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Hi,

On the exhaust valve, I have repaired the valve seat, lapped the valve, replaced the valve seal and head gasket. Set the valve clearances. It started right up but It started but immediately blew out the valve seal because I did not understand how to seat it firmly. Lots of oily smoke. So I replaced the seal and the head gasket and set the valve clearances again. On impulse, I tested the compression and on cranking the engine, the resulting compression was 160. Valves too tight. So I adjusted the valve clearances again. It would not start.

The gas line was full of air, so I pulled the fuel line off the carbuerator and it pumped out the air and gave a normal gas flow.

It still wouldn't start. Good spark. No compression.

I pulled the valve cover gasket and on cranking the engine, saw that the intake valve, rocker arm and push rod are not moving.

Do you know what might be wrong? The mower was working fine until the exhaust valve seat failed.

By the way, the push rods are intact, straight.

The valves , valve guides & springs are identical
So they should be in identical positions in the head with the piston TDC on the firing stroke
If not then the intake valve guide has shifted in the head
This happens because the head has been allowed to get too hot and the alloy expands so much that it looses grip on the guide

It is very possible you don't have the push rod on the tappet. It won't be the first this has happen either.

Thank you for the responses. I am pretty new to small engine repair.

Bertsmobile1 - Thanks for the tip on checking on the intake valve guide.

TDC firing stroke, meaning both valves closed and piston at TDC, correct?

Regarding the exhaust valve I just repaired, the valve guide broke free. Could you tell me what would get the head that hot? It appeared to be running just fine when the valve guide broke free. I shut it off and it just wouldn't start again.

Star Tech - Thanks!. How would I make sure I've got the pushrod properly located on the tappet?

Pretty sure you have a Briggs 310000 series; although, a few had the 330000 series. Take flashlight (torch) and shine light into push rod gallery while installing the push rod. You will see the tapper recess that the rod goes into. Btw the aluminum rod goes on the intake side which is the one closest to the pto end of the engine.

Star Tech! That was it! You taught me something important! Now it's running great except for the smoking! Think it's time to adjust the carburetor.

how did you replace the valve seat? Normally that requires a machine shop do it because it is an interference fit item.

He probably reuse the current as they do come loose at times without breaking. Here is how a replacement is install locally without a machine shop. IF new seat then it will cutting seating area for the valve to specs.

It is the same thing I did on my personal 330000 engine when the exhaust seat came loose.

peening only works for a little while once the aluminum has softened from getting hot.

sgkent said:

peening only works for a little while once the aluminum has softened from getting hot.

Click to expand...

Well I have been cutting 4 acres of 6" or greater for two years now without a problem. I actually some grass waist high with the same engine but that usually a half acre at a time or one tank of fuel whichever I feel like doing.

StarTech said:

He probably reuse the current as they do come loose at times without breaking. Here is how a replacement is install locally without a machine shop. IF new seat then it will cutting seating area for the valve to specs.
View attachment 61070
It is the same thing I did on my personal 330000 engine when the exhaust seat came loose.

Click to expand...

That is exactly what I did, Star Tech! Did your repair hold up well?

farmchick said:

That is exactly what I did, Star Tech! Did your repair hold up well?

Click to expand...

So it has held for two years.

My L100 is running again. It startrs great and runs for about a minute before it begins smoking heavily. Grey smoke from exhaust area. But runs fine.

Model 31F70
Type 01121E1

History...I repaired the exhaust valve seat/guide, lapped the valve, replaced the valve seal but didn't get it fully seated. It started fine but was smoking heavily just as it is now. Replaced the valve seal. New head gasket. Didn't get the intake rod seated properly. Fixed that. Now it has still this smoking problem which I had assumed was caused by the valve seal that broke free from not having it properly seated.

Is this just burning rich which might have caused the heavy carbon deposits in the engine and possibly the valve seat failure? And if it is, how do I find the adjustment screw for the rich/lean adjustment?

The valve cover is leaking slightly. The gasket is visibly worn and I will replace it asap.

Thoughts?

Be as arrogant as you want. I worked in a machine shop. I've seen the effects of your home grown peening. As I said, it lasts a little while then one day bang the seat cocks after the aluminum gets hot, the valve head snaps off, and destroys the rest of the engine. If you are Ok with that then there is no harm. if you are not Ok with that then the head or engine, wherever the seat is needs to be disassembled, cleaned, heated, a new interference seat put in cold, stake, and then let the head shrink around it getting the proper crush, cut new angles. That will last as long or longer than the original.

Or catch it before it is loose and stake the aluminum over it with a flat punch.

Peening in the valve seat is an approved fix and shown in most Briggs service manuals. Over the last 20 years i have done a bunch and have only had one fail on a 3.5hp engine and i knew that one was iffy when i did it. On engines where the original seat is slightly below the surrounding aluminum peening works fine. On ones where the seat is level with the aluminum i don't try to fix a loose seat.