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

One guy from MSP area is selling his 15 year old HS621 (the guy from Wayzata MN who hates HomeDepot and GC engines) for $450.  Another one is selling his one year old HS520 for $400 with one year remaining on the warranty.  HS621 is a nice machine but is it really worth more than nearly new HS520?  Replacement parts for HS520 is about 50% of the cost of HS621. What do I recommend for a friend?  I think the HS621 from that guy is simply way too high (if it were as good as aa335 then it is a different story).  HS520 seems like an economical option.  What do you guys think?

you are correct but i did not go past 4000rpm. i don't have the guts to try 8000 rpm. 

blumonster wrote:
Not sure what you mean by "stabilize".  OHC engines are designed to run considerably higher rpms that a similar push rod engine.

As compared to the same displacement GX engine running at 3600 rpm, it most certainly will make more power.  For how long is another question....

The problem with running it at higher rpms on a piece of OPE is cooling.  On a small motorcycle, the engine will be whistling through the air a 50 to 60 mph at full rpm and exhaust gas heat will be dissipated through a much less restrictive/larger exhaust system. In addition, engine oil cooling will be somewhat assisted by being circulated through the transmission/crank case.  Higher rpm engines usually have a larger carburetor and air intake system that moves more cool air and fuel through the engine as well.  Those variations are essential for cooling high rpm engines. 

Trying to run a stationary engine at such high speeds would be hazardous to the engine's health even with a very good fan.  It would be dicey if run too long.  I suppose if the engine has a pressurized oil system, an oil cooler could be added to help keep temperatures down but overall, don't think OPE applications are suitable for high rpm operations unless the engine is specifically designed for it, as in four cycle trimmers etc. 

Regardless, if the small engine is mounted on a snow blower for instance and run at 7000-8000 rpm, some serious gearing would be required.  In addition to that, I think the sound of a screaming engine might become a bit objectionable after a while. 

I had the GX160 running past 4000 RPM and it did not seem right.  There was a lot of vibrations and noise.   I don't think the engine will last long running like that.   The engine was more comfortable lugging high load at low RPMs.

aa335 wrote:
A GC with overhead cam will tolerate revs much better than a push rod GX.  However, if the engine is designed to run at 3600 rpm I wouldn't be pushing it much past that unless of course it's a two cycle.  Those things love to rev. 

Another  thing to consider is where the maximum torque is achieved.  On most OPE engines it's around 3000 rpm.  Same size engine on a small motorcycle will probably be a thousand or more rpm higher.

I checked the performance curves for torque and HP.  Max torque tapers off after 2500 RPM.  HP is still increasing after 3600 RPM but not provided.

I guess going higher RPM would be useful if I regear the auger ratio.  Making it spin faster isn't going to do much if it can't be fed enough snow.  Besides, I don't have a need for a single stage snowblower to throw heavy snow more than 25 feet.  As long as it can throw it across a wide car wide driveway consistently, I'm happy.

Thank you for the explanation, Borat. I learned a few things about engines here.

By stablizing I meant keeping the RPM at these high points, not letting it to go lower than, say, 7000RPM.But as you said we would need cooling system first.

Just to get back on the OP's original query, I just picked up my 2nd HS621 yesterday. I was tooling around on CL and saw an older ad for a "good condition" HS621. I called the guy and he told me it was his father's machine and was well taken care of over its lifetime and it looked it in the photos. Long story short, I went and looked at it and sure enough it was in exceptional condition so I bought it for $400.00. I'm going to sell the HS520 and the HS621 I picked up last spring to offset the cost of my new purchase.

I swapped out the new paddles and scrapper bar I just put on the 1st HS621 to the 2nd keeper HS621 so I'm good to go for the winter. The paddles and scrapper bar from the 2nd HS621 were not too bad so I put them on the 1st HS621. #2 is actually older than #1 but it's in much better condition and was well maintained during its lifetime, it even sounds a lot smoother than #1 does.

As far as the prices for HS520's and HS621's goes, those seem to be the going rate on CL around these parts (New England) this season. I only paid $125.00 for the 1st HS621 I bought last spring and $ 250.00 for the HS520 two years ago so I should be well ahead of the game when it's all said and done (hopefully). Once again, I do not like the performance of the HS520 so I have to lean towards the HS621 even though I have not had a chance to put one through its paces yet. I can only imagine that the GX160 OHV on the HS621, which was on my trusty old HS624WA 2 stage, will out perform the GC160 OHC on the HS520. I'd go for the older HS621 if it is in good condition and has been well maintained. JMHO

@FrankMA,

Do you have any idea on how old the second HS621 that you just bought?  Any pictures of the new acquisition?

aa335: The 1st HS621 I bought last spring is S/N # SZAN-1026712, the most recent HS621 purchase is SZAN-1015460. This means my "newsest" HS621 is 11,252 machines older than the first HS621 I purchased last spring. I've got both out on my deck right now and will take pictures of both sometime tomorrow. I just really like the look of the HS621 (sleek and up to the task) and feel the GX160 OHV engine will perform great with this package. The older I get, the more I want to use a lighter, easier to handle machine for the lighter snowfall amounts we typically get in early and late winter when a single stage is better suited to the task at hand. Will post fresh pic's tomorrow providing I can remember how to do so...

Mine is even older with SZAN1006... serial number.