Harbor Freight Greyhound 79cc engine

KilroyCD · Oct 18, 2009

bandito said:
Thats a good looking motor, cant beat that price too for a 79cc brand spanking new motor. Ill bet that thing will scream on a bicycle. Being 30ccs bigger than the hua sheng I dont see how it can compare. Gotta be able to do 50mph with this motor it would seem just being stock......I just went back to looksy again at that motor how can an 79cc motor be rated 2.5hp the same as the honda 50. I know the internals but still doesnt seem right.

This motor may have the same HP rating, but it provides a lot more torque. As the Hua Sheng revs to 7500rpm, the little HS engine can propel the bike to higher speeds than the Greyhound. The Greyhound is governed to 3600rpm, and with the governor disconnected revs to around 4500rpm. So, due to the lower revs, you're limited to around 30-32mph unless you start experimenting with final drive ratios using smaller rear sprockets. But for hilly areas, big riders or a combination of both, the Greyhound would be a nice choice.

xlite · Oct 19, 2009

Not knowing details about gearing it's silly to say Honda or HS is better for speed or hills. I have one of these and with governor removed it is noticeably more powerful than the 50cc engines.

KilroyCD · Oct 19, 2009

xlite said:
Not knowing details about gearing it's silly to say Honda or HS is better for speed or hills. I have one of these and with governor removed it is noticeably more powerful than the 50cc engines.

As I had mentioned before, the Greyhound has a lot more torque. It will accellerate faster, but even with our governor removed, we were only getting it to around 4500 rpm. We are still tinkering with the bike, and we have a new throttle cable coming in that will allow us to possibly extract more rpms. The current cable is marginally too short.
That said, there were two Greyhound powered bikes at the East Coast Rally, both with the same drive system (the EZM Q-Matic). There was also a Honda GX-50 with the same drive. We had a 52 tooth rear sprocket on our Greyhound bike, I think the other Greyhound had a 56 tooth. I don't know what size was on the Honda, but it was at least a 50 tooth.
The Greyhounds could accellerate more quickly than the Honda to a certain point, but the Honda eventually wound out to a higher top speed. The Honda (or HS) can wind out to 7500+rpms, which we have not been able to coax out of our HF engine (yet).
The "kick in the butt" while accellerating was noticeably stronger with the HF Greyhound engine, and that extra power will be nice for maintaining speed going up hills in my area.
After the rally, the other Greyhound owner (Rustico Ray) swapped his out for a Hua Sheng so he could cruise faster and achieve a higher top speed than with his Greyhound.

tyrslider · Oct 19, 2009

xlite is right though, its like comparing an old muscle car to a modern v6; my Ford Ranger 3.0L revs past 7000 and any old muscle car would blow by it w/ the motor turning < 4000. More than just final drive ratio your gearbox reduction is key. And there's no replacement for displacement. Typically the benefit of faster motors (i.e. higher redline) is a wider power band, but not necessarily. Truth is hp is work (torque) multiplied by time and 2 motors w/ the same hp should be capable of vurtually the same work. That is if their powerband differences are properly taken into consideration.

KilroyCD · Oct 19, 2009

Of course, gearbox reduction is key to top speed, but I was trying to make the point that with the same ratio (in Rustico Ray's case) he is achieving higher top speeds with the smaller HS than with the Greyhound. All three bikes we tried at Cape Henlopen had the same "gearbox" (the Q-Matic) and hence the same gear reduction, but the rear wheel sprockets may not all have been the same size. In Ray's case, he had the 56-tooth on the bike and used the same drive (Q-Matic) with both engines and his bike has a higher top speed with the smaller engine.
Now, if you plan to cruise at 30mph or below and don't have any plans to push the speed envelope, the Greyhound engine is going to be a great choice, especially for the price. The extra torque is nice for those packing a few or more extra pounds, or those who live and ride where it's hilly (or both).

Quenton Guenther · Oct 19, 2009

Hi Everyone,

I was using a 56 tooth rear on my Q-Matic, and the 2.5 HP Honda motor.

The Greyhound powered bikes [I rode both of them] pulled strong at the bottom of the torque curve, but the Honda [HS also] revs so quickly it easily out distances the HF motor in short order.

The Greyhound is a great choice for "low speed grunt", and like Kilroy stated would be great for hills or heavier riders [or both] crusing at lower speeds. The Greyhound makes its HP much lower in the powerband, whereas the Honda or HS motor peaks at a much higher RPM.

It was nice to test the 79 CC Greyhound, and the 49 CC Honda with the same drive system to arrive at an honest comparision. All 3 versions of the 4 stroke motors worked well and certainly offered a different approach. During the Lewes event we also discovered the Greyhound liked the un-restriced exhaust [EZ Flex pipe] system.

If anyone has the remains of an earlier kit [tank, throttle, drive sproket, etc] the HF motor can be hooked up to the Q-Matic drive, and all that is left is to fabricate a motor mount, and go riding! It is necessary to mount the motor slightly higher in the frame because it is longer than the 49 CC 4 stroke motors, but looks great as an in frame motor.

