Briggs & Stratton Engine won't start on petrol mower

[Burnerman]

I also should have said, can you feel any escaping gas, feeling around there with your hand?
John

 

[JT101]

I had a similar problem to this on a petrol mower but it wasn't a B & S engine. I believe however that the governor works in the same manner ie centrifugal weights in the crankcase move the lever either closer to or further away from the carburettor acting like a choke and throttle at the same time. As it was a favour job I did not want to strip the crankcase so instead i fixed a piece of stiff wire to the engine then moved the lever forward and held it in place with the wire . The engine then started without any problem.

I think this is what you mean. I attached the wire to the top of the triangle of plastic which is the throttle shaft and held it to the left whilst starting, whereas normally it's tot he right. It made no difference and actually produced smoke. If you're talking abnout the governor arm, well that is controlled by the throttle lever on the handlebar, and I've tried that on max or min, which pushes the arm to it's limits. Again. Made no difference

 

[JT101]

I also should have said, can you feel any escaping gas, feeling around there with your hand?
John

I'll have to check when I reassemble it! Have really opened a hornets nest now. Took the cylinder head off. Definitely some damage to the gasket as you can see, and black soot forming at the top where it escapes. Everything looks super dry from the outside, but I can't see what's going on inside, and was really stiff to turn by hand (see video). Started to undo a small port (breather assembly) on the side to see if I could see the cylinder, but oil started to leak out. Can see small amount of oil leakage at the bottom as shown in the photo with an arrow.

 

[Burnerman]

Yep, head gasket gone right enough......time for a good clean down to bright metal and this has been your problem all along.
Time to clean it down to bright metal before refitting with a new gasket but try to avoid scratching the aluminium.
You can see the inlet and exhaust valves there, occasionally the hardened seats come loose but that doesn't seem to be the issue here.
The breather assembly cover actually reveals the valve springs should you remove it, but it's likely the thin gasket will split. There won't be much oil in there to lose.
There's plenty to see on youtube if you wish - the 'machinery restorer' in particular is well experienced.
The fact that the engine was stiff to turn is interesting......is there a brake on the flywheel that is released when you squeeze the 'Go' lever?
Enjoy your new engine experience!
Regards
John

 

[JT101]

I'll do a bit more digging. Off to get a new head gasket. Thanks so much for your help so far. What's the best thing to clean it all down with, and does anything need re-oiling or re-greasing?

 

[Burnerman]

Unfortunately solvents won't touch the baked on gasket material so it's out with a broad bladed scraper of some description, trying not to scratch the soft aluminium cylinder head or barrel. I use an old steel rule but wood chisels have been pressed into service before
If you spin the engine over you'll see the inlet and exhaust valves opening and closing in sequence.
No need for any other treatment, just wipe out any crap that has fallen into the cylinder and bolt the head back on, tightening the bolts evenly and diagonally. Sorry I don't know any torque settings for the bolts but firmly tight will do.
Check the oil level before starting up and all should be well.
Good luck with your project!
Regards
John

 

[Old Salt]

16 Nm’s according to google