Broken camshaft gear on a Confidant EZT750

[GearHead36]

I have a Cub Cadet Pro Z 154S with a Kohler Confidant EZT750-3011 (747cc, 27HP, EFI) engine. I believe the previous owner neglected it. At 385 hours, I found that the cooling fins were almost completely blocked. I cleaned them out, adjusted the valves, and did the typical year-end maintenance (change oil, sharpen blades, etc). It ran better, and ran for almost two seasons, then died about a minute after a cold startup. Turns out, the camshaft gear is toast. It's almost completely disintegrated. See photo. I consider a camshaft similar to a fuse. If a fuse blows, I don't just replace it. I ask, why did it blow? Camshafts don't break if everything is working properly. The valve guides don't appear to have moved. Using two thumbs, I can move all 4 valves about 0.5", and they move smoothly. I can't detect any binding in the linkages (lifters, push rods, rocker arms, valves, etc). The push rods don't have any obvious bends. So... what caused the cam gear to disintegrate? Overheating? Can overheating alone cause that? It ran for almost two seasons after I repaired the problem that caused the overheating.

The pistons and valves don't show any signs of collisions. I'm guessing that this is a non-interference engine. OPE engines are fairly low stress. I'm guessing that they're all non-interference.

Since I believe the engine overheated, I bought a gasket kit. I'm going to replace the head gaskets, valve seals, main oil seal, intake & exhaust manifold gaskets, and of course, the camshaft. Do I need to replace anything else?

 

[sgkent]

If a gear tooth has a flaw and breaks, the process almost immediately is like a domino effect on the remaining teeth. Also pieces that break off go thru the remaining teeth if they do mesh. That said, look for a missing nut, screw or piece of piston skirt etc., or something like that which could have gone thru the first broken teeth.

 

[slomo]

I believe the previous owner neglected it. At 385 hours, I found that the cooling fins were almost completely blocked.

NAH, I highly doubt this. LOL

 

[slomo]

The valve guides don't appear to have moved

Pull the valve springs. Make sure the valves move in the guide without a ton of slop.

Using two thumbs, I can move all 4 valves about 0.5", and they move smoothly

If I read what you said, to me, the valves are not sealing. With the spring on, a valve should not move at the face of the valve with a thumb.

So... what caused the cam gear to disintegrate?

Good question. I'm not a Kroller know it all or anything else for that matter. Maybe some of the other guys will chime in on this train wreck.

Do the cam lobes look ok?

 

[slomo]

While you got his torn down, clean the cooling fins like a new engine. Any oil, dirt, grass or bug goo will insulate the fins and not cool proper.

 

[sgkent]

sometimes a head that doesn't get proper cooling will overheat and cause a valve guide to move. That can break a cam gear if a valve and guide are seized. Any signs of valve guide migration I would replace the head and valves too.

 

[GearHead36]

If I read what you said, to me, the valves are not sealing. With the spring on, a valve should not move at the face of the valve with a thumb.

I must not have described this clearly. With two thumbs pushing down on the valve springs, I can get the valves to move, and they all seem to be moving freely.

Do the cam lobes look ok?

I don't have the cam out yet, but the new one has been delivered. Hopefully, I'll get to it this weekend. It's supposed to rain tomorrow. That would be a good time for some indoor shop time.

 

[GearHead36]

While you got his torn down, clean the cooling fins like a new engine. Any oil, dirt, grass or bug goo will insulate the fins and not cool proper.

I've pressure washed the engine already, and have found dirt & grease that I missed. I plan to pressure wash it again. I want it spotless when I get through so I can identify any oil leak.

 

[GearHead36]

sometimes a head that doesn't get proper cooling will overheat and cause a valve guide to move. That can break a cam gear if a valve and guide are seized. Any signs of valve guide migration I would replace the head and valves too.

I don't have the valves & valve springs out yet, but looking through the valve springs, I can't see that any of the guides have moved, and I was looking for that.

 

[GearHead36]

#%$^& $#@^.

I found a chipped tooth on the oil pump gear. It's only chipped, and not obvious unless viewed from the right angle. If there's any gear in the engine that I don't want to fail.... If the oil pump stops pumping, I won't know it until the engine locks up. Grrrr! So now I need to order ANOTHER part, and wait on it to come in.