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Author Topic: Rookie Build - Gilson  (Read 59369 times)
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« on: September 26, 2008, 07:49:24 AM »

Build for ARMA 09 season
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Tim Waldorf
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« Reply #1 on: September 26, 2008, 08:22:23 AM »

Hey Guys!

I just want to start off by saying what a great forum this is.  I have been reading the threads in this forum for about a year and a half now, and I have learned alot, and I am eager to learn more.  I have been tinkering around with lawn tractors since I was about 10, and now it is time to build a real racer.  The chassis I really want to start with is a mid 80's Gilson.  I like the way this mower looks, and I like the way it "feels."  I also have 3 of them so there are plenty of donor parts.  I know there are a couple other guys on here that are racing Gilsons, but I have not seen any racing a chassis like mine.  Has anyone built one of these before?  The closest thing I could find were the pictures of Lee's mowchine on G-teams slide shows.




The rear  end is where I am kind of stuck.  I was thinking about boxing it in and reinforcing it on the inside so I will have a place to mount the live axle.  From the measurements I have made, the bearings for the axle would need to be placed close to where the current axle is mounted to keep the frame sitting parallel to the ground.



Front view with the new axle.










Any suggestions you guys have would be greatly appreciated.  I am planning on starting out either in the Sportsman or Mox X classes with BSMRA.  I would also like to run at GSR.
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Tim Waldorf
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« Reply #2 on: September 26, 2008, 08:56:12 AM »

You need to tilt your King Pin rearward... this is called caster.. it does many different things.. It helps to straighten the steering wheel when you come out of a corner and it helps to get the jacking effect when you turn.

You need your king pin tilted in at the top.. This is called KPI ( King Pin Inclination). Both of these will help to wedge the chassis and help the inside left tire lift and transfer weight off of the right front to the right rear.

Here is some reading material as you build you can have somethings in the back of your mind.

Front Axle Design

Cross Wedge
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heymow.com - Lawn Mower Racing Forum
« Reply #2 on: September 26, 2008, 08:56:12 AM »

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« Reply #3 on: September 26, 2008, 10:06:55 AM »

Wheel horse racer, 

Thanks for the info.  That is a great thread.  Exactly what I was looking for when I was building my front end.  I totaly agree with the caster.  I am planning on gringing the end plates off the beam and adding plates that will alow adjustable castor.  I didnt think of that when I welded them on.  I dont know who's advise to follow when it comes to KPI though.  From what I read in the build threads, Don doesnt like KPI, and George uses it on all of his builds.  The end result the way that I understand it is personal preference.  My problem is I am completely new at this and do not have experience running a machine with or without KPI.

I am planning on making some new spindles anyway that will allow me to gain some ride height adjustment, so I may weld the next ones up with 10 degrees of KPI.
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Tim Waldorf
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« Reply #4 on: September 26, 2008, 11:29:03 AM »

I would say build with as much adjustablility as possible.. then you can fine tune..

The KPI does make steering a little difficult as you get more resistance in the steering wheel when you turn... but the payback are worth it.. ten laps and I am tired..

You can use a HEAVY spring to help and to turn the wheels to the right to reduce the effort... I just haven't done that yet..

I just put my inside tire on a 2 x 4 on it's side.. turn the wheel to the left, then adjust the heim joints so that my front tires sit flat... Then I know my tires will be flat in the turn..

Then utilizing the spindle spacers.. I can fine adjust my wedge by raising and lowering the left front spindle... to loosen or tighten the chassis..

 

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« Reply #5 on: September 26, 2008, 11:50:04 AM »

Will Do!!!!  Planning on making new spindles and adding the KPI this afternoon.  I will post pics when I get it complete.
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« Reply #6 on: September 26, 2008, 08:29:33 PM »

I have all of the parts for the new spindles cut and drilled.  Planning on welding everything up in the morning.  The new spindles will include 10 degrees of KPI.  Are most of you running 1/4" plate for your end plates?  That is what I have on the current set-up in the posted pictures, but I need to go to 2" wide so I am able to include castor adjustment.  Aparently 1/4" x 2" plate is not easy to find.  Went to 3 diffrent stores today and nobody had it.  I know a place that will have it but it is 45 mins from me.  If I need to I will make the trip next week.  I have a piece of 3/8"x2" but I think that is over kill and I only have a 110v welder and will not get good penetration.

