HRR216 S3DC: Waste Spark Ign?

[EddyCurr]

Does the ign of an HRR216 S3DC rotary mower fire each revolution?

In using a new-to-me multi-meter fitted with an inductive clamp to check RPM, the display shows 580-600 RPM on the meter's "x10" scale for four strokes.

There is no way this engine is turning 6,000 RPM. However, if fitted with a waste spark ign that fires every 360 deg, then 580-600 on the meter as configured above would translate to 2,900-3,000 RPM at the crankshaft. Those numbers are more plausible.

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[bertsmobile1]

All flywheel magneto engines are wasted spark.
That is one of the design problems with them.
It is a cost thing, a magnet in the flywheel with an external combined trigger & power source is very cheap to build
Adding 1/2 time gears complicates things and adds extra costs which no one will pay.
Way back in the 30's & 40's some engine makers tried fitting 1/2 time gears but they are no longer making engines.

 

[EddyCurr]

Thank you for the reply.

The multi-meter has a setting for "2 stroke/DIS" mode. I imagine configuring it thus will lead to the correct RPM display for my HRR216's engine speed where the ign fires each revolution.

Regards

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[bertsmobile1]

Or dividing the readings you are currently getting by 2.
All governed engines spin between 3000 & 4000 rpm
Most use 3600 but from memory Hondas run a bit slower, which is why they sound so much quieter .
I always have to check as I do not service many Honda engines.
So your 6000 rpm when divided by 2 sounds around what I would expect to see.

 

[EddyCurr]

The Honda Power Equipment Shop Manual for my model specifies a range of 2,950-3,100 RPM.

As mentioned, mine was running a bit slow according to the meter. Changing to the 2cyl/DIS meter setting had the desired result. With confidence about the numbers, instructions in the HPE manual were followed to bump the RPM to about 3,100.

Regarding Honda RPM being lower to reduce operating noise. While this may be a factor, one would want to work the numbers to determine what piston speed is at the recommended RPM before arbitarily modifying the throttle/governor relationship to achieve more RPM, ala Tim 'The Tool Man' Taylor.

Just checked piston speed while composing. The GCV160 has a 2" stroke; so at 3,100 RPM, this engine's piston speed is 1,033 fpm - very conservative compared to other engines I am familiar with (some of which operate in the range of 4,000 up to almost 5,000 fpm.)

Maybe blade speed is a consideration. Maybe, as you say, Honda is just going for noise reduction.

Thank you, again.

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[bertsmobile1]

Blade tip speed sets the upper limit as there are manditory limits to this.
Rick always seems to have his finger on them.
Honda make big advertising claims down here on the quietness of their "understressed " engines.
Dropping a few hundred RPM makes a massive difference to the engine noise which can be made lower than the blade noises.

In 1982 Victa ( local ex mower maker ) launched the "silent" vortex powered by a 160cc 2 stroke engine.
One of the tricks to make it quiet was to drop from 3600 to 3250, fit a heavier base plate and shorter swing back blades.
Knocked about 15 dBa off the noise level making it a touch quieter than the Honda powered engine which itself was a touch quieter than the B & S Sprint engine.

Having valve timing optimised for a slower top speed also allows a lot easier starting, another of Honda's big advertising points.

 

[EddyCurr]

Blade tip speed sets the upper limit as there are mandatory limits to this.
Rick always seems to have his finger on them.

To calculate tip speed, determine the length of blade under consideration in feet (21" -> 1.75ft), use blade length as diameter in the formula for circumference (Dia x 3.1415) and then multiply the result by max RPM.

Robert@Honda posted a variation of the above here on 2013.05.07 "How to Calculate Blade Speed"

The blade on my HRR216 measures 530mm or about 20-7/8". Calculation using either approach results in a blade speed of about 17,000 surface feet per minute at 3,100 RPM. My understanding is that ANSI B71.1 2012 calls for a maximum blade tip speed of 19,000 feet per minute.

Consequently, in terms of both tip speed and piston speed, it does indeed appear that this HRR216 IS understressed. There may be other limiting factors that would shorten engine life at higher RPM. For me, the ceiling is pretty much determined by how fast I need to walk to keep up in 3rd gear at top RPM.

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