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

Borat,

   Very interesting post I read today (from 2009) was signed this way by T-Man.

P.S. I LOVE the HSK850 and TVS/TVXL840 2-cycle engine. One of the
strongest engines ever built, and very simple and powerful in its design.

   T-Man was a technical guy for Tecumseh for many years and miles above anyone on the net.  His depth of knowledge about Tecumseh engines is astonishing.

   The HSK870 seems like an interesting engine.  I've never come across one.   Have you?

That's pretty cool. I was also intrigued by the mention of a 7hp version. That's pretty impressive, at least to me. I was not able to find much info at all on the 870 when I looked yesterday, though. It does sound like it could provide some interesting opportunities. If they were available, and the rest of the machine could take it, turning a 5hp SS into a 7hp, then maybe even adding some RPMs, would make it an impressive little package.

Anyone know of other high-power 2-strokes, which might be more readily available?

It does make me curious what's different between the 840 (4 hp) and 850 (5 hp). Perhaps nothing, I suppose (like is apparently the case on some larger 4-stroke engines sold as, say, 9-11 hp), but if there are differences, I wonder what they are. Muffler and carb are the two that come to mind first, if the blocks are the same.

I've yet to see anything with a HSK870 engine in it. 

I just spent some time trying to understand the differences between the two 139cc Tecumseh engines I have.  The MTD has a Tecumseh model TH139SA-8339, built in 2006 the Craftsman has the HSK850-8324C model engine built in 1997.  It seems that the more recent models of the 139cc engine had the name changed from HSK8xx to TH139.  Both engine I have are similar but there is a major difference in the crankshafts.  The MTD crank is considerably shorter.   See diagram below.

Crank no. 290614 is for the TH139SA engine in the MTD and crank no. 290627 is for the HSK850 in the Craftsman.  As you can plainly see, both engines are not easily interchangeable.   The Toro version of the crank is quite a bit closer to the Craftsman and one could probably adjust the engine mounts to make them interchangeable.  However, the MTD/Craftsman swap doesn't look too easy.   Just goes to show how much variation there is with this engine.  Nonetheless, I'll be keeping my eyes peeled for these things.



 

   One of my Tecumseh manuals had a listing of differences between dash models as in HSK850-nnnnA.

   In the HSK840, 860 and 870 the variations are:

Carburetor, muffler, governor spring, blower housing, ground wire, primer line, primer assembly, fuel cap and ring sets.  There's probably more....

  For references they refer the reader to fiche which may be where they store more detail, not paper manuals.

  The 870 only had one listing but it was interesting:

HSK870-8701A  Ariens (snow Thrower).  Refer to HSK850-831C except use 250305 cylinder: 31091 piston and rod assembly, 34043 extension spring; 570722 carburetor baffle; 390343 muffler; 590670 electric starter; 640300 carburetor.

   If you want to transform an HSK850 to an HSK870 get out the wallet otherwise look for a used Ariens 7hp.

  

Good research Trouts.  I wasn't coming up with anything that would indicate a different cylinder.  That's where the added power will come from.  Either more or lager ports. 

I'll buy anything with the 139 cc Tecumseh engine.  Regardless of what it's rated power is, we know it doesn't take too much effort to get a lot more out of it.   I'd certainly like to get my hands on a 870 though. 

Trouts:

Upon further research, I've found that the HSK850 and HSK870 share the same cylinder assembly  part number 250305.  They both use the same pisont/rod assembly.  If that's the case, one must question where the additional two horsepower is coming from?  The only place I can see it happening is possibly larger carburetor main jet/venturi and freer breathing muffler to allow for more rpm.  Otherwise, the claim for the two more ponies might be bogus. 

Comments? 

Like you said, I'd expect either something in the carb and/or muffler to let it breathe better near the peak RPM (say 3600), allowing better torque production as the speeds continue to climb. Or, there's a magic sticker that adds 2hp It's also conceivable that they use a higher RPM on the 870. Even if the torque curve was no longer climbing, the higher RPMs would still produce more power. Use a smaller pulley, and the auger speeds would stay about the same, but you'd have more hp.

