Mac's 99cc Predator build

Re: 99cc Predator Build

Thanks for posting the Pix for me AZbill, another note, I chose not to "machine the shaft down, I used a 20,000RPM die grinder with a metal rotary file on the 5/8ths pulley mounted in my mini lathe, just took a few seconds to remove .007 of material from the pulley. I did have thoughts of using some wood on each side with emery paper inside and use channel locks to apply pressure(with engine running), figured it would not be very accurate and the key-way grove on the steel engine shaft may have been an issue. Had to take it for another ride, just got back, no major issues except I keep forgetting to turn the switch on. The torque is unbelievable!!! I live on a steep hill(about 1/2 way up), with the HS I went down the hill, got up to max speed and still had to pedal like crazy to get over the hill. Now, I turned up the hill from my driveway and went right over the top without a single pedal!! I'm happy!

R/Mac

Re: 99cc Predator Build

Hi Mac,

The correct belt for the low RPM motor is an AX25. AX belts are measured differently than other belts and the AX25 is actually 27" long. The Q-Matic was designed to use notched belts [AX and Wedge] and was one of the reasons the idler is located internally to maintain the belt shape. If a notched belt has the backbone depressed it can crack the belt between the notches. Notched belts were originally designed to bend around small pulleys without "bunching up".

If you use a 4L series belt on the Q-Matic it will run hotter, stick to the pulleys when hot. The 4L belt is a FHP [fractional horse power], and will stretch much quicker than the AX or Automotive wedge belts.

If you want to really "dial in" the correct ratios on your bike, consider installing an adjustable primary drive pulley and install an AX26 belt. When your motor completes the break-in process it will have a little more power and you may find your cruising speed can be moved to a lower RPM and still have plenty of power to pull the hills without pedal assist.

The adjustable pulley can be purchased from Grainger. I would post a link, but may be considered vending. Just go to thier website and look for adjustable sheeves, however be careful as some are very expensive and some are not. 1L845 is their part number for one that adjusts from 2.4" to 3.4" and fits a 5/8" shaft. The one I use is part number 1X448 and adjusts from 2.1" to 3.1". These numbers are based on using a 1/2" belt [AX, 4L, A, etc]. The 1X448 is less expensive than the 1L845 and is the better choice because the motor doesn't have enough power to pull a light weight rider [me] on level ground when set at 3.1" to 50 MPH. I am currently running the pulley at 2.80" [corrected] and final ratio of 9.87 X 1 and it pulls hills well.

Have fun,

Re: 99cc Predator Build

Quention,
I'm typing on a laptop, had a nice response written with some interesting stuff, while signing, off the palm of my hand hit the mouse thingy.....POOF message gone!
Is that ever aggrivating! I'll re write tomorrow.

Thanks!!!

R/Mac

Re: 99cc Predator Build

I noticed the angle that you have the engine canted forward . It looks like it would effect how well the float on the carb would work .

Re: 99cc Predator Build

tn97kouki,
I thought about that too, but I figured I'd try it to see what happens, some of my 2 strokes have more angle than this one so what the heck. The carb works great, no stumbling or running out of gas or leakage. The angle is the only way I could fit the motor in the frame without major mods with the mount I have installed. Maybe a different mount in the future, or a different bike?? who knows?

R/Mac

Re: 99cc Predator Build

Pred99, OK... I had to see top speed, my ratio is 13.6:1 total, with a 90" roll-out rear tire, GPS confirmed on level ground 36MPH, after doing some math, looks like motor was doing approx. **4600rpm**, it is a fresh motor, 2 hours/50 miles on it, stock air-cleaner etc.., the motor had more but it's not broken in so I only did it for a second. The best part is the torque, got to 36 in about 6-7 seconds(slow count) I have no Tach on the bike yet. Just for info it is 32 deg out F.!
R/Mac

**My math was incorrect, actual RPM was 5,744rpm** this sounds more feasible to me.

Here is the formula:
1] {(engine RPM) divided by (TOTAL reduction)}
2] multiply that #1 result by (wheel roll out in inches)
3] Divide that #2 result by 63360(this is inch's in a mile FYI)
4] Multiply that #3 result by 60

This will give you your speed at the RPM given in step #1(just change rpm in step 1 and re-compute. You can also sub in different total reduction #'s to get your motor to run where you want it to run. Plug in my #'s so you see how it works. Good luck!

/Mac

Mac's 99cc predetor build

Some interesting stuff I encountered during the build and formulas for gearing with odd size tires etc...

