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79 CC Vs 99 CC HF w/ Q-Matic drive

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  #1  
Old 12-15-2011, 08:37 PM
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Default 79 CC Vs 99 CC HF w/ Q-Matic drive

It certainly has been a busy year, but we still managed to design the Q-Matic drive to fit the lastest 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 interchangable between the motors, and the drive side bolt pattern is also the same.
Some things are surprizing, 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 bolt holes are closer on one side than the other. The bolt hole 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, wheras my 99 CC test motor now has blue cover & blue rope starter assembly.....this means they are interchangable.

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 [gigher 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,
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Last edited by Quenton Guenther; 12-15-2011 at 11:53 PM.
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Old 12-15-2011, 11:47 PM
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Default Re: 79 CC Vs 99 CC HF w/ Q-Matic drive

More pictures.

Ran throttle cable from the front.
Stock motor mount simply drilled to match the motor footprint.

Have fun,
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Last edited by Quenton Guenther; 12-15-2011 at 11:56 PM.
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Old 12-16-2011, 03:03 PM
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Default Re: 79 CC Vs 99 CC HF w/ Q-Matic drive

Very Interesting, great pics, thanks for that Quenton!
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Old 12-17-2011, 06:19 PM
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Default Re: 79 CC Vs 99 CC HF w/ Q-Matic drive

quick question would the q-matic that is sold with and for the 48cc hondas and HS's be the same as being tested on the HF motors?.....if I had a HS with the q-matic could I take it off and fit it to a 99cc HF motor?.....you do awsome work Quenton
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Old 12-17-2011, 08:48 PM
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Default Re: 79 CC Vs 99 CC HF w/ Q-Matic drive

Hi,

The stock Q-Matic for the 49 CC four stroke motors is mounted different, and has several parts not shared between the drives. The idler arm is also located at a different location.

The drive plate must be mounted at a different angle to better fit the motors with the rear tilted cylinder. The Q-Matic for the 79 & 99 CC motors also use the AX series belt and larger primary pulley.

It is possible to convert the stock Q-Matic to fit the 79 & 99 CC motors by re-drilling the mounting holes, replace the belt, replace the primary pulley, and re-locating the idler pivot bolt.

The clutch doesn't need to be changed because the larger primary pulley makes up the difference between the high RPM motor [Honda and HS] and the low RPM motor for initial clutch enguagement [ticking speed]. The stock primary ratio on the stock Q-Matic is 2.76 X 1, whereas it is 2.06 X 1 on the HF version. Stock Q-Matic clutch speed at idle is approx 800 RMS, and approx 600 RPMs on the HF motors. During tests today I installed an adjustable primary drive pulley and increased it to a primary ratio of 1.56 X 1. The 1.56 X 1 primary ratio made the clutch spin @ 769 RPMs at idle.

The only problem with test ratio was the massive top end speed, 53 MPH @ 6000 RPMs.
The good part was the RPMs at cruising speed, only 3600 @ 31.7 MPH [3600 is the maximum rated speed]. I did a few mods to the test motor, and it quickly exceeds 6000 RPMs, but I doubt it will live for a long time at these high levels. I had the test bike to almost 54 MPH today, and noticed it was only turning 5700 RPMs at 50 MPH but wouldn't suggest anyone try it on a standard bicycle, just way too fast.


Have fun,

Last edited by Quenton Guenther; 12-17-2011 at 08:56 PM.
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Old 12-17-2011, 09:37 PM
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Default Re: 79 CC Vs 99 CC HF w/ Q-Matic drive

Thanks for the reply Q,

Once again I cant tell you how much Im in awe of the work you do to better this little hoby of ours. I can only one day hope to produce something to aquire your respect also.
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Old 12-27-2011, 11:10 AM
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Default Re: 79 CC Vs 99 CC HF w/ Q-Matic drive

Hi Jowens,

Be sure to post pictures of your next bike build.

Have fun,
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Old 12-27-2011, 02:13 PM
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Default Re: 79 CC Vs 99 CC HF w/ Q-Matic drive

How is it at climbing hills? How does the 99 compare to the 79 in hill climbing?
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Old 12-28-2011, 11:24 AM
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Default Re: 79 CC Vs 99 CC HF w/ Q-Matic drive

Hi Silverbear,

Both motors share about the same amount of power, and when geared slightly different, both have about the same top end.

The 99 CC motor does have more torque, and can pull hills slightly better under load than the 79 CC motor, and the 99 CC motor can use lower primary ratios [less RPM].

We normally ship both versions [79 CC & 99 CC] of the Q-Matic drive with a larger primary drive pulley than the stock 49 CC version. We reduce the primary ratio from 2.76 X 1 to 2.06 X 1 to take advantage of the low RPM and higher torque motors.

After installing an adjustable primary pulley and longer belt, I was able to find the peak torque threshold on the current 99 CC test motor. It takes off much slower and has a reduced top end when the primary ratio exceeds 1.70 X 1. I am a light rider [165 pounds] and on level ground the top end and reasonable take-off speeds drop drastically if the primary pulley exceeds 3".

When testing other drive system options we had to alter the primary ratio to 2.36 X 1 [11 / 26 teeth] in order to compete with the Q-Matic drive. We installed a Max Torque go kart clutch on the crankshaft, purchased a BMI drive plate with a jack shaft, installed a #35 chain on the primary, purchased sprockets, shaft, bearings, and a cover [total cost was more than the Q-Matic drive overall]. The test drive was a full 3" wider than the Q-Matic because of mounting the clutch on the motor crankshaft.

Why the difference?

Spinning the clutch at full motor speed requires more power than spinning at approx. 1/2 speed, and when only using 2, 2.5 or 3 HP, one can't afford to give up the extra power needed to spin the clutch at higher speeds. This is very apparent when climbing hills or accelerating, as the extra power needed to spin a clutch at motor speed and the extra flywheel action soon takes its toll.

We found the following:

Q-Matic drive with a final ratio off 11.55 X 1 is quick on take-off, climbs hills easy, and an average top speed of 33.4 MPH @ 5000 RPMs. Maximum RPM was 5900 [39.5 MPH]. We did several ratio tests including 8.5 X 1 and exceeded 50 MPH [53 MPH @ 5800 RPMs], but had to be slowly brought up to speed. These test ratios are like taking off in high gear in a car

Crankshaft driven clutch with a final ratio of 13.24 X 1 takes off slight slower, and has a top end speed of 29.2 MPH @ 5000 RPMs. Maximum RPM was 5200 [30.7 MPH].

All tests were conducted with the exact same 99 CC motor. The carburetor main jet was increased from .025" to .031" and a tuned flex pipe was installed. We only changed the drive system to arrive at the differences

Have fun,
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