   I would think the carb and muffler could do it.  If yours has the same piston and rod then your engine seem to be non-standard also and actually a beefier than average 5.  What’s an average 5?  I would think there is baseline 5hp like a short block stock 850 which companies can order with a mix of anything.  The book I have lists additions to the standard.  If yours has the parts called out for the Ariens 870 then I would think your engine is not stock.  If you want post your engine number with the dash listing and I’ll see if it’s in my manual.

 

    Not sure of the dates of the Ariens 7hp.  Possibly it pre-dates the newer rules on hp ratings.  Given the company I would think Ariens did their own testing and regardless of any government or agency certifications sold it as what it was.

>>>I'll buy anything with a 139cc Tecumseh engine.

    I'm getting there. 

The 1997 Craftsman has an HSK850-8324C
The 2006 MTD has a TH139SA-8339G

 

 

    Your HSK850-8324C is not listed but referenced.  It is used as a base for two other models, the HSK850-8334C and 8334D.  Both are your engine plus a governor spring, ground wire, blower housing and carburetor. 

   (There were no TC139’s listen in my manual from 2001 and 2.  It looks like the designation did not come into being at that time).

 

    What apparently is a your HSK850 model as a base with those changes to make the 8334C and D may end up having the same carb and possibly the other parts.  There’s no relying on the manf’s manual or various exploded views on the net.  They are mostly reliable but specific changes may not make it to the manuals as I've seen a number of times.  Plus, the HSK850-8334C once made up as referenced from your engine may have “attachments” like as listed in partstree views.  Those “attachments” could be a carb change on top of a carb change from the base build of your engine.  Generally the additions cover an optional electric start, recoil and different carburetor.

 

     The marketing guys sell then spec to the manufacturing department and may be a step ahead of the drafting and documentation departments, very common.

 

    The manuals from MTD for my 5.5hp single stage list it as coming with an HSK850 with no dash number.  On the machine is a TC139-8336G. 

 

    Since mine TC139 is a 5.5hp and yours a 5hp I looked for differences.  The only thing I could find was they used different flywheels.  ?  What is weird is my 5.5 uses the same flywheel as your 850 5hp Craftsman.  ?  Mine probably uses a different carb but no telling unless you got the numbers off the carb.  My TC engine is also a 2006.  Possibly your Craftsman is a sleeper 5.5.  It would be with a jet tweak.

 

    Given that your Craftsman has those similar parts you mentioned above all you lack for an 870 upgrade is a...... possibly spring, carb and muffler.  The spring is nothing, a carb a drilling and the muffler $73 online and your in there.  Pricy but your machine would be approaching a $1000 Ariens.  Plus, the augers on the Ariens are probably slower than your Craftsman.  Your Craftsman might might keep up with or beat a 870 powered Ariens.   It would have more torque at the auger tips, more foot pounds and so many you'd have leg pounds.  The boratified $1000 Craftsman.

 

    Your HSK850-8324C is not listed but referenced.  It is used as a base for two other models, the HSK850-8334C and 8334D.  Both are your engine plus a governor spring, ground wire, blower housing and carburetor. 

   (There were no TC139’s listen in my manual from 2001 and 2.  It looks like the designation did not come into being at that time).

 

    What apparently is a your HSK850 model as a base with those changes to make the 8334C and D may end up having the same carb and possibly the other parts.  There’s no relying on the manf’s manual or various exploded views on the net.  They are mostly reliable but specific changes may not make it to the manuals as I've seen a number of times.  Plus, the HSK850-8334C once made up as referenced from your engine may have “attachments” like as listed in partstree views.  Those “attachments” could be a carb change on top of a carb change from the base build of your engine.  Generally the additions cover an optional electric start, recoil and different carburetor.

 

     The marketing guys sell then spec to the manufacturing department and may be a step ahead of the drafting and documentation departments, very common.

