Engine Rock?

N941WR · #1 05-01-2010, 10:51 PM

I'm in the process of fitting the cooling plenum and Sam James cowl over the O-360 in my -9.

I have the short Sam James cowl and I noticed that there is only a 1/2" of clearance between the baffles and the cowl by the oil cooler / #4 cylinder.

Is this enough clearance when the engine rocks during startup and shutdown?

PS. To measure the clearance I put some clay on the corner of the baffle and then installed the top cowl. From that it was very easy to measure the thickness of the clay.

pierre smith · #2 05-02-2010, 05:10 AM

....but my guess is that 1/2" would be the minimum....we'll see.

If you could somehow get another 1/4" clearance, you'd be home free,

Best,

Bob Axsom · #3 05-02-2010, 06:03 AM

If it has to be close, back near the mount is the place where the least displacement (movement) will occur. The shape of the surface in the potential contact area is important (avoid sharp edges). The hard metal of my baffle is that close. Rubber pads could provide some protection like the rubber on conventional plenums which are in contact all the time. Kind of makes you wonder about the wisdom of giving up hundreds of cubic inches of plenum volume to provide contact clearance for the theoretical advantage of a plenum that does not use the inner surface of the cowl as the top closure.

Sounds like you are getting to the final assembly stages of your recovery from TDTVLIC. It will be good to hear how your new 360 effects your airplane's performance.

Bob Axsom

carguy614 · #4 05-02-2010, 06:46 AM

Bill,
Pierre is right. I have a full plenum on my 320, and with 1/2 inch of clearance I got contact with the cowl on the right side. I ended up trimming down the corner to clear the cowl, a major PIA.
In my opinion, you should try to get at least 3/4" at a bare minimum. On my current RV-9 project, I will use the plenum again, but am planning on a full inch of clearance if I can get it. I have a metal prop on my flying 9A, and it will shake like a wet dog on shutdown. The 9 will use a 2 blade Catto I bought, hopefully I will get a bit less shake.
Best to fix it now Bill. I made the mistake of surmising I had enough wiggle room. On my short list of "Things not to let bite me next time"
On another note, Would love to talk to you about you're Emag gizmo and several other RV-9 issues.
Hope to see that 9 fly again soon!

Regards,
Chris
910-620-3754

N941WR · #5 05-02-2010, 06:58 AM

Thanks everyone.

I'm not sure what I'm going to do. To gain more room, I'll have to buy new baffle pieces, which is not a big deal but the problem is the plenum is as low as it can go.

I think what I need to do is check the clearance all around the plenum and see if I have any other areas that are close before I move on.

I did round off the corner of the baffle but putting a rubber pad on there isn't a good solution IMHO. I would rather not have any contact because eventually it will cut through.

Like you Chris, I'm putting another Catto prop on it, so that might help. I'll work it some more this afternoon and see how it comes out.

carguy614 · #6 05-02-2010, 07:35 AM

Bill,
If you are using new mounts, you will probably gain a touch of clearance pretty quick as the engine sags. Lightweight prop will help as well.
Is your lower cowl attach set in stone?? If not, you may be able to get a bit more by raising the cowl about it's mounts if spinner alignment allows.
Angling in the corners to shorten the distance slightly (horizontally from the mounts) may be an option rather than lowering the side plates.
It's a tight fit with a plenum.....That's for sure!

Regards,
Chris

N941WR · #7 05-02-2010, 08:02 AM

Quote:

Originally Posted by carguy614

Bill,
If you are using new mounts, you will probably gain a touch of clearance pretty quick as the engine sags. Lightweight prop will help as well.
Is your lower cowl attach set in stone?? If not, you may be able to get a bit more by raising the cowl about it's mounts if spinner alignment allows.
Angling in the corners to shorten the distance slightly (horizontally from the mounts) may be an option rather than lowering the side plates.
It's a tight fit with a plenum.....That's for sure!

Regards,
Chris

Chris,

Yes, the cowl is set in stone. Unless I replace the cowl, which I'm not going to do. This is with the new mount, Lord vibration isolators, cowl, engine, etc.

I think I'm going to have to go with it the way it is and see what happens.

The cowl is the "Short" version so things are even tighter. Not only that, the cooling rings don't line up with the plenum so it looks like I'm going to have to cut the plenum up and move the rings over 1/4 to 3/8" inch.

hydroguy2 · #8 05-02-2010, 08:14 AM

Quote:

Originally Posted by N941WR

........ the cooling rings don't line up with the plenum so it looks like I'm going to have to cut the plenum up and move the rings over 1/4 to 3/8" inch.

Saw your pics. and you are closer fit than my plenum was. I had to slice and dice mine pretty good, still not finished, but very close.

frankh · #9 05-02-2010, 08:21 AM

but has never been a problem..maybe i have 1/2"

I would run with it and see what happens

Frank
7a..SJ cowl and plenum

DanH · #10 05-02-2010, 09:00 AM

Bill,
Minor detail, but it can make a difference........

The start/shutdown shake mode is mostly torsional. The engine case rotates around the crank center as a reaction to the prop mass, thus the critical clearance dimension should be taken perpendicular to that radius.