Introduction: Frankenciser - Magnetic Resistance Upgrade to a Vintage Friction Exercise Bike

Picture of Frankenciser - Magnetic Resistance Upgrade to a Vintage Friction Exercise Bike

Building this project out of bits and pieces made me think of the Frankenstein monster, hence the title..."It's alive!"

This is the project that started all of the Graber MAG trainer modification posts. What I had hoped to be a bolt-in project turned into a series of challenges. The roller creased in the first two minutes. Fixed that. Then there was the challenge of vibration that wouldn’t allow a cadence above 30. Fixed that, twice. Then there was the challenge of not enough resistance. Fixed the lack of resistance but not the disproportionate steps in between settings. The modifications that address these items are in several of my Graber MAG trainer posts.

Spring Loaded Passive Vibration Isolation

Increased Resistance Modification

Replacement Roller Modification

Long after I upgraded my 1980’s Panasonic EX-1000 flywheel exercise bike to Schwinn DX900 brake pads (Friction Pad Upgrade), I wanted to try out magnetic resistance. The eddy current resistance Keiser exercise bike had held my attention for many years. I knew “slapping on” a magnetic resistance unit wouldn’t result in a Keiser, but then again it wasn’t going to cost that kind of money.

The magnetic resistance donor was a Graber MAG Trainer that was discounted due to a bent frame. Because it started out damaged, I didn’t feel badly about cutting it up and tossing what wasn’t needed.

The tube with the mounting bracket was cut from the Graber MAG Trainer frame right at the upright tubes. The MAG unit and parts and the mounting bracket tube were used in the upgrade. The rest went out for the recycler.

The only realistic place for locating the mounting bracket tube and MAG unit was above the flywheel and in front of the head tube. The unit was attached using parts from the bike and over-the-counter hardware from the big box store. One advantage of the location was that gravity would pull the MAG unit down to the flywheel.

The rubber isolators were tried to see what effect they might have on damping vibration. They reduced some felt vibration and reduced some of the high frequency “singing”. A surprising “feature” during initial assembly was that the open and unobstructed mounting bracket tube was a resonance chamber and would “sing” loudly. Putting some foam in the tube and capping it with the existing “feet” damped the “singing”

Before the “springer” front end was added, tightening the adjustment knob would cause the assembly, brackets and all, to rotate at the M10 bolt. I didn’t want to mar the paint by adding toothed washers at the fork arms or collapse the fork arms from over tightening. Instead, both ends of a 36" Flat Bungee Cord were hooked to the exercise bike base with a single loop taken around the mounting bracket tube. This was done for both sides. It isn’t elegant but it works.

All-in-all, I am happy with the outcome. It is much quieter than my AirDyne, has challenging levels of resistance, and the vibration is now acceptable. It does, however, remind me of the flywheel on a steam tractor.

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Parts

From the bike

1 ea - M10-1.5 locknut

1 ea - M10 flat washer

1 ea - M10 star washer

Note: The M10-1.5 x 160 mm Hex Head bolt is not used

Purchased

1 ea - Graber MAG Trainer - Magnetic Resistance Bike Trainer FOR PARTS

1 ea - M10-1.5 x 180 mm Hex Head bolt

2 ea - Superstrut Model # ZAB201EG-10 2-Hole 90 degree Angle Bracket

4 ea - 1/2-inch flat washer

2 ea - 1/2-inch lock washer internal teeth

2 ea - Everbilt Model # 806806 1/4 in. x 1 in. x 1-13/16 in. Coarse Zinc-Plated Steel U-bolt with Nuts and Strap

2 ea – 3” square furniture cups (only one in the package gets used)

2 ea – sheets closed cell packing foam sheets

1 ea - 36" Flat Bungee Cord, 2 Pack

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Tools

Metal cutting tool (chop saw, cut-off wheel, hacksaw, etc.)

Adjustable wrench

Round file

Utility knife

Cutting guard

Pencil

Note: The usual admonitions to use safety equipment, be careful of hot, sharp, or rotating parts and equipment, and be cautious around electricity. Also, if you modify it, and they can tell, it probably voids your warranty.

Note: Modify the MAG unit for the roller and magnets using the previous posts before you attach it to the bike.

Step 1: Mounting Bracket Tube

Picture of Mounting Bracket Tube

1. You don’t have to disassemble the frame before cutting but it does make handling it easier. Remove and save the “feet” (tube caps).

