Older Saw theory

[harrygrey382]

RPM’s alone don’t have much to do with how hard a saw’s motor is working.
You must factor in the stroke. This gets you to a figure called
“Piston Speed In Feet Per Minute” .

Piston speed in feet per minute at 65 mph *
Hd 2030 fpm
Honda 1475 fpm
Care to guess what motor is working wayyyy harder than the other one?

Piston speed in feet per min at red line*
Hd 3996 feet per min
Honda 3835 feet per min
Even at 13,000 rpm honda’s 599 motor is not stressed as hard as the
harley loafing around at only 5500 rpm.

This is interesting, and a good point. But I would have thought the main stress factor would be at either end of the stroke, where the piston is being accelerated or deccelerated (f=ma, so more a (and maybe even increased m in older saws) means more force) would be the big factor contributing to wear. When the piston is racing along the bore (middle of the stroke's fasted - sine wave etc.) at high speed I wouldn't have thought this was as bad as the force from stopping it. Or is it the high temp caused by friction between rings and bore? This would point to maybe more torquey saws needing beefier bearings etc.?
These are speculations and I'm not trying to say I'm right or suggest a reason for the current arguement. I just like talking bout motors!

 

[glenn31792]

If anyone has the bore and stroke of an old motor and wants to compare it to a new one
here is the formula. I would be interested in seeing a comparison or two.

Piston Speed In Feet Per Minute = Stroke in inches x RPM / 6


I like twins too!

 

[harrygrey382]

jut so shappen to have my 056av apart right now... measure the stroke at 37mm (does this sound right?), I so I get 2913 (call it 3000) ft/min

 

[16:1mix]

If anyone has the bore and stroke of an old motor and wants to compare it to a new one
here is the formula. I would be interested in seeing a comparison or two.

Piston Speed In Feet Per Minute = Stroke in inches x RPM / 6

I like twins too!

Here is a 'twin' for you:

1940 John Deere model "A" tractor. Commonly known as a 'Poppin johnny'.

two cylinders
5.5" bore
6.75" stroke
321 cubic inch displacement
1000 rpm rated speed
about 30 horsepower - and enough torque to lift the Titanic!

6.75 x 1000 / 6= 1125 fpm

 

[glenn31792]

If you are turning 12k rpm, yes.

 

[Poley4]

To me, it all comes down to performance and what the market is asking for. I myself am a big fan of a lot of the older slower saws and the 041 has to be one of my favs. The problem is, today, people are not satisfied with a 60cc saw only producing 3.7 hp, that's 50cc territory by today's standards. Their philosophy is that faster is better and I suppose, for the true professional, that is true, but for most of us, working around the farm and cutting our own firewood, performance WITH durability should be king. Simply put, you cannot produce more horsepower per cc and not expect durability to suffer. I know a lot of people will argue that they have hopped up their sb Chevy or whatever and still got X number of miles out of it, but the problem with that comparison is, we never run our vehicles at WOT and asking it to produce 100% of it's horsepower for any sustained period of time, where as chainsaws run that way all day long. I know a lot of people complain about how slow the MS 260 is in comparison to the 5100 and suppose Husky felt they had to step up the performance of their 346 to keep up, only time will tell if that was a good move or not.

 

[Dadatwins]

but.. they made a lot of carbon which is a killer in engines...

but the open muffler designs let most of the junk fly out, I have set more than one pile of chips and leaves on fire from the old homelite wiz open muffler.