From experience in building over 120 assemblies, we make sure these are built correctly to allow no axle keyway wear, loosening or wobbling. The flywheel is built to be used as a brake rotor. We have the outside and inside diameter cut with a CNC torch. Both sides are then ground on a Blanchard grinder so they are parallel. Then we weld on a special female type hub assembly. The axle and male hub are put together and torqued up straight using a dial indicator so that the face run-out is less than .015”. We can use any axle size from 1” to 4”.Normally we use 1 ¼” stress-proof steel for flywheels under 30 hp, with keyways cut only were they need to be. We never have a keyway where the bearing is going to ride. We stock axles in 1 ¼”, 1 ½” and 1 ¾” in lengths to 47.5”. We can custom make whatever you want. We stock one-way sprag clutches and torsion shock systems and can get most sizes overnight. If you want us to ship a flywheel/axle assembly to you, we will need your zip code for a freight estimate. We use a “NEW” freight carrier (as of 11/01/08) and these guys have unreal prices compared to what I used to get. Between the drop in fuel prices and the new freight service, your cost might be 50% cheaper than it was a few months ago? Residential deliveries cost an optional $50.00. It’s best to ship to someone with a forklift and loading dock. The flywheel will be banded on a pallet and shrink wrapped. These assemblies include VERY high quality Japanese NTN ULTRA CLASS pillow block bearings with eccentric lock collars unless you do not want them. WE DO NOT RECOMMEND any cheap import pillow block bearings. I have had some of these fail in less than 30 days! We stock & do recommend Loctite Viper Lube grease for the bearings! These (flywheel assemblies) are computer balanced to less than 5 grams at 500 rpm’s. There is a heavy duty sprocket hub included with a 53 tooth #35 or #65 tooth #219 sprocket so you can dyno clutches if you buy the correct software and electronics. You must have engine rpm inductive pick-up box & wiring harness. If you plan on adding electric start or belt drive it is best to add that to axle before balancing the assembly. You can get by and add later if you have to. If you are using a clutch to dyno engines, use a 24 or 29 hp flywheel with a higher gear ratio so you aren’t so hard on your clutch or don’t bring engine rpm much below clutch engagement rpm. For 1” PTO shafts, I’d use a Tobias clutch which comes on most Slingshots karts. For ¾” shafts (Briggs 5 hp & Animals, Clones, Honda, Deco Continental, etc), I recommend a Premier Titan clutch with yellow or red springs. Horsepower ratings are for approximately 15 second dyno pulls. I highly recommend installing the flywheel so that electric start and belt drive can be added at a later date. We do sell dynos in kit form so all you do is weld it up and start using it. You will get every part with a basic blueprint. We build dynos up to 125 horsepower or more with multiple flywheels so you can do 3 hp up to 125 hp. Please note that for flywheels above 30 hp, I recommend 1 ½’’ to 1 ¾’’, or 2 1/4” stress-proof axles and those above 40 hp. The following are the most common flywheels that we sell.

We now build a custom dual #219 & #35 chain sprocket hub (1/2” bore to 2.25” bore) using a QD hub. Normal aluminum sprocket hubs have a very short life due to the constant shock load! I can custom build one a single (1/2” to 2.25” bore with correct bore & keyway) with a steel sprocket if you want?

Prices have gone down since steel has come down 25 to 30 %

1” x 28” rated at 20 hp.-sells for $1554.55

*1.25” x 28” rated 24.16 hp. sells for $1584.10

*1.50” x 28” rated 29.16 hp. sells for $1696.68

1.75”x28” rated 34 hp sells for $1786.75

2”x28” rated 39 hp sells for $1906.07

2.25”x28” rated 44 hp sells for $2442.50

2.5”x28” rated 49 hp sells for $3106.27

3”X 23” rated 26.5 hp sells for $1915.27

4” X 23” rated 35 hp sells for $2821.25

4”X30” rated 104 hp sells for $4068.45

4”x30” no machine work sells-$1556.34

8”x28” rated 158 hp sells for $6624.79


These have 1.75” axles, bearings, dual weld-on outer & inner hubs

These have minimum 2 ¼” shaft, bearings, dual outer & inner hubs

We can also make other sizes.

Remember this includes all the labor to do everything including all machine work, all set-up, all welding, several trips to pick & deliver parts, total assembly, welding, computer balancing, (3) “NEW” NTN ULTRA-CLASS bearings, key stock, H.D. sprocket hub, #53 sprocket, crating, banding, shrink wrapping, and put on a pallet for shipping. We do sell used and new data system and new & used digital weather stations.

Check this website for pictures or go to my blog, hewittsinertiadynos.wordpress.com or inertiadyno.com. Give me a call with questions, 1-641-775-3395 or my cell 1-641-512-3395. E-mail: hewittdyno@gmail.com or hewitts@netins.net .


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