View Full Version : Butler Upgrade
04-23-2005, 11:58 PM
Here are the drawings for doing the Jim Butler upgrade which consists of a stainless steel bearing housing for the lower pulley. Originally the bearings were just set in the soft aluminum of the pulley and many people had problems with ball bearings falling out on the floor after a flight, wobbly pulleys and I believe the crank failures. If you can open them in Windows Photo Viewer, it allows zooming in for a better look at the specs. I'll scan the instruction sheet and post it in awhile. I'm hoping that in the future, we can just tell people to search "Butler" for the specs. Looks like they can be enlarged twice here on the Forum by clicking on the drawing and then the enlarge icon that appears in the lower right corner when you place the cursor over the drawing again. I just opened all three and they look good enough to work from or print. This upgrade will alleviate a lot of problems. I think at the start, you're supposed to put the piece in the freezer overnight to make it easier to insert into the pulley. Oh yes, it says it at the top of the first drawing.
03-03-2011, 07:29 PM
For anyone who has done this upgrade or is considering doing this upgrade. This modification can be upgraded even further to incorporate much higher grade bearings for quieter, smoother, more stable operation.
To do this all you have to do is change the outer diameter of the bushing from .7502 inches to 20mm or slightly larger (say 20.1mm) for a tighter fit.
By doing this, you can use a metric size 6004 radial bearing which has a much higher ABEC 7 rating (7004 is angular contact and even better with the same dimensions) as compared to the original Fafnir S8PP bearing (equivalent in size to a R12 SAE bearing) which only has a ABEC 1 rating and is much noisier and not as smooth. I can only find bearings this size with a rating of ABEC 3. Also the SAE standard size bearings are much harder to come by these days besides not being available in higher quality precision.
It would be very worth while to do this upgrade to help save the life of your engine and also help it run smoother. It probably also helps transfer a bit more power to the belt and creates a better grip for the belt with less heat build up in the sprocket because there is less friction and vibration transfer.
03-03-2011, 07:46 PM
KenSandyEggo, What do you think of making this housing out of mild steel or 4140? John K.
03-03-2011, 07:57 PM
Ken only checks in here once in a great while (sometimes years). He doesn't own a gyro anymore.
But if you want my opinion, the only thing wrong with the steel is the corrosion factors over time. I would stick with a hard material like stainless that doesn't corrode and won't wear under the loads of the bearing material like the stainless steel that is suggested.
03-03-2011, 08:28 PM
Just an added note for reference.
The dimensions of the Fafnir S8PP bearing (R12 series SAE) that was originally used for this mod has these dimensions
ID = 3/4" = .75 inch = 19.05mm
OD = 1 5/8" = 1.625 inch = 41.275mm
W - 7/16" = .4375 inch = 11.112mm
The dimensions for a 6004 bearing is
ID = 20mm
OD = 42mm
W = 12mm
Since the 6004 is slightly taller by .725mm it should work but be a tighter fit to slide into the housing. Remember to change the diameter of the bearing support shaft to 20mm to accomodate this size bearing to improve the performance of the upgrade.
Also remember that this mod uses 2 bearings side by side on the bearing support bracket that is not mentioned in these drawings. It is better to use angular contact radial bearings (7004)if possible because the support much higher loads generally and run much smoother at much higher RPM ratings than the regular radial bearings.
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