Hi Mac,


If you are using a 2.5" primary pulley, and the original 15 series belt the primary ratio would be 2.136 X 1. If the final ratio is 5.6 X 1 [56 tooth rear sprocket], then the total ratio would be 11.96 X 1.

If you change the primary drive belt to the AX series then the primary ratio would be 2.06 X 1 and the final [wth a 56 tooth rear sprocket] would be 11.557 X 1.

With 29" wheels @ 11.96 X 1................
26 MPH = 3600 RPMs
36 MPH = 5000 RPMs
40 MPH = 5600 RPMs

With 29" wheels @ 11.557 X 1.............
26.9 MPH = 3600 RPMs
37.0 MPH = 5000 RPMs
41.8 MPH = 5600 RPMs

If you install a 2.75" primary pulley with an AX series belt.......
1.865 X 1 primary ratio, total ratio is 10.45 X 1
2500 RPMs = 20.646 MPH
3600 RPMs = 29.731 MPH
5000 RPMs = 41.293 MPH
5600 RPMs = 46.248 MPH

I reset my adjustable primary pulley yesterday to 2.95" [2.80" corrected 9.7 X 1].......
2300 RPMs = 20 MPH
3600 RPMs = 32 MPH
4500 RPMs = 40 MPH
5650 RPMs = 50 MPH

Have fun,

Quenton,
I am using a 68T rear sprocket. Good for hills around here and the great acceleration I'm getting. I am using a 2.5" sprocket up front, 2.75" are hard to find, Tractor supply didn't have the AX25 belt but I found a Hydraulic shop that had 6 of 'em in stock and 10 AX26's! Glad I got it at the hyd.warehouse, Tractor supply wanted $21.00 for a std 27" non cogged belt,The AX was only $12.99 at the Hyd. supply store, I never even knew that place existed up here, they can custom bend pipe(thinking exhaust), The guy showed me around a bit, every fitting imaginable, hoses, a trillion different bearings Just a big WOW factor! They are also business partners with 5 other local warehouses that carry different stuff! What a find just looking for a belt!!
On another note, I was putting the Q-matic cover on and had to push it quite a bit to get the expandable pins in the holes, now I know why, the Pred99 shaft is a bit long, by say 1" it "machined" a nice hole on the cover, no bother to me, Ill bolt a plate to it maybe with the hypnotist swirl on it or a smiley face... or maybe a alternator stator with magnets... The possibilities are endless!!

Quenton Guenther said:

Hi Mac,



I reset my adjustable primary pulley yesterday to 2.95" [2.80" corrected 9.7 X 1].......
2300 RPMs = 20 MPH
3600 RPMs = 32 MPH
4500 RPMs = 40 MPH
5650 RPMs = 50 MPH

Have fun,

Click to expand...

Hi Quenton,
Quick question....wouldnt this gearing be a little too tall?....I like the numbers shown for cruising and live in flat Florida...but how much stress would this put to the clutch?...and is 9.7 X 1 the final ratio at rear wheel from the crankshaft?

Hi Guys,

We normally set the primary ratio of the Q-Matic @ 2.764 X 1 on the 49 CC 4 stroke motors [Honda & HS] and the secondary ratio @ 5.6 X 1 for a total of 15.48 X 1.

All of our test bikes have a 56 tooth rear sprocket and sets the stage for our testing.

The stock Q-Matic clutch is a Max Torque version made to our specs. and has the "ticking" and "enguagement" speeds based from a high RPM motor. The stock Q-Matic clutch is located at the rear of the drive and ratio-reduced via a wedge belt. In order to make it tick and enguage at the correct time the clutch needs to spin at a pre-determined speed. In order to make the clutch spin faster on a low RPM motor [Most B & S, Clinton, H.F., and many Honda motors, etc] the primary drive pulley needs to be larger. Although we could ask Max Torque to make a special clutch for us, it would be costly and isn't really needed if we simply use the stock Q-Matic unit and take advantage of the higher torque of the HF 79 and 99 CC motor by altering the primary ratio.

Both H.F. motors tested did very well using a 2.5" primary pulley, and both pulled the 3" primary pulley. The 79 CC was happier with the 2.5" pulley than the 99 CC motor. The 99 CC is much happier at slightly under a 3" primary drive pulley. Having said all this, tests were using a light rider [me], and on level ground, therefore the ratios should be different for average riders with hills.