Have fun,

xlite · Oct 20, 2009

Try a smaller rear sprocket on the HF and you may find, as I did, a lot of that low end torque will dissapear with equivalent boost in top speed. I don't know about the Honda but my HS motor proved markedly inferior in terms of both low and high end with rear sprocket optimized for each. It had more low end AND top end.

Quenton Guenther · Oct 20, 2009

Hi xlite,

Have any pictures of the HF motor mounted on a bike? Sure would like to see how you fitted it into the frame. How did you route the exhaust?

Have fun,

lovehamr · Oct 20, 2009

Quenton Guenther said:
It was nice to test the 79 CC Greyhound, and the 49 CC Honda with the same drive system to arrive at an honest comparision. All 3 versions of the 4 stroke motors worked well and certainly offered a different approach.

I believe that the point is unless the gearing is adjusted for the specific engine's RPM band then the comparison is flawed from the begining. As far as I can tell, all it showed was that that drive system didn't work as well for some engine's as it did for others. Can the qmatic's primary gearing be changed by the builder?

Steve
.wee.

KilroyCD · Oct 20, 2009

lovehamr said:
I believe that the point is unless the gearing is adjusted for the specific engine's RPM band then the comparison is flawed from the begining. As far as I can tell, all it showed was that that drive system didn't work as well for some engine's as it did for others. Can the qmatic's primary gearing be changed by the builder?

Steve

The Q-Matic uses no gearing, but instead it has a belt in the primary drive. Jim and I are using an adjustable pulley in front to experiment with changing ratios. Ultimately we'll find (between front pulley size and rear sprocket size) the combination that works best for us.

azbill · Oct 20, 2009

I know the changing the rear sprocket alone will make a big difference
I am waiting for a Q-matic, and have already changed my rear from a 50 to a 56 tooth
right now(with the 56), my gearing is approx 19:1 using a manual 'silent-drive' trans (2500+ miles

)
the news auto trans will be be 17.5-18:1
with the hills here, and pulling the girls/trailer,I am going to be working it very hard to see if it can be broken !!!
if it can, I will, and then we will make it better (^)

xlite · Oct 21, 2009

Quenton Guenther said:
Hi xlite,

Have any pictures of the HF motor mounted on a bike? Sure would like to see how you fitted it into the frame. How did you route the exhaust?

Have fun,

The install was a half-fast experiment to see if there was any potential to that motor and compare it to a HS. I would never trust the fragile brackets for long trips (or even short ones for that matter) but was able to determine it had more power than the HS. Spent more time screwing with the governor than anything else. It was also my first venture into a shifter type setup and arranged similar to the Dax in-frame. Stock exhaust. Gave a new meaning to the phrase "hot pants".

I plan to do a more permanent job and will do a build log with photos like I did with the SBP pipe.

bandito · Oct 21, 2009

I notice on the specs for that motor it has a 5/8ths tapered shaft, the q-matic will work with that shaft? I couldnt find any where as to its weight, how much does it weigh?

Fossil · Oct 21, 2009

The spec sheet pictures an engine with a tapered shaft but in fact it is not tapered and the Q-Matic works just fine on this engine. The two that I have seen are not tapered. The only thing I needed to do to mount the drive was to drill 4 holes in the drive plate so I could clock the drive at a slight downward angle. This needed to be done so the drive would clear the cylinder that is at a slant instead of vertical like the HS or Honda engines and the exhaust manifold. I think the weight is close to 24lbs. Hope this helps.

Jim

bandito said:
I notice on the specs for that motor it has a 5/8ths tapered shaft, the q-matic will work with that shaft? I couldnt find any where as to its weight, how much does it weigh?

xlite · Oct 22, 2009

The HF shaft is compatible with standard bike motor kit clutches but the hole pattern is not and must be re-drilled.

omegaunderground · Oct 22, 2009

that motor looks sweet, I am gonna see if my local harbor freight store has one in stock to check out today

xlite · Oct 22, 2009

omegaunderground said:
that motor looks sweet, I am gonna see if my local harbor freight store has one in stock to check out today

They are on sale for $89.00 in latest flyer.

professor · Oct 23, 2009

I have been following this post, was at HF and they were sold out (and will have some more in after the sale is over), so if that happens to you- get a rain check from the store and they said they would honor the sale price.

professor · Oct 30, 2009

I just weighed the greyhound on my scale @ 20 # (no oil or gas). It is wide though,and fairly quiet. The throttle drag is easily adjustabe by backing off the tension nut that it pivots on.

RusticoRay · Nov 5, 2009

The HF motor has found a new home. It's going on this one's twin that I rode on tuesday 30.9 MPH on flat ground WOT. As mentioned before it has plenty of grunt and will climb at 20mph until it runs out of fuel.

Thats a rack mount, frame mount and pusher seems like with a little modification all are viable.

Harbor Freight Greyhound 79cc engine

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