2. Cut the tube with the attached mounting bracket, just inside the uprights. This gives you the most space for side-to-side adjustment. Make the cuts as square as you can and knock off any burrs with a file.

3. Insert foam into the tube. I used closed cell packing foam sheets that were rolled up and slipped into the mounting bracket tube and then slipped on the tube caps. The tube is a resonance chamber and will “sing” loudly.

Step 2: Make the Vibration Isolators

Picture of Make the Vibration Isolators

1. Cut one furniture cup in half in the direction of the ribs. You are best off using a cutting guard for safety. Be very careful, utility knives can instantly make nasty cuts through any soft portion of your body they encounter.

2. Remove the lip from each half and cut each in half again (quarters).

3. Slot both sides of the quarter enough to allow then to slip inside the U-bolts.

4. Insert the quarters between the mounting bracket tube and the 90 degree Angle Brackets and between the U-bolt straps and the 90 degree Angle Brackets.

Step 3: Brackets and Mounting Bracket Tube

Picture of Brackets and Mounting Bracket Tube

1. The fork arms are cross bolted through the head tube by a single M10-1.5 x 160 mm bolt. Unthread the nut and remove the bolt and washers

2. Assemble the brackets in the following order

Bolt, 180 mm

External star

90 degree Angle Bracket, leg facing inward

Internal star

2 flat washers

Insert bolt through both fork arms and head tube

2 flat washers

Internal star

90 degree Angle Bracket, leg facing inward

flat washer

locknut

3. With the U-bolts slipped over the mounting bracket tube, hold them up to the 90 degree Angle Brackets. Determine where to notch the 90 degree Angle Brackets for clearance for the U-bolts, straps, and nuts and mark the brackets. If clearance can’t be found, disassemble and reverse the 90 degree Angle Brackets to face out and then mark.

4. Disassemble and file indents in the 90 degree Angle Brackets. Remove equal amounts on the top and bottom of the bracket. Test fit the U-bolts frequently. They need to just slip over the 90 degree Angle Brackets.

Step 4: MAG Unit Attachment

Picture of MAG Unit Attachment

Modify the MAG unit for the roller and magnets using the previous posts before you attach it to the bike for the "final" time.

1. Attach the MAG unit

1.1 Slip the smooth leg of the l-bolt into the fitting on the mounting tube.

1.2 Slip the MAG unit over the threaded leg of the L-bolt.

1.3 Slide the hinge bolt through the unit and make sure the square shoulder is seated.

1.4 Tighten the hinge nut.

1.5 Put on a modified fender washer, the spring, another modified fender washer, and the knob.

2. Align the 90 degree Angle Brackets parallel to the ground. Rotate the mounting bracket tube until the bottom edge of the mounting bracket is about 1-inch above the flywheel. Tighten all of the nuts.

3. Install both 36" Flat Bungee Cords. On each side, hook both ends of one bungee cord to the exercise bike base and make a single loop round the mounting bracket tube.

4. Finish spring setup.

4.1 Screw the knob down so there is slight compression on the spring.

4.2 Ride and adjust the compression for the smoothest ride.

4.3 Put a cap on the exposed end of the “L” bolt to keep it from becoming a skewer. I had a spare star knob so I used it.

5. Test ride. Initially, there was a lot of vibration. A 30 cadence was about the maximum before the vibration really kicked in. The flywheel and, to a lesser degree, the skate wheel roller needed to be “rounded”.

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Smoothing the “Ride” (for an EX-1000)

1. The flywheel has two plastic trim pieces. They were about 0.040 inches out of round. The roller was removed and a Shinto saw rasp rubber banded to the bottom of the MAG unit body. The body was lowered using the adjustment knob while turning the flywheel by hand until the saw rasp contacted the high spot. The bike was pedaled for a couple of minutes. You could hear the high spots being scraped. The knob was tightened slightly to lower the MAG unit body and the bike pedaled until there was continuous scraping for the complete circumference. Be careful where you do this. It will generate a lot of small black particles.

2, The skate wheel roller was about 0.005 inches out of round. With the roller off the axle, a 10mm drill bit was chucked in an electric drill and the roller axle secured to the part of the bit without cutting edges. The drill was clamped with the roller squared. A board and heavy paper spacers were used to get a Shinto saw rasp to the correct height. The drill was run until there was only a light pull on the Shinto saw rasp. Be careful where you do this. It can generate a lot of small white particles.

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