 

    The manuals from MTD for my 5.5hp single stage list it as coming with an HSK850 with no dash number.  On the machine is a TC139-8336G. 

 

    Since mine TC139 is a 5.5hp and yours a 5hp I looked for differences.  The only thing I could find was they used different flywheels.  ?  What is weird is my 5.5 uses the same flywheel as your 850 5hp Craftsman.  ?  Mine probably uses a different carb but no telling unless you got the numbers off the carb.  My TC engine is also a 2006.  Possibly your Craftsman is a sleeper 5.5.  It would be with a jet tweak.

 

    Given that your Craftsman has those similar parts you mentioned above all you lack for an 870 upgrade is a...... possibly spring, carb and muffler.  The spring is nothing, a carb a drilling and the muffler $73 online and your in there.  Pricy but your machine would be approaching a $1000 Ariens.  Plus, the augers on the Ariens are probably slower than your Craftsman.  Your Craftsman might might keep up with or beat a 870 powered Ariens.   It would have more torque at the auger tips, more foot pounds and so many you'd have leg pounds.  The boratified $1000 Craftsman.

 

    .

 

  

 

Thanks for the research Trouts.  It's awfully confusing trying to establish exactly which engine these Tecumseh's are.  Far too many variables.  If and when I come across a 139cc Tecumseh, I'll just buy it outright and figure out what it is later. 

Not too interested in putting in any money to enhance performance.  The piece of string does that. 

This threads reminds of the discussion a year ago about the Briggs & Stratton 7 HP R-tek engine that is used on the Toro Snow Commander.  This is a comparable engine to the HSK850, similar displacement.  May not a cheap route to add power, but an option to drop into a Toro 221Q.  Has anybody done this yet?

   Went through exploded views of carbs 640300, 640011, 640012 and a non-EPA carb.  All 640xxx's are EPA carbs.   The 11 and 12 are used in lower HP versions of the HSK850 (lower than 7hp)   Since the HSK870 uses the 640300 I assumed it contributed to its HP boost.   The exploded views showed that to not be the case.  The differences are in things unrelated to power, more to connections and fit.  The fix idle meter jet, bowl nut jet and emulsion tube are the same in these carbs.

Well, if the carb is the same, the cylinder is the same, crank piston the same, I think it would be safe to assume that the extra power is coming from the 7 h.p. decal on whatever machine has the dubious honour to wear it. 

With all the above parts being equal, the only place the power will come from is engine speed and I don't recall seeing an increase in rpms  listed in anything I've seen for the HSK870. 

Borat,

   Saw your T-man post and posted there myself. 

    The only difference I can see in a 5hp version of the HSK850 and the HSK870 is the muffler.  The 5hp uses 390325.  The HSK870 uses 390343.  I can't find anything about these mufflers other than prices.   The difference may be the finish like galvanized or some fit thing but it could be the 343 is tuned. 

    It's too much for me to imagine Ariens reworking an SS522 body to be a SS722 and charging $2-400 more for it with an unmodified HSK850 used in the 5hp version.  Ariens in the past has used a tuned muffler to boost a HSSK50 to HSSK55.   They have made engine changes to stock versions often in the past like special cranks. 

It's possible that a freer breathing exhaust might contribute a power gain.  However, from my experience, to gain substantial power, an air intake and carburetor enhancement is usually required to go with the improved muffler/exhaust. 

I've worked on hot-rodding my Yamaha RDs and changing the exhaust alone had some, but by itself, little effect on power gain.  Improving the air intake system and increasing the size of the pilot and main jets along with the exhaust change made all the difference in the world.  A freer exhaust will expedite gas flow but only as much as the engine can produce exhaust gasses.  Without more fuel, the engine cannot provide the additional combustion required to capitalize on the more efficient exhaust.   Being that the 850 has no air intake restriction, there is nothing to be done there to improve power. 

I'm with T-Man on this one.   We're probably looking at decal power unless the 870 engine is being run at considerably higher rpm.