Briggs 12.5 hp rocker stud

[38racing]

I was just chatting with a local auto mechanic. He says that he has repaired sveral low end john deere with no start. It's been that the exhaust rocker stud has pulled out of the aluminum head. He's used helicoil to repair them. Anyone else seen this issue.

[Skywatcher]

Hi 38

Although I've never seen one of these studs pull out of the aluminum, I've seen quite a few of them come loose over the years. You get to recognize the sound the engine makes when it cranks but won't start, so that's one of the first things I check on these brand-B OHV engines. A 10mm crowfoot wrench on a ¼" x 6" extension and flex handle come in pretty handy for tightening these up without having to removed the rocker. All the best,

Sky

[KE4AVB]

And for I only seen one stud loosen in ten yrs and it was because the owner tried adjusting the valves himself.

[Skywatcher]

Hi KE4

Would this have anything to do with the difference in coefficient of expansion between aluminum and steel? The lawn tractors up here get frozen down into the -30's every winter, then worked hard when it's in the +30's Celsius (high 80's Fahrenheit) with 85% humidity. Just a thought,

Sky

[KE4AVB]

Very possible...I know aluminum heads on cars are easily warped when overheated due to different expansion rates of the heads and the cast iron block. I didn't in older cars that both the heads and blocks were cast iron, but I did see several crack heads.

Also aluminum wiring in homes back in the '70's caused a lot of home to burn cause it would expand during use (heating wire due higher per foot resistance than copper) and then when it cooled it leave loose connection creating areas where electrical arcing could occur heating things to combustion points. My mother's first home had it and I was constantly having to replace wiring, switches, and wall outlets. I always replaced with copper wiring as I went thru all the problems. Thinking back I am very surprise the home didn't burn down to ground as we had electric wall heaters; several homes in the neighborhood did.