I am looking for a decent used pair of 8x8 4 on 3 rear rims.  Anyone got anything they want to sell?  I am on a budget with this mowchine, so I do not need anything fancy.  My wife and I just had our first child 5 months ago and funds are definatly on the tight side!!!!

I am also looking for a good rear axle.  I would like to run a 1.25."  Anyone have any suggestions as to the best place to get one of those from?  I know there are a lot of places that sell them, but where do you guys usually go for them?
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« Reply #7 on: September 26, 2008, 09:19:24 PM »

Ty,

I see your from Bear Creek WI.  My brother-in-law and sister-in-law live there.  I am up there quite a bit.  I really dig your monster mowers!!!!  That is some cool stuff!
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Tim Waldorf
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« Reply #8 on: September 27, 2008, 07:22:48 AM »

I don't run caster adjustment.. I set mine at 14 degrees and weld it.. it makes it very aggressive and actually tiring to drive.. but it works great... if it's too aggressive.. you can use a HEAVY spring to help and pull the steering to the left...

BUT.. you have to factor  in the rake of the chassis... the more tilt in the chassis the more it removes castor degrees if you measure perpendicular to the tube you used for an axle...

You need to know the amount of rake you will have before you set the castor angle for sure...
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« Reply #9 on: September 28, 2008, 02:16:06 AM »

Got the new spindles welded up today.  The new ones are in the front and the old ones are in the rear.  With the new setup I will have almost 2" of ride height adjustment.


Also cut the old end plates off the front beam and added 10 degrees of KPI.  Got one end plate machined and tacked into place.  The other is layed out and just needs to get drilled.



New end plates currently have 12 degrees of positive or negative castor adjustment.  That is assuming the frame has no rake to it.  I have room to make the slots bigger if I need more.



Also got some more frame stiffining done.  Didnt clean up the welds yet because I have more to do tomorrow.









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Tim Waldorf
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« Reply #10 on: September 28, 2008, 08:15:34 AM »

Looking really good... your well on your way..
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« Reply #11 on: September 28, 2008, 06:51:27 PM »

Ty,

I see your from Bear Creek WI.  My brother-in-law and sister-in-law live there.  I am up there quite a bit.  I really dig your monster mowers!!!!  That is some cool stuff!
Who's your inlaws? If in the area,need some help with anything,stop by.

By the way, lookin good so far.
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Ty Rindt
BSMRA - Sportsman
2010 BSMRA Sportsman Champion
2010 BSMRA Most Improved Driver of the Year
2010 2nd ARMA Sportsman MidWest regional points
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« Reply #12 on: September 28, 2008, 07:22:58 PM »

Got the front axle put together today.  Need to get the spacers for the king pin yet.  The frame is upside down in the picture obviously.



I need some suggestions on the rear end.  The center line from the front axle comes out 2.5" above the frame.  (if you are looking at the frame upside down as it is pictured.)  The top of the bar in the picture is the centerline from the front axle.





I plan on running 13 inch tires on the front and 16 inch tires on the rear.  I am not sure how I should mount the rear axle.  I was thinking of this...



But I really do not like it.  It looks stupid, and it will also add a lot of weight.  Not to mention I am not so sure it will be sturdy anoug.  Of course I would frame it in on the inside with 3/4" tube but I still dont like it. 

My second thought was to build a small sub-frame on the inside along the frame rails out of 1" square tubing, and mount pillow block bearings to that frame.  I think that will be a lot stronger and will weigh less.  The 1-1/4" pillow blocks through McMaster Carr are not cheap though!!!  Anyone have any suggestions?  Am I going about this all wrong by having the centerlines of the axles in line?



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Tim Waldorf
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« Reply #13 on: September 28, 2008, 07:37:11 PM »

I personally think you should use independent steering rods for the steering.. 

With the front end using a common bar to tie thenm together you will end up with Ackerman issues..

The key to having good steering is to have the inside wheel turn a sharper radius than the outside..

The way to do this is with a center pivot and the tie rods on top of each other in the middle.. this will allow for the tighter turn on the inside wheel..

With the two tires locked together.. they share the same arc and if you will always have the outside tire scrubbing.. scrubbing reduces speed.




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« Reply #14 on: September 28, 2008, 08:29:03 PM »

I may have to use two tie-rods in the front because of the way the frame lies with the front end, it will make it very difficult to attach the drag link to the spindle.  If the steering systems with the single tie rod in the front do not work well, how come there are so many of them out there?  I am sure a lot of it has to do with personal preference, but is one really better than the other? 
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