Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

Guys,

I may get to go check out some SS's. One is a Yardman 21" 5hp 2-stroke. The other is a Toro CCR2000e 2-stroke.

I am leaning towards the Yardman, based on boratification possibilities. I'm guessing/hoping it has a 5hp Tecumseh, maybe the HSK850. The Toro would have a 4.5hp Suzuki engine, from what I understand. I don't care about electric start. Any reason to avoid the Yardman? I realize it's probably not as solid/durable a machine as the Toro. But if it could be ramped up more in the power department, I could live with that. Thanks for any feedback.

I'm just kidding about the forced induction on a 2 stroke. The fact that 2 stroke are powerful, simple and lightweight is enough not to mess with them.

When you think of it, these 140ish cc engines are very mildly tuned.  Even when cranked up, making maybe 10 h.p. that's relatively tame.  Back in the 60s to mid 70s, single cylinder air cooled 125 cc off road motocross racing engines were making 20 to 25 h.p. and spinning at 9000+ rpm. 

People don't try to "supercharge" two cycle engines.  As Red pointed out, that's not how to make power with these things.  The secrets for power gains is in making the air/fuel mix and exhaust flow quickly through the engine.  Easiest way is to improve air intake to make it less restrictive and same for exhaust.  Next step is to re-jet the carb to take advantage of the freer breathing engine.  A great deal of instant power can be had this way.  If one wants more power yet, porting is the next step.  However, without the thorough understanding, machining skills and equipment, Joe average, such as myself, won't be doing that kind of work. 

In addition to being "skills/tools" intensive, the end result often creates an engine that's got a power band narrower than one would want.   Not that the power band would really matter that much with an engine on a piece of OPE.  On a racing motorcycle, it would make a great deal of difference.  That's why certain very talented riders (Kenny Roberts) could ride championship winning killer motorcycles (Yamaha TZ750 two stroke) when other very competent riders couldn't manage the power band.   Back in the 70s, the TZ750 was making 140+ r.w.h.p. at 10700 rpm.  The power band was reportedly like a light switch. 

The same engine was detuned to 125 h.p. and used in a flat track race bike piloted by Kenny Roberts.   The following is an entertaining excerpt that I found in an article about the TZ750:

"It’s the bike that inspired Kenny Roberts, one of the most fearless motorcycle racers that ever lived, to utter these immortal words: “They don’t pay me enough to ride that thing!” Desperate to compete with the dominant  HD  XR750s in the 1975 AMA Grand National championship, tuner Kel Carruthers shoe-horned the two-stroke four-cylinder from King Kenny’s TZ750 road racer into a Champion flat track frame and set him loose at the 1975 Indy Mile. Roberts won that race from a near-last-place start, cementing his name forever in flat track history. The TZ750 flat tracker made 125 horsepower, had a light-switch power band, a 150-plus mph top speed and no front brake. It was so fast, and so difficult to control, that the AMA banned it from competition after just three races—before someone got killed."

Fact of the matter is that the TZ750 wasn't banned so much for worry that "someone would be killed" as much as being such a dominant machine that fans (HD fans in particular) would lose interest in the sport causing a serious drop in attendance and revenue. 

Got the Yardman reassembled tonight, in preparation for the (disappointingly small) amount of snow we're supposed to get tomorrow. Bent the governor tab to raise the RPMs from 3900, where it had been, to 4500. I have no idea what the RPM spec is for this machine, but it appears that 3700 might be the spec for the 850 (based on the info I found on the 845, showing 3700). It's nice that, on this machine, there is no lower-rear cover to obscure the engine (like in the Ariens, where it's completely enclosed). So I can make "fixed" governor adjustments with just a pair of needlenose pliers, at any time. Adding true, on-demand, boratification will come later. I want to get a chance to actually try the machine before messing with it *too* much.

Boy, I don't know how the current fuel/oil was mixed by the PO, but it sure is smoking at the moment. No risk of oil starvation, or of mosquitoes bothering me! Based on your advice, borat, I have a can of dino 32:1 that I may use in it, vs my planned synthetic (Stihl Ultra) 50:1. Perhaps when I mix my next batch of Ultra I'll go for around 40:1, so I can just use one tank of gas.

