Engine Knock

greg r · #1 06-28-2009, 07:26 PM

I've had this 1650 QL with the K341 for about a month and half now. A couple of weeks ago while doing some heavy mowing, the engine started having some "knock" to it. I couldn't really hear it as the mower deck was extremely loud. I've since totally rebuilt the deck with new spindles, bearings and pulleys. Boy did that cost, but it's pretty quiet for it's size now. The engine knock has since gotten pretty bad, and is most noticeable at mid range rpm when say I'm just cruising back to the shop.
The season started with an oil change and other PM stuff.
Today I drained the oil. There's quite a bit of metal in it, looks like anti-sieze in the light, and a magnet picks up a lot of particles; but a lot won't attract either.
The engine was replaced with a short block sometime in the late 90's.
Numbers: Engine S/N 2430505211; Spec # 4552241
The tag on the side says to order internal components as "for the short block" referring to the part number on the side instead of the spec number. That part number is gone, gad I hate this photo engraving that always disappears.
Any thoughts or advice on this scenario?

#2 06-28-2009, 07:42 PM

DON'T use it anymore! You're about to put a rod through something, time to rebuild. Your K341 is common and parts are readily availible, you'll need to find a competent machine shop in your area that will grind your crank and bore your block and do a valve job. My guess is it will cost you around $400 parts and labor.

Scott

greg r · #3 09-22-2009, 11:25 PM

Well here it is about 3 months later and I've finally got the motor off the tractor and the pan off. I'm stumped at this point.
My 1st guess to the knock was a rod or gudgeon pin. Whoops, that's what grandad called a wrist pin.
It's neither as far as I can tell. I checked the rod end and cap, they look perfect. I further checked with Plasti-gage, and it shows about a tad under .002" so I'm okay there. I removed the piston and rod assembly, no slop in the wrist pin either.
There was a severe score in the lower piston skirt on the side that faces the breather chamber where the valve tappets are. There was some very light scoring in the cylinder on that side as well. I don't believe it's trashed, some light work with a jeweler's file will make the piston okay.
On to the crankcase, clean as can be, it looks almost new with just a spot of rust on the cam. The PO must've changed the oil regularly.
The balance gears and crank gear have a slight scoring in a couple of them like something got munched.
The things in question are:
1 What got munched? Nothing appears missing.
2 The exhaust valve is missing an upper spring retainer, item 27 on the parts list. With a very small breather hole, I can't see anything going into the crankcase.
3 The balance gears are pretty wobbly. The side clearance is on spec, but they wobble quite a bit on their shafts.
4 Spinning the crank, can't determine at this point what would make such a severe knock.

Any insights are greatly appreciated.

Greg

Merk · #4 09-23-2009, 12:13 AM

Quote:

by greg r
I further checked with Plasti-gage, and it shows about a tad under .002" so I'm okay there. I removed the piston and rod assembly, no slop in the wrist pin either.

Plasti-Gage is not a very good tool to measure connecting rod-crankshaft journal clearance. You need to check the crank journal. A micrometer is the tool to use. Max clearance is .0025. You are close to being out of tolorance already. The crank journal should be miked in 2 to 4 places.

I like to measure 4 different places: both sides of a crank journal and 90 degrees from the first measurement.

Any scoring on the piston tells me the cylinder wall has some wear in it. The particles in the oil are cylinder wall, piston skirt and rings. The piston needs to be replaced. Odds are the block will need to be bored at least .010 to correct the taper in the cylinder.

The wobbly balance gears are part of the reason for the knock. The munched is from a wobbly balance gear. You are lucky one of the balance gears didn't come loose. I don't replace balance gears when I do a rebuild.

You need to find someone who has the propper tools to measure the bore in 6 places as the Kohler manual shows. Sections 10 thru 12 in a Kohler manual shows the correct way to rebuild a Kohler motor.

Matt G. · #5 09-23-2009, 08:27 AM

Take those balance gears out RIGHT NOW and toss them in your recycle pile. As Merk said, you are extremely lucky one of those didn't go out the side of the block.

greg r · #6 09-24-2009, 08:13 PM

I got the micrometers, inside gauges, and specifications out. Technically it all looks good enough to go a few more years, ALL within wear limits but; no root cause on what got trashed(something scored the piston in the exact place the skirt cross the hole for the breather chamber) and the roller bearings in the balance gears are severely worn and their journals.

I figure at this point with this much work in it, I might as well do a proper overhaul/rebuild that should last as long as I continue to own her. There are several shops within driving distance that handle Kohler, and a good machine shop in the next town that the local restorers and racers like. I've used them before on small engines some time ago, I hope they haven't changed.

What's y'all take on the balance gears? I get from Merk & Matt to toss them, I suspect the engine would be much rougher without them than it already is. This my 1st engine with balance gears. The iso-mounts will get changed too.

Matt G. · #7 09-24-2009, 08:36 PM

I removed them from a 1650 that I had, and there was no noticeable difference. Remember, the earlier engines didn't have them.

bigmike · #8 09-25-2009, 09:12 PM

I vote for using the balance gears as fishing sinkers.If you tie the engine mounting rails together,front and rear,and install new iso mounts you will never miss the grenade gears.

cubcraig · #9 09-25-2009, 09:37 PM

I am with everyone else on the balance gears, leave them out, do your self a favor use geniune Kohler parts, Stens and Rotary Parts do not meet the same specs as the factory parts. Good Luck

Yosemite Sam · #10 09-25-2009, 11:22 PM

Throw the gears away...

From what you have written, it almost sounds like the motor didn't knock all the time, and when it did, it wasn't under much of a load...

If there doesn't appear to be anything worn concerning the piston, wrist pin, rod or crank, and there is a lot of metal in the oil, I would bet that there are no shims left on the camshaft pin and the knock was from the end of the cam hitting the side of the block. Just a guess but worth looking into...