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?

I thought they were identical but there are some subtle differences between GC160 vs. GX160.  GC has slightly longer stroke and smaller bore compared to GX.  GX is 163cc vs. 160cc and hp and torque are slightly higher for GX - perhaps just enough to make the difference.   The GX160 on the HS621 appears be the low profile kind of GX160 variations.

Generally speaking torque and power of push-rod ohv engines is a bit better at lower rpms vs. an ohc engine of the same displacement.  I've read that more than a few times.  Something to do with valve angle and efficiency at lower engine speeds. 

Ohc engines are capable of much higher rpm and that's where the configuration shines.  At higher engine speeds ohc engines will run more efficiently and make more power because there is no "valve float" that can be experienced with a push rod engine being run a too high rpms. 

Bottom line is that using ohc engines for OPE isn't the best application for that type of engine.  Put the same or similar ohc engine in a small displacement motorcycle and spin it up to eight or nine thousand rpm and it will be right at home.  In that application it will make considerably more power and live longer than a push rod engine of similar size.  It's all about the rpm range.  

borat wrote:

So, Borat, if we stabilize the the RPM on an OHC engine at 7-8000 we would have a more powerful engine than GX160?

blumonster wrote:

If it does not blow up first and throws the piston out.  Borat likes to rev it very high.

:D I remember you tried increasing the RPM on HS35 and it sounded not that great. :D

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.