FR651V Dead Cylinder

I have a FR651V on a 5 year old SS5000 Toro. I've never had an issue with it other than routine maintenance. Last time out was just mowing normally when I felt a jerk and a slight popping noise and a sudden noticeable loss of power. Upon checking, I found one plug fouled, which I changed and it didn't help. Pull one plug wire and it doesn't change at all. Pull the second plug wire and it stalls immediately. Checked the air filter and found that it was totally packed by a rodents nest. Bought a new filter, added fuel treatment to the gas and sprayed the carb with carb cleaner. Nothing made a difference. Getting spark to both cylinders but I swapped the coils to make sure the spark was strong enough from both coils. No change. Checked the engine compression and the good cylinder is around 85 and the bad cylinder was at 30. According to the manual has to be at least 64. Took the rocker cover off the dead cylinder and both push rods were bent. Took the head off and the cylinder walls look fine. When I hold the push rods to where they go they seem to go up and down fine.

I apologize for my long winded first post but I wanted to be complete. My question is, what caused the push rods to bend? Is it possible a piece of junk from the rodent nest entered the cylinder and caused the damage? I've checked both the head and the cylinder and they don't seem to be warped. I should have mentioned that when I took the engine cover off, I found another rodent nest packed into the fins around the same cylinder. Could this have caused it to overheat and do that damage? Parts are about $50 which I don't mind if I've got a decent chance of the same thing not happening immediately again.

Thanks for any help!

None of the rodent's nest could have made it into the cylinder unless there was a gaping hole in your air filter element. That assumes, of course, that the nest was on the dirty side of the element?

Your compression test is invalid if you did it with bent pushrods.

Did you see any evidence on the top of the piston of the piston hitting the valves?

When did you do your last routine maintenance, including adjusting the valve clearance?

cpurvis said:

None of the rodent's nest could have made it into the cylinder unless there was a gaping hole in your air filter element. That assumes, of course, that the nest was on the dirty side of the element?

Your compression test is invalid if you did it with bent pushrods.

Did you see any evidence on the top of the piston of the piston hitting the valves?

When did you do your last routine maintenance, including adjusting the valve clearance?

Click to expand...

The whole area around the filter was packed solid and I was surprised it ran at all but I didn't see any holes in it.

I didn't see any evidence of anything hitting the valves or the pistons. The valves seem to move up and down without binding and it looks like they're sealing okay. There's a lot of carbon buildup on the top of the piston but no impact marks.

I only had the valves adjusted once at the start of year two. Could the lack of valve adjustment do it ? If they were too tight I assume?

Thanks for the reply.

cpurvis said:

None of the rodent's nest could have made it into the cylinder unless there was a gaping hole in your air filter element. That assumes, of course, that the nest was on the dirty side of the element?

Your compression test is invalid if you did it with bent pushrods.

Did you see any evidence on the top of the piston of the piston hitting the valves?

When did you do your last routine maintenance, including adjusting the valve clearance?

Click to expand...

Should have mentioned too that when I removed the air filter hose, the carb throat was covered with an oily black coating that sprayed right off with carb cleaner.

I only had the valves adjusted once at the start of year two. Could the lack of valve adjustment do it ? If they were too tight I assume?

Click to expand...

I would assume the opposite--that too much lash might allow the pushrods to get out of position.

The oily black film is from crankcase fumes that get fed back into the carburetor.

I think your next step is to get two new pushrods installed and fire it up and see what happens. Have the valves examined, too.

cpurvis said:

I would assume the opposite--that too much lash might allow the pushrods to get out of position.

The oily black film is from crankcase fumes that get fed back into the carburetor.

I think your next step is to get two new pushrods installed and fire it up and see what happens. Have the valves examined, too.

Click to expand...

Thanks for the help. In your opinion should I order two new push rods for the other side too?

Thanks again!

Not if you can adjust the lash correctly. They're not something that wears out; the only time they need to be replaced is if they get damaged.

"I found another rodent nest packed into the fins around the same cylinder. Could this have caused it to overheat and do that damage?

I have to say Yes on the overheating of that bad cylinder, that overheating could swell up the valve guides causing resistance, & as a result cause the push rods to bend. When it cools they move normally.

After each mow with my Toro / Kaw FR651, I always flip-open the air filter cover to see how dirty my filter is, & the side holes that feed cool air to the filter when running, I use my leaf blower & point it down each hole & blow it out.
Every years end I also remove the engine cover, very simple procedure to make sure my fins etc are clean.

Get the rodent poison or traps out, that is the root of this problem imo.

How many hours on this engine ? Book says set valves @ 300 hours.

Yep, overheating.
New pushrods to replace the bent ones.
New head gaskets & rocker cover gaskets.
Coat one side with wheel bearing grease so they strip off clean.
When you tension the heads, do it very slowly in small stages.
Good chance the overheating could also have softened the block so if the threads seem like they are starting to go you will have to helicoil them.
As for the rodents, use a cat for the reason we originally domisticed them.
Get a kitten and make a bed for it in your shed.
Feed it in the morning & lock it in overnight.
Never ever let it in the house & only ever play with it in the shed

Before you reinstall the heads. Pour a thin liquid into the intake port and see if the intake valve leaks. If it is leaking, grind the valve and valve seat and re-seat the valve. Do this in the exhaust port and follow the same procedure for the exhaust and you'll be making maximum compression. You do not want any leakage around the valves and seat. Now, follow Bert's advice and you should be up and running.