JD La105 mower problem

The loud metal noise and pop has me puzzled but I'm willing to bet the white smoke is due to a blown head gasket. My brother has a LA105 and we just replaced his head gasket last year. The single cylinder B&S engine used in the LA105 is notorious for blowing the head gasket. It's a fairly easy job to replace. During the course of replacing the head gasket you may be able to discover where the other noise is coming from.

When you remove the valve cover, turn the engine over slowly and verify if the automatic compression release is working. These engines are also notorious for breaking the ACR flyweight.

You will definitely want to have an engine repair manual handy. You can get a B&S repair manual on-line for way less money than what JD will charge.

I’m actually betting a carb/float problem.

The gas leaks through the carb then floods the cylinder, engines will run rediculously rich up until it generates a little heat. I believe the fuel I’m the cylinder vaporizes fast enough to prevent air entering during the intranet stroke, but that’s just a guess based on observation.

The bang is a predestination, with many possible causes that all revolve around raw fuel and a little heat.

On a side note, if you are going to do the head gasket yourself, spend the extra 5 minutes and take the hood off. Your back will thank you for not having to spend over sideways.

Also, there are a handful of Youtube videos of changing the head gasket...... like @
jgayman said, it really is quite easy.

Hmm, "every once in a while " has me doubting a head gasket issue. They normally don't seal themselves and run fine! I'm prone to going with an overheating issue.

Remove all external engine tins and blow off cooling fins. Running after the key is "off" IS pre-detonation, typically caused by carbon in the heads...creating "hot spots" and igniting fuel. Run some sea foam for a few tanks of fuel and see if it improves. Regular use of sea foam or other fuel additive won't hurt either!

If you do decide to replace the head gasket, remove the bolts & head ONLY after the engine has cooled down. Remove head, clean gasket surface, place on a FLAT surface and check with a .003" feeler gauge. If this goes under head at any point, the head needs to be resurfaced...either by you with emery cloth or my a machining service. Bob