Thorp Air Command - T18.net

Hello, I am trying to get my pig flying again... I'm installing new Lord J-7402-1 mounts on an 0-290 (non focused mount). The drawing calls for Lord J-7401-1... But apparently this PN is for only one sandwich. According to Lord, the 7402-1 PN includes both sandwiches & the tube spacer.
Now on the the actual question...
These mounts come with a small hole that would clock them on a pin on a certified install... I found mention of a lancair install using these mounts on a dynafocal ring, the said to clock the mounts so the long side of the spacer points into the center. How do I clock these mounts for a non focused mount??? The tube spacer flat would either zero degrees or 90, I'm guessing??

Any help?
Thanks!

The long axis of the spacer is installed radially with respect to the crankshaft. They take up pulses in engine firing strokes. That said, those do not appear to be the correct mounts for a conical mount.

_________________
Bob Highley
N711SH
SN 835
KLAL

The weirdness of it all, is that the original Thorp drawing calls for machining bushings to take the place of the conical mount on the engine & to use the dynafocal style sandwich mount bushing on a non-focused mount (see pic). On the drawing it says to use a tube to make the spacer for the sandwich mounts but Lord only sells the mounts as a set (including two sandwich mount halves & the spacer). This aircraft was built per the drawing & has been this way since then.

I have mine off the mount right now. Here is the stack up per the plans you show.

Rob

Thanks Rob!
Are you using a tube cut to length for the mount spacer, or the spacer that comes with the lord mounts that has the rectangle rubber bonded to it (see my pic)?
My question really is how are people clocking the rectangle spacer? This is probably more important for daynafocal mount installs but probably should be considered for this install too??

I stand corrected guys. Your setup is correct. There was a setup at one time that used the conical mounts that fit engine bosses. Turned out that the rubber mounts readily available were, in fact, shipping rubber mounts that were not aircraft quality. As to the setup you have, the trick is that the internal spacer required between the isolators is not the standard, but 1.92" in length as shown in DWG #479. This is due, I guess, that the ring plate thickness is different than the dynafocal mount dimension that the Lord J-7401-1 isolator was designed for. The center vibration tube and rubber most likely won't fit without modification. This was covered in some long lost newsletter. As I mentioned before, if you get the center pieces to work, they are installed lined up to counter the torque pulses of the prop/engine. While we are at it, I remind you not to use standard torque values for the AN 7-40 mounting bolts as you will crush the spacer. Snug is good.

_________________
Bob Highley
N711SH
SN 835
KLAL

Thanks for the follow-up Bob. When you say to lone the spacers up, which direction... I understand the orientation for dynafocal, just not on this application. I'm assuming that either the long axis vertical or an x pattern would make most sense.
I definitely agree 40 ft lbs is high, anyone have a good torque number to use?

Rotate each one in the bottom picture 90 degrees. You are trying to mitigate the rotational pulses of the power strokes of the crank.

_________________
Bob Highley
N711SH
SN 835
KLAL

Well, after all that discussion... It doesn't matter. The Lord spacer is 1.801", the thorp drawing calls for 1.92". Looks like I'm getting spacers made.

Washers?

_________________
Bob Highley
N711SH
SN 835
KLAL

No, the spacer between the sandwich mounts... See the drawing I attached. Thorp calls for making one out of tube material.

Washers to make up the .12" you are short. Or have new tubes made and lose the dampening effect of the isolators. I know what I would do.

_________________
Bob Highley
N711SH
SN 835
KLAL