The following is recommendations only
- Choose a class to race in, BP and FX is not for the first time racer,IMOW SP CP AP is.
- Consult USLMRA rule book on build specifications for your class
- I build a chassis to BP specs this will allow me to start in a slower class(IMOW,SP,CP) and work my way into BP with a change of the engine.
- Build it yourself or buy one ready to race??? If you choose to buy,Mike Cupps at Acme Mower Sports can be your one stop shop. Mike sells parts to build a mower or a complete ready to race mower or any thing in between his web site is www.acmemowersports.com . Don Gienger at www.g-team.us also sells rolling chassis and many other parts. Don is my choice for machine work on the engine parts.
- I built winning racers with average shop tools, and a lot of Internet research and advice from other racers, now you can purchase how to DVD's A great deal of that research has been applied to this document.Some racers in the PREPARED class, change the front axle, remove the engine governor, change pulleys and go race. Some build to max width and minimum ground clearance with many engine mod's. The choice is yours, this is what make this sport so appealing. You can have fun racing on a small budget and be competitive.
- There is a number of FORUM's on the web to assist you. I mostly use www.heymow.com and listen closely to what the proven racers and builders have to say.
- Reference material
- TECUMSEH & PEERLESS transmission and drive products. Form No. 691218 (most lawn mower shops have these). This technician's handbook covers most transaxle's and 700 Series transmissions.
- How to DVD's these are a must have if you build your self. G-Team has videos on engine building and chassis building. www.g-team.us
- BRIGGS & STRATTON Repair Manual (Briggs & Stratton most popular engine used)
- www.acmemowersports.com for illustrations and parts. Mike also has parts kits available.
- FOUR MAJOR COMPONENTS ----- All components have an equal value of 25%.
- 1. CHASSIS SETUP
- 2. DRIVE LINE
- 3. ENGINE
- 4. DRIVER
- 1. CHASSIE SETUP ---
- I prefer to start with a bare frame. Keep parts, some will be used later. By doing this it allows me to strengthen the frame, prepare for paint and only reassemble what is needed to build a racer. This will cut down on weight and help when moving stuff to the front to achieve 60/40 weight ratio. What is 60/40 weight ratio? With driver sitting on mower and mower sitting on cheap bath room scales. You want 60% of the total weight on the rear wheels and 40% on the front. You also want more weight on your left front tire then right front. And less on your left rear then your right rear, I know this sounds complicated, but its really not. By following the ratios your mower will turn better and have less push in the curves. What is push?? Push is when you turn the steering wheel and the mower does not turn, this is caused by having a solid rear axle,and both rear tires having the same amount of weight and traction, now you see why less weight is better on left rear. Steering geometry plays an important role in reducing left rear wheel weight when turning left, most of your racing turns will be to the left. You can achieve these ratios by having adjustable front and rear axles(up and down adjustment). ww.heymow.com has more info on this. Front axle, consult USLMRA rule book for your class. Some racers build there own or purchase from shops such as www.acmemowersports.com or www.g-team.us. If you decide to build your own go to www.heymow.com for more info. Front axle geometry plays an important roll in cornering, so do this wright.
- 2. Drive line, refer to rule book for your class. IMOW Transmission or Transaxle must be shift able and of
lawnmower origin and gear ratio in highest gear is to be no less than 8 to
1. Example: while in the highest gear the rear wheels can turn no more than
one revolution every time the engine rotates eight times.
- PREPARED class has a choice of two set ups. Transaxle or kart axle, (kart axle must have a shift able lawn mower transmission) most use a peerless 700 series. FX class drive line is open. What seems to be the trans axle of choice in PREPARED class, is the peerless 820 with a 017 gear train. Kart axle of choice, inch or inch and a quarter diameter, with a peerless 700 transmission. If you want to run a trans axle, there is a number of them that will hold up under racing conditions. For more information go to www.heymow.com Tires and rims--again refer to rule book for specs. I prefer the shortest lawn tire for my rim size with a 4 ply sidewall. This allows me to run lower air pressure with less tire roll.
- Rear axle must be installed in original location, your only choice is to move the axle up or down to achieve 4" ground clearance from lowest point of frame. Again refer to rule book. The choice is yours whether to lower or not to lower. I recommend to lower. This creates a lower center of gravity and allows for faster cornering.
- Assemble rear axle and front axle including tires. Clamp front axle to original mounting position (see rule book), clamp rear axle to original location. Now you can get an accurate measurement to lower to 4" min. ground clearance. Some builders notch the frame or drill a hole to mount the rear axle, reinforce this area. Now you should have a rolling chassis. The hard part is done. I mount my peerless trasmission on 1/4 plate that just fits between the frame, Don covers this in the chassis 101 video.