Interestingly, as an aside, the HSK845 engine is described as 4.5 hp at 3700 in the Tecumseh info document that trouts2 posted previously. That document shows nothing on the 850. But my 850 engine was right at 3900 when I checked it. If you scale the rated hp of the 845 from 3700 to 3900, you get 4.74 hp. Based on OPE engine hp math, which apparently involves an awful lot of rounding up, one could infer that perhaps the only difference between the HSK845 and KSH850 is simply 200 RPM?

RedOctobyr wrote:

   It's looking like that.  I picked up an MTD HSK845 and comparing it to a few HSK850's.  The HSK845 has the same piston, rings, crank, muffler as many HSK850's.  The carb and governor spring are different in most.  There are many models of both engines and the parts not always exactly a match but mostly are.  The HSK845 is basically an HSK850 with a carb and governor spring difference.   The 3700 rpm limit in the HSK845 spec page is just a limit for the way that block was configured.  The HSK845 could be run at the same limits spec'ed for any HSK850 so 4500 no problem.

   The one variation that seemed to vary the most was the governor spring.  Since the HSK850 is bumped to 5.5, 6, 6.5 and 7hp that's reasonable.

   Another difference from one HSK850 to another was crank weight which can be a few ounces.  I'm not sure exacely what that would do to HP but for torque I would imagine that the same amount of gas would keep a heavier crank going through a load at higher torque.

   While poking around I found the base level HSK830, HSK835 and HSK845 all had cast iron sleeves.

Two strokes generally smoke quite a bit more when cold than warm.   What's strange is that with the R-tek engine in the Toro, when I first fire it up, there's very little smoke.  As it warms up with the choke on, it starts to smoke quite a bit.  Take the choke off and it clears right up. 

If an engine isn't seeing the extreme operating conditions to warrant synthetic oil, it just doesn't make economical sense to spend that kind of money for it.  I buy Canadian Tire TC-3 oil by the gallons.   It's know to be an excellent two stroke oil and relatively inexpensive.  I've been using it in everything I own (30+ engines) for over 25 years.   It's never caused me a lubrication problem in all those engines over all those years.  I also use CTC TCW-3 in my outboards.  What I've noticed lately is that two cycle engine manufacturers (B&S R-tek for instance) recommend TCW-3 oil.  Not going to happen.  I'm positive that it's likely an effort to meet EPA requirements by using a lower ash oil at the expense of not providing the best choice of oil for an air cooled engine.  Chances are that in a snow blower application, with relatively lower rpms, TCW-3 will work.  However, higher speeds and higher temperatures would lead me to believe that TC-3 would be the oil of choice.  Personally, I use TC-3 in all air cooled engines and TCW-3 in liquid cooled engines.

trouts2 wrote:
So, if I'm reading that right, are you saying there were HSK850's spec'd at 4500? Just curious because that's what I currently have mine set to. If that was an officially-sanctioned speed, that would be nice to know (I wouldn't feel that I'm pushing the engine as hard).

As far as crank weight, I'd expect:
- If the change was to a counterweight, the change might be to help properly balance out pistons & connecting rods with different weights (but it doesn't sound like there were different versions of those?)
- If it were a "nonspecific" weight change, I'd expect the extra mass would primarily act like a very small flywheel addition. It could help the RPM stay a bit more constant through small & quick loads. Flywheels only help smooth the quick bumps & dips due to changing engine loads. They won't help for prolonged added loads (a bigger flywheel will just make the engine take a bit longer to slow down). But a crank change would do much less than a true flywheel, and would make a very  small difference, I'd think.
- I presume the difference is not just due to differences in the PTO area (different length & diameter sticking out of the engine, etc)?

So, if I'm reading that right, are you saying there were HSK850's spec'd at 4500? Just curious because that's what I currently have mine set to. If that was an officially-sanctioned speed, that would be nice to know (I wouldn't feel that I'm pushing the engine as hard).

 

   Oops, that should be 4300 Max from factory 4000 +- 300.

 

The following from Tecumseh manuals.  These manuals predate later maker models past 2002 which have mostly been rpm bumped.

