fix this engine. Kohler 20 hp on a walker mower.

[doc henderson]

went over to look at a walnut tree with burl near my buddy Steve.  he and his brother were tearing down and trouble shooting his mower engine.  



 

this is the crank area the has a gear on it to turn the cam shaft to lift the valves and on the bottom it interacts with the oil pump.



 

this is the gear that turns the valve shaft and oil pump from the crank.  it had a crack in it .  hard to see. does he just replace the gear and reassemble or let someone rebuild the whole thing.  a brand new engine is 2300 bucks.



 

the engine was running then stopped.  timing was off after the gear cracked.

[doc henderson]

so replace gear and reassemble. rebuild, or buy a new engine

[RetiredTech]

  For me it would depend on the rest of the engines condition and how well it was running before. If it wasn't using any oil, still has good compression and the engine has a reasonable number of hours on it I'd probably just repair it. I'd want to check those valves to make sure the pistons didn't hit them. If it's up in hours rebuild or replace as the wallet allows. Disclaimer: Just my opinion, your mileage may vary.

[doc henderson]

he may try to look in the cylinder.  good compression in that if the plugs are in, he cannot turn the crank too far.

[Ianab]

Looking at the pics the engine seems in good condition. If the gears were showing signs of wear or broken teeth that would be different. Metal fragments might have travelled though the engine and damaged all sorts of things. Metal shavings in the bottom of the sump is a bad sign as they are probably spread through all the bearings etc. That would call for a full strip down and rebuild (or a new engine) 

But that looks like a hidden manufacturing defect in the gear has led to a fracture. Hopefully hasn't harmed anything else in the system. 

[chevytaHOE5674]

As long as none of the valves collided with pistons then I would replace the gear and go on with my day.

[Don P]

That deep in and ~$100 to keep going down that road which doesn't look bad, vs  $2300. That'd be an easy call here. Tell them they need a new engine and you'll dispose of the wrecked one.

[Wlmedley]

A couple years ago my Lincoln welder with a similar engine was using a lot of oil and I was planning to rebuild it.Pulled heads and found that head gasket had blown between cylinder and push rod galley on one cylinder causing high crankcase pressure.Just replaced gaskets and reassembled and has been running fine ever since.Found out later that certain year Kohlers had head gasket trouble.Point is that he might want to pull heads off to inspect for damage and replacing head gaskets might save him trouble down the road.

[Southside]

Boy oh boy, with friends like Don P...  :D

[rusticretreater]

It isn't apparent in the pictures, but I would think the crank timing gear is keyed to the crankshaft.  It also appears the gear didn't break.   This means the camshaft timing didn't get too far out of alignment.  The gears didn't skip teeth did they?

My immediate feeling is that the engine is ok and just needs a new gear installed and the timing set.  Still it would be wise to check on things to confirm everything is ok.

Assuming the engine still has a good amount of working life in its current condition:

Remove the spark plugs and find some way to turn the crank to get a piston to TDC.  Then turn the camshaft at least one complete revolution watching the rocker arms to make sure both valves open and close.  Then do the same with the second cylinder.  This will reveal if the engine is a non-interference engine(when valve timing is lost, the valves don't hit the pistons) which I believe it is.   I was unable to find anything online stating this.  You could also disassemble the valve train and remove the cylinder heads for visual inspection.

If the crank journal isn't burned due to the mishap, simply replace the gear and set the timing.

Then turn the engine over a few times watching the valve operation.  Install the plugs and again turn the engine, listening for the hiss of compressed air escaping in the exhaust port.

[doc henderson]

the gear has a crack on one side.  ring structures normally beak in two places. think ribs and pelvis.  the hope is the crack allowed it to slip over the crank against the resistance of turning the cam and oil pump.  the engine just died.  no big clunk or sudden stop.

we did not find a key way.  the gear and cam gear have drilled marks.  so you have to figure how to get it pressed on the shaft in the proper orientation I assume.

[doc henderson]

I assume the gear is tempered.  if we want to heat it to get the new one on, now hot is safe to not damage the gear.  to expand enough to slip on the shaft.

[chevytaHOE5674]

I have a toaster oven in the shop that I heat bearings and gears up to around 200-250 degrees to get them to slide on, checking temp with an IR temp gun. Also been known to spray a flipped over a can of computer duster, or get some dry ice to shrink up the receiving end, just be sure to wipe the frost off as that can cause interference issues.

[doc henderson]

I think he has both a freezer and oven in his shop. 8)

[Big_eddy]

we did not find a key way.  the gear and cam gear have drilled marks.  so you have to figure how to get it pressed on the shaft in the proper orientation I assume.

I'm guessing you will find the new gear does not have a mark. Press it on in any orientation. Then you have to set both cams and pistons to TDC during assembly and mark the gear tooth that matches the cam gear mark for next time.   In your case, after the gear cracked, it twisted on the shaft slightly and then timing was off. No slipped teeth needed 

[scsmith42]

Doc, the first question that your friends need to ask is "why" did the gear crack?  In looking at it, from the pix it appears that there is excessive wear on the right side of the teeth, and they appear to be bent slightly to the left.  Perhaps that is due to the photo angle, but maybe not.

My deduction is that there is something in the valvetrain that is causing some type of restriction on the cam gear, leading to the wear and tracking.  At a minimum, I'd tear down the valet rain all the way and closely inspect the components.

Sticking valves can cause this (coupled with a piston strike).

YMMV.

Scott

[rusticretreater]

Ok, so the gear just slipped, the timing went off and it shut down. Actually, that's good news.  I would try to find a shop manual or online listing of what the journal on the crank should measure.  It's probably ok, but it could end up in the same spot again or worse if the gear slips again.  There are probably a few tricks to join the gear to the crankshaft in a more positive fashion.

A propane torch would also heat things up, but a high temp air gun would be more uniform in heating.

Of course, it is wise to spend some time with the shop manual for the engine.

https://kohlerpower.com/en/engines/manuals

[doc henderson]

thanks rustic.  the inner gear and area on the crank feel smooth and not galled.  thanks for the manual.  Doc.

[JD Guy]

@rusticretreater has great info with his Kohler link. Have used in past and they are almost invaluable, especially if going through an engine for the first time!

[sharp edge]

The wall looks to thin for a press fit.... it  should be internal welded on.  my .002


SE 

[hedgerow]

Doc Those Kohler engines have had issues with that crank gear. I would pull the heads and make sure the valves aren't bent and its a good time for new head gaskets. They make a aftermarket steel gear that uses a dowel pin to drive the gear. You have to drill the crank for the pin. You heat the gear up and drop it on the crank. There are a lot of U-tube videos about this. Had a buddy that ran many of those Kohler engines and had to replace the gear on several.

[Tom King]

That was some useful info!

V-Twin Kohler Command Crank Gear - YouTube


edited to add:    https://mwsc.co/products/command-crank-gear

[Hilltop366]

A quick way to test valves is to put a liquid in the ports and see if it pours out the valve. We use to use gas but diesel or wd40 would work too and less flammable.