John Deere la 145 engine bent camshaft

rocky4 · Sep 11, 2019

I have a John Deere LA145 riding mower with a 20 hp B&S 4077770146 B1 v engine. The engine bent the camshaft, broke the connecting rod on one cylinder and did unrepairable damage to housing. Did not bend/brake the push rods,also of course damaged the crank shaft and busted a small section of the piston out.
I'm trying to determin what could have caused this all to happen for future use.
Any thoughts on this? Thanks in advance for any help.

ILENGINE · Sep 11, 2019

Good quality pictures would tell a story of what cause of failure was.

Deleted member 97405 · Sep 11, 2019

ILENGINE said:
Good quality pictures would tell a story of what cause of failure was.

I'm going to say the rod broke first then came around and whacked the cam. I have seen this failure happen when the oil gets too low. The rod will usually break first then act as a battering ram and cause all kinds of damage as the engine is coming to a stop, but pictures will tell the story.

rocky4 · Sep 11, 2019

Will1988 said:
I'm going to say the rod broke first then came around and whacked the cam. I have seen this failure happen when the oil gets too low. The rod will usually break first then act as a battering ram and cause all kinds of damage as the engine is coming to a stop, but pictures will tell the story.

Thanks for replying.My son was using the mower and he said the cap on the oil drain plug blew off and all the oil came out.
Dont have any idea why the cap blew off, pressure or what.
Would a exhaust valve guide that had worked its way up cause this? It looks as though the exhaust valve guide is a little high.

Deleted member 97405 · Sep 12, 2019

rocky4 said:
Thanks for replying.My son was using the mower and he said the cap on the oil drain plug blew off and all the oil came out.
Dont have any idea why the cap blew off, pressure or what.
Would a exhaust valve guide that had worked its way up cause this? It looks as though the exhaust valve guide is a little high.

That definitely explains why the rod broke.
I don't know what caused the cap to come off.
The engine creates a vacuum inside the crankcase, so unless something else was going on, the cap should not have come off due to pressure.
If some debris collected on top of the cylinder head and blocked the cooling fins, the head will overheat and the valve guides will move.
The fan on the flywheel is what cools the engine as it's running.
So if grass or a mouse nest is blocking the cooling fins on any of the cylinder heads, it will overheat.
Unfortunately, your engine is most likely ruined beyond repair.
Even if fixable, it would probably be cheaper to replace it anyway.

rocky4 · Sep 12, 2019

Will1988 said:
That definitely explains why the rod broke.
I don't know what caused the cap to come off.
The engine creates a vacuum inside the crankcase, so unless something else was going on, the cap should not have come off due to pressure.
If some debris collected on top of the cylinder head and blocked the cooling fins, the head will overheat and the valve guides will move.
The fan on the flywheel is what cools the engine as it's running.
So if grass or a mouse nest is blocking the cooling fins on any of the cylinder heads, it will overheat.
Unfortunately, your engine is most likely ruined beyond repair.
Even if fixable, it would probably be cheaper to replace it anyway.

Thanks, The engine is shot, not repairable. I was thinkig if the reed valve ( vent) stuck and could not release pressure in crankcase
would that cause the cap on oil drain to pop off? Engine is clean so it should have not over heated.

tom3 · Sep 12, 2019

Does this motor have the plastic drain cap that you twist 1/4 turn to release and drain the oil? I'm sure not a fan of that deal on such a critical part. Wondering if it wasn't on completely - or just failed because it's plastic?

Romore · Sep 12, 2019

The valve guide is a seperate problem, it results in bent or broken push rod but won't cause the crankcase to pressurize. Your best bet is replacing the engine with a 44Q777-3137, it is cheaper than a short block and you need a new head anyway. Transfer the wiring harness, regulator and governor spring to the new engine.

Deleted member 97405 · Sep 13, 2019

Romore said:
The valve guide is a seperate problem, it results in bent or broken push rod but won't cause the crankcase to pressurize. Your best bet is replacing the engine with a 44Q777-3137, it is cheaper than a short block and you need a new head anyway. Transfer the wiring harness, regulator and governor spring to the new engine.

If you get the engine through Deere, it will drop right in and plug right up. I've done quite a few. I have researched the parts pages and all serial number ranges and engines are subbing to part number MIA12623. At almost $800, your money may be better spent on an updated machine unless you're putting it in yourself. Unless the rest of the tractor is mint, if it were mine, I'd be pricing a newer machine. You may be able to get another engine model cheaper that would require modification. It just depends on how far you want to go with it. Good luck!

John Deere la 145 engine bent camshaft

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