 

HSK600

Toro      290607,  fixed speed top governed speed 4500

MTD      290609, fixed speed top governed speed 4700

Snapper 290607, fixed speed, top governed speed 4500

Toro       290602, fixed speed, top governed speed 4700

Murray   290607, fixed speed, top governed speed 4500

 

For HSK845 also listed as TH139SA (<<<---same as HSK850)

MTD      290614, fixed speed, top governed speed 3800

Toro       290681, fixed speed, top governed speed 3850

Service   290627, fixed speed, top governed speed 4000

 

   For some reason they have tied these spec's to a given crank.  I have HSK600's with these cranks so it looks like I'm legal for 4700.

   For reference on the HSK870 to HSK850 crank difference it was 2.825lb (870) vs 2.481lb

 

>>I presume the difference is not just due to differences in the PTO area (different length & diameter sticking out of the engine, etc)?

 

    For the SHK870 vs 850 difference I don’t know where the wight diff is.  I have seen 8hp crank differences in the lobe masses next to the journals.  The lesser crank was on a Craftsman so I thought it might be to cut the crank cost but just a guess.

I got to play around briefly today with boratifying the Yardman. I tried tying a string at the upper governor linkage connection, where it goes to the throttle plate. I ran it through an existing screw hole in the lower housing (which was already missing its screw and open- if that's not a sign to boratify it, I don't know what is ), out the side of the machine, and up to the handle, where I tried attaching it to the bail.

I liked how it worked. Squeeze the bail, the RPMs climb; let go, and they drop. For the way I tend to use it (squeeze then release at the end of a run), that sounds good. I could lower the fixed-governed speed to even below-stock (for warming up, etc), and keep a high speed for doing work. I didn't have much time to mess with it, and I don't have any springs sitting around, so I need to revisit this. I'd like to add a spring, and perhaps something like a turnbuckle adjuster, or some other means to make controlled adjustments to the high-speed setting.

I was at Home Depot yesterday and took a look through their OPE-parts section. They have a universal throttle assembly (lever and cable) for $7. That could be a pretty convenient way to add a control that you can simply set & forget. An advantage over simply pulling a string by hand is that the lever would reach some maximum setting. Once properly adjusted, you couldn't accidentally take it to 9000 or something (that would be my fear if I was yanking on the string manually. Have it catch on my glove or something, and send the RPMs to the moon). Heck, with an appropriate-stiffness spring between the throttle cable and the governor, you might be able to make it such that lowering the lever would give you a nice idle, and you could perhaps use pretty much the whole range of the lever to adjust your speed.

I'm not knocking your approach of simply pulling on the string, borat. That's simple, cheap, effective, etc. Just trying to tweak it slightly based on what I think will work better for me. For all I know, I could get this sorted out, then find out you really need the ability to adjust the high-RPM's on the fly, for heavier/lighter snow.

Hey, Red, it's your machine to do as you wish.  All the power to you.  Just let us in on your mods.  Always enjoy to see what tricks guys are cooking up for their machines.

I don't think the 139cc Tecumseh engine can rev past 6500 rpm.  I pegged mine for a couple seconds unloaded and that's about it's limit.   I think the exhaust ports are probably  the most restrictive part of the system.  Those three little holes are pretty tiny for 139 cc engine.  If you ever saw the exhaust port on a 125 cc motocross bike engine, you'd know what I'm talking about.  They're positively huge by comparison.  You can stick a fresh bar of soap through the exhaust port on those things. 

    It's 50+ here and feeling like summer.   Out putzing with the machines and noticed the MTD 7hp SS had the cowling bolt but no support bracket.  It's an earlier model like Red's.  They probably did not come with with engine supports like later models.  The bar the clamp is on is a stablizing bar welded to the side of each intake housing side. 

   The brown bar is the wheel axle.  In later models they removed the stablizing bar and left just the axle which is where the bracket runs to on later models.  The bracket connected the axle, engine and back of the intake housing making a nice brace.   The added bracket is a RedOctber-like motor stablizer out of a steel steel.  Can't see the bolt and nut very well as they were slimed with grease.  The brace dampens the engine considerably and even noticable at the handles.  Probably would never had added it if I did not see Reds.   

   It's a 7hp now as it got update 803554, RMP Enhancement String Kit.