Pmr Jackshaft confusion

aztec warrior

aztec warrior

Member
#1
#1
Hey been a while since I've been to the forum so here it goes. I just purchased a Pmr Jackshaft. I want more torque not worried about speed. Ok the sprocket on the hf 6.5 shaft has a 13t sprocket, and the doodle bug has a 72t on the rear wheel sprocket. The jack shaft also came with a 13 & 15 tooth sprocket to run to the engine and rear wheels. Which sprocket runs to the engine shaft and rear wheel sprocket for more torque? Please any help would be appreciated...

Thanks in advance,
Martin
 
cheezy1

cheezy1

#5
#5
Higher the number (8.0:1)...the more torque and more likely to flip backwards. The lower the number (5.0:1) the higher the speed and slower take off. And if you have a PMR jackshaft...just stop and look at it and fill in the numbers on the chart. Clutch...next gear...gear goin out to rear wheel...rear sprocket/axle.
 
C

control4userguy

New Member
#6
#6
I'll to help this along. Using the included sprockets, by themselves, will most likely get you nowhere near what you are expecting to see as an improvement. You might want to consider replacing the engine sprocket with something more suitable for lower ground-speed work. Say,for example a 10T. Use the included 15T in the input side of the JS and the 13T on the output. 8.3:1 net ratio. If you are looking for more then try a 9T on the PTO and a 18T on the JS-IN for 11:1 action.
 
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OND

OND

#7
#7
So by your numbers on the first post...I think you have a 4.800 total ratio. What are you looking for more torque ?

Taking it as the 13 in and the 15 out.

15 in and 13 out would be a 6.391..I like this one better my self.
 
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C

control4userguy

New Member
#10
#10
Yes. It's $10~$20 per sprocket so it's not a big investment to experiment with different ratios. We can't see how you are planning to use the machine and therefore can't decide for you what ratio is ideal. I personally don't care for "leisurely" ratios myself. That would include what you are running now and what your existing sprockets can provide. This is why I suggested starting out by getting rid of the 13T on the PTO for a 9 or 10T.

You probably already understand the benefits of a JS so you are now free to compound ratios such as these combos:

9>13>15>72=6.9:1
10>15>13>72=8.3:1
9>15>13>72=9.2:1
 
aztec warrior

aztec warrior

Member
#12
#12
control4userguy said:
Yes. It's $10~$20 per sprocket so it's not a big investment to experiment with different ratios. We can't see how you are planning to use the machine and therefore can't decide for you what ratio is ideal. I personally don't care for "leisurely" ratios myself. That would include what you are running now and what your existing sprockets can provide. This is why I suggested starting out by getting rid of the 13T on the PTO for a 9 or 10T.

You probably already understand the benefits of a JS so you are now free to compound ratios such as these combos:

9>13>15>72=6.9:1
10>15>13>72=8.3:1
9>15>13>72=9.2:1
Click to expand...

I'm basically using it for recreational use for my two boys and myself will have fun with it. Lots of flat roads here but also want it to climb a hill if there is one. We still want a little speed but also want it to climb. From the 3 ratios you posted for me which one do you recommend for me?
 
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control4userguy

New Member
#13
#13
Again, I can't foresee what kind of "hill" you are thinking of. 6:1 fits most users, that's a given. Beyond that, total weight, tires/wheel size and certainly, rider skill will and should dictate where you need to be. I mentioned that there is very low cost associated with experimentation.

You are at 5.5:1. For $15 you could start by replacing the 13T with a 10T (7.2:1). If that's not to your liking then install the JS and do 10>15>13>72 (8.3:1). This doesn't have to be a one-time thing, play around a little.
 
massacre

massacre

#15
#15
It can take a while to experiment and get the bike tuned perfectly for your riding style and situation. I have gone up in 1-tooth increments until I found the proper ratio. It is time consuming but makes the bike so much more fun to drive.
 
pomfish

pomfish

Well-Known Member
#16
#16
I found these sprockets at local hardware store for like $6-7 so shop around. At $11-$15 mail order (plus added shipping in many cases) it adds up quick when you keep fiddling with ratios.
If you only run the sprocket for a couple minutes and don't beat it up you could probably even return it for the next size locally depending on your store's return policy.

At a ratio of 8.3:1 you will feel this change.
HTH
Keith
 
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control4userguy

New Member
#17
#17
I agree. I have several sprockets myself. Maybe 5 mins run on each. It all sells so I'm not too concerned. Like massacre mentions, it's all worth it in the end when the mini does what you want. I'm not there yet so it is a little frustrating...
 
pomfish

pomfish

Well-Known Member
#18
#18
As cheap as those Torque Converter clones have become, I don't see using a jackshaft anymore unless the TQ will not fit the application.
I am going to order one for my beater Baja 165 later today. $75 shipped is hard to resist and some vendors send both the #41 and #35 sprockets.
 
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