$10 DIY Gravely Flywheel Truing Stand

The Stand

Here is an incredibly cheap and easy-to-build truing stand for those of you that do not have access to a lathe to measure Gravely flywheel concentricity (runout). It is made from a single 1” X 4” X 8’ piece of lumber and can be fabricated in about 15 minutes. The other parts required to complete the fixture are two bearings. The bearings I used are 1638-ZZ (3/4” ID X 2” OD X 9/16” thick) and a 1640-ZZ (7/8” ID X 2” OD X 9/16” thick). These bearings fit on the drive pinion shaft and timing pinion shaft respectively. The common 2” OD allows the flywheel assembly to be on the same plane in the fixtures. The parts and total cash outlay for me was as follows:

$1.99 for the 1” X 4” X 8” piece of wood from a local salvage yard

$3.24 for a KML 1638 ¾” x 2” 9/16” Double Shield Ball Bearing (KML 1638-ZZ 3/4″ x 2″ x 9/16″ Double Shield Ball Bearing | eBay)

$3.42 for a 1640-ZZ 7/8” X 2” X 9/16” Double Shield Ball Bearing (KML 1640-ZZ 7/8″ x 2″ x 9/16″ Double Shield Ball Bearing | eBay)

The final piece of the stand is the base plate. I used a 11-3/4” X 11-3/4” X 3/8” plate from John Deere. This plate is used when shipping a loader for tractors – more specifically, it holds the bucket while the unit is in transit. Visit your local John Deere dealership and be nice (and ask if you can have one as these just end up in the scrap bin or offer scrap price for this plate). The dial indicator’s magnetic base works VERY well with this plate (and it was free to me).

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Materials for a nice, accurate, and inexpensive concentricity stand can be built for less than $10 – not bad for a functional truing stand!

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Measuring Equipment

Of course, you will need a method of measuring the runout as well as making dimensional checks on the flywheel assembly. For measuring the runout I purchased the following dial indicator.

$25.99 for a Dial Indicator with Magnetic Base – 0.0005” Resolution (https://www.amazon.com/Magnetic-Adj…&sr=8-8&keywords=dial+indicator+magnetic+base)

Now, the question is how many dial indicators. The runout checks can certainly be performed using one dial indicator but I used two (I viewed many videos and two dial indicators seemed to make this project easier). With the project now complete, I am happy I had a pair of dial indicators.

A pair of calibers are also needed. I already had a pair of calipers in my tool box but here is a similar set for $18.49 (I prefer the non-digital version) 6″ DIAL CALIPER STAINLESS STEEL SHOCKPROOF .001″ OF ONE INCH. | eBay

The remaining components are some sort of straightedge for checking the parallelism of the flywheels and a brass hammer to coerce the flywheels in the proper position.

Stand Details
I used Trimble Sketchup to make the drawings. Interestingly, I had drawn eight iterations of the truing stand… with each version becoming simpler and simpler. The final design is practically identical to what appears in PEIrving’s “Tuning For Speed” (Tuning for Speed) page 103. Please note that it is not critical to support The flywheel assembly perfectly level in the stand – this is simply a means to obtain measurements as accurate runout measurements will still come from the dial indicator(s). If, for example, the V-groove cutouts are 1/16” higher on one side than the other, rotating the assembly and measuring runout will still yield accurate readings.

The 1” X 4” X 8′ piece of lumber is cut to yield four 9” lengths. Two of those lengths have two additional 45° cuts made in the middle (this is the area where the bearings rest – see drawing below) and the other two pieces simply serve as a base for the vertical pieces (since the actual height of the lumber is only 3-1/2” the stand must be raised so that the ~7-3/8” flywheel diameter will clear the bottom). There is no gluing or nailing of these pieces of wood in my fixture – gravity fit only. Here are the drawings I used to make mine (pardon the simplicity but this design works!).

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Place the four wood pieces on the plate, position the bearings on their respective ends of the flywheel assembly, and set the flywheel assembly in the stand. There should be absolutely NO wobbling of the stands when the flywheel assembly is hand-rotated in the stand. Note that the measurements via the dial indicator(s) are taken at the areas where the assembled bearings will reside.

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The video above did a great job of demonstrating the alignment/truing process. Granted, some ‘best practices’ are not always present BUT it did clarify many of the points that the articles I read simply glazed over. Interestingly, and if I understood everything correctly, interpreting the dial indicator readings will reveal where the alignment issues exist. Looking strictly at the dial indicator readings from top and bottom of the connecting rod pin (12 o’clock and 6 o’clock respectively) represent flywheels out of parallel (ie, flywheel rims are ‘pinched’ or ‘spread’). Conversely, rear and front dial indicator readings (9 o’clock and 3 o’clock respectively) signify an out of alignment issue (ie, ‘scissoring’ of the flywheels). After truing my flywheels, I concluded that I did not entirely agree with everything regarding the top and bottom, and the nearest and furthest references from the connecting rod pin but this video was tremendously helpful.

Again, “Tuning For Speed” has some nice directions in this old motorcycle tuning book regarding methods of bringing the flywheels back into proper alignment. Additionally, another great reference source for truing procedures is Donny Peterson’s book entitled “Donny’s Unauthorized Technical Guide to Harley Davidson, 1936 to Present” (pages 132-134). One noteworthy point from the Donny Peterson book was the directions for reducing/removing the spread on the flywheels. The instructions are to: “Tap the vice with steel hammer near the clamping area. The indirect shock will help the flywheels align.”

One thing I changed was how the measuring of the parallelism of the flywheels with respect to one another was performed. I had seen several references to measuring the outside faces of the flywheels in 90° increments to determine if the wheels were pinched or spread. This measurement is required but I opted to measure between the flywheels rather than on the outside because there were still some non-machined casting surfaces on my flywheels. These non-machined surfaces would certainly affect the measurements… as they did on mine.

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After using the straightedge, I used chalkboard chalk to mark which flywheel to move and where the blow should be directed. If I overshot the desired tolerance, I could almost undo the previous hammer strike by filling the flywheel assembly around (180° from the previous strike) and applying a new hit. During this rough alignment process, I still measured the runout after each adjustment. Once the flywheels appeared to be true to one another, I made subtler adjustments (again, marking with chalk) and really, really studied the dial movement indicators to get these flywheels as close as possible with the smallest amount of runout.

Please, please, please for your own sanity, once you get it within a total runout of 0.001″, put your hammer down (else you will be spending the next 90 minutes trying to get the readings back to where they were)! In the end, I was able to get the total runout (timing pinion dial indicator runout + drive pinion dial indicator runout) to less than 0.001”.

The most intimidating portion of the project was purposely taking a well-running Gravely engine, albeit a slightly shaking Gravely, to the required level of disassembly to make the necessary brutal adjustments with a soft hammer. However, now since this project is complete, I can safely state that it was much less work that I had imagined and bringing the flywheels back into their proper alignment was not as daunting of a job that I originally thought. The aligning process took me about two hours to complete (I would have been finished in 45 minutes if I would have put the hammer down earlier when I had it almost right…

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