Track Tac

Jackshaft question

J

johnelliott

Member
I realize I need to shorten my chain to run a jackshaft--the question is if I end up with the rear of the motor mount where it was origionally, the chain will be awfully short--would I be better off to end up with the motor an inch or so farther forward than it was pre-jackshaft? Thanks for any insight, John
 
You don't want the chain to short. How can I word this? If the engine is back to far the chain will try to skip the teeth on the clutch due to the rear sprocket being larger than the clutch sprocket. Does that make sense? This is how it was explained to me.

Frankie
 
This is going from a stock class clone to a SA clone on a very small bull ring( we ran a 11/70 combination for the stock clone) Yammy I think I understand your post.(clutch will be on the motor. John
 
johnelliott said:
This is going from a stock class clone to a SA clone on a very small bull ring( we ran a 11/70 combination for the stock clone) Yammy I think I understand your post.(clutch will be on the motor. John
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just for clarification, I call the chain from the engine to the Jack shaft, the primary side. It's been recommended that the primary ratio should be between 2.5 and 3.0. That would call for a 11/28 (or 11/27) on thru 11/33 gear ratio on the primary side. That makes for a very fast chain speed. If you don't get the tension just right, the chain could ride up on the 11 tooth and skip. It's not a given, just a possibility. In any case, you might be better off with a bigger engine sprocket. Maybe a 13/32 (2.5) or 13/39 (3.0) or somewhere in between.

As far as moving the engine is concerned, I can't understand the need for pushing the engine forward.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
The builder of the jackshaft recommended a 16 tooth on the motor, there is a 30 coming into the js and a 15 going out--at the track in question I will start with a 60 on the axle---that will give me an overall ratio of 7.5-----If the engine motor mount is left in the same position as it was when running the stock clone the chain will need shortened a lot--I was thinking move the motor ahead a bit just so that chain to the axle would be a little longer, and not have to be shortened so much. I realize moving the engine will affect nose weight, but I have a little room to play with on that as I will have to add weight for the class. John
 
johnelliott said:
The builder of the jackshaft recommended a 16 tooth on the motor, there is a 30 coming into the js and a 15 going out--at the track in question I will start with a 60 on the axle---that will give me an overall ratio of 7.5-----If the engine motor mount is left in the same position as it was when running the stock clone the chain will need shortened a lot--I was thinking move the motor ahead a bit just so that chain to the axle would be a little longer, and not have to be shortened so much. I realize moving the engine will affect nose weight, but I have a little room to play with on that as I will have to add weight for the class. John
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that's a 1.88 primary ratio. That's a very high rate of speed for the chain. If you're going to run a 16 on the engine, better you put a 40 on the Jack shaft. I'm guessing you could get by with a 14 on the engine and a 35 on the Jack shaft.

Comments compliments criticisms and questions always welcome.
If the data does not support the theory, get a new theory.(Al Nunley)
 
I find that it's best to position things so that the J/S pulley and belt don't rub on the RR tire, and its also a good idea to leave some room so that you can add or subtract some teeth without things hitting, I also change my J/S clutch drivers so that the engine assy. don't need to be moved too much, because it can affect your scale numbers. Just remember to check 2ndary sprocket alignment otten, I use a hunk of keystock because it also allows me to check parallelism. I try to not move mount more than 1".
 
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