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- Jul 16, 2020
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For Sale or trade.........
- Thread starter kschauweker
- Start date
wemay
Site Donor 2023
I'd suggest using 15w-40 Rotella in that, 20hr OCI. UOA to confirm after first dump & fill.
Fixed it for you. Nobody wants to undergo an amputation with a dull blade or with dirty oil.
Why?
Most push mowers are under 3000 rpm from the factory, and must be "turned up" to exceed the limit you set.
Realizing that this is a humor thread but still as a bit of fact on this...
From what I can find, ANSI specifies 19,000fpm(or about 216mph) as the maximum safe blade tip velocity.
For a typical push mower with a nominal blade size of 21", you will hit this speed at ~3,456rpm. The blades I'm familiar with have an actual blade size of around 20.9", which actually gives a bit of a safety margin if you set the governor at ~3400rpms. Drop the blade size to 19"(I have one that I sometimes use to trim) and you find you can actually run at 3800 RPMs and stay under this speed.
One particular model of lawn mower engine I know well and have worked on a decent bit specifies 2900rpms +/- 300rpms as the governed speed of the engine. I will say I tend to adjust to the upper end of that tolerance, and might or might not have the governor adjusted such that this speed can be exceeded(I have a tachometer fitted to one I use all the time, and this one also has a "throttle"/governor tension adjustment up on the handle). Doing that not only cuts more efficiently but also gets further up into the power band of the engine so it really does feel unstoppable. AFAIK, this engine was only ever fitted to a 21" deck. It was also used in snow blowers where it was governed above 4K RPMs so it's certainly mechanically capable of running that fast.
I'll also mention that I just checked(because I wasn't sure) the service manual for the specs on older engines from this same maker. One model engine that was introduced in the 60s and sold in various forms through the early 80s says 3200rpms(no tolerance range given) for all models on the "high speed" setting, although lists one available governor spring that will give 4000rpms. Since I like these engines and want to go easy on them, I run them at 3200rpms. A slightly newer engine covered in the same manual that was introduced in the late 70s and used through the late 90s says 3100-3300rpms on the fast setting for the governor.
