Part number for 4 bolt hydro flange

[GyroRon]

I bought a new flange today to replace the cracked one on the new two place. The one on it now is a standard Dominator 2 bolt flange and this one is cracked in half.... my last gyro I ended up with 3 cracked flanges in a row in less than 50 hours and I replaced it with a four bolt flange and never had another problem.

TO use a 4 bolt flange, a new plate of aluminum has to be cut and machined with the proper holes and slots like the plate that comes with the hydro pre rotator. The reason for this is there is a large hole in the aluminum plate that the pump comes through towards the prop and this hole helps center and support the hydro pump. The two bolt flange needs a larger diameter hole than the 4 bolt flange, so trying to bolt the 4 bolt flange to the old plate will not work. After you make a new plate it is very easy to install the flange and put it all back together. There is some possibility that Ernie at RFD could possibly sell you a aluminum plate already machined and ready to use but WITHOUT the centering hole already cut, so you could cut your own hole, or maybe even could get him to cut the smaller hole you will need since it is still a rather large hole and a normal drill bit won't do it - maybe a hole saw, but I am not sure....

Anyhow the place to buy it from is called FLORIG EQ and the part number is 909102 and their phone number is 1-800-535-1608

[MMorgan]

Ditto above.....I went through two flanges last year and recently bought a four bolt flange from the same people.

My mounting plate could be reused....It now has two extra holes in it.

[GyroRon]

Mike when you say you reused your old plate, are you saying that the new 4 bolt flange is not tight up again the sides of the hole it sticks through towards the prop?

[13brv3]

Well done Ron. Thanks.

When you remove the flange, do you lose any oil? I'm guessing you probably don't, but it doesn't hurt to ask. I might just go ahead and switch to this now, rather than having problems later.

I guess the 2 bolt motor flange is never a problem???

Thanks,
Rusty

[GyroRon]

you might loose a oz of hydro oil, but not much. The motor flange has not given me any problems yet.

[Joe Pires]

For the technically illiterate. Is this an issue with only hyrdo pre-rotators? Can you show a picture of this flange?

[13brv3]

Hi Joe,

Yes, it's the pump portion of the hydraulic pre-rotator. Here's Ron's earlier 4 bolt post with pics of his new flange. There's at least a drawing of the two bolt flange as well.

http://www.rotaryforum.com/forum/showthread.php?t=6654

Rusty

[Timchick]

In Ron's photos it doesn't look like those small washers spread the torque of the bolts over a very large area of the flange. Should larger washers or a fitted piece be used under the nuts?

[GyroRon]

In Ron's photos it doesn't look like those small washers spread the torque of the bolts over a very large area of the flange. Should larger washers or a fitted piece be used under the nuts?

The newer pre rotators Ernie is sending out has a aluminum washer he machines to help to more securly spread the load onto the flange over the old washer arrangement I had on my old White dominators system. BUT.... the flange still cracked clean in half. The only GOOD thing about the newer washers Ernie is sending is it still held the pre rotator in firmly to the mounting plate, even with the flange cracked in half.

My machinist friend made me a new mounting plate and it worked great this weekend. He made a drawing of the part and I have a copy and he kept a copy. If anyone wants to have him machine a new plate for you, I am sure he will do it for a small fee. Let me know and I can pass on his contact info. Elsewise I have a copy of the drawing and could scan it and forward it to you if you have the machine tools to make your own. Personally I feel the 2 bolt flange is a POS and should be swapped over to the 4 bolt version if you want to eliminate this cracking problem. Of course not everyone is having problems with cracks and if your 2 bolt flange is holding up then don't worry about it, but you really should be checking it closely during pre flights.

[MMorgan]

Sorry for the slow response but I was out of town for a few days....

The old flange had two holes at the 3 & 9 o'clock postions and my new one is like the photos in the link above. It fits exactly the same but the holes are on the corners. I used some larger washers.

[GyroRon]

Mike, anyone could take off the 2 bolt flange that Ernie provides, and bolt the 4 bolt flange to the pump, then drill 4 new holes to attach it to the mounting plate Ernie provides.... which is what it sounds like you did ...... But the problem with doing this is, the large hole in the mounting plate that the flange fits into is now too large when you go from the 2 bolt to the 4 bolt flange. So a new plate has to be made with a smaller hole for the flange to sit into. If you don't and use the old plate then the 4 bolts on the flange take all the loading, where as with a proper sized - smaller - hole in the mounting plate would help take some of the loads placed on the pump. Or maybe I am wrong... maybe you don't need the support that hole and tight fit of the flange in that hole is needed.... I can tell you that the hole that Ernie machines into that plate fits the 2 bolt flange very tightly and I believe he did that for a reason. The 4 bolt flange can move 1/8 to 1/4 of a inch in all directions when placed in that hole because of it's smaller size.

[13brv3]

I've had another thought about this situation. I noticed on mine that the pulley needs to be way out on the shaft of the pump to line up. This gives it lots of leverage to work on the flange. If the whole plate were spaced toward the prop, the pulley could be much closer to the pump, and wouldn't stress the flange as much.

Rusty (no flange stress yet)