Testing the 79 & 99 CC HF motors

It certainly has been a busy year, but we still managed to design the Q-Matic drive to fit the latest motor from Harbor Freight. We produced a fair number of drives for the 79 CC and finally had time to test the drive on the current 99 CC HF motor. Many parts are interchangeable between the motors, and the drive side bolt pattern is also the same.
Some things are surprising, including the 5/16 fine thread bolt used on the 99 CC in place of the 8 MM on the 79 CC. The 79 CC was rated to use 89 octane, however the 99 CC wants 87 octane. The "foot" bolt pattern is very close on both motors, however the 99 CC uses a staggered system, meaning the boltholes are closer on one side than the other. The bolthole centers are 102 MM on one side and 104 MM on the other. This was first discovered when we noticed the extra mounting [foot] plate holes didn't line up, if we rotated the plate the holes lined up. Next we noticed the crankshaft on the 99 CC is over size, and requires the pulley I.D. size increased to fit.

The 79 CC is 80.7 CC and the 99 CC is 98.5 CC a difference of 17.8 CC. The 79 CC has the same size 15 MM carburetor, but loses the air/fuel mixture screw on the 99 CC motor. The motors produce very similar power, however the 99 CC is slightly slower in stock form. The 79 CC has a higher top end with identical drive ratios, but the 99 CC pulls harder on the way to top end. After a few minor modifications, the 99 CC will pull harder and reach a higher top speed.

Blue or black? My test bike is blue; the 79 CC motor housing is blue. The 99 CC used to have black covers and didn't match my blue bike. The used test 79 CC motor now has black cover & black rope start, whereas my 99 CC test motor now has blue cover & blue rope starter assembly.....this means they are interchangeable.

After the few minor modifications to the 99 CC motor and some break-in time, here are the facts.. Easily hits 6000 RPMs, pulls very hard, can pull a harder ratio [gig her top end, slower start]. With the ratio of 11.55 X 1 the following numbers were the results 3000 RPMs = 20 MPH 3600 RPMs = 24 MPH, 4500 RPMs = 30 MPH, and 6000 RPMs = 40 MPH.

If I can find a little extra time I will try changing the Q-Matic ratios and see what happens at 9.52 X 1..... Should easily pull the numbers and should look like this:
3000 RPMs = 24 MPH
3600 RPMs = 29 MPH
4500 RPMs = 36 MPH
6000 RPMs = 48 MPH
6155 RPMs = 50 MPH

Way too fast for a bicycle, and I am sure no one will want to go that fast. BTW I had the test bike at 6300 RPMs several times during testing using the 11.55 ratio drive.

Have fun,


__________________
Quenton

More pictures


Have fun,

All the pics are mini???

Hi Stoney,

Thanks for letting me know they were small. I just "upsized" them all. Let me know if anyone needs any more pictures.

Have Fun,

Changed the primary ratios yesterday. At 8.5 X 1 it was too tall and stopped the motor from reaching the same 6300 RPM level. The top speed was also lower as the motor simply ran out of power under the harder load. The bike was only able to reach 46 MPH @ 5100 RPMs.
I reset the adjustable pulley to a slightly lower size and found the bike with a quicker take-off and higher top end speeds. The current ratio is 9.87 X 1 and produced a top end of 49.3 MPH @ 6300 RPMs

Final conclusion:
Ratio should be 11.55 X 1 for heavy riders or hilly areas [or both].
11.55 X 1 is supplied by using a 2.5" primary pulley on the Q-Matic drive.

Using a 3" primary pulley on the Q-Matic drve supplies a 9.53 X 1 ratio. 9.53 X 1 is good for average riders on slighty hilly roads. The 9.53 X 1 ratio allows the motor to run at lower RPM levels at crusing speeds.

Light weight rider or flat ground travel can use a ratio of 9.876 X 1 on the Q-Matic drive. The adjustable primary pulley was set at 2.90" to cause the 9.876 ratio.

Happy New Year and Have fun,

Just completed another round of ratio tests on the 99 CC HF motor, and will share the results. The following ratios are used on a 26" bicycle, AX series belt, with a 56 tooth rear sprocket.

Primary pulley set at 2.95" [total corrected ratio = 9.7 X 1]
Primary pulley set at 2.90" [total corrected ratio = 9.87 X 1]
Primary pulley set at 2.85" [total corrected ratio = 10 X 1]
Primary pulley set at 2.80" [total corrected ratio = 10.24 X 1]
Primary pulley set at 2.75" [total corrected ratio = 10.45 X 1]

I will only list the speed at 2500, 3500, and 5500 RPMs on the various ratios

9.7 X 1:
2500 RPMs = 19.9 MPH
3500 RPMs = 27.9 MPH
5500 RPMs = 43.8 MPH

9.87 X 1:
2500 RPMs = 19.5 MPH
3500 RPMs = 27.4 MPH
5500 RPMs = 43.1 MPH

10 X 1:
2500 RPMs = 19.3 MPH
3500 RPMs = 27 MPH
5500 RPMs = 42.5 MPH

10.24 X 1:
2500 RPMs = 18.9 MPH
3500 RPMs = 26.4 MPH
5500 RPMs = 41.5 MPH

10.45 X 1:
2500 RPMs = 18.5 MPH
3500 RPMs = 25.9 MPH
5500 RPMs = 40.7 MPH

The ratio choices can be expanded by replacing the AX series belt with the 15 series wedge belt.

26" wheels, 56 tooth rear sprocket, 3" primary pulley, wedge belt:
9.748 X 1:
2500 RPMs = 19.8 MPH
5500 RPMs = 43.6 MPH

26" wheels, 56 tooth rear sprocket. 2.5" primary pulley, wedge belt:
11.96 X 1:
2500 RPMs = 16.17 MPH
5500 RPMs = 35.57 MPH

Hope this infomation is helpful.

Have fun,



After several more tests and some high winds, I have determined using a 3" primary pulley is too much. It works well on flat ground, no wind, and a light rider, which isn't the average riding conditions. Simply dropping the 3" pulley to 2.90" made a lot of difference, however if hills or rider weight are considered, the primary pulley should be reduced to 2.75" as this ratio will keep the bike within acceptable limits.

Have fun,

I ordered one of these 99cc engines from Harbor freight. Too much good talk about them to pass it up. It's going in my blue bike.

Hi Jay,

It appears the HF 99 CC 4-stroke is the motor of current choice.

We have done a lot of research and testing on both the 79 CC and the 99 CC, and have lots of information if anyone needs it.


Have fun,

my blue bike should really run with the 99cc

Harbor Freight Q-matic choices

Hi all, well I have a quandary, I have both a Big Blue Dog (greyhound) and a Black Predator.
The choice is, I have a drop-loop Model 08 Simpson Racer, chopped to a bit radical in the front end, Worksman Wheelset, 60 tooth Maniac Mechanic rear.

Looks like my adjustable pulley should be at about 2 3/4, ax 25 belt, BUT, shall I try Blue, or Black????

Sadly, the blue MIGHT go well with the proposed blue paint for the bike, BUT the 99 might haul my big self better?

This should be fun?

Mike