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Rocket - Lord engine mount isolators

larryj

Well Known Member
I'm trying to collect all the information for engine mount isolators for Rockets and coming up short.
John Harmon calls for Lord p/n J-9613-12. Period.
Mark Frederick calls for Barry p/n 94011-02.
A Google search indicates these two p/n's are equivalent.
Good so far; but I know I have heard and read that there is another Lord p/n for a slightly stiffer isolator often referred to as an "aerobatic" mount. This specifically is what I'm after. I have a hot-rod motor and think the "aerobatic" isolators will be better suited to the bigger horsepower.

On top of this, I've seen that a Piper Malibu (turbocharged) with 300hp uses Lord p/n's J-7763-23 and J-9612-8. This is a similar horsepower to mine but angle-valve (heavier) than my 320hp parallel-valve. I've seen a lot of Lord installations that use 2 different isolators; and switch their locations for the upper ears vrs lower ears. Are we using the one isolator for all 8 positions ??

All help is greatly appreciated.
 
I wrote to Lord about aerobatic mounts for my F1 a few years ago (2007) and received this info from Paul Snyder:
The J-9613-12 is used for straight and level flying and the J-7764-31 is for aerobatics. The J-9613-12 has a "compression" sandwich and a
"tension" sandwich on each side of the engine mount - the compression
side takes the 1G weight of the overhanging engine. That's why the
sandwiches are reversed top to bottom. I wouldn't normally recommend
flying negative g's with this arrangement since the engine motion will
be higher upside down. It's a softer system than the
J-7764-31, which has compression sandwiches all around, so you'll get
better vibration isolation.

When I asked about the higher cost he said: These
aerobatic parts are made in a natural rubber that uses a special cure
system that's 3+ times longer than standard. The press time makes them
more expensive, but I can tell you that they'll out-last anything out
there by far.
Our distributor, Herber Aircraft Services (800-544-0050), may have both
parts in stock - ask for Ryan, she's very helpful.
 
Good info!!!

Mark:

Would you pst this to the TR Forum too? This is great info to have on hand.

Carry on!
Mark
 
It also depends on the prop. Isolators are set up for particular vibration levels. I did some testing a few years back on mounts and airframe vibes. A number of mounts from barry and lord. It was not cheap. I did however settle in on the Lord J-9613-12. Maybe you are trying to track down vibration in your search for the right isolator? Prop clocking may be your friend. Some info here on my experience.
http://mstewart.net/super8/propclock/index.htm

Prop clocking made an 85% improvement in vibration levels at my butt.
 
The Heat is on...

I wrote to Lord about aerobatic mounts for my F1 a few years ago (2007) and received this info from Paul Snyder:
The J-9613-12 is used for straight and level flying and the J-7764-31 is for aerobatics. The J-9613-12 has a "compression" sandwich and a
"tension" sandwich on each side of the engine mount - the compression
side takes the 1G weight of the overhanging engine. That's why the
sandwiches are reversed top to bottom. I wouldn't normally recommend
flying negative g's with this arrangement since the engine motion will
be higher upside down. It's a softer system than the
J-7764-31, which has compression sandwiches all around, so you'll get
better vibration isolation.

When I asked about the higher cost he said: These
aerobatic parts are made in a natural rubber that uses a special cure
system that's 3+ times longer than standard. The press time makes them
more expensive, but I can tell you that they'll out-last anything out
there by far.
Our distributor, Herber Aircraft Services (800-544-0050), may have both
parts in stock - ask for Ryan, she's very helpful.

MJ,
One thing to add for Rocketeers. Having purchased those exact same (expensive) mounts for my HR2 several years ago, I found the lower mounts are very close to the stock Harmon exhaust pipes. Heat cracking forced the replacement of the originals. Fortunately, the Vetterman Rocket exhaust system I replaced it with does not have this issue. If you have an older Harmon system, you may want to install heat shields, FYI...

V/R
Smokey

PS: The aerobatic mount vibration levels compared to the stock mounts is noticeable, but not disconcerting. I have flown an HR2 with the non-aerobatic mounts and didn't notice a huge variation. As mentioned, the prop makes a big difference as does the engine balancing itself. Remember, these are the same mounts an Extra 300 uses to pull +9/-4. Not the Rockets forte'
 
Last edited:
+1 for the heat shield. I had to fabricate one to protect the mount and cables running through there.

1zb56b9.jpg
 
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