K321 rebuild / vibration

[Enosgl]

Hi all,

I am a very experienced engine rebuilder, having been in the business years ago. I just completed a rebuild on a 1450 with available, ie, aftermarket parts. No complaints, seems to be of decent quality, all went together well, and runs well. One thing I did NOT do is weigh the replaced components against the weight of the new parts. The wrist pin wall was thicker, but I assume the aftermarket manufacturer's piston was perhaps lighter than OEM and the combined reciprocating weight is similar. Has anyone else experienced this? Engine runs good on the floor, but does vibrate a bit. I know the Quiet Line CC tractors were not counter balanced which is why they use rubber mounts, but how much is normal? Trying to not overthink it, but don't want to complete the install just to take it out and change a wrist pin. Many thanks!

[Ambush]

I had the same issue on two K321’s. Thicker wrist pin and slightly heavier piston. Both had balance gears that I left out. I rebalanced both cranks and did a thread on it here. One crank I bolted a weight too just like the Kirk Engines kit, The other had been drilled to factory balance and I poured lead into that one.

[Enosgl]

How much shake is too much? I do not even really know that there is a balance issue. I was guessing since when sitting on the floor running while bolted to two 4x4s it walks a bit.

[PBIjim]

Can you get a lower weight wrist pin made out of a better quality material?? Replacing that part might be an easier way to adjust the balance. A wrist pin may be something that a local machine shop can make.

[Ambush]

Haha, it will hop around if not bolted down!

[ol'George]

It IS a BIG single, a THUMPER, just one step smaller than a 16 hp.
That said,
that is why DEERE chose to mount it with the crank at a right angle to the frame, so the frame could smooth/absorb the firing impulses somewhat.
And they cradled it so the motor mounts were inline with the crankshaft.

Cub, on the other hand, chose to set it on rubber at the base,so it dances like a fat lady in heels on a bar room table.( no offence to large wimin)

The "balance Gears" help, but they come with their problems after many hours of use.

IIRR, Plymouth in the early 30's came out with "floating power"
it reduced engine vibration,and was adopted buy other makers.
in '58 chevy mover their engine mounts to the side of the block,instead of "cups" bolted to the front of the block and on pads on the bottom side of the bellhousing, in an effort to supress vibratrions/noise.
Enjoy your rebuild it will prolly out live your affection for your cubs.

[Enosgl]

Thanks everybody for the input. I am not sure if the vibration I have is normal. I would have not assembled it with this pin, but the one I replaced was visibly worn. It was "rebuilt" by the previous owner, and am sure it was aftermarket parts, so am not sure if the bouncing around I have is normal for a non balance gear engine, and if the worn pin I replaced was a cheap knockoff that was too light, or if the aftermarket (Performance Saw Supply/Stens) is too thick. Kohler does not even LIST a separate p/n for a piston pin, otherwise I would just replace it before installing. I could WEIGH the old parts vs the WORN parts, but again, that baseline is meaningless, since it was aftermarket, AND STD vs the .030 I installed. Thanks again for your input.

[West Valley G]

I own several and they have there own vibrate. I mean vibrate and not
jumping around when in use. I would not overthink it. Enjoy the work
you did and move on. Just an attitude age has blessed me with I reckon.

Ken

[Enosgl]

Thanks, everybody, for the responses. I am inclined to "roll with it", as has been suggested. We will see how it goes.

[ol'George]

Rotational vibration (bottom end) has more effect on balance than piston/pin/rings do.
Yes it is factored into the bob weights used to do a correct balance, but not so much precentage ways
And all small engines will dance around the floor, even the ones mounted on a 2x8 or 2x10.
I like to set them on on a old unmounted tire so they can do their thing while I run them in, checking for leaks, setting carbs etc.