offset woodruff key for changing engine torque curve

[dnix71]

Does anyone here have experience doing this? I have a 2 blade mower with a single cylinder 16HP Briggs engine that is over 20 years old. The faster I run the engine, the faster things break from vibration and poor design. One blade unscrews and the other tightens because of the way the belt drives them. Keeping the blades sharp helps, but slowing the engine down helps more.

From videos I have seen, the usual fixed timing is about 25 degrees before TDC. If I could make that 20 degrees BTDC the engine would have more torque at a lower RPM. When mowing, torque matters more than instantaneous HP. I do not like running any engine above 2/3's max for any amount of time., esp. a mower. Speed kills when parts fail.

A new machine would cost about $1700 at Lowes, and I don't have that kind of money to spend right now.

[Mary B]

If it loosens I suspect it is worn and that blade hub should be replaced... threads get rusty and loosen over time

[DanG]

I've seen that - eerie as heck, JD three-blade deck, the outboard right blade hits sapling stump that halts its swing and outboard left blade falls to the ground at zero-speed, cupped over nut and washer against the ground. And that was resharpened blade installed w/ 1/2" drive breaker bar and torqued to OEM spec w/ torque wrench.

A point to inspect - does the deck still have the belt // pulley tensioner(s) installed with fresh springs? When belts go into oscillation flopping taut and slack at certain RPMs and load, then all sorts of similar weirdness can occur... And I know that JD had one of its tensioners mounted to a barrel spacer with one end cupped with a recess that if installed basackward warped the deck and self-loosened that likely contributed to the flywheel & anti-flywheel effect I saw...

[dnix71]

The blade towers are all old and I don't have spares. But I tighten the blades with a long wrench and breaker bar. The blades only have a round center hole for mounting. They were made to slip as the blade towers are made of pot metal. Better to slip than break. I have almost resorted to spot welding the blade in place a few times, but there are lots of tree roots growing above ground because of rocky soil, so it wouldn't be long before I hit one.

Both belts are fairly new. The drive belt was replaced last and that requires major disassembly as the steering column, battery, back seat/frame support and a drive tension pulley have to be removed to get the belt in and out. This is not a JD, it's a Murray. Home Depot no longer sells any riders here. Lowes does as they bought the rights to sell "Craftsman" tools and that includes riding mowers. They look nice but that's $1700 I don't have to spend right now.

[Mary B]

Locktite blue? The kind designed to be removed?

[dnix71]

Locktite blue? Locktite red maybe. Marine grade JB Weld maybe. What I really need is a reel mower. Those don't involve high speed spinning flat steel.