I will caculate some alternate ratios in a later post to show the many options available.
Have fun,

Hi jowens,

The 99 CC motor has a narrow power range, and is peaked at 3600 RPMs [maximum listed RPM speed]. This basically means we need to operate the motorbike between 1000 and 3600 RPMs [2600 RPM range]. The biggest advantage to the Q-Matic is the "adjustability", and increasing the primary drive pulley size makes the largest % difference in the final ratio. Narrow RPM motors also have a lower idle speed and the clutch needs to be spun faster to "hook" it up soon above idle. The ideal drive system should keep the chosen motor at or near the peak torque at cruising speed and still take off without pedal assist.

Here are some numbers to consider:
11.55 X 1 ratio [2.5" primary pulley, AX belt], 26" wheels
2500 RPMs = 16.7 MPH
3600 RPMs = 24.1 MPH [maximum rated RPM level]

9.74 X 1 ratio [3" primary pulley Wedge belt], 26" wheels
2000 RPMs = 15.8 MPH
2500 RPMs = 19.8 MPH
3600 RPMs = 28.5 MPH [maximum rated RPM level]

10.44 X 1 ratio [2.75" primary pulley, AX belt], 26" wheels
2500 RPMs = 18.5 MPH
3600 RPMs = 26.6 MPH [maximum rated RPM level]

Using an adjustable primary pulley is a wise idea, as it can be fine tuned to fit your exact requirements. The 10.44 X 1 ratio is a good example, as 2 3/4" pulley are much harder to locate, and often cost more than the adjustable version.

I only listed the top RPM level at 3600 RPMs because it is within the limits listed for the 99 CC motor, however it can rev much higher, but who knows for how long?

Hope this helps.

Have fun,

Hi Mac,

Here are the corrected numbers using a 68 rear sprocket and 29" wheels.

14.52 X 1 [2.5" primary, wedge belt]:
2500 RPMs = 14.8 MPH
3600 RPMs = 21.3 MPH [maximum rated RPM level]
5000 RPMs = 29.7 MPH

12.68 X 1 [2.75" primary, AX belt]:
2500 RPMs = 17 MPH
3600 RPMs = 24.5 MPH [maximum rated RPM level]
5000 RPMs = 34 MPH

11.83 X 1 [3" primary, wedge belt]:
2500 RPMs = 18.2 MPH
3600 RPMs = 26.2 MPH [maximum rated RPM level]
5000 RPMs = 36.4 MPH

Have fun,

My Predator seems to pull hard up tp abput 5000 rpm. It will rev higher but it seems to be happy at 5k for as long as there's gas in the tank.
They are governed to 3600 because that is the standard speed for lawn equipment or other accesories designeed to run on small engines.
Sure, they will prolly wear out faster at higher rpm full time, but motorbikes also spend a lot of time at low rpm too, so I don't think going over the standard of 3600 will cause major issues with this little engine.
I have about 700 miles on mine so far, and cruise a lot at 4000-4500rpm and wind it up to 5000 quite frequently just to wring it out and see how it holds up. So far, so good.

wayne,
When I did my 36mph run I noticed the same thing, over 5K your just accumulating speed until the valves float(which they did). I hope AGK comes out with a billet rod and some better springs, Cam and piston. We could do a bit of port matching, the usual stuff like hard corners and casting removal.(head milling, adjustable pushrods, turbo charger and a wet nitrous with fuel injection... Roller rockers would be nice too!!)
OK I got a bit carried away... But some aftermarket parts would be nice.

R/Mac

I normally run all my test motors at WOT for long periods of time to see how long they survive, but only after a good break-in period.

I made the following changes to the motor, increased the main jet from .025" to .031", installed and tuned a flex pipe [real exhaust pipe, smooth inside], reset the valve clearance [intake was at .028"] to .005" intake , and .006" exhaust. Motor pulls hard to approx 5500, and then floats its way to slightly over 6000 RPMs. The only scary part is the plastic shrouded flywheel, but when it explodes it should be held inside by the metal cover.

Last time I saw nitros used on a motorbike, the spokes went from 36 per wheel to several hundred [lots of bent and broken spokes], LOL. The same day I watched a comet torque converter snap the end of a Whizzer flywheel and travel down the street at a very high rate of speed [the Whizzer was strapped to a DYNO and stayed in place], LOL.
Been around too many people wanting to go too fast, for too long!

Have fun,

Yeah, I think that with the stock flywheel, rod, springs, 5000 is about the max safe speed.
The only mods to mine are aftermkt air cleaner and EMT 3/4" strait pipe with 3/4 " hotdog muff, and drilled main jet to .028.
Mine runs so good and dependable, I see no reason to try to wring out any more power from it.