- 3.Engine,If racing IMOW refer to rule book on engine size IMOW runs a stock engine. Don Gienger has a DVD on how to build a flat head 28 CI briggs engine. This engine is used in the SP class, the flat head is the least expensive performance engine to build. I built my flat heads at home using Don's Motor 101 DVD. I sent my cam and crank to Don for modification, I use a briggs piston and rod alone with a stock flywheel and won the Texas Points Championship for 2006. I have since built a flat head with ARC billet rod and the Briggs AVS piston along with a Don Gienger cam. CP class allows us to run an over head valve single cylinder or OPPOSING Flat head Twin (NOT the Vtwin). BP class runs the V-Twin.
This is how my #117 SP and CP mowers are set up.
MTD Chassis is what I like to use. That's just my option. I also built my front axle.
I Built the chassis to the BP wheel base.
This is not a complete list
Chassis Parts for 1 ¼ kart axle setup Using 6 inch front rims and 8 inch rear.
I like the 1 1/4 set up better because there seems to be more parts available.
If I were building my first racer I would get the following from http://stores.ebay.com/G-Team-Racing
- Chassis 101 video
- rear axle kit
- rear break kit
- front axle kit ----- or build your own
- 7 x 8 Douglas Polished Aluminum wheels 4 on 4
- 4 on 4 hubs
The parts needed from www.Arcracing.com
Quantity 2 - 9015 Front hub, 5/8" id. WITH bearings installed
2- 9750 6 x 6 - 2.50 Machined Q+ Front rims
Parts needed from American Power Sports
Front sprocket for 700 Transmission
AP4420 17T #40 CHAIN ALUM. SPROCKET
Rear sprocket for 1 ¼ kart axle hub 6 on 5 ¼
AZ531444S 44T #41 CHAIN SPLIT SPROCKET
This sprocket will get you in the ball park.
KEYSTOCK 1\4" X 1/4" X 1'
Parts needed from Acme Mower Sports http://acmemowersports.com/
Splined steering hub used to mount 17 tooth sprocket to transmission
Steering shaft and kit
Complete wiring kit
Cart spindles For those who want to build there own axle. You will also need tie rods and ball joints and 1x2 sq tubing.
I use 13x600x6 or 13x650x6 for front tires
I like Maxxis Pro Tec 16x6.50x8 rear tires
I also use tubes in my tires.
Purchase Pulleys from Tomossie Supply in Lake Charles or Acme Mower Sports etc.
I use 8 inch diameter by 5/8 pulley on the engine and a 5 1/2inch on SP and a 6 inch on CP by 5/8 on the transmission.
Use a ½ inch belt. The 1/2 belt rides deeper in the 5/8 pulley, I have found that the clutch work better and the belt last longer. I also us a kevlar belt, not your average auto supply belt. I get my belts at Belts Plus in Lake Charles.
Throttle Lever for steering wheel
The clamp pivots in the middle so you install on an automotive steering wheel.
Front Axle with 12 degree spindles
This is how I build my front axles.
- 1 - 1”by 2” stock for beam 23” long finished length before angled
- 2 - spindles and bracket 5/8 Axle Diameter 3.75 axle length. I modify to 12 degrees off square, see picture below
- 2 - 10 “ female tie rods
- 4 - 3/8 Male Heim Ends (Tie Rod End Bearings)
- 2 – female 3/8 Heim Ends (Tie Rod End Bearings)
- 6 – 3/8 bolts 1”1/2 long with lock nuts
I use two pieces of 1 inch square tubing and weld together to form a 1 by 2 inch beam. Cut beam 23 inches long with square ends. Using a degree square mark and cut the ends of the beam to 102 degrees. This make the end of the beam 12 degrees off square. The bottom of the beam will be 23 inches long and the top will be about 22 1/8 inches long. The angle of the cut has to point in. this will allow you weld the 12 degree spindle bracket to the end of the beam, the bracket must be leaning in 12 degrees, this will make the axle bolt level.
Put the beam on a level surface,(make sure its level, not close, not good enough, but perfect) tack the brackets on, place a small level on the axle bolt, axle bolt must be in line with the axle, and check for level, if its not level adjust the bracket till level and plum, then weld in place.
Axle with 12 degree ends, 2”tall by 1” wide
The least expensive and easiest way to build your own 12 degree spindles is buying a set of 90 degree spindle(shown below) and cutting the weld at the axle bolt head, about ¾ of the way down, (don’t cut completely off) use a chisel between the axle bolt head and spindle to separate the top of the bolt head from the spindle till the axle bolt is 12 degrees off square, and weld in place. You may also cut and relocate the tie rod arms to fit your setup. Search the web for 5/8 kart spindles.
Spindle Kits – 5/8” Kingpin
I prefer center steering, center steering is were the two tie rods meet in the middle of the axle and a bell crank is use to transfer the motion to each spindle , this causes the inside tire to turn a bit more then the out side tire resulting in a stable turn.