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Hope it is ok to ask question on snowblower. Engine is a Briggs 21m307-01307-0135-f1. Would not start and had no compression. I removed valve cover and found exhaust pushrod disconnected and intake valve bent. Checked valve guides, not worn but can not tell if they moved in the head. Could not see any specs in the manual. Any idea what I should do?

Hello Kenneth2,

I suspect valve adjustment was way overdue. That happens a lot.

Also, a possible overheat would stick a valve and cause it to be bent. The valve guide could have risen up and impeded the correct valve operation. B&S has had a lot of problems with this over the years.

I'm not sure about the exact valve guide height on the top when installed in the head. Has the guided recessed up out of the head when looking at the combustion chamber side where the valve goes?

A picture would help showing the combustion side.

Teryl Fixes All has a good valve guide fix video on You Tube. It is on a Kawasaki, but Kohler and B&S also have the same problem.

Likely a replacement head is needed, if a new one can be found. The part number does show to be superseded in what research I have done. Jack's small engine.

I went back and read this again. The exhaust valve push rod was found disconnected?

Did it bend the intake valve or the intake valve push rod? Please clarify.

The only way to bend a valve is for the piston to collide with a valve that is not on the seat.
A sticky valve can cause the valve to remain off the seat.
The bent pushrod can be caused by too much clearance allowing the push rod to fall out of the rocker arm and get tangled with the mechanism when out of position. It can also be caused by a sticking valve, or a valve guide so out of position that it does not let the valve open to its normal travel, and when the cam pushes, the spring collides and stops the rocker short of its travel.
If you remove the valve seal on the intake you can compare the height of the valve stems. They should be the same. If one is higher, it likely have started to move up out of the head. Taryl does have a video about pushing it back in place, adding some loctite, and then staking it around the periphery to keep it in its normal position.
tom

Can we see photos of the combustion chamber side of the head, and the piston please. A lot of mechanics say that old ethanol in fuel can cause valves to stick but I personally have never seen it. I have seen valves stick because of carbon build up on the stems. Many small engine manufacturers specify that heads and chambers are to be decarbonized every so many hours of running time. It isn't hard on a small engine, it is hard on a big V6 or V8 with a plethora of emissions equipment and accessories on it.

Ok here is photo. I am inclined to think it was a stuck or loose valve the pushrod disconnected and other one bent had to happen at same time. Thinking I am gonna put back together and see what happens

Cannot even see down into the one valve guide hole, it's shadowed. Can you lay out the "bent" parts and take a picture for us to help you evaluate the entire problem, not just bits of it?

This is turning into a "Where's Waldo" story.

Ok here we are . I do not have picture of bent pushrod, already threw it away

kenneth2 said:

Ok here we are . I do not have picture of bent pushrod, already threw it away

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A basic rule is to never throw away any parts until you are absolutely sure the job is done. Cannot really see anything wrong with the valves except the one on the left of the picture has been getting hot on the stem portion.

How did you determine a valve was bent?

Actually intake pushrod was bent, exhaust pushrod was disconnected.

Sorry, did not include photo

Thanks for the update picture.

Now, I think that picture better confirms the exhaust valve guide has moved up in the casting due to an overheat condition. (Poor B&S design) I can see that the exhaust valve guide is not sticking very far at all on the combustion chamber side.

At the moment, I do not have a used head to inspect and verify.

I suggest you temporarily reassemble the head and install tight with the old head gasket, set the valve lash and rotate the engine by hand slowly to see if the valve rotor (spring retainer) is close making contact with the top of the valve guide has the exhaust valve operates.

Just driving/pressing the guide back down, just means it will do it again.

kenneth2 said:

I removed valve cover and found exhaust pushrod disconnected and intake valve bent.

Click to expand...

Are you clear on what caused this issue? Lack of valve lash checks or over heated the block, maybe both? Both of these are YEARLY maintenance items in every engine manual out there. Just letting you know this was all preventable.