Author Topic: jackshafts  (Read 6984 times)

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Offline TomC

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« on: November 05, 2005, 11:10:41 am »
Post by mowmanscott on Sept 23, 2005, 7:06am

Does anyone know a good jackshaft set up. what I'm looking for is pully
sizes for engine to shaft and shaft to transaxel I'm looking for power
and speed? this is going to be for a twin 18-20 hp stock engine. Thank
you Scott
*Re: jackshafts*
Post by HotRodLawnTractor on Oct 1, 2005, 1:15am

Ok. I have a craftsman 2 with the 14HP opposed twin and this is what I
run: So far I have tried two different pulley setups, all on the back
half of the jackshaft. I tried a 9"-3" and it slipped too much, so I
went to 10" to 4.5" with a 5/8 belt and slippage is gone. On the front
half, currently, it uses stock diameter pulleys 4" on motor 4.25" on
jackshaft. The front belt slips bad and I am currently in the process of
building a whole new setup for the clutch and pulleys up front. The way
it is, I figure I get up to 40-45mph top speed in 5th gear at full
throttle. Problem is with pulley sizes on the jackshaft is that if you
have a large engine pulley to a small jackshaft pulley the rpms on the
bearings for the shaft will be way too high. The bearings I use are
chevron flange ball bearings from mc master carr with a 6800rpm max
speed for 1" dia shaft. They were $55 a piece but should hold up to
anything I can throw at them. The new pulley setup I am working on will
use a 6" on the motor and a 5" on the shaft. This will give me slight
overdrive and should keep bearing speed low enough not to max out AND I
am setting it up for a 5/8" belt instead of the 1/2" belt I just smoked.
I am also adding blocks I fabricated with idlers to draw the belt
together directly in back of the engine and bottom jackshaft pulleys to
maximize belt contact. I will try to get some new pictures this weekend.
*Re: jackshafts*
Post by mowmanscott on Oct 1, 2005, 9:11am

Thanks hot rod keep me posted. also have you lowerd your rear axel to
make this set up work? I nead all the help so I can HOPELY beat my
fellow racers. By the way who do you race with? Iam up hear in ny.
*Re: jackshafts*
Post by HotRodLawnTractor on Oct 6, 2005, 12:20am

Ok, I did some work both saturday and sunday, but I was helping my
brother put the engine back in his ranger most of the day sat, so I
didn't get much time to work on //my// parts. I stripped off the old
pulley setup and removed the clutch pedal/shaft and idlers from the
bottom of my tractor and test fitted one of the idler block setups . I
should be able to finish the 2nd block this weekend and paint it, if all
goes according to plan. I have a few pics you might like to see.
This is one that shows you the c-notch in the frame I made to lower the rear.
The first setup for rear of jackshaft. Here you can see the 9" pulley.
Here is the underside of the jackshaft setup. This shows the mounting block
I made from 1/2 steel for the bearings to hold the shaft. Note the green
fuzz covering everything, yep, you guessed it: that's belt all over it
from slippage.
Reardisc brake setup from gokart parts.
Gas and brake pedals.
Here is the finished idler block I was describing. These will mount in front of
the motor and jackshaft pulleys to draw the belt together and maximize
pulley contact.
Here is the 2nd, and as yet unfinished idler block. Check it out, those are
probably the best welds I have EVER made.

So far, I haven't raced it, as it is still unfinished, but I spoke with
Tom Lavalette, the pres of the Pennsylvania Lawn mower Racing
Association earlier this year and he gave me a list of tracks when I'm
ready. Right now I just terrorize... and entertain the neighbors with it.
*Re: jackshafts*
Post by mowmanscott on Oct 6, 2005, 6:04am

hotrod I couldn't get the pic's this morning I'll try to night, BTW were
is Hamburg ? I also talked to some one on the old school I-mow class,
though about racing that class.
*Re: jackshafts*
Post by HotRodLawnTractor on Oct 6, 2005, 11:28am

Hamburg is in Northern Berks county, about 90 miles north of
Philadelphia. They built a Cabela's store here a few years ago, don't
know if you heard about that. I chose BP as what I wanted to race in
because it allowed me the greatest creative freedom and because my
tractor would not have fit in any of the other classes.
*Re: jackshafts*
Post by mowmanscott on Oct 6, 2005, 7:15pm

got the pics. tonight looks good I liked the idler pull set up. Im from
Syracuse right in the middle of the state.
*Re: jackshafts*
Post by 1031 on Oct 13, 2005, 11:56pm

May I add a question here under Jack shafts?
Why run a jackshaft setup? Why not just run a longer belt ?
Does the jackshaft help in speed and torque?
Thanks 1031
*Re: jackshafts*
Post by HotRodLawnTractor on Oct 14, 2005, 1:11am

When you lower a rear end of a tractor, you are actually /raising/ the
transaxle in relation to the original position on the frame. This,
correspondingly raises the position of the pulley within the frame. In
my case, I lowered the rear end 5 inches so the pulley ended up 5 inches
higher up within the frame than in stock position. Jackshafts provide an
intermediate shaft with a pulley on each end, one aligned with the
engine pulley and one aligned with the raised pulley on the transaxle. I
hope that explains things a little better.
*Re: jackshafts*
Post by mowmanscott on Oct 14, 2005, 5:40am

I cant lower my frame in my class I'm trying to find a way to use a jack
shaft set up with out droping the frame..tork and speed is all in the
way you set it up...Any help would would be great.
*Re: jackshafts*
Post by 1031 on Oct 14, 2005, 8:46pm

Thanks for the explanation of the jackshaft. I too can not lower my
mower. The transaxel has to remain in the original spot. Thanks for the

*Re: jackshafts*
Post by mowmanscott on Oct 14, 2005, 9:53pm

1031 who do you race with? Scott
*Re: jackshafts*
Post by 1031 on Oct 14, 2005, 10:48pm

Yes I race with a scott, but he is in the super mod class and one heck
of a driver.
I am just a newbie learning the trick to go fast and turn left!
*Re: jackshafts*
Post by mowmanscott on Oct 15, 2005, 7:00am

1031 No what club and were... Scott
*Re: jackshafts*
Post by 1031 on Oct 15, 2005, 7:09pm

try this link if you want. Our Club is in Southeast Missouri <> hope this helps
you out Scott