sparrow psru?

[Sapientino]

I would like to have some information on Sparrow subaru psru:
which belt does it use? reduction?
has a roller bearing on engine output to support belt tension?
who does it manufacture? how much does it cost?

thanks for your kind informations

Paolo

[skyking]

Gates POWERGRIP GT2 880-8MGT85. I have to look at the Dwgs. in the hanger but I do not believe there is a roller bearing used in belt tensioner.

[jcarleto]

I've read the horribly massive specification for the Gates belt after having a problem with my re-drive. Believe me, with respect to a roller tension wheel, you DON'T WANT ONE.

The short "why" answer is that the belts with grip teeth really need a toothy tension roller inside the belt pulling out instead of s smooth roller pushing in to prevent premature belt cracking. The recommended contact point for such a device is a minimum of 6" from each pulley. You'd have to significantly increase the distance between the crankshaft and thrust axis to accommodate such a device. Then there's the weight. The stock Gates tensioner is just under 10 pounds.

You really don't need one anyway. If you properly tension the belt cold, it will actually become slightly tighter as it runs. The belt doesn't change, but the sprocket pulleys increase slightly as they heat up. You actually have to be careful not to over-tension the belt cold, or you will find it over-tight when it has been run, shortening the belt life.

Don't quote me, as the following figures come from my feeble memory, but I believe the cold tension setting was 1/32" side-play per inch between contact points. It does vary by belt size and type. On my re-drive, that translates to 1/4" play between contact points. After flying, my belt measures 3/16" play between contact points.

[MichaelBurton]

Gates POWERGRIP GT2 880-8MGT85. I have to look at the Dwgs. in the hanger but I do not believe there is a roller bearing used in belt tensioner.

There is no external belt tension bearing on the PSRU. There is a bearing used to support the end of the small drive pully. the gear ratio is 2.1:1. Also I don't think you can order these parts from GBA unless it is as support for an existing SH gyro.

[Sapientino]

There is no external belt tension bearing on the PSRU. There is a bearing used to support the end of the small drive pully. the gear ratio is 2.1:1. Also I don't think you can order these parts from GBA unless it is as support for an existing SH gyro.

thanks everybody for these usefull infos.
I ment the bearing on small drive pully not a tensioner.
can you sen me some detailed pics of the prsu?

[MichaelBurton]

http://www.rotaryforum.com/forum/album.php?do=editpictures&albumid=42&pictureids[]=248&pictureids[]=249&pictureids[]=250
Not much detail but it is what I have.

[Sapientino]

http://www.rotaryforum.com/forum/album.php?do=editpictures&albumid=42&pictureids[]=248&pictureids[]=249&pictureids[]=250
Not much detail but it is what I have.

I cannot access

[MichaelBurton]

try this link
http://www.rotaryforum.com/forum/album.php?albumid=42

[Sapientino]

try this link
http://www.rotaryforum.com/forum/album.php?albumid=42

very nice
thanks!!!