hours ago, rmaynard said:

If you removed the rod cap, be sure to put it back on with the oil hole facing the cam shaft, otherwise you will not get proper lubrication and you will definitely lose that rod.

 

that might well be what is causing the noise, uncle and me replaced the rodcaps the wrong way round in his tractor and it made one hell of a racket, once turned around it was like it just left the factory

[Shynon 7,435]

10 hours ago, MalMac said:

I would tear it back down and get some measurements on that crank journal and pull that rod and visually inspect it.

If the rod journal is still in spec. I would buy a new rod and install it, the rod may stretched on the bottom end due to engine being run over 3600rpm

[520HC 207]

Sounds like spark knock. Adjust your points a little wider and see if it goes away.

[mikeeyre74 289]

The solution!

 

As it turns out, after doing a lot of reading up on this issue, it sounded most to me like the timing issue that Woodchuck and 520HC mentioned. So, I went in with the timing light and found it was actually running at 22-23BTDC when measured dynamically with a timing light. I brought it in to 18 and gave it a try there and it now runs quiet and strong. It was a spark knock after all! Man, was that loud.. I'm really surprised. 

 

Mike

[woodchuckfarmer 333]

The k91 I just rebuilt did the same thing. Set the point at 20 tho , fired right up . out the driveway I went knock knock. came back , reset the points to 18 tho and it ran like a top with no more spark knock.        Wayne