Briggs 23Hp Model 44L777 V-Twin Bent Push Rods

[TiIngot]

Running on one cylinder with both sides getting spark and fuel. When running the cylinder opposite fuel pump makes no change when pulling spark plug but engine dies when pulling plug wire on the fuel pump side. On the dead cylinder I removed the valve rocker cover and found both push rods bent with the upper intake aluminum one broke in two.

When I manually push on the intake valve it goes in with no restrictions. However when pushing in on the bottom exhaust valve it only opens a small amount and seems to hit something. Is this normal? (Just found the exhaust valve guide is restricting the valve movement). Rotating the crank by hand while placing a screw driver in the plug hole shows the piston moving up and down.

I straightened the exhaust pushrod and inserted it onto both valve tappets and each is moving when the crank is turned by hand. (I do not intend to reuse this pushrod)

Other than replacing a cam (compression release broke) in my Deere D105, I have never been inside one of these engines. So ..... what is going on inside with the crank or cam on this engine, if anything? Is it worth going further into the internals? It is on a Snapper Model 2690872 from 2011 and the tractor is in great shape.

Last notes, when I was given this tractor, BOTH cylinder heads were completely covered with mouse nests under their shrouds so I know the cylinders were probably overheating. Also, I just went back and checked and found the exhaust valve guide is what is limiting the movement of the valve. It has come out. I am hoping all that is necessary is cylinder head work.

Thank you in advance,

Lee A

 

[Bertrrr]

If your push rods are bent it's because something got between the piston and the valves or somehow the valve timing got out of wack. Never seen this and had an engine still run. You'll need to pull the head and valves / push rods etc. and inspect completely and also try and determine why it happened in the first place.

 

[StarTech]

The exhaust valve guide has moved out place. Multiple causes among which the cylinder head overheated or carbon on the exhaust valve stem. You can't simply drive back the valve either as it will be loose and just move out again.

Just did one a couple weeks ago where a DIYer had installed a carburetor that had too lean of metering jets. Not only the intake push rod broken and the exhaust but had a blown head gasket. You will drop the sump and find the other half of the intake push rod and replace the cylinder head.

New complete cylinder head is around $170 list.

And if the camshaft is moving the lifters than the broken push rod done internal damage to the engine which you will only know what damage when open up the crankcase. But doubt it is damaged as the engine is running on the other cylinder.

 

[TiIngot]

The exhaust valve guide has moved out place. Multiple causes among which the cylinder head overheated or carbon on the exhaust valve stem. You can't simply drive back the valve either as it will be loose and just move out again.

Just did one a couple weeks ago where a DIYer had installed a carburetor that had too lean of metering jets. Not only the intake push rod broken and the exhaust but had a blown head gasket. You will drop the sump and find the other half of the intake push rod and replace the cylinder head.

New complete cylinder head is around $170 list.

And if the camshaft is moving the lifters than the broken push rod done internal damage to the engine which you will only know what damage when open up the crankcase. But doubt it is damaged as the engine is running on the other cylinder.

Thank you. I edited the original post. The valve tappets are moving free and that both cylinder heads were heavily covered in mouse nests so I know it had to of over heated. All parts of both pushrods are accounted for so I do not think I don't need to do anything other than head replacement on the one side.

 

[StarTech]

You got lucky on the push rods then. I wasn't.

 

[bertsmobile1]

FWIW
Both cam lobes are the same
Both valves are the same length
Both valve guides are installed to the same depth
So you can usually see that one valve is lower than the other at either full lift or closed position
On top of that the exhaust valve head runs at yellow heat which is above forging temperatures so will bend very easy in use
Guide needs to be "Staked" back in the correct position as replacement guides are not available
Lots of You Tube videos on how to do this
Also check the valve seats as they can come loose as well
Generally the exhaust guide shifts & the inlet seat gets loose nut that is not a hard & fast rule

 

[Tiger Small Engine]

FWIW
Both cam lobes are the same
Both valves are the same length
Both valve guides are installed to the same depth
So you can usually see that one valve is lower than the other at either full lift or closed position
On top of that the exhaust valve head runs at yellow heat which is above forging temperatures so will bend very easy in use
Guide needs to be "Staked" back in the correct position as replacement guides are not available
Lots of You Tube videos on how to do this
Also check the valve seats as they can come loose as well
Generally the exhaust guide shifts & the inlet seat gets loose nut that is not a hard & fast rule

Bertsmobile-
Have you had good long term results with peening valve guides that have moved? I have peened a valve seat before and it lasted, but never a valve guide.

 

[bertsmobile1]

Only ever done 1 mower guide and it is still running fine 5 years latter on
It just depends if you know what you are doing & how to do it
As I hope you know there is more to peening than smacking a punch with a hammer
I used a long fine punch on the mower head so it went in deep from both sides
People forget that you have to deform both the head & the guide to lock it in place .

 

[Tiger Small Engine]

Only ever done 1 mower guide and it is still running fine 5 years latter on
It just depends if you know what you are doing & how to do it
As I hope you know there is more to peening than smacking a punch with a hammer
I used a long fine punch on the mower head so it went in deep from both sides
People forget that you have to deform both the head & the guide to lock it in place .

I welded a valve guide one time. It held but the mower continued to only run on one cylinder.

Method two is to remove valve guide, cut a small groove(s) around it, and install c-clips, e-clips, circlips. I have not done it, but a small engine business owner told me he has used this method successfully.

 

[TiIngot]

Running on one cylinder with both sides getting spark and fuel. When running the cylinder opposite fuel pump makes no change when pulling spark plug but engine dies when pulling plug wire on the fuel pump side. On the dead cylinder I removed the valve rocker cover and found both push rods bent with the upper intake aluminum one broke in two.

When I manually push on the intake valve it goes in with no restrictions. However when pushing in on the bottom exhaust valve it only opens a small amount and seems to hit something. Is this normal? (Just found the exhaust valve guide is restricting the valve movement). Rotating the crank by hand while placing a screw driver in the plug hole shows the piston moving up and down.

I straightened the exhaust pushrod and inserted it onto both valve tappets and each is moving when the crank is turned by hand. (I do not intend to reuse this pushrod)

Other than replacing a cam (compression release broke) in my Deere D105, I have never been inside one of these engines. So ..... what is going on inside with the crank or cam on this engine, if anything? Is it worth going further into the internals? It is on a Snapper Model 2690872 from 2011 and the tractor is in great shape.

Last notes, when I was given this tractor, BOTH cylinder heads were completely covered with mouse nests under their shrouds so I know the cylinders were probably overheating. Also, I just went back and checked and found the exhaust valve guide is what is limiting the movement of the valve. It has come out. I am hoping all that is necessary is cylinder head work.

Thank you in advance,

Lee A

Follow up - Still have issues. Cleaned and removed all carbon from the piston head and head gasket contact surface. Checked gap on both spark armatures. Installed new #1 cylinder head assembly w new valves, a new head gasket and new push rods. Cylinder walls were smooth as h*ll with no scoring at all. Adjusted both valves to .005.

Started it up and after about 45 seconds it began to backfire from #1 side. (Note: there was no backfire when it was running on only #2 cylinder only.) Shut off engine and rechecked valve gap settings and installed new spark plug. Started it up and still backfiring after 45 seconds. I do not have any history on this tractor since it was given to me by a scrapper.

Edit: The backfire or miss in coming out the exhaust not the carb.

Also when I received the mower I know the carb was removed at some point because the choke linkage was hooked up backwards.

Any suggestions on what to address next?